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Abstracts

SPIE Proceedings Vol. 3334

Optical Microlithography XI

Editor(s): Luc Van den hove, IMEC, Leuven, Belgium.

ISBN: 0-8194-2779-9, 1106 pages Published 1998
Meeting Date: 02/22 - 02/27/98, Santa Clara, CA, USA

Abstracts for the papers in this volume are located in this file immediately following the contents list below. All papers are published by SPIE--The International Society for Optical Engineering, P.O. Box 10, Bellingham, Washington, 98227-0010, USA.


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Contents


* Application of alternating phase-shifting masks to 140-nm gate
  patterning: II. Mask design and manufacturing tolerances (Paper
  #: 3334-01)
* Impact of coma on CD control for multiphase PSM designs (Paper
  #: 3334-02)
* 0.18-um optical lithography performances using an alternating
  DUV phase-shift mask (Paper #: 3334-03)
* Narrow-pitch contact array patterning technique for Gb DRAM
  using multi-phase-shifting mask (Paper #: 3334-04)
* Evaluation of phase-edge phase-shifting mask for sub-0.18-um
  gate patterns in logic devices (Paper #: 3334-05)
* CD control comparison of step-and-repeat versus step-and-scan
  DUV lithography for sub-0.25-um gate printing (Paper #: 3334-06)
* Effect of stage synchronization error of KrF scan on 0.18-um
  patterning (Paper #: 3334-08)
* Intrafield critical dimension variation using KrF scanner system
  for 0.18-um lithography (Paper #: 3334-09)
* Contributors to focal plane nonuniformity and their impact on
  linewidth control in DUV step-and-scan system (Paper #: 3334-64)
* Lithographic effects of mask critical dimension error (Paper #:
  3334-10)
* Lithography of 180-nm design rule for 1-Gb DRAM (Paper #:
  3334-11)
* Reduction of mask-induced CD errors by optical proximity
  correction (Paper #: 3334-12)
* Subresolution assist feature and off-axis illumination
  optimization for 200- and 240-nm contact windows using 248-nm
  lithography (Paper #: 3334-13)
* Revalidation of the Rayleigh resolution and DOF limits (Paper #:
  3334-14)
* Quasi-physical model for fast resist contour simulation:
  importance of lens aberrations and acid diffusion in LSI pattern
  design (Paper #: 3334-15)
* Lithographic process simulation for scanners (Paper #: 3334-16)
* Lithography simulation employing rigorous solutions to Maxwell's
  equations (Paper #: 3334-17)
* LAVA: lithography analysis using virtual access (Paper #:
  3334-18)
* 0.25-um logic manufacturability using practical 2D optical
  proximity correction (Paper #: 3334-19)
* Practical approach to control the full-chip-level gate CD in DUV
  lithography (Paper #: 3334-20)
* Accurate proximity correction method with total-process
  proximity-based correction factor (TCF) (Paper #: 3334-21)
* Applications of enhanced optical proximity correction models
  (Paper #: 3334-22)
* Process proximity correction using an automated software tool
  (Paper #: 3334-23)
* Optical lens specifications from the user's perspective (Paper
  #: 3334-24)
* Aberration evaluation and tolerancing of 193-nm lithographic
  objective lenses (Paper #: 3334-25)
* Pupil illumination: in-situ measurement of partial coherence
  (Paper #: 3334-26)
* Characterization of spatial coherence uniformity in exposure
  tools (Paper #: 3334-27)
* Evaluation of coma aberration in projection lens by various
  measurements (Paper #: 3334-28)
* ArF excimer laser lithography with bottom antireflective coating
  (Paper #: 3334-29)
* Bottom-ARC optimization methodology for 0.25-um lithography and
  beyond (Paper #: 3334-30)
* Inorganic antireflective coating process for deep-UV lithography
  (Paper #: 3334-31)
* Influence of underlayer reflection on optical proximity effects
  in sub-quarter-micron lithography (Paper #: 3334-32)
* Deep-UV reflection control for patterning dielectric layers
  (Paper #: 3334-33)
* Simulation and experimental evaluation of double-exposure
  techniques (Paper #: 3334-36)
* Illumination pupil filtering using modified quadrupole apertures
  (Paper #: 3334-37)
* New variable-transmission illumination technique optimized with
  design rule criteria (Paper #: 3334-121)
* DUV stability of carbon films for attenuated phase-shift mask
  applications (Paper #: 3334-38)
* New projection optical system for beyond 150-nm patterning with
  KrF and ArF sources (Paper #: 3334-39)
* Performance of an i-line step-and-scan system for sub-0.25-um
  mix-and-match applications (Paper #: 3334-40)
* Imaging performance of scanning exposure systems (Paper #:
  3334-41)
* Characterization of a next-generation step-and-scan system
  (Paper #: 3334-42)
* Laser pattern-generation technology below 0.25 um (Paper #:
  3334-43)
* Assessment of optical coatings for 193-nm lithography (Paper #:
  3334-45)
* Damage testing of pellicles for 193-nm lithography (Paper #:
  3334-46)
* Alignment performance versus mark quality (Paper #: 3334-47)
* High-accuracy alignment based on subspace decomposition (Paper
  #: 3334-48)
* Impacts of reticle and wafer elasticity control on overall
  alignment management strategy (Paper #: 3334-49)
* Proposal of a composite phase-shifting mask for 0.15-um
  hole-pattern delineation using KrF exposure (Paper #: 3334-51)
* Optimization of stepper parameters and its design rule for an
  attenuated phase-shifting mask (Paper #: 3334-52)
* Preventing sidelobe printing in applying attenuated phase-shift
  reticles (Paper #: 3334-53)
* Resist and oxide thickness effect on process window for 0.2-um
  contact patterns with off-axis illumination and attenuated
  phase-shift mask (Paper #: 3334-54)
* Optimization of DUV photolithography for sub-250-nm technology:
  contact patterning with attenuated phase-shift mask (Paper #:
  3334-55)
* New method for improving the practical resolution of complex
  patterns in sub-half-micron lithography (Paper #: 3334-57)
* Enhanced microlithography using coated objectives and image
  duplication (Paper #: 3334-58)
* Printing sub-100-nm random logic patterns using binary masks and
  synthetic-aperture lithography (SAL) (Paper #: 3334-59)
* Optimization of exposure procedures for sub-quarter-micron CMOS
  applications (Paper #: 3334-60)
* CD control of ASIC polysilicon gate level (Paper #: 3334-61)
* Reticle contributions to CD uniformity for 0.25-um DUV
  lithography (Paper #: 3334-62)
* CD control for quarter-micron logic device gates using iso-pitch
  bias (Paper #: 3334-63)
* Killer defects caused by localized sub-100-nm critical dimension
  reticle errors (Paper #: 3334-66)
* Overlay accuracy of reticles (Paper #: 3334-67)
* Challenge of 0.3-k1 lithography by optimizing NA/sigma, OAI,
  biasing, and BARC: practical approach to quarter-micron i-line
  process (Paper #: 3334-69)
* NA optimization of 360-nm and 300-nm pitch devices (Paper #:
  3334-72)
* Conformality of photoresist and antireflective coatings over
  topography (Paper #: 3334-74)
* Thin-film interference effects for thin resist films on a
  broadband scanner (Paper #: 3334-75)
* Optimization of ARC process in DUV lithography (Paper #:
  3334-76)
* Three-dimensional mask transmission simulation using a single
  integral equation method (Paper #: 3334-80)
* Use of melting inorganic photoresist for microlens array
  fabrication (Paper #: 3334-81)
* Metropole-3D: a rigorous 3D topography simulator (Paper #:
  3334-82)
* Cross-sectional critical shape error: a novel methodology for
  quantifying process simulation accuracy (Paper #: 3334-83)
* High-NA illumination: a simulation study (Paper #: 3334-84)
* Novel approximate model for resist process (Paper #: 3334-85)
* Three-dimensional photolithography simulator including rigorous
  nonplanar exposure simulation for off-axis illumination (Paper #:
  3334-86)
* Development of an integrated 3D lithography simulator (Paper #:
  3334-87)
* Chip-scale 3D topography synthesis (Paper #: 3334-88)
* Application of substructuring method to three-dimensional
  optical lithography simulation (Paper #: 3334-89)
* Net-Faim: distributed computation of aerial images (Paper #:
  3334-90)
* Exposure effects on deep-ultraviolet resist thickness (Paper #:
  3334-91)
* Application of artificial neural networks (ANN) and response
  surface model (RSM) in optical microlithographic process modeling
  (Paper #: 3334-92)
* Coping with the impact of lens aberrations in the context of
  wavefront engineering (Paper #: 3334-93)
* Effect of lens aberrations as a function of illumination
  condition on full-field process windows (Paper #: 3334-94)
* Measurment of astigmatism in microlithography lenses (Paper #:
  3334-95)
* Influence of aberration on performance during use of resolution
  enhancement technology (Paper #: 3334-96)
* Differences in pattern displacement error under different
  illumination conditions (Paper #: 3334-97)
* Optimal proximity correction: application for flash memory
  design (Paper #: 3334-98)
* Strategy for manipulating the optical proximity effect by
  postexposure bake processing (Paper #: 3334-99)
* SEMATECH J111 project: OPC validation (Paper #: 3334-100)
* Reducing or eliminating line-end shortening and iso/dense bias
  by tuning NA and sigma (Paper #: 3334-101)
* Benchmarking of software tools for optical proximity correction
  (Paper #: 3334-102)
* New method for optical proximity correction with gray-level
  serifs (Paper #: 3334-103)
* New distortion metrology using reticle coordinate error (Paper
  #: 3334-105)
* Application of the Brewster angle illumination technique to
  eliminate resist-induced alignment errors (Paper #: 3334-106)
* Alignment system for ArF excimer-laser-based step-and-scan
  system (Paper #: 3334-107)
* Chromatic aberration-free TTL alignment system for 193-nm
  step-and-scan exposure system by using phase conjugate waves
  (Paper #: 3334-120)
* Improvement of overlay in the oxide- and W-chemical-mechanical
  polish processes (Paper #: 3334-122)
* Laser alignment strictness for optical diffraction effect in
  lithography processes (Paper #: 3334-109)
* Design of illumination system for ArF excimer laser
  step-and-scanner (Paper #: 3334-110)
* DUV synchrotron exposure station at CAMD (Paper #: 3334-111)
* ArF excimer laser for 193-nm lithography (Paper #: 3334-112)
* ArF lasers for production of semiconductor devices with CD<0.15
  um (Paper #: 3334-113)
* Feasibility studies of operating KrF lasers at ultranarrow
  spectral bandwidths for 0.18-um line widths (Paper #: 3334-114)
* High-spectral-purity and high-durability kHz KrF excimer laser
  with advanced rf preionization discharge (Paper #: 3334-115)
* Stability of optical interference coatings exposed to
  low-fluence 193-nm ArF radiation (Paper #: 3334-116)
* Surface finish and optical quality of CaF2 for UV lithography
  applications (Paper #: 3334-117)
* Characterizing the absorption and aging behavior of DUV optical
  material by high-resolution excimer laser calorimetry (Paper #:
  3334-119)
* Reformulation for latent image formation model in
  photolithography using numerical absorbing boundary condition
  (Paper #: 3334-123)
* Modifications of polymeric ARC films by UV irradiation (Paper #:
  3334-124)


Abstracts:

Paper #: 3334-01
Application of alternating phase-shifting masks to 140-nm gate
patterning: II. Mask design and manufacturing tolerances, pp.2-14
Author(s):  Hua-Yu Liu, Hewlett Packard Labs., Austin, TX, USA;
            Linard Karklin, Numerical Technologies, Inc.,
            Santa Clara, CA, USA;
            Yao Ting Wang, Numerical Technologies, Inc.,
            Santa Clara, CA, USA;
            Yagyensh C. Pati, Numerical Technologies, Inc.,
            Santa Clara, CA, USA.

Abstract: In this paper we present the results of experimental
       patterning 140 nm poly gates with double-exposure
       alternating phase-shifting masks (PSM) using a Nikon
       EX-1 (KrF, 0.42NA) stepper. We show that: systematic
       intrafield line width variations can be controlled
       within 10 nm (3$sigma@), interfield variations across
       the wafer to within 6 nm (3$sigma@), and total
       variation across the wafer held to within 15 nm
       (3$sigma@), with a target k$-1$/ factor of k$-1$/
       equals 0.237 (140 nm target gate lengths). We also
       present the results of studies addressing several
       issues related to the production application of
       alternating PSM's, including mask manufacturing
       tolerances and full chip PSM design capabilities. We
       show that, in comparison to conventional binary masks,
       alternating PSM's reduce the criticality of mask line
       width control and reduce the sensitivity to mask
       defects. Furthermore tolerance to PSM phase errors can
       be significantly improved by placing a chrome regulator
       between phase-shifters. Automatic, high-speed full chip
       design of alternating strong PSM is now possible. !4 


Paper #: 3334-02
Impact of coma on CD control for multiphase PSM designs, pp.15-24
Author(s):  Regina T. Schmidt, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Christopher A. Spence, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Luigi Capodieci, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Zoran Krivokapic, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Bernd Geh, Carl Zeiss, Oberkochen, Germany;
            Donis G. Flagello, ASM Lithography BV, Veldhoven,
            Netherlands.

Abstract: Alternating PSM applied selectively to transistor
       regions on the poly gate mask is one way to achieve
       smaller gate CDs and tighter CD control. When using
       multiphase PSMs we have observed, experimentally, a
       difference between the CDs of isolated lines when the
       phase shifter is on the right side compared to the left
       side (we have called this effect the PSM right-left
       effect). The effect is shown to correlate with lens
       coma and the magnitude of the effect is also a strong
       function of defocus. In this paper we present
       experimental data showing the magnitude of the effect
       and how it can be minimized by choosing optimum values
       of numerical aperture (NA) and partial coherence
       ($sigma@). The magnitude of the effect within the
       stepper field is shown to correlate with measured coma
       values. The sensitivity of the effect to defocus was
       calculated. Aerial Image simulation was performed and
       found to predict the experimental behavior to within a
       factor of two. Variations in PSM design were explored
       using simulation. In general, the effect is reduced if
       the PSM layout is symmetrical. By comparing the
       sensitivity to coma of various PSM designs with the
       sensitivity of line pair structures on binary masks we
       were able to determine which designs had acceptable
       coma sensitivity. !4 


Paper #: 3334-03
0.18-um optical lithography performances using an alternating DUV
phase-shift mask, pp.25-35
Author(s):  Yorick Trouiller, CEA-LETI, Grenoble Cedex 9,
            France;
            N.Buffet, CEA-LETI, Grenoble Cedex 9, France;
            Thierry Mourier, CEA-LETI, Grenoble Cedex 9, France;
            Patrick Schiavone, France Telecom CNET-CNS,
            Meylan Cedex, France;
            Y.Quere, CEA-LETI, Grenoble Cedex 9, France.

Abstract: The phase shift mask (PSM) is a key emerging technology
       thought to be extending 248 nm lithography. In this
       paper, we describe the lithographic performances of
       Shipley UV5 photoresist on SiOxNy Bottom Anti
       Reflective coating (BARC), using alternating PSM and
       ASM/90 Deep-UV stepper. Results on 0.18 micrometer
       design rules are presented: lithographic performances,
       comparison between PSM and binary mask, sub 0.18
       micrometer performances ($LFBC@1$RTBC@) and the
       ultimate resolution of this technology are reported. To
       conclude we demonstrated the 0.18 micrometer
       lithography feasibility with alternating mask and KrF
       stepper, and showed that all the necessary tools are
       today available to achieve such goals. !5 


Paper #: 3334-04
Narrow-pitch contact array patterning technique for Gb DRAM using
multi-phase-shifting mask, pp.36-45
Author(s):  Takashi Nakabayashi, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan;
            Koji Matsuoka, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan;
            Shigeo Irie, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan;
            Hiromasa Fujimoto, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan;
            Takayuki Yamada, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan;
            Shuichi Mayumi, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan.

Abstract: Application of a multi-phase-shifting mask to hole
       arrays for giga-bit DRAM has been studied. Self-aligned
       contact plugs for a cell pitch of 0.38 micrometer under
       the bit-line contacts and the storage-node contacts
       have been formed at the same time by using a
       multi-phase-shifting mask with two different
       phase-shifters. Sufficient depth of focus (DOF) of 0.8
       micrometer has been obtained. Furthermore, hole-shape
       distortion caused by focus offset can be suppressed
       under the off-axis illumination condition with a
       quadrupole aperture !19 


Paper #: 3334-05
Evaluation of phase-edge phase-shifting mask for sub-0.18-um gate
patterns in logic devices, pp.46-54
Author(s):  Dong H. Cha, Samsung Electronics Co., Ltd.,
            Yongin-Goon Kyungki-Do, South Korea;
            Jongwook Kye, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea;
            Nakgeuon G. Seong, Samsung Electronics Co., Ltd.,
            Yongin-city Kyungki-Do, South Korea;
            Ho Young Kang, Samsung Electronics Co., Ltd.,
            Suwon City, South Korea;
            Han K. Cho, Samsung Electronics Co., Ltd.,
            Kyungki-do, South Korea;
            Jootae Moon, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea.

Abstract: The speed of logic device is mainly dependent on gate
       length. To achieve process margin (DOF, E/T, etc.) and
       minimize On Chip Variation (OCV) of logic gate with sub
       0.18 mm design rule, the need for phase-edge PSM
       technology that has the advantages of minimum
       resolution and Critical Dimension (CD) control has been
       increased. In this paper, performance and feasibility
       of phase-edge PSM technology were investigated. Using
       phase-edge PSM and positive resist process at DUV
       wavelength ($lambda equals 248 nm), the possibility of
       0.10 micrometer logic gate patterning was confirmed and
       0.18 micrometer gate lines with DOF larger than 1.0
       micrometer and plus or minus 6% CD variation were
       obtained. And design rules for phase-edge layout
       generation were extracted. Then the possibility of
       layout generation by the extracted design rules and
       layout conversion tool was confirmed. Also, the
       feasibility of mask CD uniformity and phase uniformity,
       and alignment between phase-edge mask and normal chrome
       (Cr) mask was investigated and confirmed. Considering
       lithographic performance and process feasibility,
       phase-edge PSM technology is a very promising method
       for patterning sub 0.18 micrometer gate in logic
       devices. !4 


Paper #: 3334-06
CD control comparison of step-and-repeat versus step-and-scan DUV
lithography for sub-0.25-um gate printing, pp.56-66
Author(s):  Kurt Ronse, IMEC, Leuven, Belgium;
            Mireille Maenhoudt, IMEC, Leuven, Belgium;
            Thomas Marschner, IMEC, Leuven, Belgium;
            Luc Van den hove, IMEC, Leuven, Belgium;
            Bob Streefkerk, ASM Lithography BV, Veldhoven,
            Netherlands;
            Jo Finders, ASM Lithography BV, Veldhoven,
            Netherlands;
            Jan van Schoot, ASM Lithography BV, Veldhoven,
            Netherlands;
            Paul F. Luehrmann, Jr., ASM Lithography BV,
            Veldhoven, Netherlands;
            Anna M. Minvielle, Advanced Micro Devices, Inc.,
            San Jose, CA, USA.

Abstract: In this paper, the intra-field critical dimension (CD)
       control of a KrF step&scan and step&repeat system are
       investigated and compared. The scanners are expected to
       replace the conventional steppers in the manufacturing
       of integrated circuit generation of 0.18 micrometer and
       beyond, because of the larger field size and the
       intrinsic improvement in intra- field CD and overlay
       control using comparable lens design, complexity and
       cost. The work has been focused on sub-0.25 micrometer
       critical dimensions. A reticle design for both top-
       down CD measurements and electrical linewidth probing
       has allowed massive data collection and investigation
       of the impact of the metrology technique in CD control
       studies. From this study, it can be concluded that the
       stepper and scanner exhibit similar CD control at best
       focus, but the scanner improves the CD control of the
       stepper if the considered focus range increases. The CD
       control is governed by the reticle CD non-uniformity.
       Focus budget calculations indicate that reticle CD
       ranges of 40 nm (4x) are needed to bring the CD control
       of 0.2 micrometer grouped lines within acceptable
       ranges for realistic gate levels. For isolated lines,
       dedicated deep-UV resists and resolution enhancement
       techniques will be needed on top of this to obtain
       similar CD control. !10 


Paper #: 3334-08
Effect of stage synchronization error of KrF scan on 0.18-um
patterning, pp.67-76
Author(s):  Takayuki Uchiyama, NEC Corp., Sagamihara Kanagawa,
            Japan;
            Takeo Hashimoto, NEC Corp., Kanagawa, Japan;
            Masashi Fujimoto, NEC Corp., Sagamihara Kanagawa,
            Japan;
            Seiji Matsuura, NEC Corp., Sagamihara Kanagawa,
            Japan;
            Tamio Yamazaki, NEC Corp., Sagamihara Kanagawa,
            Japan;
            Kunihiko Kasama, NEC Corp., Sagamihara-shi Kanagawa,
            Japan.

Abstract: The stage vibration effect on imaging performance, such
       as DOF and CD uniformity is evaluated experimentally
       and compared with simulation analysis. Various kinds of
       0.25 - 0.18 micrometer patterns are investigated by
       using KrF excimer scanner with 0.6 NA and 0.75 partial
       coherency and two types of chemically amplified
       positive resists. In the case of a standard resist for
       0.25 micrometer level patterning, the CD at the best
       focus changed and the DOF decreased rapidly with
       increasing moving standard deviation (MSD) in 0.18
       micrometer level pattern formation. Allowable MSD value
       of L&S pattern was estimated to be around 25 nm. To
       improve the stage synchronous error margin, the
       application of a high resolution resist was effective
       on L&S and isolated space patterns (about 40 nm), but
       showed little improvement for isolated line and hole
       patterns. Therefore, totally allowable MSD value was
       still about 30 nm. In particular it was found that both
       isolated line and hole patterns were very sensitive to
       stage vibration effect. Strict stage control has to be
       required for 0.18 micrometer patterns even if the high
       resolution resist is used. !11 


Paper #: 3334-09
Intrafield critical dimension variation using KrF scanner system
for 0.18-um lithography, pp.77-91
Author(s):  Donggyu Yim,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-si Kyoungki-do, South Korea;
            Hyeong-Soo Kim,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-kun, Kyungiki-do, South Korea;
            Ki-Ho Baik,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-si, Kyoungki-do, South Korea.

Abstract: Causes of intra field critical dimension variation
       using KrF scanner for 0.18 micrometer lithography have
       been investigated. Scanner is different from
       traditional stepper system. Scanner might have
       synchronization error, which results in degrading
       contrast over full intra field. Aberration of
       illumination optics brings about coherence difference
       between field center and edge. In a scanner system,
       vertical patterns (cross scan direction) are
       geometrically tangential, and horizontal patterns are
       sagittal. Such a H/V different ray tracing results in
       horizontal pattern having better contrast than vertical
       one under diffraction limited design rule patterning.
       Mask error can be a very critical issue in 4X system.
       Focus drift and exposure dose change during scan
       exposing result in intra field CD variation, and some
       stray light is a cause of intra field CD variation
       also. !9 


Paper #: 3334-64
Contributors to focal plane nonuniformity and their impact on
linewidth control in DUV step-and-scan system, pp.92-103
Author(s):  Pradeep K. Govil, SVG Lithography Systems Inc.,
            Ridgefield, CT, USA;
            James G. Tsacoyeanes, SVG Lithography Systems Inc.,
            Ridgefield, CT, USA;
            Randell P. Eron, SVG Lithography Systems Inc.,
            Mohegan Lake, NY, USA;
            Dave Walters, SVG Lithography Systems Inc.,
            Ridgefield, CT, USA.

Abstract: A significant contributor to linewidth control in a
       step and scan system is the focal plane nonuniformity.
       The various sources contributing to this focus
       nonuniformity such as wafer and reticle flatness will
       be discussed. Effective wafer flatness presented in the
       form of flatness variation histograms, as a function of
       focus sensor fill factor will be presented. A clear
       understanding of the effective wafer plane flatness
       variation is important in predicting lithographic tool
       linewidth control performance. Statistical approaches
       using joint probability distributions to combine
       various error sources will be developed. Data will be
       presented to show that the systematic error sources can
       be represented reasonably well by uniform
       distributions, and random error sources by Gaussian
       distributions. It will also be shown that the focal
       system performance estimated using this approach could
       accurately predict system performance and its impact on
       linewidth control. This allows determination of
       significant contributors to the focal plane
       nonuniformity, which is important in establishing the
       lithographic tool areas of improvements. Data
       illustrating the influence of contributors such as
       wafer and reticle flatness, and optical field curvature
       on linewidth control will presented together with a
       statistical metrology for incorporating them into a
       meaningful focal plane error budget. !0 


Paper #: 3334-10
Lithographic effects of mask critical dimension error, pp.106-116
Author(s):  Alfred K. Wong, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Richard A. Ferguson, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Lars W. Liebmann, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Scott M. Mansfield, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Antoinette F. Molless, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Mark O. Neisser, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA.

Abstract: Magnification of mask dimensional error is examined and
       quantified in terms of the mask error factor (MEF) for
       line and hole patterns on three types of masks:
       chrome-on-glass (COG), attenuated phase-shifting mask
       (PSM) and alternating PSM. The MEF is unity for large
       features, but increases rapidly when the critical
       dimension (CD) is less than 0.5 $lambda@/NA for
       line-space patterns and 0.75 $lambda@/NA for contacts.
       In general dark-field spaces exhibit higher sensitivity
       to mask dimensional error than light-field lines.
       Sensitivity of attenuated PSMs is similar to COG masks,
       even for applications in which attenuated PSMs provide
       benefits in process latitude. Alternating PSMs have the
       lowest MEF values. Although the MEF has only a slight
       dependence on feature nesting for contacts, dense lines
       and spaces exhibit markedly higher MEF values than
       isolated features. The MEF of a 0.35 $lambda@/NA
       isolated line is 1.6 whereas that of a dense line of
       the same dimension is 4.3! Annular illumination is
       effective in reducing the mask error sensitivity of
       dense lines. Dose variation causes changes in the MEF
       of contacts but has little effect on line-space
       features; focus error degrades (increases the value of)
       the MEF of both pattern types. A high diffusion and low
       contrast photoresist process also worsens the MEF.
       Consequences of mask CD error amplification include
       tightening of mask specification, design grid
       reduction, shift in optimal mask bias and enhanced
       defect printability. !32 


Paper #: 3334-11
Lithography of 180-nm design rule for 1-Gb DRAM, pp.117-123
Author(s):  Dong-Seok Nam, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea;
            Junghyeon Lee, Samsung Electronics Co., Ltd.,
            Yongin-Shi Kyungi-Do, South Korea;
            Changhwan Kim, Samsung Electronics Co., Ltd.,
            Yongin-Goon, Kyungki-Do, South Korea;
            Sung-Woon Choi, Samsung Electronics Co., Ltd.,
            Kyungki-Do Suwon, South Korea;
            Ho Young Kang, Samsung Electronics Co., Ltd.,
            Suwon City, South Korea;
            Jootae Moon, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea.

Abstract: Optical lithography is the most fundamental technology
       for the development of 1 Gbit DRAM device. As a current
       status, KrF lithography is a powerful candidate for 180
       nm generation because of relatively high cost of ArF
       lithography and its untimely applicability to mass
       production. In this paper, we showed that the optimized
       OAI system with large quadrupole offset and small
       opening could improve the resolution and process margin
       in the photo process of 180 nm level DRAM devices. We
       also demonstrated what the effect of CD amplification
       factor ($alpha@) was related to the mask CD control and
       resist tone under the optimized OAI system. The result
       shows that the combination of the optimized OAI system
       and positive tone resist can give rise to the reduction
       of $alpha from 4.5 to almost 1 and provide a reasonable
       margin. !7 


Paper #: 3334-12
Reduction of mask-induced CD errors by optical proximity
correction, pp.124-130
Author(s):  John Randall, Texas Instruments and IMEC, Leuven,
            Belgium;
            Alexander Tritchkov, IMEC, Leuven, Belgium;
            Rik Jonckheere, IMEC, Leuven, Belgium;
            Patrick Jaenen, IMEC, Leuven, Belgium;
            Kurt Ronse, IMEC, Leuven, Belgium.

Abstract: The critical dimension (CD) tolerance specifications
       for masks have not only been required to keep up with
       the unrelenting drive of downscaling and a shift from
       5X to 4X reticles, but will soon have to deal with
       lithographic magnification of mask CD errors.
       Nonlinearities in both the imaging system and resist
       response will exacerbate CD errors in the mask. A pupil
       filtering technique has been proposed to reduce the
       optical component of mask error magnification, but this
       is only effective for dense features. This paper
       describes a possible method of reducing the effect of
       mask CD errors for isolated features. Sub-resolution
       assisting features or outriggers are used to reduce
       proximity effects and to improve the depth of focus of
       isolated lines. We have demonstrated that correlated
       errors in lines and associated outriggers can reduce
       the impact of mask CD errors. The experiments used to
       verify this effect in 248 nm lithography also
       demonstrated nonlinearity in the resist that increased
       the mask error magnification. !9 


Paper #: 3334-13
Subresolution assist feature and off-axis illumination
optimization for 200- and 240-nm contact windows using 248-nm
lithography, pp.131-139
Author(s):  George P. Watson, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Raymond A. Cirelli, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Allen G. Timko, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Omkaram Nalamasu, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Carl Lockstamphor, Lucent Technologies/Bell Labs.,
            Peabody, MA, USA;
            Steven D. Berger, Micrion Corp., Tewksbury, MA, USA;
            Neil Bassom, Micrion Corp., Peabody, MA, USA;
            Ganesh Sundaram, Micrion Corp., Peabody, MA, USA.

Abstract: Sub-resolution assist features, coupled with
       appropriate off- axis illumination conditions, have
       been studied with the goal of fabricating 200 and 240
       nm contact windows with uniform critical dimensions
       over a range of pitches and with large depths of focus
       (DOF). Results show that 240 nm isolated contacts
       without assist features possessed a useful DOF of less
       than 0.4 microns. The same features with 140 nm assist
       slots on each window edge, located 190 nm away,
       possessed a DOF of over 0.8 microns, using quadrupole
       illumination. Soft quadrupole illumination, where a
       mixture of quadrupole and conventional illumination is
       employed, yielded nearly the same DOF as quadrupole and
       printed both semi-dense and isolated contact windows
       near their optimum size as well. Contact holes, 200 nm
       wide, have been printed with smaller sub- resolution
       features, soft quadrupole illumination, and higher
       performance resists with a DOF of over 0.6 microns
       using a stepper with a numerical aperture of 0.53. !4 


Paper #: 3334-14
Revalidation of the Rayleigh resolution and DOF limits,
pp.142-153
Author(s):  Bruce W. Smith, Rochester Institute of Technology,
            Rochester, NY, USA.

Abstract: Currently, the fundamental relationships which
       establish the limits to optical imaging appear useful
       only as comparative metrics for microlithographic
       applications. Furthermore, with the continual advances
       in optical lithography, the validity of such
       'rules-of-thumb' become suspect. A set of universal
       equations would be useful but additional description
       and expansion beyond the Rayleigh definitions is needed
       for application to current technologies. Relationships
       which govern the limits of resolution and focal depth
       are presented here in order to develop a more complete
       description for various lithographic imaging
       situations. Expanded Rayleigh definitions can then
       allow for insight into fundamental limitations and
       scaling for conventional partially coherent imaging,
       imaging with off-axis illumination, and phase-shift
       masking. Depth of focus relationships are also expanded
       to describe the distribution of diffraction orders over
       the lens pupil and are modified to accommodate feature
       pitch and partial coherence. Such analysis can allow
       for a more thorough understanding and prediction of
       performance for a given lithographic technology. !3 


Paper #: 3334-15
Quasi-physical model for fast resist contour simulation:
importance of lens aberrations and acid diffusion in LSI pattern
design, pp.154-163
Author(s):  Hiroshi Fukuda, Hitachi Central Research Lab.,
            Kokubunji-shi, Tokyo, Japan;
            Keiko T. Hattori, Hitachi Central Research Lab.,
            Kokubunji Tokyo, Japan.

Abstract: The aberration in optics and acid diffusion in resist
       films have a great influence on proximity effects in
       optical lithography. Our analysis clarified that (1) a
       local (random) pupil-phase variation (higher-order
       aberration) degrades imaging performance under highly
       coherent illumination often used with periodic
       phase-shifting masks, and (2) in some positive-tone
       chemically amplified resists, the non-Fickean diffusion
       process changes effective image distributions,
       depending on the patterns features and mask tonality.
       Although the latter has a potential to achieve high
       resolution capability for isolated bright features,
       these effects generally pronounce proximity effects and
       make their correction difficult. Simple modeling of
       these effects and their simulation implementation are
       also discussed. !10 


Paper #: 3334-16
Lithographic process simulation for scanners, pp.164-175
Author(s):  Andreas Erdmann,
            Fraunhofer Institute for Silicon Technology,
            Itzehoe, Germany;
            Michael Arnz, Carl Zeiss, Oberkochen, Germany;
            Mireille Maenhoudt, IMEC, Leuven, Belgium;
            Jan Baselmans, ASM Lithography BV, Veldhoven,
            Netherlands;
            J.C. van Osnabrugge, ASM Lithography BV, Velhoven,
            Netherlands.

Abstract: In scanner systems wafer and reticle move continuously
       with respect to the projection optics. This movement
       across the image field results in varying lateral shift
       and focus positions and in an averaging of aberrations
       from different field positions of the projection
       system. Several approaches for the effective simulation
       of these effects are discussed. Based on simulated and
       experimental data, scanner effect are quantified and
       compared to results of static stepper exposure. !9 


Paper #: 3334-17
Lithography simulation employing rigorous solutions to Maxwell's
equations, pp.176-196
Author(s):  Ronald L. Gordon, FINLE Technologies, Inc., Austin,
            TX, USA;
            Chris A. Mack, FINLE Technologies, Inc., Austin, TX,
            USA.

Abstract: A method of obtaining rigorous solutions to Maxwell's
       equations for the transmission of light through a
       photomask, both chrome-based and phase-shifting, is
       presented. The electromagnetic simulator will predict
       the transmission of light through the mask taking into
       account material properties, width, and thickness of
       the structures on the mask. This electromagnetic
       simulation will then be incorporated into the software
       package PROLITH/2 for complete simulation down to the
       resist level. Examples of lithography simulation using
       these rigorous solutions will be presented. !26 


Paper #: 3334-18
LAVA: lithography analysis using virtual access, pp.197-201
Author(s):  Chang Hsu, Univ. of California/Berkeley, Berkeley,
            CA, USA;
            Rona Yang, Univ. of California/Berkeley, Berkeley,
            CA, USA;
            Jeffery Cheng, Univ. of California/Berkeley,
            Berkeley, CA, USA;
            Peter Chien, Univ. of California/Berkeley, Berkeley,
            CA, USA;
            Victor Wen, Univ. of California/Berkeley, Berkeley,
            CA, USA;
            Andrew R. Neureuther, Univ. of California/Berkeley,
            Berkeley, CA, USA.

Abstract: A web site allowing remote operation of the SPLAT,
       SAMPLE, TEMPEST and SIMPL simulators has been developed
       to promote collaborative work on lithography and in
       particular on EUV technology. Based on the extensive
       use of platform independent programming languages, LAVA
       is accessible from all modern computing platforms. The
       software supporting the web site is available to others
       in creating similar web site sites and in making
       simulators such as those from other universities 'play'
       together. The web site explores new paradigms in remote
       operation of lithography simulators and introduces more
       application-oriented modes of interaction with
       technologists. The LAVA web site URL is
       http://cuervo.eecs.berkeley.edu/Volcano/ !4 


Paper #: 3334-19
0.25-um logic manufacturability using practical 2D optical
proximity correction, pp.204-214
Author(s):  Michael E. Kling, Motorola, Austin, TX, USA;
            Kevin D. Lucas, Motorola, Austin, TX, USA;
            A.Reich, Motorola, Austin, TX, USA;
            Bernard J. Roman, Motorola, Austin, TX, USA;
            Harry Chuang, Motorola, Austin, TX, USA;
            Percy V. Gilbert, Motorola, Austin, TX, USA;
            Warren D. Grobman, Motorola, Austin, TX, USA;
            Edward O. Travis, Motorola, Austin, TX, USA;
            Paul Tsui, Motorola, Austin, TX, USA;
            Tam Vuong, Motorola, Austin, TX, USA;
            Jeff P. West, Motorola, Austin, TX, USA.

Abstract: Simplified 2-D Optical Proximity Correction (OPC)
       algorithms have been devised, calibrated and
       implemented on a state-of- the-art 0.25 micrometer
       random logic process in order to reduce metal line
       pullback on critical layers. The techniques used are
       rules-based, but are characterized by fast and robust
       data conversion algorithms, calibrations based on
       actual process data improvements in reticle
       manufacturability, and inspectability of the resultant
       OPC corrected reticles. Application to local
       interconnect and metal patterning has corrected
       fundamental yield-limiting mechanisms in these levels.
       !4 


Paper #: 3334-20
Practical approach to control the full-chip-level gate CD in DUV
lithography, pp.215-223
Author(s):  Chul-Hong Park, Samsung Electronics Co., Ltd.,
            Yongin-Gun Kyungki-do, South Korea;
            Yoo-Hyon Kim, Samsung Electronics Co., Ltd.,
            Kyungki-do, South Korea;
            Hoong-Joo Lee, Samsung Electronics Co., Ltd.,
            Kyungki-do, South Korea;
            Jeong-Taek Kong, Samsung Electronics Co., Ltd.,
            Yongin-Gun Kyungki-do, South Korea;
            Sang-Hoon Lee, Samsung Electronics Co., Ltd.,
            Yongin-Gun Kyungki-do, South Korea.

Abstract: A practical method to control the full chip level gate
       CD of a logic device with a 0.28 micrometer minimum
       design rule in DUV lithography is evaluated using an
       automatic optical proximity correction (OPC) software
       with empirical modeling. The CD variation on a chip
       results from the proximity and uniformity CD errors.
       The proximity error occupying more than 40% of total CD
       variation is caused by the pattern geometry, resist
       process, and mask CD error. In this paper, the OPC has
       been applied to line width narrowing and line-end
       shortening. The line-end shortening has been corrected
       by only the line- end extension instead of adding
       serifs which can be mistaken for defects during mask
       inspection. From this work, 43% reduction of the CD
       variation induced by proximity in the 3$sigma standard
       deviation has been achieved at the 14 nm correction
       unit. Furthermore, the focus margin of 1.2 micrometer
       after OPC has been guaranteed. The results of line- end
       correction show that the line-end extension correction
       is sufficient to correct the overlap mismatching
       between the active and gate layers. !13 


Paper #: 3334-21
Accurate proximity correction method with total-process
proximity-based correction factor (TCF), pp.224-233
Author(s):  Kohji Hashimoto, Toshiba Corp., Yokohama, Japan;
            Satoshi Usui, Toshiba Corp., Yokohama, Japan;
            Shigeru Hasebe, Toshiba Corp., Kawasaki, Japan;
            Masayuki Murota, Toshiba Corp., Kawasaki, Japan;
            Takeo Nakayama, Toshiba Corp., Saiwai-ku Kawasaki,
            Japan;
            Fumitomo Matsuoka, Toshiba Corp.,
            Saiwai-ku Kawasaki, Japan;
            Soichi Inoue, Toshiba Corp., Kanagawa, Japan;
            Sachiko Kobayashi, Toshiba Corp., Kawasaki, Japan;
            Kazuko Yamamoto, Toshiba Corp., Kawasaki, Japan.

Abstract: A novel, accurate, one-dimensional process proximity
       correction method is proposed. The method is based on
       the relationship between a line width variation and the
       bias which should be corrected. This relationship is
       characterized by the Total process proximity-based
       Correction Factor (TCF) which is defined as the slope
       of the wafer CD variation curve to the mask design CD
       under a constant pattern pitch condition. At a TCF
       greater than 1, patterns should be corrected with
       values less than the line width deviation. By applying
       the new PPC method to 0.25 micrometer logic gate
       patterns, a correction rule table was experimentally
       obtained. The new PPC mask fabricated with the
       correction rule exhibited a significant improvement
       over the conventional correction technique in the logic
       device. !3 


Paper #: 3334-22
Applications of enhanced optical proximity correction models,
pp.234-244
Author(s):  Jack Q. Zhao, Lucent Technologies/Bell Labs.,
            Orlando, FL, USA;
            Joseph G. Garofalo, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            James Blatchford, Lucent Technologies/Bell Labs.,
            Orlando, FL, USA;
            Edward Ehrlacher, Lucent Technologies/Bell Labs.,
            Orlando, FL, USA;
            Ellis Nease, Lucent Technologies, Allentown, PA,
            USA.

Abstract: The accurate prediction of relevant optical and other
       processing effects is the essential first element of
       optical proximity effect (OPC) methodologies. A
       quasi-empirical modeling technique has been devised.
       Starting from standard aerial-image energy deposition,
       an exponential transfer function is employed to account
       for saturation effects. This is then followed by a
       double-Gaussian diffusion convolution. Finally, a novel
       2-dimensional log-slope model was devised to better
       predict some DUV processes. The model parameters are
       derived from a few empirical measurements and a fitting
       process. The calibrated model is then used by a
       rule-based OPC package to correct a variety of
       structures. Efficient verification techniques suitable
       for large area designs are introduced. !3 


Paper #: 3334-23
Process proximity correction using an automated software tool,
pp.245-253
Author(s):  Wilhelm Maurer, Siemens AG, Muenchen, Germany;
            Christoph Dolainsky, aiss GmbH, Munich, Germany;
            Joerg Thiele, Siemens AG, Munich, Germany;
            Christoph Friedrich, Siemens AG, Muenchen, Germany;
            Paul Karakatsanis, aiss GmbH, Munich, Germany.

Abstract: The pattern transfer process from the chip layout data
       to the structures on the finished wafer consists of
       many process steps. Although desired, none of these
       steps is linear in all aspects of the pattern transfer.
       Approaching the process limits due to the
       ever-shrinking linewidth, the non- linearities of the
       pattern transfer clearly show up. This means, that one
       cannot continue the practice to summarize all process
       influences into one bias between the data used for mask
       making and the final chip structure. The correction of
       process non-linearities is a necessity. This correction
       is usually called optical proximity correction (OPC),
       although not all effects intended for correction are of
       optical origin and/or not all these are effects of the
       neighborhood. We therefore propose to use the term PPC
       (process proximity correction). This paper reports our
       experiences with the application of OPTISSIMO, a
       software tool developed to perform automatically
       OPC/PPC for full chip designs. First, we provide a
       definition of PPC, which in our view has to correct all
       non- linearities of the pattern transfer process from
       layout data to the final electrically measured
       structures. Then, the strategy of the OPC/PPC tool
       OPTISSIMO, a software package to perform PPC based on
       process simulation, is discussed. We focus on the data
       handling strategy and on the process modeling of the
       tool under evaluation. It is shown, that full chip
       OPC/PPC is practicable using a well-designed hierarchy
       management system combined with a pattern library.
       Finally, it is demonstrated, that a model-based OPC/PPC
       tool is by definition a process simulation tool, that
       is able to perform all simulation tasks (like defect
       printability) at reasonable accuracy. !7 


Paper #: 3334-24
Optical lens specifications from the user's perspective,
pp.256-268
Author(s):  Christopher J. Progler,
            IBM Semiconductor Research and Development Ctr.,
            Hopewell Jct, NY, USA;
            Donald C. Wheeler,
            IBM Semiconductor Research and Development Ctr.,
            Hopewell Junction, NY, USA.

Abstract: We develop three main topics in support of further
       understanding and specifying wavefront aberrations from
       the lithographer's point of view. The concept of the
       Magnitude Weighted Aberration is introduced providing a
       convenient and rapid numerical method for assessing the
       interaction of wavefront aberrations with reticle
       pattern and illumination mode. This analysis suggests
       that the advanced lithographic lens user will require
       unprecedented correction on the total wavefront
       aberration to realize the full potential of the imaging
       system in high yielding integrated circuit fabrication.
       Specific details on the required aberration control are
       provided with a Monte Carlo tolerancing analysis of the
       RMS wavefront error using lithographic CD control and
       pattern placement as quality metrics. Patten placement
       proves to be as sensitive to wavefront aberrations as
       CD control forcing a tight specification on the
       asymmetric aberration components even when a large
       focus and exposure latitude is available. Based on the
       wavefront specifications generated it is imperative
       that the lithographic lens user be able to
       independently de-couple and quantify the state of
       certain aberration coefficients. Toward this goal, we
       demonstrate an aberration reverse engineering procedure
       using experimental pattern placement error as the input
       response. !15 


Paper #: 3334-25
Aberration evaluation and tolerancing of 193-nm lithographic
objective lenses, pp.269-280
Author(s):  Bruce W. Smith, Rochester Institute of Technology,
            Rochester, NY, USA;
            James E. Webb, Tropel Corp., Fairport, NY, USA;
            John S. Petersen, SEMATECH, Austin, TX, USA;
            Jeff Meute, SEMATECH, Austin, TX, USA.

Abstract: Described here is an approach to aberration tolerancing
       utilizing aerial image parameterization based on
       photoresist capability. A minimum aerial image metric
       is determined from either a characterized resist
       process or desirable resist attributes and includes
       definition of resist exposure, diffusion, and
       development properties. Minimum aerial image
       requirements can then be correlated to resist
       performance to allow for the evaluation of various
       feature sizes and types. This allows, for example, the
       prediction of lens performance through focus, across
       the field, and in the presence of small levels of
       internal flare. Results can then be compared with more
       conventional optical metrics such as Strehl ratio,
       partial coherence contrast, or image threshold CD.
       Results are presented for three commercial small field
       catadioptric 193 nm lithographic lenses. Aberration
       levels for each lens at several field positions and at
       several wavelengths has been described using 37.
       Zernike polynomial coefficients. Minimum aerial image
       requirements have been correlated to resist performance
       to allow the evaluation of various feature types, a
       unique situation when no mature 193 nm resist process
       existed. Additionally, the impact of modified
       illumination on aberrations is presented. !10 


Paper #: 3334-26
Pupil illumination: in-situ measurement of partial coherence,
pp.281-288
Author(s):  Joseph P. Kirk, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Christopher J. Progler, IBM Microelectronics Div.,
            Hopewell Jct, NY, USA.

Abstract: Lithographic tool performance depends in part on the
       partial coherence (how the lens pupil is illuminated)
       during photoresist exposure. The partial coherence dial
       is set prior to exposure and it is usually assumed it
       correctly indicates actual pupil illumination. The
       validity of this assumption is tested in situ by
       utilizing a 'negative pinhole,' an occluding spot on
       the back side of a clear reticule, that forms a
       negative image of the pupil illumination. A
       quantitative sequence of dose contours is obtained from
       the resist boundaries of images formed by exposing
       positive photoresist through a clearing dose sequence.
       These contours are pieced together and generate a
       source file describing the illumination distribution
       that is used as input to a lithography simulator to
       determine tool performance under actual operating
       conditions. !6 


Paper #: 3334-27
Characterization of spatial coherence uniformity in exposure
tools, pp.289-296
Author(s):  Ilya M. Grodnensky, Nikon Precision Inc.,
            Foster City, CA, USA;
            Etsuya Morita, Nikon Precision Inc., Belmont, CA,
            USA;
            Kyoichi Suwa, Nikon Corp., Shinagawa Tokyo, Japan;
            Shigeru Hirukawa, Nikon Corp., Shinagawa-ku, Tokyo,
            Japan.

Abstract: A novel technique to characterize variations of the
       spatial (partial) coherence $sigma across the image
       field in modern steppers and scanners has been
       developed and experimentally tested. It is based on the
       high sensitivity of the length L of macroscopically
       large diamond-shaped marks printed in photoresist to
       $sigma variation. Variations in the $sigma value across
       the image field lead to variations in the length of
       marks printed at different image field locations. The
       mark lengths are measured rapidly with high accuracy by
       a built-in optical system and then converted into
       $sigma values using the calibration dependence
       L($sigma@) measured in the same exposure tool.
       Simulation and experimental studies show that the level
       of projection lens aberrations in modern Nikon tools
       have practically no effect on $sigma measurements
       obtained with this technique. Our results demonstrate
       that in the conventional illumination scheme, $sigma
       distribution can be measured with an accuracy of 2.5%.
       The main advantage of the presented method is that
       $sigma variation over the image field is characterized
       by the exposure tool itself, avoiding expensive and
       time-consuming SEM measurements. Moreover, since the
       measurement procedure is based on the wedge-shaped
       marks and laser scanning system currently used in Nikon
       tools for automated focus detection, implementation of
       the technique does not require any hardware or software
       modification. !6 


Paper #: 3334-28
Evaluation of coma aberration in projection lens by various
measurements, pp.297-308
Author(s):  Takashi Saito, Matsushita Electronics Corp.,
            Minami-ku Kyoto, Japan;
            Hisashi Watanabe, Matsushita Electronics Corp.,
            Minami-ku Kyoto, Japan;
            Yoshimitsu Okuda, Matsushita Electronics Corp.,
            Minami-ku, Kyoto, Japan.

Abstract: In this paper, evaluation of lens coma aberration in
       projection lens of a stepper by various measurement
       methods is described. The measurement methods were
       based on asymmetry of the printed images caused by coma
       aberration. We used three measurement methods. They are
       conventionally used method and two new methods. The
       three methods are: (a) measuring the CD difference
       between both ends of line-and-space, (b) observing the
       side lobe patterns using an attenuated phase shifting
       mask (a-PSM), and (c) measuring the registration error
       using overlay patterns that have assist patterns. These
       measurement patterns are printed on Si wafers by a KrF
       stepper (NA equals 0.55) with various $sigma@. The
       dependence of the feature size and $sigma on the
       influence of coma aberration was easily measured by
       these methods. As each method has merits and demerits,
       proper use of each method is necessary. Then the
       influence of coma aberration was evaluated by method
       (a). The influence of coma aberration had two
       components and they were due to primary coma aberration
       and de-centering coma aberration respectively. We
       estimated the influence of coma aberration by
       simulation and got good agrement with the experimental
       results. The measurement methods we demonstrated here
       are applicable for lens evaluation of steppers by the
       users. !10 


Paper #: 3334-29
ArF excimer laser lithography with bottom antireflective coating,
pp.310-321
Author(s):  Shinji Kishimura,
            Association of Super-Advanced Electronics Technologie
            s, Yokohama, Japan;
            Makoto Takahashi,
            Association of Super-Advanced Electronics Technologie
            s, Yokohama Kanagawa, Japan;
            Keisuke Nakazawa,
            Association of Super-Advanced Electronics Technologie
            s, Yokohama Kanagawa, Japan;
            Takeshi Ohfuji,
            Association of Super-Advanced Electronics Technologie
            s, Yokohama Kanagawa, Japan;
            Masaru Sasago,
            Association of Super-Advanced Electronics Technologie
            s, Yokohama-shi Kanagawa, Japan;
            Masaya Uematsu,
            Semiconductor Leading Edge Technologies, Inc.,
            Totsuka-ku Kanagawa, Japan;
            Tohru Ogawa,
            Semiconductor Leading Edge Technologies, Inc.,
            Yokohama Kanagawa, Japan;
            Hiroshi Ohtsuka,
            Semiconductor Leading Edge Technologies, Inc.,
            Yokohama Kanagawa, Japan.

Abstract: In ArF excimer laser lithography, the bottom
       antireflective coating (BARC) technique is essential in
       inhibiting the effect of interference and reflective
       notching. We investigated the antireflective effect of
       commercially available organic BARCs, that had
       originally been designed for KrF and i-line
       lithography, and also the patterning characteristics of
       ArF resists with BARCs. The refractive indices of
       various materials were measured with a spectroscopic
       ellipsometer. The real part (n) and the imaginary part
       (k) of the complex refractive index at 193 nm were 1.4
       to 1.7 and 0.1 to 0.8 respectively. Almost all the
       materials had sufficient antireflectivity at 193 nm. We
       investigated the patterning characteristics of
       chemically amplified ArF positive resists with suitable
       BARC materials. The resolution, the depth-of- focus of
       patterns below 0.16-micrometer lines and spaces, and
       the exposure latitude were improved and good critical
       dimensional control over topography was achieved by
       using BARC. An acceptable profile after gate structure
       (BARC, W-Si, and Poly-Si) etching could be obtained
       under the typical etching conditions used for KrF
       resists. !12 


Paper #: 3334-30
Bottom-ARC optimization methodology for 0.25-um lithography and
beyond, pp.322-336
Author(s):  Maaike Op de Beeck, IMEC, Leuven, Belgium;
            Geert Vandenberghe, IMEC, Leuven, Belgium;
            Patrick Jaenen, IMEC, Leuven, Belgium;
            Feng-Hong Zhang, IMEC, Leuven, Belgium;
            Christie Delvaux, IMEC, Leuven, Belgium;
            Paul Richardson, IMEC, Leuven, Belgium;
            Ilse van Puyenbroeck, IMEC, Leuven, Belgium;
            Kurt Ronse, IMEC, Leuven, Belgium;
            James E. Lamb, III, Brewer Science, Inc., Rolla, MO,
            USA;
            Johan B. van der Hilst, ASM Japan, Tama-shi Tokyo,
            Japan;
            Johannes van Wingerden, Philips Research Labs.,
            Eindhoven, Netherlands.

Abstract: This paper reports on an optimization methodology for
       BARC/resist processes in order to obtain best
       CD-control on various substrate topographies. A
       selection of resist and BARC materials is studied by
       means of simulations and experiments. Two BARC
       properties, turned out to be of major importance:
       planarization effects on topography and etch behavior.
       The topography itself is very important too: step
       height and lateral dimensions have a severe influence
       on CD control. Based on a new evaluation technique, the
       use of topographical swing curves, the optimum
       thickness of the BARC layer and of the resist layer are
       determined. !7 


Paper #: 3334-31
Inorganic antireflective coating process for deep-UV lithography,
pp.337-346
Author(s):  Qizhi He, Texas Instruments Inc., Plano, TX, USA;
            Wei W. Lee, Texas Instruments Inc., Dallas, TX, USA;
            Maureen A. Hanratty, Texas Instruments Inc., Dallas,
            TX, USA;
            Daty Rogers, Texas Instruments Inc., Dallas, TX,
            USA;
            Guoqiang Xing, Texas Instruments Inc., Dallas, TX,
            USA;
            Abha Singh, Texas Instruments Inc., Dallas, TX, USA;
            Eden Zielinski, Texas Instruments Inc., Dallas, TX,
            USA.

Abstract: Antireflective coatings (ARCs) have been used to
       enhance IC lithography for years, however, many
       conventional bottom ARCs can no longer maintain
       acceptable linewidth control, cannot meet stringent
       deep-UV (DUV) photoresist processing requirements, and
       increase the etch complexity. In this paper, we report
       the development of an inorganic ARC for DUV lithography
       in sub-0.25 micrometer advanced device applications.
       Plasma-enhanced chemical vapor deposition (PECVD) is
       employed to deposit a dielectric film silicon
       oxynitride (Si$-x$/O$-y$/N$-z$/) with specific optical
       properties. The three optical parameters of the
       Si$-x$/O$- y$/N$-z$/ film: refractive index n,
       extinction coefficient k, and thickness d are
       specifically designed to ensure that the reflection
       light that passes through the ARC/substrate is equal in
       amplitude and opposite in phase to the reflected light
       from the resist/ARC interface. The reflection light is
       canceled by destructive interference and therefore
       photoresist receives the minimum substrate reflection
       wave. Using this technique, we have successfully
       patterned features at 0.25 micrometer and below. The
       dielectric film can not only function as an ARC layer,
       but also serve as a hardmask for the pattern transfer
       etch process. With an aggressive etch bias process,
       linewidths down to 0.60 micrometer poly-Si gate are
       achieved with good linewidth control (3$sigma less than
       12 nm) and a near perfect linearity. For the marginal
       metal etch resistance of DUV photoresist, the designed
       Si$-x$/O$-y$/N$- z$/ is effective in imparting more
       etch resistance and suppressing metal substrate
       reflection. Excellent optical uniformity of the n, k
       and thickness d of the Si$-x$/O$-y$/N$- z$/ ARC is
       obtained with a manufacturable PECVD deposition
       process. !8 


Paper #: 3334-32
Influence of underlayer reflection on optical proximity effects
in sub-quarter-micron lithography, pp.347-355
Author(s):  Atsushi Sekiguchi, Sony Corp.,
            Atsugi-shi, Kanagawa-ken, Japan;
            Fumikatsu Uesawa, Sony Corp., Atsugi-Shi, Japan;
            Koichi Takeuchi, Sony Corp.,
            Atsugi-shi Kanagawa-ken, Japan;
            Tatsuji Oda, Sony Corp., Atsugi-shi Kanagawa, Japan.

Abstract: The relationship between the optical proximity effect
       (OPE) and the underlayer reflection has been
       investigated by using negative and positive resists in
       sub-quarter-micrometer lithography. A new evaluation
       method that uses the center exposure dose of the
       ED-window (1-2) is been proposed. This technique takes
       the manufacturing margin into consideration and can be
       used to obtain the common ED-window of isolated and
       density patterns. The negative resists show a small
       critical dimension variation between isolated and
       density lines (CD bias) with the most suitable exposure
       dose and best focus conditions. However, the common
       ED-window of the isolated and density patterns is poor
       in terms of the manufacturing margin. Furthermore, the
       $sigma dependence of the negative resist is too weak to
       improve the manufacturing margin. The effect of the
       underlayer reflection on the CD bias of the negative
       resist is significant in our experiment. On the other
       hand, the positive resist shows strong $sigma
       dependence. Because the influence of the underlayer
       reflection on the positive resist is small, it is
       important to optimize $sigma when improving the CD bias
       for the positive resist. In order to compare the
       negative and positive resists under equivalent
       conditions, a resist development simulation was used.
       The simulation results show the negative resist could
       be capable of high performance. !13 


Paper #: 3334-33
Deep-UV reflection control for patterning dielectric layers,
pp.356-370
Author(s):  Ramkumar Subramanian, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Gurjeet S. Bains, Advanced Micro Devices, Inc.,
            San Jose, CA, USA;
            Christopher F. Lyons, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Bhanwar Singh, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA;
            Ernesto Gallardo, Advanced Micro Devices, Inc.,
            Sunnyvale, CA, USA.

Abstract: This paper describes the results of CD control studies
       on a dielectric layer that has both dense & isolated
       trenches and dense contact holes. Both top and bottom
       anti-reflective coatings were explored as well as the
       standard process without ARC. All wafers had a standard
       logic technology process flow and had been through
       Chemical-Mechanical Planarization prior to patterning.
       Stepper exposure conditions were varied in the form of
       partial coherence to obtain maximum depth of focus and
       exposure latitude. The results of this study were
       characterized in the form of a CD process window in
       which Exposure Dose was plotted vs. Defocus for all the
       3 patterns i.e. dense & isolated trenches and dense
       contact holes. The effect of BARC etch was also
       explored. !10 


Paper #: 3334-36
Simulation and experimental evaluation of double-exposure
techniques, pp.372-383
Author(s):  Mark O. Neisser, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Antoinette F. Molless, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA.

Abstract: The process windows and capabilities of double exposure
       techniques with binary and attenuated masks are
       explored using simulation and experiment, including the
       effects of resist properties, illumination conditions
       and overlay error. Here it is shown that by using a low
       partial coherence factor (sigma) for the two exposures,
       the total window is considerably improved over that
       obtained using higher partial coherence illumination.
       We call this process ORAMEX, which stands for Ordinary
       Resist And Multiple EXposure. It was found that the
       process window for nested lines and spaces using ORAMEX
       is considerably better than that for conventional
       illumination. This is shown for aerial images and for
       aerial images plus a resist model with contrast and
       diffusion length similar to that of state of the art
       Deep UV resists. In fact, the total process windows
       found for ORAMEX show good process latitudes for both
       dense and isolated features, with ORAMEX usually
       enhancing dose latitude more than single exposure off
       axis illumination does. Overlay errors are found not to
       affect the process window for individual features.
       However, they do affect the common window for every
       other line (in positive resist) but not spaces. It was
       also found that using attenuated masks instead of
       binary masks further improves the process window and
       resolution of ORAMEX. Experimental results agree with
       simulation and show a process window for 150 nm lines
       and spaces with over 0.4 micrometer depth of focus and
       15% dose latitude in 0.6 micrometer of resist using
       ORAMEX and chrome on glass masks. Using attenuated
       masks and ORAMEX a similar process window (0.4
       micrometer DOF and 16% dose latitude) was obtained for
       125 nm lines and spaces. Both results were obtained on
       a 0.6 NA Deep UV stepper using commercial positive
       resist. !9 


Paper #: 3334-37
Illumination pupil filtering using modified quadrupole apertures,
pp.384-394
Author(s):  Bruce W. Smith, Rochester Institute of Technology,
            Rochester, NY, USA;
            Lena Zavyalova, Rochester Institute of Technology,
            Rochester, NY, USA;
            John S. Petersen, SEMATECH, Austin, TX, USA.

Abstract: Off-axis illumination schemes have been developed that
       can enhance both the resolution and focal depth
       performance for an optical exposure tool. One approach
       introduced modifies the illumination profile, filling
       the condenser lens pupil with weak Gaussian quadrupoles
       where energy is distributed within and between poles.
       This method has demonstrated better control of DOF and
       proximity effect for a variety of feature types. Other
       possibilities also exist. Presented here are approaches
       to illumination modification through use of condenser
       lens masking apertures, fabricated as attenuating fused
       silica reticles which are inserted at the lens pupil
       plane. Application of this technique for use in high NA
       248 nm and 193 nm exposure tools is shown. For each
       case, optimization of illumination profiles has been
       conducted. Optimized source files have been converted
       to halftone (dithered) masking files for electron beam
       patterning on fused silica with chromium and
       anti-reflective (AR) films. Analysis of these modified
       illumination techniques in terms of resolution, focal
       depth, throughput, and aberration performance is also
       presented. !6 


Paper #: 3334-121
New variable-transmission illumination technique optimized with
design rule criteria, pp.395-405
Author(s):  Raymond A. Cirelli, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Masis M. Mkrtchyan, Lucent Technologies/Bell Labs.,
            Gillette, NJ, USA;
            George P. Watson, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Lee E. Trimble, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Gary R. Weber, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            David L. Windt, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA;
            Omkaram Nalamasu, Lucent Technologies/Bell Labs.,
            Murray Hill, NJ, USA.

Abstract: We report on a novel technique for tuning the
       illumination of a lithography tool through the use of
       variable transmission apertures. In conjunction with
       this illumination technique, we have developed
       simulation software capable of identifying the optimum
       source plane coherence and intensity distribution to
       increase process latitude. This 'system' approach is
       capable of analyzing features specific to a given
       device level, or selected subsets of structure types
       within a given level. The fabrication of the aperture
       involves selectively depositing $alpha@-C onto a quartz
       plate that is inserted into the illuminator.
       Experimental testing has shown this film to be stable
       in its optical properties with extended exposure to DUV
       light. A description of the simulation software,
       aperture fabrication techniques, materials used, and
       experimental results for several aperture
       configurations are reported. !7 


Paper #: 3334-38
DUV stability of carbon films for attenuated phase-shift mask
applications, pp.406-411
Author(s):  Alessandro Callegari,
            IBM Thomas J. Watson Research Ctr.,
            Yorktown Heights, NY, USA;
            Katherina Babich,
            IBM Thomas J. Watson Research Ctr.,
            Yorktown Heights, NY, USA;
            Fuad Doany, IBM Thomas J. Watson Research Ctr.,
            Yorktown Heights, NY, USA;
            Frank Cardone, IBM Thomas J. Watson Research Ctr.,
            Yorktown Heights, NY, USA;
            Sampath Purushothaman,
            IBM Thomas J. Watson Research Ctr.,
            Yorktown Heights, NY, USA.

Abstract: The UV stability of a-C:H films was investigated by
       irradiating them with a 248 nm excimer laser or a DUV
       lamp with a 248 nm filter. Both transmittance and phase
       angle of the film at 248 nm were measured at different
       UV dose intervals up to a cumulative dose of 10,000
       J/cm$+2$/. We found that film stability was dependent
       on processing conditions. Excellent stability was
       achieved when the a-C:H films were sputtered from a
       graphite target in a Ar/hydrocarbon process gas mixture
       with the substrate held at an rf bias. If no substrate
       bias was used, films were stable only up to a maximum
       of 1,000 J/cm$+2$/ for a nominal transmittance of about
       6%. These instabilities were attributed to adsorption
       of oxygen on the film and its subsequent diffusion into
       the films. X-ray photoelectron spectroscopy (XPS) shows
       that under DUV irradiation the oxygen content increases
       from 13 to 29 at.% on the carbon surface. Secondary ion
       mass spectrometry (SIMS) shows also oxygen diffusion
       into the carbon film. It appears that the oxygen first
       removes the graphitic content since film transmittance
       was found to increase. It is believed that rf bias
       sputtering results in denser films that are more
       impervious to oxygen penetration and hence more durable
       to this UV assisted oxidative degradation process. The
       sputtered films with no substrate bias were found
       stable when irradiated in a nitrogen atmosphere. !7 


Paper #: 3334-39
New projection optical system for beyond 150-nm patterning with
KrF and ArF sources, pp.414-422
Author(s):  Shigeru Hirukawa, Nikon Corp., Shinagawa-ku, Tokyo,
            Japan;
            Koichi Matsumoto, Nikon Corp., Shinagawa-ku Tokyo,
            Japan;
            Kengo Takemasa, Nikon Corp., Kumagaya-shi Saitama,
            Japan.

Abstract: Two types of new optical system for 150 nm lithography
       are studied. One is the system with KrF source and high
       numerical aperture (NA), the other is the system with
       ArF source. By aerial image simulation, the adequate NA
       of each projection lens is searched, and the value was
       0.68 for KrF source and 0.60 for ArF source. Then the
       projection lens is fabricated and evaluated. The
       results are almost same as those of simulation. !2 


Paper #: 3334-40
Performance of an i-line step-and-scan system for sub-0.25-um
mix-and-match applications, pp.423-436
Author(s):  Peter van Oorschot, ASM Lithography BV, Veldhoven,
            Netherlands;
            Bert Koek, ASM Lithography BV, Veldoven,
            Netherlands;
            Jeroen van der Spek, ASM Lithography BV, Veldhoven,
            Netherlands;
            Eric Stuiver, ASM Lithography BV, Veldhoven,
            Netherlands;
            Hans Franken, ASM Lithography BV, Veldhoven,
            Netherlands;
            Herman Botter, ASM Lithography BV, La Veldhoven,
            Netherlands;
            Reiner Garreis, Carl Zeiss, Oberkochen, Germany.

Abstract: Step & Scan technology will be used for the next
       generation of semiconductor lithography tools. This
       technology has matured over the last year, and results
       from several DUV tools have been reported. For
       economical mass production in sub 0.25 micrometer
       applications, DUV and i-line lithography have to be
       combined (mix and match). This paper reports on the
       performance of a new high throughput, high resolution
       i-line Step & Scan system. The system has a 0.65 NA, 4X
       projection lens which, together with the AERIAL$+TM$/
       illuminator, provides a resolution of at least 0.28
       micrometer. The identical field sizes and the Step &
       Scan principle, result in a matched machine overlay,
       which is comparable to matching only DUV Step & Scan
       systems. !10 


Paper #: 3334-41
Imaging performance of scanning exposure systems, pp.437-447
Author(s):  Ryuichi Ebinuma, Canon Inc., Tochigi-ken, Japan;
            Kazunori Iwamoto, Canon Inc., Tochigi-ken, Japan;
            Hiroaki Takeishi, Canon Inc., Tochigi-ken, Japan;
            Hiroshi Itoh, Canon Inc., Tochigi-ken, Japan;
            Mitsuru Inoue, Canon Inc., Tochigi-ken, Japan;
            Kazuhiro Takahashi, Canon Inc., Utsunomiya Tochigi,
            Japan;
            Masakatsu Ohta, Canon Inc., Kanagawa, Japan.

Abstract: Relative position between the projected image on the
       wafer and the wafer itself changes during exposure.
       Factors of change are, for example, stage control
       error, difference of scanning direction between wafer
       stage and reticle stage (skew) and distortion of
       projection optics. We can define a kind of probability
       density function (PDF) concerning these changes of
       relative position. Fourier transform of this PDF is the
       transfer function of image transformation by relative
       motion. In this paper, we call this transfer function
       MoTF. The modulation of MoTF becomes a barometer of
       image contrast and the phase of MoTF gives position
       deviation (distortion). By analytical study of MoTF,
       standard deviation and expected value of said PDF are
       found to be the key parameters. Derived approximate
       equation in this paper agree with a computer simulation
       result of image contrast deterioration by vibration.
       With these studies, we can establish adequate
       specifications of scanning stage control demanded by
       imaging performance. Canon has developed a new stage
       structure for scanning exposures. By this structure the
       wafer stage is separated from main body on which
       projection optics and measurement systems are mounted
       so that reaction forces of stage acceleration can not
       be transferred directly to the maim body. With this
       structure we achieved excellent stage performance which
       has achieved imaging performance below 0.18 micrometer
       with high speed scanning. !4 


Paper #: 3334-42
Characterization of a next-generation step-and-scan system,
pp.448-459
Author(s):  Timothy J. Wiltshire, IBM Microelectronics Corp.,
            Hopewell Jct, NY, USA;
            Joseph P. Kirk, IBM Microelectronics Corp.,
            Hopewell Junction, NY, USA;
            Donald C. Wheeler, IBM Microelectronics Corp.,
            Hopewell Junction, NY, USA;
            Christopher Obszarny, IBM Microelectronics Corp.,
            Hopewell Junction, NY, USA;
            James T. Marsh, IBM Microelectronics Corp.,
            Hopewell Junction, NY, USA;
            Donald M. Odiwo, IBM Microelectronics Corp.,
            Hopewell Jct, NY, USA.

Abstract: Deep-ultaviolet (DUV) step-and-scan projection systems
       have been increasing in semiconductor manufacturing
       importance in recent years. IBM and other semiconductor
       manufacturers have made substantial use of 0.50
       numerical aperture (NA) step-and- scan systems for
       production resolutions down to approximately 250 nm
       resolution. This paper describes the initial system
       characterization and product performance of a next
       generation, 0.60 NA scanner system in early
       semiconductor production. !7 


Paper #: 3334-43
Laser pattern-generation technology below 0.25 um, pp.460-468
Author(s):  Paul C. Allen, Etec Systems, Inc., Beaverton, OR,
            USA.

Abstract: The projected rapid reduction in mask minimum feature
       size from the 250 nm to the 100 nm wafer generation
       will drive laser pattern generators to deep UV
       wavelengths. Commercially available sources exist in
       the 250 nm wavelength region using nonlinear optical
       materials to frequency double longer wavelength laser
       lines. Nonlinear optical materials, such as SBBO and
       KBBF, exist for wavelengths below 200 nm but they have
       not been commercialized. Second harmonic generation in
       intracavity or mode-locked, external resonant-ring
       laser configurations can be used to produce sub-200 nm
       radiation. Existing system architectures are shown to
       be easily modified to use pulsed sources with a high
       repetition rate. Advances in nonlinear optical
       materials, laser design, and system architecture will
       ensure that laser pattern generation will be an
       effective maskmaking technology for the next decade. !7


Paper #: 3334-45
Assessment of optical coatings for 193-nm lithography, pp.470-479
Author(s):  Vladimir Liberman, MIT Lincoln Lab., Lexington, MA,
            USA;
            Mordechai Rothschild, MIT Lincoln Lab., Lexington,
            MA, USA;
            Jan H. Sedlacek, MIT Lincoln Lab., Lexington, MA,
            USA;
            Ray S. Uttaro, MIT Lincoln Lab., Lexington, MA, USA;
            Andrew Grenville, Intel Corp., Lexington, MA, USA;
            Allen K. Bates, IBM Corp. and SEMATECH, Lexington,
            MA, USA;
            Chris K. Van Peski, SEMATECH, Austin, TX, USA.

Abstract: We present an assessment of antireflective coatings for
       193-nm lithography. Coatings from nine suppliers were
       exposed in a nitrogen ambient for up to 1.5 billion
       pulses at 15 mJ/cm$+2$//pulse at 400 Hz. Sensitive
       metrology, developed for this study, included
       reflectance/transmittance measurements, in-situ
       ratiometric transmission measurements, and
       interferometric calorimetry for absorption
       measurements. The coatings from at least two suppliers
       withstood greater than 1 billion pulses with no
       observable degradation. Catastrophic damage observed on
       some samples included blistering and a dramatic
       transmission drop. Such damage occurred rather early
       (less than 100 million pulses). !8 


Paper #: 3334-46
Damage testing of pellicles for 193-nm lithography, pp.480-495
Author(s):  Vladimir Liberman, MIT Lincoln Lab., Lexington, MA,
            USA;
            Roderick R. Kunz, MIT Lincoln Lab., Lexington, MA,
            USA;
            Mordechai Rothschild, MIT Lincoln Lab., Lexington,
            MA, USA;
            Jan H. Sedlacek, MIT Lincoln Lab., Lexington, MA,
            USA;
            Ray S. Uttaro, MIT Lincoln Lab., Lexington, MA, USA;
            Andrew Grenville, Intel Corp., Lexington, MA, USA;
            Allen K. Bates, IBM Corp. and SEMATECH, Lexington,
            MA, USA;
            Chris K. Van Peski, SEMATECH, Austin, TX, USA.

Abstract: We investigated laser-induced damage of pellicles for
       193-nm lithography. We surveyed 193-nm-optimized
       material from three pellicle suppliers. Pellicles were
       irradiated under realistic reticle plane conditions
       (0.04 mJ/cm$+2$//pulse - 0.12 mJ/cm$+2$//pulse for up
       to 100 million pulses). Pellicles from two suppliers
       were found to meet lifetime requirements of the
       industry. Pellicles from the third supplier do not
       appear to meet the lifetime requirements. We present
       fluence scaling of pellicle damage and discuss effects
       of the ambient on pellicle degradation rates. We
       present results of the outgassing studies of pellicle
       material under irradiation using a separate gas
       chromatograph-mass spectrometer-based detection
       apparatus. From the results of these studies, we
       suggest possible photochemical pathways for pellicle
       degradation as a function of ambient. !12 


Paper #: 3334-47
Alignment performance versus mark quality, pp.496-501
Author(s):  Joseph P. Kirk, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA;
            Jung H. Yoon, IBM Microelectronics Div.,
            Hopewell Jct, NY, USA;
            Timothy J. Wiltshire, IBM Microelectronics Div.,
            Hopewell Jct, NY, USA.

Abstract: A procedure is described for preparing relief alignment
       marks with precisely degraded quality that are then
       used to calibrate alignment performance. Alignment
       degrades with mark quality, eventually failing when the
       marks are no longer found. Using conventional processes
       it is difficult to accurately find this threshold and
       virtually impossible to experimentally establish the
       functional relationship between alignment mark quality
       and alignment precision. Marks that simulate a full
       range of process conditions, including planarization
       and granularity, are formed utilizing the continuous
       tone relief response of I-line photoresist to $lambda
       equals 248 nm dose, thereby avoiding the complication
       of fabricating wafers through selective steps of the
       actual semiconductor manufacturing process. The usual
       box in box overlay measurement problem, caused by boxes
       formed by different processes, is avoided by printing
       high contrast overlay evaluation structures regardless
       of the alignment mark quality. Overlay is measured and
       plotted as a function of mark quality and the
       lithography engineer knows precisely the condition of
       the alignment system. For example; it is easily
       established by direct measurement the alignment
       system's ability to control magnification as the relief
       of the alignment marks change. !1 


Paper #: 3334-48
High-accuracy alignment based on subspace decomposition,
pp.502-509
Author(s):  Amir Aalam Ghazanfarian, Stanford Univ., Palo Alto,
            CA, USA;
            Xun Chen, Stanford Univ., Stanford, CA, USA;
            Mark A. McCord, Stanford Univ., Stanford, CA, USA;
            R. Fabian W. Pease, Stanford Univ., Arlington, VA,
            USA.

Abstract: One of the most crucial emerging challenges in
       Lithography is achieving rapid and accurate alignment
       under a wide variety of conditions brought about by
       different overlying films occluding the marks. The
       problem is exacerbated by planarizing processes such as
       Chemical Mechanical Polishing (CMP) and asymmetric
       processes such as metal deposition and photoresist
       coating. These processes give rise to displacement of
       the perceived position of the alignment mark. Thus, any
       effective algorithm must be based on the history of
       such displacements. A new approach based on subspace
       decomposition of the alignment signals is described.
       The method only applies to imaging and/or scanning
       based alignment signals. The main assumption is that
       the process-induced asymmetries are small enough such
       that only linear effects need to be considered. We
       first find the subspace of alignment signals using a
       set of alignment signals with pre-known positions. The
       positions of the new signals are measured based on the
       fact that, if shifted correctly, they will lie in the
       same subspace as the previous signals. Current
       alignment algorithms assume symmetric alignment
       signals. Since this method exploits the structure of
       the signals, it results in more accurate measurement of
       the position than the current algorithms. Simulation
       results show that the alignment error is about an order
       of magnitude smaller than that achieved with
       conventional Maximum Likelihood or phase-fitting
       approaches. The computational complexity also increases
       linearly with the dimension of the subspace and is
       linearly proportional to signal bandwidth. !4 


Paper #: 3334-49
Impacts of reticle and wafer elasticity control on overall
alignment management strategy, pp.510-519
Author(s):  Etsuya Morita, Nikon Precision Inc., Belmont, CA,
            USA;
            Masaharu Kawakubo, Nikon Precision Inc., Belmont,
            CA, USA;
            Frank C. Leung, Nikon Precision Inc., Belmont, CA,
            USA;
            Sean J. McNamara, Nikon Precision Inc., Belmont, CA,
            USA;
            Joseph T. Parry, Nikon Precision Inc., Belmont, CA,
            USA.

Abstract: Maintaining projection-aligners' stage grids-is
       critical for maximum overlay performance of production
       lithography. It seems that, particularly in the U.S.,
       the industry has chosen the 'artifact-wafer' strategy
       as the standard technique to achieve this goal. This
       paper is intended to identify problems in overlay
       management using artifact wafers and to provide
       solutions to address the issues. One of the major
       sources that degrade accuracy in overlay management is
       the expansion/shrinkage of wafers and reticles. Both
       wafers and reticles expand during printing due to the
       heat delivered from the illumination source. The amount
       of the expansion tends to increase as the power of the
       illumination source increases per industry's demand on
       higher throughput. Wafers and reticles expand/shrink
       also due to environmental temperature change. The
       significance of wafer expansion/shrinkage in this mode
       has tended to be neglected. This is probably because,
       since it is measured and compensated by the 2nd print
       alignment, wafer scaling in the first print does not
       impact overlay performance evaluated at the shot
       center. Wafer expansion/shrinkage, however, does cause
       intra-shot scaling errors in overlay. And more
       importantly, since artifact wafers serve as absolute
       stage-grid-references, their expansion/shrinkage
       directly impact accuracy of overlay management. Reticle
       expansion/shrinkage due to temperature difference
       between where the reticles were created and where they
       are used along with reticle manufacturing errors causes
       inaccuracy in intra- shot performance evaluation. As
       product design rules continues to tighten, the
       intra-shot overlay performance can no longer be
       neglected. The impacts of reticle- and wafer-elasticity
       on total overlay management will be discussed. Multiple
       techniques to address the elasticity issues will be
       demonstrated. The discussion will conclude with
       recommendations for generation and usage of the
       artifact wafers. !0 


Paper #: 3334-51
Proposal of a composite phase-shifting mask for 0.15-um
hole-pattern delineation using KrF exposure, pp.522-531
Author(s):  Norio Hasegawa, Hitachi, Ltd., Ome-shi Tokyo, Japan;
            Katsuya Hayano, Hitachi, Ltd., Tokyo, Japan;
            Akira Imai, Hitachi, Ltd., Ome-shi Tokyo, Japan;
            Naoko Asai, Hitachi, Ltd., Ome-shi Tokyo, Japan;
            Shinji Okazaki, Hitachi, Ltd., Ome-shi Tokyo, Japan.

Abstract: We propose a new pattern delineation technology where
       composite phase-shifting masks are used for KrF
       exposure. Half-tone phase-shifting masks (HTPSMs) are
       widely used for delineating 0.20- to 0.25-micrometer
       hole patterns. However, the process latitude of the
       pattern transfer for 0.18- micrometer hole patterns or
       smaller is very tight, and it is quite difficult to
       delineate such small patterns using conventional HTPSMs
       with KrF exposure for mass production. However, by
       using a newly developed composite phase-shifting mask,
       we have been able to simultaneously delineate 0.18-
       micrometer or smaller isolated hole patterns and dense
       hole patterns with sufficient process latitude. Two
       types of phase- shifting technology were integrated in
       a single phase-shifting mask that had both a Cr region
       and a halftone region. For the delineation of isolated
       hole patterns, eight outrigger sub- slots were
       octagonally arrayed around each isolated hole pattern
       (00-HTPSM: octagonal outrigger HTPSM). For the
       delineation of dense hole patterns, an alternating
       phase assignment was applied (alternating PSM). We
       found through both simulation and experiment that the
       focus latitude could be expanded by the use of this
       composite phase-shifting mask. !8 


Paper #: 3334-52
Optimization of stepper parameters and its design rule for an
attenuated phase-shifting mask, pp.532-542
Author(s):  Hung-Eil Kim, Integrated Device Technology, Inc.,
            Santa Clara, CA, USA;
            Stanley Barnett, Integrated Device Technology, Inc.,
            Santa Clara, CA, USA;
            James Shih, Integrated Device Technology, Inc.,
            Santa Clara, CA, USA.

Abstract: An attenuated phase-shifting mask is favorable
       lithography technique for enhancing the depth-of-focus
       for isolated hole. However, it is restricted by
       sidelobe printing at dense array holes. To reduce the
       sidelobe printing, various methods such as surface
       insoluble layer, add an auxiliary hole, and
       optimization of NA and sigma were investigated. The
       method of surface insoluble layer was not effective for
       the dense array holes and CD uniformity was not
       improved. The method that adds an auxiliary hole at
       sidelobe position of highly dense array pattern can
       reduce the sidelobe printing completely, but mask CD
       and mask defect inspection as well as automatic layout
       of auxiliary holes for nonrepeating patterns in
       periphery area will be issued. In order to optimize the
       NA and sigma value, DOF and sidelobe printing were
       considered. Also CD control is studied by considering
       the CD linearity and optical proximity correction (OPC)
       as mask print bias is applied. Design rule for attPSM
       was suggested at optimized and fixed conditions. !4 


Paper #: 3334-53
Preventing sidelobe printing in applying attenuated phase-shift
reticles, pp.543-552
Author(s):  Z. Mark Ma, Texas Instruments Inc., Dallas, TX, USA;
            Andrew Andersson, Texas Instruments Inc., Dallas,
            TX, USA.

Abstract: One major limitation of applying attenuated phase shift
       mask (PSM) is sidelobe printing. The sidelobe is caused
       by constructive interference of the first order of
       diffraction maximum from nearby features, plus the
       electrical fields from semi-transparent materials in
       the surrounding area. The impact of defocus, lens
       aberration, and layout design on sidelobe printing are
       discussed. A detailed comparison between printed wafers
       and aerial image simulations shows how these factors
       affect sidelobe printing. Data show tight control on
       both the third and the fifth order aberrations is
       critical in PSM application. Since the degree of
       coherence and the stepper's response to coherence
       transfer function will significantly affect the
       performance of PSM, tests on phase shift mask are
       necessary to qualify a stepper. An alternative approach
       that uses attenuated rim shifter PSM to prevent
       sidelobe printing is presented and discussed. !10 


Paper #: 3334-54
Resist and oxide thickness effect on process window for 0.2-um
contact patterns with off-axis illumination and attenuated
phase-shift mask, pp.553-558
Author(s):  Chuen-Huei Yang,
            Industrial Technology Research Institute,
            Chutung Hsinchu, Taiwan;
            Chang-Ming Dai,
            Industrial Technology Research Institute, Hsinchu,
            Taiwan.

Abstract: The resist dimples caused by the sidelobe effect are
       the unexpected by-products at printing 0.2-micrometer
       dense contact holes with attenuated phase-shift mask
       (PSM) and KrF laser stepper. We found that not only the
       printing bias and duty ratio but also the film
       thickness of the resist and the oxide layer underneath
       the resist affect the generation of the dimples. The
       0.2-micrometer contact holes on 0.52-micrometer pitch
       were printed successfully without resist dimples by
       controlling the mentioned factors. Furthermore, the
       depth margin of the dimples was accessed in real
       etching process. The residual resist at dimples was
       3150 Angstrom at least after development in order to
       against the etching process. !2 


Paper #: 3334-55
Optimization of DUV photolithography for sub-250-nm technology:
contact patterning with attenuated phase-shift mask, pp.559-566
Author(s):  Lay-Cheng Choo, Nanyang Technological Univ.,
            Singapore, Singapore;
            Siu-Chung Tam, Nanyang Technological Univ.,
            Singapore, Singapore;
            Alex Cheng,
            Chartered Semiconductor Manufacturing Ltd., USA;
            Ida C. Ho,
            Chartered Semiconductor Manufacturing Ltd.,
            Singapore, Singapore.

Abstract: Attenuated phase shift mask (APSM) has been considered
       a viable technique for contact patterning. For 250 nm
       lithography technology, 300 nm contact patterns are to
       be defined. In this paper, Solid-C has been used for
       aerial image simulations. Conventional and annular
       illumination settings are optimized for better focus
       latitudes, that is, large depth-of-focus (DOF), for
       sufficient throughput. In addition, mask transmission
       is optimized for different illumination settings. From
       our simulations of aerial images, it has been shown
       that a DOF of 1.35 micrometer is achieved when
       conventional illumination is combined with APSM at high
       mask transmission (approximately 8 - 10%). However a
       larger DOF of 1.55 micrometer can be obtained when
       annular illumination is used with APSM at low mask
       transmission (approximately 3 - 4%). !10 


Paper #: 3334-57
New method for improving the practical resolution of complex
patterns in sub-half-micron lithography, pp.567-578
Author(s):  Xunan Chen, Institute of Optics and Electronics,
            Chengdu Sichuan, China;
            Xiangang Luo, Institute of Optics and Electronics,
            Sichuan, China;
            Hanmin Yao, Institute of Optics and Electronics,
            Shuangliu, Chengdu, China;
            Qian Xiao, Institute of Optics and Electronics,
            Academia Sinica, China;
            Guobin Yu, Institute of Optics and Electronics,
            Academia Sinica, China.

Abstract: A new approach, based on the optimization of
       illumination light by micro-optical element, is applied
       to improve the practical resolution of complex pattern
       in sub-half micron lithography. Several micro optical
       plates are devised to optimize the illumination light.
       Through the detailed theoretical expansion of the
       optics for the new structure, simulation of the aerial
       image is carried out. And the experiments verify the
       results of simulation. !7 


Paper #: 3334-58
Enhanced microlithography using coated objectives and image
duplication, pp.579-589
Author(s):  Miklos Erdelyi, Jozsef Attila Univ., Houston, TX,
            USA;
            Zsolt Bor, Jozsef Attila Univ., Szeged, Hungary;
            Gabor Szabo, Jozsef Attila Univ., Szeged, Hungary;
            Frank K. Tittel, Rice Univ., Houston, TX, USA.

Abstract: Two processes were investigated theoretically using
       both a scalar wave optics model and a microlithography
       simulation tool (Solid-C). The first method introduces
       a phase- transmission filter into the exit pupil plane.
       The results of both the scalar optics calculation
       (aerial image) and the Solid-C simulation (resist
       image) show that the final image profile is optimum,
       when the exit pupil plane filter is divided into two
       zones with the inner zone having a phase retardation of
       $pi rad with respect to the outer one and the ratio of
       the radii of the zones is 0.3. Using this optimized
       filter for the fabrication of isolated contact holes,
       the focus-exposure process window increases
       significantly, and the depth of focus (DOF) can be
       enhanced by a factor of 1.5 to 2. The second technique
       enhances the DOF of the aerial image by means of a
       birefringent plate inserted between the projection lens
       and the wafer. As the shift in focus introduced by the
       plate strongly depends on the refractive index, two
       focal points will appear when using a birefringent
       plate instead of an isotropic plate: the first one is
       created by the ordinary, and the second one is created
       by the extraordinary ray. The distance between these
       images can be controlled by the thickness of the plate.
       The results of the calculations show that application
       of a thin but strongly birefringent material is a
       better candidate than using a slightly birefringent but
       thick plate, since aberrations proportional to the
       thickness can cause undesirable effects. !11 


Paper #: 3334-59
Printing sub-100-nm random logic patterns using binary masks and
synthetic-aperture lithography (SAL), pp.590-596
Author(s):  Torbjorn Sandstroem, Micronic Laser Systems AB,
            Taeby, Sweden.

Abstract: Synthetic-aperture lithography (SAL) is proposed as a
       means for reaching design-rules of 0.1 micrometer and
       below. By a combination of oblique illumination and
       pupil filtering the relation between high and low
       spatial frequencies in the image is altered.
       Simulations indicate that random-logic patterns can be
       printed at k$-1$/ equals 0.40 with only modest OPC.
       With some design constraints and/or a corrective
       auxiliary exposure k$-1$/ equals 0.32 is possible. The
       main disadvantages are a complex stepper design and low
       light transmission, the advantages are the use of
       standard binary masks and good useful resolution. !5 


Paper #: 3334-60
Optimization of exposure procedures for sub-quarter-micron CMOS
applications, pp.598-606
Author(s):  Shoji Hotta, Hitachi, Ltd., Ome-shi, Tokyo, Japan;
            Toshihiko Onozuka, Hitachi, Ltd., Ome-shi, Tokyo,
            Japan;
            Keiko Fukumoto, Hitachi, Ltd., Ome-shi, Tokyo,
            Japan;
            Seiichiro Shirai, Hitachi, Ltd., Ome-shi, Tokyo,
            Japan;
            Shinji Okazaki, Hitachi, Ltd., Ome-shi Tokyo, Japan.

Abstract: We investigated various exposure procedures to minimize
       the Critical Dimension (CD) variation for the
       patterning of sub- quarter micron gates. To examine
       dependence of the CD variation on the pattern pitch and
       defocus conditions, the light intensity profiles of
       four different mask structures: (1) a binary mask with
       clear field, (2) a binary mask with dark field, (3) a
       phase-edge type phase-shifting mask (a phase-edge PSM)
       with clear field, and (4) a halftone phase- shifting
       mask (a halftone PSM) were compared, where exposure
       wavelength was 248 nm and numerical aperture (NA) of
       KrF stepper was 0.55. For 200-nm gate patterns,
       dependence of the CD variation on the pattern pitch and
       defocus conditions was minimized by a phase-edge PSM
       with clear field. By optimizing the illumination
       condition for a phase-edge PSM exposure, we obtained
       the CD variation of 10 nm at the minimum gate pitch of
       0.8 micrometer and the defocus condition of plus or
       minus 0.4 micrometer. Applying the optimized exposure
       procedure to the device fabrication process, we
       obtained the total CD variation of plus or minus 27 nm.
       !7 


Paper #: 3334-61
CD control of ASIC polysilicon gate level, pp.607-619
Author(s):  Jacek K. Tyminski, Nikon Precision Inc., Belmont,
            CA, USA;
            Sean J. McNamara, Nikon Precision Inc., Belmont, CA,
            USA;
            Stephen A. Meisner, Cirent Semiconductor, Orlando,
            FL, USA;
            Ronald R. Gorham, Cirent Semiconductor, Orlando, FL,
            USA.

Abstract: As ASIC manufacture continues to evolve towards 0.35
       micrometer, photolithography optimization becomes
       increasingly complex. I-line photolithography at these
       feature sizes results in proximity effects contributing
       to CD budgets and dominating the CD control. One of the
       critical levels of the current generation ASIC devices
       is the polysilicon gate level containing a set of lines
       in nesting configurations ranging from dense to
       isolated. The optical proximity effects of such
       geometries are pitch-dependent. Thus the key challenge
       of the gate level exposure is CD control of the
       features nested on a wide range of pitches. The
       state-of-the-art photolithography tools used for
       critical level manufacture are equipped with a wide
       range of illumination options including conventional,
       small-sigma, and off-axis. These options expand the
       exposure capabilities of steppers and complicate the
       optimization of the photolithography. The complexity of
       the image formation, coupled with the number of stepper
       exposure options, vastly expands the parameter space of
       photolithography optimization. The optimization of the
       photolithography process has to take into consideration
       the requirements of IC manufacture. These requirements
       include the CD tolerance, the depth of focus and the
       exposure latitude. The numeric value of each represents
       statistical and systematic factors influencing the
       yield of manufacture as well as the CD tolerance
       reflecting the IC performance goals. Our goal was to
       optimize the CD performance of critical level i-line
       photolithography. Our strategy combined resist model
       simulation and proof-of-principle testing. We analyzed
       a set of features with the nominal, pitch-independent
       CDs. We analyzed the CD range of variation for
       different pitches characteristic for the polysilicon
       gate level. The analysis was performed for a wide range
       of illumination/exposure conditions representing
       capabilities of the state-of-the-art, commercial i-line
       steppers. To qualify the exposure options, we have
       developed a metric taking into consideration the
       requirements of IC manufacture. We conducted systematic
       studies of the CD range versus illumination and
       exposure conditions. As a result, we identified the
       exposure strategies leading to the range of CD
       variation meeting the tolerance requirements of the
       ASIC manufacture. A methodology combining the resist
       image simulation and limited resist testing allowed us
       to find quickly the optimum exposure strategy
       supportive of manufacturing requirements. It also
       resulted in a great reduction of resources required to
       conduct the process characterization and the CD
       metrology. We applied this methodology to optimize the
       exposure condition of a current generation ASIC
       polysilicon gate level. The optimization methodology
       was verified experimentally. This discussion presents
       examples of optimization solutions. The report reviews
       the results of the resist modeling simulation, and
       reviews the results of the proof-of-principle
       metrology. We compare the modeling and the metrology
       and draw conclusions on the quality of the models'
       predictions. We interpret the model results in terms of
       CD characteristics of the critical level features
       exposed and developed in the resist. Finally, we assess
       the value of anchored resist simulation as a predictor
       of the CD characteristics. !2 


Paper #: 3334-62
Reticle contributions to CD uniformity for 0.25-um DUV
lithography, pp.620-628
Author(s):  Jan P. Kuijten, ASM Lithography BV, Veldhoven,
            Netherlands;
            Frank Duray, ASM Lithography BV, Veldhoven,
            Netherlands;
            Ted der Kinderen, ASM Lithography BV, Veldhoven,
            Netherlands.

Abstract: The trend in the semiconductor industry is towards
       superior imaging performance requiring fundamentally
       tighter control of device Critical Dimensions (CD) and
       yield. This paper focuses on the analysis of reticle
       contributions to intrafield CD Uniformity for step and
       repeat 0.25 micrometer DUV Lithography. A method is
       described to subtract the reticle fingerprint
       contribution from the CD measurement data. The method
       demonstrated that CD Uniformity, in terms of 3$sigma@,
       is perhaps only a valid statically allowed estimate if
       it is used after reticle correction. The extensive
       intrafield CD uniformity evaluation was performed on a
       typical ASML PAS 5500/300 DUV stepper to determine the
       impact of various illumination conditions. For
       APEX-E2408 photoresist, the actual intrafield CD
       uniformity was 13 nm (3$sigma@) at best focus and 14 nm
       (3$sigma@) over a 0.6 micrometer focus range for 0.25
       micrometer dense lines and annular illumination with a
       NA equals 0.54. Subtracting the reticle fingerprint
       yields the exposure tool CD component of 8 nm
       (3$sigma@) at best focus and 8 nm (3$sigma@) over a 0.6
       micrometer focus range. This is smaller than the
       reticle CD error component of 10 nm (3$sigma@) which
       results from 32 nm (3$sigma@) mask CD uniformity and a
       reticle sensitivity factor of 1.3. It is, therefore,
       imperative to reduce the reticle CD influence to
       realize further resolution reductions in manufacturing.
       Subtracting the reticle CD non-uniformity contribution
       allows us more accurately to determine the lithographic
       tool contribution to the CD uniformity budget. !12 


Paper #: 3334-63
CD control for quarter-micron logic device gates using iso-pitch
bias, pp.629-639
Author(s):  Young-Chang Kim, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyoungki-Do, South Korea;
            Gi-Sung Yeo, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyoungki-Do, South Korea;
            Hye-soo Shin, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyoungki-Do, South Korea;
            Hak Kim, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea;
            Ho Young Kang, Samsung Electronics Co., Ltd.,
            Suwon City, South Korea;
            U-In Chung, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyoungki-Do, South Korea.

Abstract: The process optimization and optical proximity effect
       for 0.25 micrometer gates of logic device were studied
       to minimize line width variation. The total line width
       variation was found to be composed of optical proximity
       effect and process uniformity. Process optimization was
       preceded to minimize the contribution of process
       uniformity, and the quantitative analysis could be done
       by measuring some patterns that were intentionally
       chosen for evaluating the optical proximity effect and
       other factors. It was found that the line width
       variation due to optical proximity effect was closely
       related to mask bias through this quantitative
       analysis. Simulations and experimental results give an
       important conclusion that there is a special mask bias
       where the degree of optical proximity effect among the
       different pitched patterns could be nearly neglected
       under certain process condition. This new condition was
       defined as 'Iso-Pitch Bias' and applied to decrease the
       optical proximity effect. Finally, CD variation as
       small as 20 nm, was obtained at real logic device gate
       patterns with optimized condition. !7 


Paper #: 3334-66
Killer defects caused by localized sub-100-nm critical dimension
reticle errors, pp.642-648
Author(s):  Anthony Vacca, KLA-Tencor Corp., Austin, TX, USA;
            Benjamin G. Eynon, Jr., DuPont Photomasks, Inc.,
            Round Rock, TX, USA;
            Steve Yeomans, Micron Technology, Boise, ID, USA.

Abstract: For obvious cost reasons, semiconductor manufacturers
       are constantly striving to produce ever smaller wafer
       geometries with the current installed base of wafer
       steppers. Many techniques (phase shifting, optical
       proximity correction, etc.) have been used successfully
       to 'squeeze' more resolution from these steppers than
       was once thought possible. Wafers processed using
       non-aggressive k$-1$/ factors provided a linear
       correlation between mask and wafer feature sizes.
       However, it has been shown that pushing k$-1$/ factors
       to very low levels causes a nonlinear response between
       changes in photomask and wafer critical dimension. This
       non-linearity demands extremely tight photomask CD
       control specifications. Total CD errors 50 nm and
       smaller can cause unacceptable wafer CD variation.
       Current high end reticle manufacturers are capable of
       meeting a total CD uniformity specification of
       approximately 40 nm as measured by sampling strategies
       using optical metrology tools. These tools are very
       useful for detecting macro changes in CD; however, they
       will only detect a localized error if it happens to
       occur precisely at the point of measurement. In
       contrast, a pattern inspection system employing a
       linewidth measurement algorithm can ensure detection of
       all localized errors within the detection and review
       capability of the system. The problem with reticle CD
       error detection capability is that there is a large
       discrepancy between currently available detection of
       greater than or equal to 150 nm and required detection
       of less than or equal to 50 nm necessary for proper
       wafer functionality at low k$-1$/ lithography. In this
       paper, defect sensitivity and false detection
       performance of a new advanced line measurement
       algorithm was tested. The test vehicles included both
       an industry standard and a custom designed programmed
       defect test mask. In addition, production masks with
       naturally occurring localized CD errors that caused
       wafer pattern bridging were analyzed. This new
       experimental algorithm has shown localized CD error
       detection of less than or equal to 100 nm reticle
       defects. !1 


Paper #: 3334-67
Overlay accuracy of reticles, pp.649-657
Author(s):  Hisatsugu Shirai, Fujitsu Ltd., Mie, Japan;
            Kanji Takeuchi, Fujitsu Ltd., Mie, Japan;
            Kazumasa Shigematsu, Fujitsu Ltd., Mie, Japan.

Abstract: This paper describes the study on overlay accuracy of
       reticles, using a reticle set for DRAM. It is found
       that single reticle pattern placement has to be higher
       accuracy than overlay of reticles, which may be a
       majority in the total overlay accuracy. Concerning some
       points of a reticle set, we found that there is a very
       large value. To match overlay accuracy of reticles with
       the demand of devices, we have shown that the suitable
       reticle exposure system has to be used and managed
       exactly. In order to assure overlay accuracy of a
       reticle set, it was proposed that single reticle
       pattern placement accuracy must be higher than overlay
       accuracy demand and the overlay accuracy yield also
       should be shown in some cases. !4 


Paper #: 3334-69
Challenge of 0.3-k1 lithography by optimizing NA/sigma, OAI,
biasing, and BARC: practical approach to quarter-micron i-line
process, pp.660-672
Author(s):  Keun-Young Kim, Integrated Device Technology, Inc.,
            Santa Clara, CA, USA;
            Stanley Barnett, Integrated Device Technology, Inc.,
            Santa Clara, CA, USA;
            James Shih, Integrated Device Technology, Inc.,
            Santa Clara, CA, USA.

Abstract: One more study for pushing resolution limit down below
       industry agreed optical limit was performed. It was
       pursued for practical application, not limited to
       experimental purpose only. The first work was
       concentrated on studying how much we could lower the
       resolution and improve the process latitude of dense
       lines, which was thought as the most critical one. OAI
       and BARC played a role for that purpose, were expected
       to improve DOF as much as 105% and 15%, compared to
       conventional illumination and non-BARC process,
       respectively. It was also known from simulation that
       mask biasing was important to maximize DOF for dense
       and isolated line. It could be used to reduce CD and
       resist profile difference of dense and isolated
       features as well. Ultimate resolution was only possible
       by very high contrast resist. All the efforts in this
       work achieved quarter micron i-line process which has
       1.2 micrometer DOF for dense lines, 0.8 micrometer
       overlap DOF and 10% exposure latitude both for dense
       and isolated features. !8 


Paper #: 3334-72
NA optimization of 360-nm and 300-nm pitch devices, pp.673-677
Author(s):  Hyoungjoon Kim, Samsung Electronics Co., Ltd.,
            Kyungki-do, South Korea;
            Sunggi Kim, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea;
            Changhwan Kim, Samsung Electronics Co., Ltd.,
            Yongin-Goon, Kyungki-Do, South Korea;
            Jinseog Hong, Samsung Electronics Co., Ltd.,
            Kyungki-do, South Korea;
            Junghyeon Lee, Samsung Electronics Co., Ltd.,
            Yongin-Shi Kyungi-Do, South Korea;
            Ho Young Kang, Samsung Electronics Co., Ltd.,
            Suwon City, South Korea;
            Jootae Moon, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea.

Abstract: KrF extendibility to 180 nm and 150 nm L/S patterns and
       optimized NA were investigated by simulation. Mask CD
       error and exposure dose error are very important factor
       in photo process of device manufacture. We took 2 level
       of expected mask quality and dose control. The mask CD
       error of plus or minus 15 nm and dose error of plus or
       minus 4% are very tight but possible level in near
       future, and plus or minus 10 nm and 3% as extremely
       tight level but expected to be achieved in sometime.
       0.6 NA and quadrupole illumination (pole offset 0.75,
       diameter 0.1) shows 0.8 micrometer depth of focus (DOF)
       with mask CD error of plus or minus 15 nm and dose
       error of plus or minus 4% for 180 nm patterns and
       bigger in our simulation. This shows that the 0.6 NA
       KrF exposure tool could be applied to 180 nm devices
       with acceptable mask and dose errors, but there are
       still problems of illumination uniformity and
       throughput caused by extreme off axis condition.
       Including 150 nm pattern, only 0.7 NA shows 0.6
       micrometer DOF with mask CD error of plus or minus 10
       nm and dose error of plus or minus 3% which is
       extremely tight condition. !4 


Paper #: 3334-74
Conformality of photoresist and antireflective coatings over
topography, pp.680-684
Author(s):  James A. Bruce, IBM Microelectronics Div.,
            Essex Junction, VT, USA;
            Ellen Wallander, IBM Microelectronics Div.,
            Essex Jct, VT, USA.

Abstract: Scanned probe microscopy (SPM) and optical thickness
       measurements were used to study conformality of a 0.5
       micrometer-thick photoresist and two different ARCs (75
       nm thick). One ARC (ARC A) was a thermally stable
       system as applied. (The molecular weight did not change
       with the normal post-apply bake.) The other ARC (ARC B)
       was a thermally cross- linking system. (Cross-linking
       occurs on the wafer during post-apply bake, thus
       increasing molecular weight.) Three different step
       heights, ranging from 44 to 150 nm, were studied. Two
       measures of conformality were used: the 'planarization
       length' or distance from an edge for which the material
       reaches nominal thickness, and the film thickness loss
       over a given feature width. For the photoresist, the
       planarization length was 30 - 50 micrometer, and a 1
       micrometer-wide ridge was almost completely planarized.
       (Resist thickness loss was 70 - 80% of the step height,
       vs 100% for complete planarization.) As expected, the
       much thinner ARC films were more conformal than the
       resist film; however, each behaved quite differently:
       the thermally stable system (ARC A) was more conformal
       than the thermally cross- linking system (ARC B). The
       planarization length for ARC A was 5 - 10 micrometer
       while, for ARC B, it was 20 - 40 micrometer. ARC A also
       showed less thickness loss for 1 to 10 micrometer- wide
       ridges. For a 1 micrometer-wide ridge, ARC A showed a
       thickness loss of 40% of the step height; for ARC B,
       the loss was 50%. For a 10 micrometer-wide ridge, the
       thickness losses were 5% and 15% for ARCs A and B,
       respectively. !5 


Paper #: 3334-75
Thin-film interference effects for thin resist films on a
broadband scanner, pp.685-691
Author(s):  James A. Bruce, IBM Microelectronics Div.,
            Essex Junction, VT, USA;
            Michael D. Caterer, IBM Microelectronics Div.,
            Essex Jct, VT, USA;
            Dianne L. Sundling, IBM Microelectronics Div.,
            Huntington, VT, USA.

Abstract: The relative benefit of using a broadband illumination
       system to reduce thin-film interference is impacted
       when using thinner resist films. For example, with a 1
       micrometer resist film, a 43% reduction in swing curve
       is predicted for broadband vs. monochromatic
       illumination, while for a 0.5 micrometer film the
       reduction is only 25%. For a 0.5 micrometer resist film
       over an organic ARC exposed on a broadband system, such
       as a SVGL Micrascan-2, both simulations and
       experimental data show a 10 - 16% swing curve. These
       are results for an ARC with a relatively low absorbance
       (k equals .22). Results are given for several
       approaches that were investigated to reduce this swing
       curve, including improved ARC materials and resist
       thickness optimization; e.g., with a CVD ARC, the swing
       curve can be reduced to less than 10 nm. Resist and ARC
       thickness optimizations are normally done
       independently; however, resist and ARC thicknesses may
       not be independent. Much of the thickness variation is
       caused by the topography, with the resist and ARC
       behaving in the same qualitative fashion (e.g., both
       the ARC and resist tend to planarize over a ridge;
       thus, both will be thinner over a ridge). A method for
       optimizing interdependent resist and ARC thicknesses is
       also presented; it couples modeled linewidth data with
       ARC and resist planarization data to predict the
       optimum resist and ARC thickness. !4 


Paper #: 3334-76
Optimization of ARC process in DUV lithography, pp.692-701
Author(s):  Kyung-Jin Shim,
            Hyundai Electronics Industries Co., Ltd.,
            Kyoungki-do, South Korea;
            Byoung-Il Choi,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-kun, Kyoungki-do, South Korea;
            Ki-Yeop Park,
            Hyundai Electronics Industries Co., Ltd.,
            Kyoungki-do, South Korea;
            Won-Kyu Lee,
            Hyundai Electronics Industries Co.,Ltd.,
            Ichon-si Kyoungki-do, South Korea.

Abstract: Inorganic Anti Reflective Coating (ARC) improves
       Critical Dimension (CD) uniformity over an exposing
       field by reducing the reflectivity of the ARC/substrate
       system in photoresist. A key parameter of the
       lithographic performance of an inorganic ARC is
       therefore the reflectivity of the ARC/substrate system
       in photoresist. But it isn't a directly measurable
       quantity. In this paper we estimate the reflectivity of
       the ARC/substrate system in photoresist by measuring
       the reflectivity swing of the photoresist/ARC/substrate
       system in air. We also derive a useful relation
       connecting the reflectivity of the ARC/substrate system
       in photoresist to that in air. In the case of organic
       ARC, due to the planarization of the organic ARC on
       topography, optimization is achieved not by minimizing
       the reflectivity of the ARC/substrate system in
       photoresist but by minimizing the variation of the
       light intensity within the photoresist. The performance
       of the inorganic and organic ARC for DUV lithography is
       evaluated, and their differences are investigated. !8 


Paper #: 3334-80
Three-dimensional mask transmission simulation using a single
integral equation method, pp.704-713
Author(s):  Michael S. Yeung, Boston Univ., Boston, MA, USA;
            Eytan Barouch, Boston Univ., Boston, MA, USA.

Abstract: A single integral equation formulation for
       electromagnetic scattering from three-dimensional
       dielectric objects is discussed. The new formulation
       converges significantly faster than the traditional,
       coupled integral equation formulation. The new
       formulation is extended to incorporate the exact
       boundary conditions for isolated mask features by using
       dyadic Green's functions for the stratified medium
       background. Results of three-dimensional phase-shifting
       mask simulation are presented. !9 


Paper #: 3334-81
Use of melting inorganic photoresist for microlens array
fabrication, pp.714-716
Author(s):  Chang Tai Yu, Zhejiang Univ., Hangzhou Zhejiang,
            China;
            Fengzhen Guo, Zhejiang Univ., Hangzhou Zhejiang,
            China;
            Ying Chen, Zhejiang Univ., Hangzhou, China;
            Hua Yu, Cymer Corp., San Diego, CA, USA.

Abstract: In this paper, we will show that it is possible to
       generate very small lenses by melting islands of
       inorganic photoresist on a glass substrate. The
       inorganic photoresist composited by us is suitable to
       be exposed by Electron Beam (EBE) or X-Ray. We have
       obtained the lithophotography pattern with 0.6
       micrometer line width by EBE exposure. Because the
       resist pattern will not swell and distort in the
       developing solution, so there is no problem of
       shelf-life. We have made lenses with diameter ranging
       from 0.8 mm to 1.0 mm in the form of spheres and also
       have studied their optical properties. !2 


Paper #: 3334-82
Metropole-3D: a rigorous 3D topography simulator, pp.717-728
Author(s):  Xiaolei Li, Carnegie Mellon Univ., San Jose, CA,
            USA;
            Kevin D. Lucas, Motorola, Austin, TX, USA;
            Aaron L. Swecker, Carnegie Mellon Univ., San Jose,
            CA, USA;
            Andrzej J. Strojwas, Carnegie Mellon Univ.,
            Pittsburgh, PA, USA.

Abstract: We have extended the capability of a vector 3D
       lithography simulator METROPOLE-3D from a photomask
       simulator to become a full 3D photolithography
       simulator. It is designed to run moderately fast on
       conventional engineering workstations. METROPOLE-3D
       solves Maxwell's equations rigorously in three
       dimensions to model how non-vertically incident light
       is scattered and transmitted in non-planar structures.
       METROPOLE- 3D consists of several simulation modules:
       photomask simulator which models the aerial image of
       any mask pattern (including phase-shifting masks);
       exposure simulator which models light intensity
       distribution within the photoresist and arbitrary
       underlying non-planar substrate structures;
       post-exposure baking module which models the
       photo-active compound diffusion, chemically amplified
       (CA) photoresist cross-linking and de-protection
       processes; and finally, 3D development module which
       models the photoresist development process using the
       level-set algorithm. This simulator has a wide range of
       applications in studying the pressing engineering
       problems encountered in state-of-the-art VLSI
       fabrication processes. The simulator has been applied
       to the layout printability/manufacturability analysis
       to study the dominant physical phenomena in
       lithography, deposition, CMP and etching processes that
       affect the transfer of mask patterns to the final
       etched structures on the wafers. Using this new 3D
       rigorous photolithography simulator, optical proximity
       effects have been studied. A reflective notching
       problem caused by the reflective substrate structure
       has been thoroughly studied, and an anti-reflective
       coating (ARC) solution to this notching problem has
       been optimized by the simulations. Finally, a 3D
       contamination to defect transformation study was
       successfully performed using our rigorous simulator.
       !22 


Paper #: 3334-83
Cross-sectional critical shape error: a novel methodology for
quantifying process simulation accuracy, pp.729-738
Author(s):  Mark E. Mason, Texas Instruments Inc., Dallas, TX,
            USA;
            Robert A. Soper, Texas Instruments Inc., Dallas, TX,
            USA.

Abstract: In an effort to quantify simulator performance, we
       propose a new metric - the cross-sectional critical
       shape error (CCSE). This tool allows quantified
       comparison of actual resist patterns to simulator
       predictions, condensing two- and three- dimensional
       simulation errors into a scalar error value. This value
       can be used as a figure of merit to ascertain optimum
       simulator settings for matching actual experimental
       output. This effort extends previous work by Mack on
       the so-called 'critical shape error' (CSE) metric for
       evaluating differences between the mask and simulated
       resist patterns. While the work by Mack was directed
       primarily at OPC, CCSE is appropriate for quantitative
       simulator evaluations, simulator anchoring, head-
       to-head simulator evaluations, and use in optimizing
       cost functions (e.g. for use in Genetic Algorithms,
       etc.) since it compares the simulator output directly
       to the resist cross section. !7 


Paper #: 3334-84
High-NA illumination: a simulation study, pp.739-751
Author(s):  Leonhard Mader, Siemens AG, Muenchen, Germany;
            Christoph Friedrich, Siemens AG, Muenchen, Germany.

Abstract: Lithography simulation was used to calculate the
       influence of high-NA illumination on resolution,
       depth-of-focus, and exposure latitude evaluating the
       aerial image. Contour plots of exposure latitude versus
       NA & $sigma at constant depth-of- focus values were
       calculated for dense lines, single contacts and
       isolated lines. All features were investigated using
       standard illumination and enhancement techniques (PSMs
       and/or annular illumination). For standard illumination
       the maximum exposure latitude is achieved for the
       highest NA possible if only small depth-of-focus is
       required e.g. thin resist layers over nearly plain or
       planarized substrates. In a production environment
       higher depth-of-focus values are necessary. In this
       case the optimum NA moves to lower values even for
       feature sizes near the resolution limit. However, in
       combination with PSMs (and/or annular illumination) the
       best conditions move to higher NA with decreasing
       feature sizes. !5 


Paper #: 3334-85
Novel approximate model for resist process, pp.752-763
Author(s):  Chang-Nam Ahn,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-si, Kyoungki-do, South Korea;
            Hee-Bom Kim,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-si, Kyoungki-do, South Korea;
            Ki-Ho Baik,
            Hyundai Electronics Industries Co., Ltd.,
            Ichon-si, Kyoungki-do, South Korea.

Abstract: Optical proximity correction technique has been
       studied. The occurrence of proximity effect in the
       optical lithography is composed of an element caused by
       diffraction of light, which can be explained by aerial
       image simulation, and an element caused by resist
       process, in which acid diffusion is a major factor
       causing non-linearity. In the case of very thin resist,
       absorbed energy that generates the acid can be
       described by two-dimensional instead of
       three-dimensional distribution. Under this simple
       assumption, acid diffusion by post exposure bake is
       equivalent to the diffusion of aerial image, and
       chemical amplification can be analytically described
       also. Modified aerial image including diffusion and
       chemical amplification, we call it diffused aerial
       image, can give the information for patterning status
       directly. Therefore, diffused aerial image model can
       explain experimental results very well compared to the
       expectation by using aerial image only without loss of
       simplicity and calculation speed. !6 


Paper #: 3334-86
Three-dimensional photolithography simulator including rigorous
nonplanar exposure simulation for off-axis illumination,
pp.764-776
Author(s):  Heinrich Kirchauer, Technical Univ. Vienna, Vienna,
            Austria;
            Siegfried Selberherr, Technical Univ. Vienna,
            Vienna, Austria.

Abstract: Progress in today's semiconductor industry has been
       mainly achieved by decreasing the minimal feature size
       and increasing the complexity and thus the nonplanarity
       of the devices. Therefore lithography tools have to
       provide high resolution with a reasonably large depth
       of focus. Well-established methods to achieve both
       requirements are off-axis illumination techniques. As
       topography effects such as nonplanar electromagnetic
       scattering and notching are critical for line- width
       control, a rigorous three-dimensional exposure
       simulation considering both nonplanar surfaces as well
       as off- axis illumination is of utmost interest. We
       propose a rigorous method that meets the two challenges
       of nonplanar substrates and off-axis illumination. Our
       approach is based on a novel extension of the
       differential method to the third dimension. It is based
       on a Fourier expansion of the electromagnetic field in
       the lateral coordinates and thus belongs to the
       category of frequency-domain solvers. Due to the
       moderate computational costs nonplanar topography
       simulations including off-axis illumination can be
       performed on common engineering workstations. We will
       give a survey over the numerical algorithm of the
       differential method, describe the interface to the
       imaging and development module, and demonstrate the
       ability of the overall simulator by comparing
       simulation results for contact-hole printing over a
       dielectric and reflective substrates for various
       illumination apertures. !27 


Paper #: 3334-87
Development of an integrated 3D lithography simulator, pp.777-784
Author(s):  Choong-Ki Seo, Inha Univ., Inchon, South Korea;
            Seung Gol Lee, Inha Univ., Nam-gu Inchon,
            South Korea;
            Jong-Ung Lee, Chongju Univ., Chongju, South Korea.

Abstract: We have developed our own three-dimensional optical
       lithography simulator, LG-OLiS (LG-Optical Lithography
       Simulator), which can be applied to both the 2-D and
       the 3-D non-planar cases. It includes with all
       processes of optical lithography such as the formation
       of an aerial image, the exposure, the post-exposure
       bake (PEB), and the development processes. Several
       kinds of numerical methods are adopted for numerical
       implementation and the simulation of an aerial image
       and the exposure process are based on both the
       approximate theory and the rigorous theory. Therefore,
       our LG-OLiS can simulate the topological case
       efficiently nd exactly. !9 


Paper #: 3334-88
Chip-scale 3D topography synthesis, pp.785-794
Author(s):  Mariusz Niewczas, Carnegie Mellon Univ., Pittsburgh,
            PA, USA;
            Xiaolei Li, Carnegie Mellon Univ., San Jose, CA,
            USA;
            Andrzej J. Strojwas, Carnegie Mellon Univ.,
            Pittsburgh, PA, USA;
            Wojciech P. Maly, Carnegie Mellon Univ., Pittsburgh,
            PA, USA.

Abstract: We propose a novel approach to perform the chip scale
       mask to topography mapping by building a library of
       repetitive mask patterns. We call them vicinity
       patterns. They describe a collection of mask features
       in close proximity. This pattern library is used to
       synthesize 3-D topography of an arbitrary part of the
       chip topography. We define some process-related
       parameters, which we call critical interaction lengths,
       as a basis for mask decomposition into the vicinity
       patterns. !5 


Paper #: 3334-89
Application of substructuring method to three-dimensional optical
lithography simulation, pp.795-802
Author(s):  Seung Gol Lee, Inha Univ., Nam-gu Inchon,
            South Korea;
            Choong-Ki Seo, Inha Univ., Inchon, South Korea;
            Dong-Hoon Lee, Inha Univ., Pusan, South Korea;
            Jong-Ung Lee, Chongju Univ., Chongju, South Korea;
            MeangHyo Cho, Inha Univ., Inchon, South Korea.

Abstract: The three-dimensional optical lithography simulator on
       the basis of finite element method is newly introduced.
       Contrary to the conventional direct finite element
       method, the problem of huge memory requirement can be
       resolved by applying the substructuring method to
       finite element method. In our scheme, the global
       domain, which consists of photoresist, interlayers, and
       the substrate, is divided into several subdomains.
       After each subdomain is treated locally, the
       calculation results are integrated altogether. Since
       the consuming memory is tremendously reduced by the
       substructuring method, the three- dimensional case can
       be successfully simulated at the engineering
       workstation. We have compared our scheme with the
       conventional direct finite element, and investigated
       the reduction of computational memory by the
       substructuring method. !13 


Paper #: 3334-90
Net-Faim: distributed computation of aerial images, pp.803-813
Author(s):  Uwe Hollerbach, Boston Univ., Boston, MA, USA.

Abstract: Simulation of aerial images is an important part of
       modern microchip manufacturing, but computation of the
       image of an entire mask is a challenging problem
       requiring a large amount of memory and CPU time.
       Fortunately, it is possible to decompose the large
       problem of computing the full image into many smaller,
       mostly independent, sub-problems. In this paper, one
       particular decomposition is described and implemented.
       The target platform is a heterogeneous group of
       networked workstations. The program, net-faim, was
       designed to be robust, to scale well with available
       resources, and to place modest demands on participating
       workstations. All of these design criteria have been
       realized. The overall performance of the distributed
       computation is linearly proportional to the sum of the
       performances of the individual processors, up to a
       rather high level of parallelism. Robustness is
       achieved by not relying on any one server to complete a
       given task; instead, if an idle server is available,
       the task is sent out to the idle server even if it has
       previously been sent to another server. The task is
       only retired when a server returns the completed
       answer. This 'paranoid' method of processing tasks has
       the pleasant side effect of doing automatic dynamic
       load balancing. The results of runs with several
       different configurations, both of participating
       workstations and of sub- domain sizes, are displayed.
       !10 


Paper #: 3334-91
Exposure effects on deep-ultraviolet resist thickness, pp.814-819
Author(s):  Pary Baluswamy, Micron Technology, Inc., Boise, ID,
            USA;
            Thomas R. Glass, Micron Technology, Inc., Boise, ID,
            USA.

Abstract: Most deep ultraviolet (DUV) resist models available
       today utilize the Dill parameters to characterize
       resist exposure. These models assume that the thickness
       of the resist remains constant through exposure and
       post-exposure bake (PEB). The thickness is only
       affected by development in the models when resist is
       removed from the exposed or unexposed regions,
       depending on whether it is a positive or negative
       resist. It has been observed that a number of DUV
       resists change thickness upon exposure. This effect is
       expected to have an impact on the post-exposure acid
       profile calculated for modeling purposes. In this
       paper, we present data on the thickness changes for
       different resists and the effect of exposure to PEB
       delay on the change. !8 


Paper #: 3334-92
Application of artificial neural networks (ANN) and response
surface model (RSM) in optical microlithographic process
modeling, pp.820-830
Author(s):  Bo Zhou, Storage Technology Corp., Louisville, CO,
            USA;
            Barry A. McPherron, Motorola, Louisville, CO, USA.

Abstract: Optical microlithography represents one of the most
       sophisticated processes in the manufacturing of
       microelectronics devices. Accurate process models are
       highly desirable for process control, process
       optimization, yield improvement, and cost reduction.
       Design of experiments (DOE) and response surface model
       (RSM) are traditional tools for empirical modeling.
       This paper presents an alternative by using artificial
       neural networks (ANNs) to model the intricate
       relationship between the critical dimension (CD) and
       three key lithographic process variables, soft bake
       time, exposure stage speed, and develop time. A set of
       data obtained from a designed experiment is used to
       train a three-layer neural network. A comparison of the
       ANN model with the RSM model shows that ANN model
       provides higher accuracy and greater capability of
       generalization. !21 


Paper #: 3334-93
Coping with the impact of lens aberrations in the context of
wavefront engineering, pp.832-838
Author(s):  Armen Kroyan, Rice Univ., Houston, TX, USA;
            Marc D. Levenson, Microlithography World, Campbell,
            CA, USA;
            Frank K. Tittel, Rice Univ., Houston, TX, USA.

Abstract: Variations of lens aberrations of optical projection
       systems can have undesirable effects on critical
       dimension (CD) uniformity and depth of focus (DOF) of
       printed microelectronic circuit patterns. The principal
       objective of this paper is to investigate how lens
       aberrations along with variations of partial coherence
       of the illumination source of an optical stepper affect
       critical dimensions of dark gate lines when using
       conventional and phase-shifting masks (PSMs) with and
       without optical proximity corrections (OPC). The
       investigations are performed using lithography
       simulation software tools which help to evaluate
       different optical projection systems and diverse types
       of masks. For the purpose of accurate evaluation of the
       effects of different types of aberrations on printed
       patterns, 37 Zernike polynomial coefficients
       representing lens aberrations were normalized using the
       Strehl test. The impact of aberrations on 0.25
       micrometer and 0.18 micrometer dark gate lines is
       studied by analyzing data obtained from simulations
       using four different optical projection system set-ups.
       The results show that lens aberrations do not
       significantly reduce CD uniformity and DOF or destroy
       the process window if we use an optimal numerical
       aperture (NA) and high resist contrast. It was observed
       that high resist contrast is more important than NA in
       terms of dealing with the impact of lens aberrations.
       The effectiveness of masks with OPC for aberrated
       images was analyzed, and we have been able to show that
       OPC does not always improve CD uniformity and DOF. This
       paper describes methods for maintaining tighter control
       of CD errors in the manufacturing process of integrated
       circuits using optical lithography. !7 


Paper #: 3334-94
Effect of lens aberrations as a function of illumination
condition on full-field process windows, pp.839-847
Author(s):  Audrey M. Davis, SGS-Thomson Microelectronics,
            Phoenix, AZ, USA;
            Andrew E. Bair, SGS-Thomson Microelectronics,
            Phoenix, AZ, USA;
            Bradley D. Lantz, SGS-Thomson Microelectronics,
            Phoenix, AZ, USA;
            Jeffrey R. Johnson, SGS-Thomson Microelectronics,
            Phoenix, AZ, USA;
            Charles R. Spinner, III,
            SGS-Thomson Microelectronics, Phoenix, AZ, USA.

Abstract: The effect of lens aberrations on the process windows
       of a 248 nm stepper is presented for multiple locations
       within the exposure field and for various illumination
       conditions. It is shown that the effect on the process
       window depends on the field location and the
       illumination condition. The common process window for
       multiple field locations is significantly reduced from
       the single location result. Process window data
       obtained with one illumination condition is shown to be
       useful in predicting results with other illumination
       conditions. !4 


Paper #: 3334-95
Measurment of astigmatism in microlithography lenses, pp.848-854
Author(s):  Joseph P. Kirk, IBM Microelectronics Div.,
            Hopewell Junction, NY, USA.

Abstract: The direction, $phi@, and magnitude, A$-1$/, of
       residual astigmatism in microlithography lenses used
       for semiconductor circuit fabrication is determined by
       measuring the focal position, F, of lines orientated at
       four values of $Theta equals 0 degrees, 45 degrees, 90
       degrees, 135 degrees. These parameters are related by F
       equals A$-0$/ plus A$-1$/ cos2($Theta $PLU $phi@) which
       is solved for the four measured values of F. If the
       lens is axially symmetric the angle $phi will be that
       of the field diameter, but real lenses have fabrication
       errors that may introduce non-classical astigmatism, so
       $phi may have values 0 less than or equal to $phi less
       than or equal to $pi at any point in the field. It is
       for this reason that conventional resolution reticles
       with perpendicular resolution targets are inadequate to
       accurately measure residual astigmatism. Using such a
       reticle will result in under estimation of the actual
       astigmatism. Wafers are exposed through focus using a
       reticle having an array of resolution targets, each
       having the four orientations. Measuring the focal
       position of each of the four orientations by
       examination of their photoresist images with a dark
       field optical microscope enables determination of
       astigmatism with a standard deviation 7 nm. Application
       of this procedure used to evaluate the residual
       astigmatism in high quality lithography lens is
       reported. !6 


Paper #: 3334-96
Influence of aberration on performance during use of resolution
enhancement technology, pp.855-867
Author(s):  Kouichirou Tsujita, Mitsubishi Electric Corp.,
            Hyogo, Japan;
            Junjiro Sakai, Mitsubishi Electric Corp., Hyogo,
            Japan;
            Akihiro Nakae, Mitsubishi Electric Corp., Hyogo,
            Japan;
            Shuji Nakao, Mitsubishi Electric Corp., Hyogo,
            Japan;
            Wataru Wakamiya, Mitsubishi Electric Corp.,
            Itami, Hyogo, Japan.

Abstract: We have investigated the influence of a spherical
       aberration on the printing characteristics with
       modified illumination. At first, we have developed a
       simple method for measuring the aberration function
       with an alternating phase shift mask (PSM), and have
       measured that in the projection optics of a
       commercially available KrF stepper. Then the anomalous
       phenomena observed in the printing with modified
       illumination are examined with the simulated aerial
       images with the measured spherical aberration. As a
       result, we found good coincidence between the simulated
       images and the anomalies. In conclusion, the origin of
       the anomalies is ascribed to the spherical aberration
       in the projection optics. !3 


Paper #: 3334-97
Differences in pattern displacement error under different
illumination conditions, pp.868-872
Author(s):  Nakgeuon G. Seong, Samsung Electronics Co., Ltd.,
            Yongin-city Kyungki-Do, South Korea;
            Jongwook Kye, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea;
            Ho Young Kang, Samsung Electronics Co., Ltd.,
            Suwon City, South Korea;
            Jootae Moon, Samsung Electronics Co., Ltd.,
            Yongin-City, Kyungki-Do, South Korea.

Abstract: Off-axis illumination (OAI) technique is one of the
       most widely used resolution enhancement methods for sub
       0.2 micrometer resolution in KrF lithography. Repeated
       patterns in DRAM drove many applications of OAI
       technique, such as annular, quadruple. There are
       optimum illumination shapes depending on pattern shapes
       and pitches. We measured pattern displacement error
       differences under two types of illumination shapes
       using box-and-box type overlay keys and real patterns
       to which we optimized illumination shapes. We focused
       on the differences of pattern displacement error
       between two pattern sets rather than pattern
       displacement error itself. The results show huge
       differences of overlay readings under various strong
       OAI settings. Finally, we suggested applying correction
       tables calculated by simulation with aberration data.
       !5 


Paper #: 3334-98
Optimal proximity correction: application for flash memory
design, pp.874-884
Author(s):  Y.G. Chen, Mosel Vitelic Corp., Hsinchu, Taiwan;
            D.L. Huang, Mosel Vitelic Corp., Hsinchu, Taiwan;
            K.T. Sung, Mosel Vitelic Corp., Hsinchu, Taiwan;
            J.J. Chiang, Mosel Vitelic Corp., Hsinchu, Taiwan;
            M.Yu, Mosel Vitelic Corp., Hsinchu, Taiwan;
            F.Teng, Mosel Vitelic Corp., Hsinchu, Taiwan;
            Lung Chu, Technology Modeling Associates, Inc.,
            Fremont, CA, USA;
            Juan C. Rey, Technology Modeling Associates, Inc.,
            Fremont, CA, USA;
            Douglas A. Bernard,
            Technology Modeling Associates, Inc., San Jose, CA,
            USA;
            Jiangwei Li, Technology Modeling Associates, Inc.,
            Fremont, CA, USA;
            Junling Li, Technology Modeling Associates, Inc.,
            Fremont, CA, USA;
            V.Moroz, Technology Modeling Associates, Inc.,
            Fremont, CA, USA;
            Victor V. Boksha,
            Technology Modeling Associates, Inc., Fremont, CA,
            USA.

Abstract: Proximity Correction is the technology for which the
       most of IC manufacturers are committed already. The
       final intended result of correction is affected by many
       factors other than the optical characteristics of the
       mask-stepper system, such as photoresist exposure,
       post-exposure bake and development parameters, etch
       selectivity and anisotropy, and underlying topography.
       The most advanced industry and research groups already
       reported immediate need to consider wafer topography as
       one of the major components during a Proximity
       Correction procedure. In the present work we are
       discussing the corners rounding effect (which
       eventually cause electrical leakage) observed for the
       elements of Poly2 layer for a Flash Memory Design. It
       was found that the rounding originated by three-
       dimensional effects due to variation of photoresist
       thickness resulting from the non-planar substrate. Our
       major goal was to understand the reasons and correct
       corner rounding. As a result of this work highly
       effective layout correction methodology was
       demonstrated and manufacturable Depth Of Focus was
       achieved. Another purpose of the work was to
       demonstrate complete integration flow for a Flash
       Memory Design based on photolithography;
       deposition/etch; ion implantation/oxidation/diffusion;
       and device simulators. !11 


Paper #: 3334-99
Strategy for manipulating the optical proximity effect by
postexposure bake processing, pp.885-891
Author(s):  Tsai Sheng Gau,
            Industrial Technology Research Institute,
            Chutung Hsinchu, Taiwan;
            Chien-Ming Wang,
            Industrial Technology Research Institute,
            Chutung Hsinchu, Taiwan;
            Chang-Ming Dai,
            Industrial Technology Research Institute, Hsinchu,
            Taiwan.

Abstract: It is very easy to manipulate the optical proximity
       effect (OPE), when the new concept of the post-exposure
       bake (PEB) processing is suggested. By changing the
       temperature of the PEB, the bias of the line width
       between the packed lines and the isolated line varies
       drastically. The OPE is thus faithfully controllable
       through the PEB processing. On the other hand, by
       putting the experimental data in contrast with the
       theoretical simulation, the OPE is resolved into the
       resist effect and the optical effect. The resist effect
       could be eliminated by lowering the PEB temperature,
       while the optical effect is reduced from choosing a
       proper stepper illumination setting, NA & $sigma@.
       Moreover, the linearity and the line-end shortening
       also get benefits from this new process. !15 


Paper #: 3334-100
SEMATECH J111 project: OPC validation, pp.892-911
Author(s):  Franklin M. Schellenberg, SEMATECH, San Jose, CA,
            USA;
            Hua Zhang, SEMATECH, Newport Beach, CA, USA;
            Jim Morrow, SEMATECH, Austin, TX, USA.

Abstract: OPC (Optimized Process Correction) Technology is an
       approach for improving lithographic performance that
       has received much attention recently. The core of OPC
       technology is the modification of IC pattern layouts to
       compensate or 'correct' for IC manufacturing process
       distortions. This presentation summarizes the results
       of the SEMATECH project in OPC Validation, designated
       as project J111. The goal of the project was to examine
       the present status of OPC technology, to determine some
       measure of the efficacy of OPC technology, and
       determine which components (if any) require additional
       development to be suitable for manufacturing. To this
       end, an elaborate set of test patterns was created and
       provided to several commercially viable OPC suppliers.
       These suppliers converted these using their OPC
       software for 6 degrees of OPC 'aggressiveness' and
       returned the converted files to SEMATECH. A jobdeck
       containing all the converted patterns were created, and
       reticles were fabricated from this jobdeck using 6
       different maskmaking processes. Each reticle was then
       exposed onto standard wafers using plan-of record
       processes at SEMATECH member companies. The efficacy of
       the various OPC approaches was then determined by
       measuring and comparing the patterns produced on these
       wafers after processing and etching. This protocol was
       followed for both an I-line process and a DUV process.
       Significant improvements in lithographic performance
       were observed in many cases, for both I-line and DUV
       processes. In the best cases, the data suggested that
       OPC can improve lithographic performance by $HLF a
       generation. The degree of success, however, depended
       heavily on the choice of maskmaking technique and OPC
       software supplier, with some combinations significantly
       better at addressing 1-D bias problems, while others
       made dramatic improvements for 1.5-D or 2-D problems.
       !12 


Paper #: 3334-101
Reducing or eliminating line-end shortening and iso/dense bias by
tuning NA and sigma, pp.912-920
Author(s):  Olivier Toublan, France Telecom CNET, Meylan Cedex,
            France;
            Patrick Schiavone, France Telecom CNET,
            Meylan Cedex, France.

Abstract: As the critical dimension is reduced, the most severe
       Optical Proximity Effect (OPE) are the Iso/Dense Bias
       (IDB) and the Line-End Shortening (LES). Before using
       an automatic software to correct such effects, it can
       be interesting to find the Numerical Aperture (NA),
       Filling Factor ($sigma@) couple which gives the best
       result in term of reduction of IDB and LES. This study
       focuses on the behavior of LES and IDB as a function of
       NA and $sigma on 0.35 micrometer/I-line and 0.25
       micrometer/DUV design rules. On both IDB, and LES,
       interesting results have been obtained. Results
       obtained for IDB confirm previously published data and
       show that it is possible to reduce, in a significant
       manor, the IDB in conventional illumination mode, by
       taking a suitable NA, $sigma couple. Moreover we
       emphasize in this paper that $sigma has no significant
       effect on LES unlike previously published data, and
       that it is possible to reduce LES to an acceptable
       level by tuning NA. Regarding the results obtained in
       this study, it appears to be possible to reduce both
       IDB and LES by fine tuning NA and $sigma. Effectiveness
       of serifs and hammerheads in reducing LES is also
       discussed. !8 


Paper #: 3334-102
Benchmarking of software tools for optical proximity correction,
pp.921-931
Author(s):  Angelika Jungmann, Siemens AG, Munich, Germany;
            Joerg Thiele, Siemens AG, Munich, Germany;
            Christoph Friedrich, Siemens AG, Muenchen, Germany;
            Rainer Pforr, SIMEC GmbH, Dresden, Germany;
            Wilhelm Maurer, Siemens AG, Muenchen, Germany.

Abstract: The point when optical proximity correction (OPC) will
       become a routine procedure for every design is not far
       away. For such a daily use the requirements for an OPC
       tool go far beyond the principal functionality of OPC
       that was proven by a number of approaches and is
       documented well in literature. In this paper we first
       discuss the requirements for a productive OPC tool.
       Against these requirements a benchmarking was performed
       with three different OPC tools available on market
       (OPRX from TVT, OPTISSIMO from aiss and PROTEUS from
       TMA). Each of these tools uses a different approach to
       perform the correction (rules, simulation or model). To
       assess the accuracy of the correction, a test chip was
       fabricated, which contains corrections done by each
       software tool. The advantages and weakness of the
       several solutions are discussed. !7 


Paper #: 3334-103
New method for optical proximity correction with gray-level
serifs, pp.932-938
Author(s):  Jinglei Du, Sichuan Univ., Chengdu Sichuan, China;
            Qizhong Huang, Sichuan Univ., Chengdu Sichuan,
            China;
            Yongkang Guo, Sichuan Univ., Chengdu Sichuan, China;
            Zheng Cui, Rutherford Appleton Lab.,
            Chilton, Didcot Oxon, United Kingdom.

Abstract: Based on analysis of physical mechanics on optical
       proximity effect, we present a new method for fine
       correction of optical proximity effect and point out
       that the optimum of amplitude distribution on mask can
       improve distribution of spatial frequency spectrum, so
       intensity distribution of printed image near ideal
       distribution can be obtained. The simulation results
       show that deviation between contour of image after OPC
       and contour of ideal image is less than 0.009. !6 


Paper #: 3334-105
New distortion metrology using reticle coordinate error,
pp.940-950
Author(s):  Izumi Tsukamoto, Canon Inc., Utsunomiya-shi Tochigi,
            Japan;
            Hirohiko Shinonaga, Canon Inc.,
            Utsunomiya-shi Tochigi, Japan.

Abstract: There are several ways to measure distortion of
       lithography exposure equipment, and with each of the
       distortion metrology technique, coordinate errors of
       distortion measurement pattern on the reticle affect
       distortion measurements. The most common way to remove
       the impact of the reticle coordinate error is to
       measure such errors in advance using a pattern
       placement metrology tool and correct distortion
       measurements based on the coordinate error. We have
       found, however, that when measuring distortion using
       two different reticles on the same exposure tool, the
       two measurement results did not agree with each other
       with a difference at a 20 nm level (3 sigma) even after
       being corrected according to the measured reticle
       coordinate error. After studying this problem, we
       successfully had distortion measurements on the wafer
       using two different reticles agree with each other at a
       10 nm level (3 sigma) by introducing a technique called
       STofs., system offset, method. This paper reports that
       exposure tool distortion can be extracted with more
       precision by applying the new reticle coordinate error
       measurement technique. !0 


Paper #: 3334-106
Application of the Brewster angle illumination technique to
eliminate resist-induced alignment errors, pp.951-957
Author(s):  Xun Chen, Stanford Univ., Stanford, CA, USA;
            Amir Aalam Ghazanfarian, Stanford Univ., Palo Alto,
            CA, USA;
            Mark A. McCord, Stanford Univ., Stanford, CA, USA;
            R. Fabian W. Pease, Stanford Univ., Arlington, VA,
            USA.

Abstract: Resist coating on alignment marks can be asymmetrical
       due to the spinning motion. Alignment errors may result
       from this asymmetrical coating because the alignment
       signal can contain asymmetry when the optics detects
       the mark through the resist. The amount of signal
       asymmetry depends on the mark topography, resist
       thickness, spin speed, location on the wafer and the
       alignment technique. We have proposed a Brewster angle
       illumination technique (BAIT) as an effective means to
       greatly reduce the resist-induced alignment error by
       reducing alignment signal reflections from the surface
       of the resist. In this paper, we present the
       experimental results. We built an interferometric
       alignment system to implement BAIT. By scanning a
       resist-coated mark in close proximity to an exposed
       reference mark, drift and other system offsets are
       minimized, allowing an offset detectability of 6 nm.
       Resist-induced alignment errors with a radial
       dependence on mark position and magnitudes up to 25 nm
       have been measured when BAIT is not used. However, when
       BAIT is employed the resist-induced errors at all
       positions on the wafer are reduced to less than 10 nm
       and are close to the resolution limit of the alignment
       setup. The validity of the data was established by
       changing the polarization of the light from TM to TE,
       thereby destroying the BAIT condition while holding all
       other parameters constant. A study of the dependence of
       resist-induced alignment error on spin speed reveals
       that the amount of asymmetry in the resist profile
       increases monotonically as the spin speed increases.
       This effect is due to two factors: that the resist is
       thinner and that the spin speed is also faster. Further
       study using a thinner to dilute the resist isolated
       these factors and showed that the resist-induced
       alignment errors depend more sensitively on spin speed
       than the resist thickness. In most of the cases, the
       BAIT alignment system is immune to resist coating
       asymmetry and the error magnitude stays below 10 nm.
       However, the BAIT cannot work effectively when resist
       thickness becomes thinner than 0.6 micrometer. This
       limitation of BAIT technique was attributed to the
       ripples in the resist profile causing local impinging
       angles to deviate significantly from the Brewster
       angle. !5 


Paper #: 3334-107
Alignment system for ArF excimer-laser-based step-and-scan
system, pp.958-970
Author(s):  Doh H. Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Jong-Soo Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Yeung J. Sohn,
            Electronics and Telecommunications Research Institute
            , USA;
            Jin H. Kwon, Yeungnam Univ., Gyongsan, South Korea;
            Kag Hyeon Lee,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejeon, South Korea;
            Sang-Soo Choi,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejeon, South Korea;
            Hai Bin Chung,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Hyung Joun Yoo,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Bo Woo Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea.

Abstract: ArF excimer laser exposure tool is expected as a
       workhorse in gigabit DRAM mass production era. It can
       resolve 0.18 micrometer or finer patterns due to its
       short wavelength of illumination light. Also, the
       step-and-repeat photolithography system is changing to
       more complicated step-and-scan system. On the other
       hand, this in turn requires alignment system to work to
       tighter budgets. In the 0.18 micrometer optical
       lithography performance level, overlay error should be
       maximum 40 nm. In this paper, we report the theory and
       design parameters of the alignment system for home made
       ArF excimer laser based step & scan system. We have
       examined the advantages of our alignment system, and
       have implemented a trade-off strategy. Our discussion
       includes an overview of the alignment system which
       composed of reticle alignment system, wafer alignment
       system (off-axis and TTL) and auto focus/leveling
       system. !5 


Paper #: 3334-120
Chromatic aberration-free TTL alignment system for 193-nm
step-and-scan exposure system by using phase conjugate waves,
pp.971-977
Author(s):  Jin H. Kwon, Yeungnam Univ., Gyongsan, South Korea;
            Yeung J. Sohn, Yeungnam Univ., USA;
            Hyo C. Hwang, Yeungnam Univ., Gyongsan, South Korea;
            Doh H. Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Hai Bin Chung,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea.

Abstract: A TTL (through-the-lens) alignment system using the
       holographic phase conjugation in photopolymer films for
       application to ArF step-and-scan exposure system was
       designed, and the TTL alignment signals were obtained.
       The optical setup is similar to the DFWM (degenerate
       four-wave mixing). The recording materials were HRF 150
       photopolymer films of Du Pont corporation, and the
       recording wavelength was 476 nm of argon ion laser with
       400 mW output power. The diffraction efficiencies of
       photopolymer film were typically around 50%. Fine
       patterns as small as 1 micron were imaged successfully
       by the phase conjugate waves generated by DFWM
       holography. For TTL alignment, the 'X' or chevron
       patterns of the 1 or 2 micron linewidths were recorded
       as hologram and the reconstructed phase conjugate beams
       were used as the align beam through the projection lens
       which has strong chromatic aberration. TTL alignment
       signals were obtained by scanning the wafer with
       alignment mark under the align beam. !10 


Paper #: 3334-122
Improvement of overlay in the oxide- and W-chemical-mechanical
polish processes, pp.978-985
Author(s):  Sen-Shan Yang,
            World-Wide Semiconductor Manufacturing Corp.,
            Hsinchu, Taiwan.

Abstract: The issue regarding wafer alignment is arisen due to
       flattening of the alignment mark topography by oxide-
       and W- CMP process. This results in degradation in
       alignment signal intensity which is a crucial factor
       affecting overlay accuracy. Computer simulation of
       alignment signal intensity for the oxide- and W-CMP
       processes has been successfully performed. Result
       indicates alignment signal intensity swings with depth
       of the phase grating alignment mark. A critical range
       of depth has to be maintained for achieving alignment
       signal intensity high enough for overlay accuracy. The
       W-CMP process is thus utilized for obtaining depth of
       alignment mark within this range. Experiment has
       successfully demonstrated improvement in overlay. !3 


Paper #: 3334-109
Laser alignment strictness for optical diffraction effect in
lithography processes, pp.986-996
Author(s):  Hsun-Peng Lin,
            Taiwan Semiconductor Manufacturing Co.,
            Chu-Tung Hsin-Chu, Taiwan;
            Chih-Hsiung Lee,
            Taiwan Semiconductor Manufacturing Co.,
            Chu-Tung Hsin-Chu, Taiwan;
            Yi-Chyuan Lo,
            Taiwan Semiconductor Manufacturing Co.,
            Chu-Tung Hsin-Chu, Taiwan;
            Kuo-Liang Lu,
            Taiwan Semiconductor Manufacturing Co.,
            Chu-Tung Hsin-Chu, Taiwan.

Abstract: In the photo process, the product wafers' overlay
       accuracy mostly depends on the global alignment and
       final alignment result. Therefore, the key parameter of
       product wafer will be calculated via the laser onto the
       grating mark resulted in moire signal. The key
       parameter includes x, y coordinate, wafer rotation
       data, wafer orthogonal data, step scaling data. The
       alignment failed issues always suffer from the various
       films and thickness by laser alignment. Such as figure
       1 is the power IC device for failed laser alignment.
       Figure 2 is the compared laser alignment issue about
       the WGA and LSA multiple grating mark, figure 3 is the
       compared laser alignment issue about the moire signal.
       In this paper, we provide several methods to improve
       the laser alignment issue. Specially, according to
       experimental results, we find out the improved
       direction for the laser alignment. The improved
       direction is that changed grating mark width, using the
       convex grating mark, using the higher viscosity photo
       resist and using the dry etching grating mark in
       etching process. !2 


Paper #: 3334-110
Design of illumination system for ArF excimer laser
step-and-scanner, pp.997-1004
Author(s):  Kag Hyeon Lee,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejeon, South Korea;
            Doh H. Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Jong-Soo Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Sang-Soo Choi,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejeon, South Korea;
            Hai Bin Chung,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Hyung Joun Yoo,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea;
            Bo Woo Kim,
            Electronics and Telecommunications Research Institute
            , Yusong, Taejon, South Korea.

Abstract: In a lithography tool, illumination uniformity on the
       wafer surface is important, because the variance of
       intensity on the wafer surface makes it hard to control
       the line width of the pattern. An illuminating system
       for ArF excimer laser step- and-scanner has been
       designed and assessed. The system showed good
       illumination homogeneity in both of the reticle and
       pupil plane with a reasonable light transmission
       efficiency. The goal of design is the uniformity within
       plus or minus 1% on the reticle surface. In order to
       achieve the goal, the output beam of the excimer laser
       with nonuniform intensity distribution was re-shaped by
       using a beam expander which is composed of 4
       cylindrical lenses, and the zoom lens varying the beam
       size according to the aperture of fly's eye lens
       integrator. The fly's eye lens integrator consists of
       208 lenses and generates the good homogeneity in the
       reticle plane. The effective light sources, i.e. the
       images made by fly's eye lenses, were projected onto
       the entrance pupil of the combined system of projection
       and relay lenses. The exposure field at reticle plane
       is 104 $MUL 20 mm$+2$/, and is defined as the image of
       reticle blinder by the 1x relay optics. The designed
       illumination system showed good performance by
       simulation and it will be adequate to the ArF excimer
       laser step-and-scanner under development. !6 


Paper #: 3334-111
DUV synchrotron exposure station at CAMD, pp.1005-1009
Author(s):  Chantal Khan Malek, Louisiana State Univ.,
            Baton Rouge, LA, USA;
            Volker Saile, Louisiana State Univ., Baton Rouge,
            LA, USA;
            J. Michael Klopf, Louisiana State Univ.,
            Baton Rouge, LA, USA;
            Louis Rupp, Louisiana State Univ., Baton Rouge, LA,
            USA;
            Steven Nguyen, Louisiana State Univ., Baton Rouge,
            LA, USA.

Abstract: A new synchrotron radiation exposure station dedicated
       to deep-UV exposures has been installed at the
       synchrotron light source at the Center for Advanced
       Microstructures and Devices (CAMD). It complements the
       activities in synchrotron-based lithography including
       X-ray lithography, deep X-ray lithography, and under
       way, ultra-deep X-ray lithography. The UV station
       branches out of the X-ray lithography beamline. A
       retractable Si mirror reflects the incoming synchrotron
       radiation beam by 90 deg through a CaF$-2$/ window.
       Three insertable bandpass filters allow the selection
       of broad-band transmission spectra around the
       wavelengths of two excimer lasers at 248 nm (KrF) and
       193 nm (ArF), and at a shorter wavelength of 187 nm.
       The station allows for exposures under vacuum or in an
       inert gas atmosphere. !5 


Paper #: 3334-112
ArF excimer laser for 193-nm lithography, pp.1010-1013
Author(s):  Uwe Stamm, Lambda Physik GmbH, Goettingen, Germany;
            Reiner Paetzel, Lambda Physik GmbH, Goettingen,
            Germany;
            Juergen Kleinschmidt, Lambda Physik GmbH,
            Goettingen, Germany;
            Klaus Vogler, Lambda Physik GmbH, Goettingen,
            Germany;
            Wolfgang Zschocke, Lambda Physik GmbH, Goettingen,
            Germany;
            Igor Bragin, Lambda Physik GmbH, Goettingen,
            Germany;
            Dirk Basting, Lambda Physik GmbH, Ft. Lauderdale,
            FL, USA.

Abstract: Considerable progress has been made in the development
       of the major components for 193 nm lithography tools.
       Here we describe the parameters of a line-narrowed ArF
       excimer laser for microlithography. With a specified
       FWHM bandwidth of less than 0.7 pm, the laser is
       applicable for refractive steppers and scanners which
       utilize some degree of achromatization. Prototype
       lasers have been built to study the optimum parameters.
       The main challenge of the development was the
       achievement of high efficiency in the conversion from
       the laser's broadband emission into line-narrowed
       emission. The lasers are operated at up to 1 kHz
       repetition rate with a maximum power of 10 W. This
       paper provides an overview of the currently achievable
       power levels, energy stability and bandwidths and
       discusses future trends. !3 


Paper #: 3334-113
ArF lasers for production of semiconductor devices with CD<0.15
um, pp.1014-1020
Author(s):  Thomas P. Duffey, Cymer, Inc., San Diego, CA, USA;
            Todd J. Embree, Cymer, Inc., San Diego, CA, USA;
            Toshihiko Ishihara, Cymer, Inc., San Diego, CA, USA;
            Richard G. Morton, Cymer, Inc., San Diego, CA, USA;
            William N. Partlo, Cymer, Inc., San Diego, CA, USA;
            Tom A. Watson, Cymer, Inc., Carlsbad, CA, USA;
            Richard L. Sandstrom, Cymer, Inc., San Diego, CA,
            USA.

Abstract: The present day notion of the extensibility of KrF
       laser technology to ArF is revisited. We show that a
       robust solution to ArF requirements can be met by
       significantly altering the laser's core
       technology-discharge chamber, pulsed power and optics.
       With these changes, a practical ArF tool can be
       developed. Some of the laser specifications are:
       Bandwidth: 0.6 pm (FWHM) 1.75 pm (95% Included Energy);
       Average Power: 5 W; Repetition Rate: 1000 Hz; Energy
       Stability (3$sigma@): 20% (burst mode) 8% (continuous);
       Pulse Width: 25 ns. !6 


Paper #: 3334-114
Feasibility studies of operating KrF lasers at ultranarrow
spectral bandwidths for 0.18-um line widths, pp.1021-1030
Author(s):  Alex I. Ershov, Cymer, Inc., San Diego, CA, USA;
            Thomas Hofmann, Cymer, Inc., San Diego, CA, USA;
            William N. Partlo, Cymer, Inc., San Diego, CA, USA;
            Igor V. Fomenkov, Cymer, Inc., San Diego, CA, USA;
            George Everage, Cymer, Inc., San Diego, CA, USA;
            Palash P. Das, Cymer, Inc., San Diego, CA, USA;
            David Myers, Cymer, Inc., San Diego, CA, USA.

Abstract: The use of higher NA lenses and higher throughput of
       the next generation 248 nm microlithography systems
       sets tight requirements on the spectral properties of
       the laser as well as its power output and dose
       stability. We demonstrate that such scaling of spectral
       widths, power and repetition rates is possible by
       revisiting some of the dynamics of evolution of laser
       spectrum and stability of laser discharge. In the
       following, we present results of several optical
       configurations, that result in spectral widths between
       1.0 and 2.0 pm (95% integrated linewidth). The optical
       configurations are derivatives of Cymer's standard
       Littrow grating and prism expander configuration.
       Thereby, the other parameters (beam size, coherence,
       etc.) are not impacted. Simultaneously, we provide
       results of scaling a laser to 2 kHz with a dose
       stability of less than plus or minus 0.5% over a 16 ms
       window. The resulting laser is now capable of meeting
       the technical requirements of the next generation
       microlithography scanners. !7 


Paper #: 3334-115
High-spectral-purity and high-durability kHz KrF excimer laser
with advanced rf preionization discharge, pp.1031-1040
Author(s):  Tatsuo Enami, Komatsu Ltd., Hiratsuka-shi Kanagawa,
            Japan;
            Osamu Wakabayashi, Komatsu Ltd., Hiratsuka Kanagawa,
            Japan;
            Toshihiro Nishisaka, Komatsu Ltd., Tochigi-ken,
            Japan;
            Natsushi Suzuki, Komatsu Ltd., Kanagawa, Japan;
            Takashi Nire, Komatsu Ltd., Kanagawa, Japan;
            Hakaru Mizoguchi, Komatsu Ltd., Hiratsuka, Kanagawa,
            Japan;
            Hiroaki Nakarai, Komatsu Ltd.,
            Oyama-shi Tochigi-ken, Japan;
            Hirokazu Tanaka, Komatsu Ltd., Tochigi-ken, Japan;
            Tatsuya Ariga, Komatsu Ltd., Tochigi-ken, Japan;
            Kouji Shio, Komatsu Ltd., Oyama-Shi Tochigi, Japan;
            Takeshi Okamoto, Komatsu Ltd.,
            Oyama-shi Tochigi-ken, Japan;
            Ryouichi Noudomi, Komatsu Ltd., Oyama-Shi Tochigi,
            Japan;
            Hitoshi Tomaru, Komatsu Ltd., Tochigi-ken, Japan;
            Kiyoharu Nakao, Komatsu Ltd., Tochigi-ken, Japan.

Abstract: We present the performance and durability of the newest
       model of the KrF excimer laser for microlithography
       KLES-G10K. The laser achieves 10 W of output power with
       0.7 pm bandwidth at 1000 Hz with newly developed solid
       state pulsed power module and the high precise
       narrowing module. The durability of laser tube achieves
       5 billion pulses with the new radio frequency
       preionization scheme, which reduces consumption of
       fluorine gas and maintenance of laser tube drastically.
       !8 


Paper #: 3334-116
Stability of optical interference coatings exposed to low-fluence
193-nm ArF radiation, pp.1041-1047
Author(s):  Joerg Heber,
            Fraunhofer Institute for Applied Optics and Precision
             Engineering, Jena, Germany;
            Roland Thielsch,
            Fraunhofer Institute for Applied Optics and Precision
             Engineering, Jena, Germany;
            H.Blaschke,
            Fraunhofer Institute for Applied Optics and Precision
             Engineering, Jena, Germany;
            Norbert Kaiser,
            Fraunhofer Institute for Applied Optics and Precision
             Engineering, Jena, Germany;
            Klaus R. Mann, Laser Lab. Goettingen e.V.,
            Goettingen, Germany;
            Eric Eva, Laser Lab. Goettingen e.V., Goettingen,
            Germany;
            U.Leinhos, Lambda Physik GmbH, Goettingen, Germany;
            Andreas Goertler, Lambda Physik GmbH, Erlangen,
            Germany.

Abstract: We report on our investigations on the long-term
       behavior of optical coatings under 193 nm laser
       irradiation in dependence on coating materials,
       radiation conditions, and substrate properties. A wide
       variety of different highly reflective dielectric
       mirrors and antireflective coatings, deposited by an
       ultra low loss evaporation process onto calcium
       fluoride and fused silica, has been tested. Irradiation
       experiments with highly reflective coatings show that
       fluoride coatings exhibit nearly no changes of their
       optical function in air as well as in argon atmosphere
       due to low initial absorption levels. Temporal
       atmospheric contaminations can be removed by using
       appropriate irradiation conditions. Oxide layers tend
       to post-oxidize during 193 nm exposure in air and the
       DUV absorption level will be reduced. Effectively,
       reflectance of multilayer coatings on the basis of
       oxide materials can be improved through laser
       irradiation. Irradiation experiments with
       antireflective coatings point out the dominant role of
       bulk and surface properties of the substrate for
       prolonged laser irradiation. In addition, we present
       laser induced damage thresholds to demonstrate upper
       limits of laser radiation resistance that can be
       achieved nowadays with several types of coatings. !14 


Paper #: 3334-117
Surface finish and optical quality of CaF2 for UV lithography
applications, pp.1048-1054
Author(s):  Angela Duparre,
            Fraunhofer-Institut fuer Angewandte Optik und Feinmec
            hanik, Jena, Germany;
            Roland Thielsch,
            Fraunhofer-Institut fuer Angewandte Optik und Feinmec
            hanik, Jena, Germany;
            Norbert Kaiser,
            Fraunhofer-Institut fuer Angewandte Optik und Feinmec
            hanik, Jena, Germany;
            Stefan Jakobs,
            Fraunhofer-Institut fuer Angewandte Optik und Feinmec
            hanik, Jena, Germany;
            Klaus R. Mann, Laser Lab. Goettingen e.V.,
            Goettingen, Germany;
            Eric Eva, Laser Lab. Goettingen e.V., Goettingen,
            Germany.

Abstract: CaF$-2$/ has received increasing attention as a
       promising substrate for coatings in the VUV range.
       Optimization of the optical properties of these optical
       components requires the study of basic characteristics
       of the coated and uncoated CaF$-2$/ substrates such as
       surface roughness, optical performance, absorption and
       scatter losses, and laser induced damage threshold. The
       investigations reveal the influence of different
       substrate polishing grades on the quality of the coated
       components. !5 


Paper #: 3334-119
Characterizing the absorption and aging behavior of DUV optical
material by high-resolution excimer laser calorimetry,
pp.1055-1061
Author(s):  Klaus R. Mann, Laser Lab. Goettingen e.V.,
            Goettingen, Germany;
            Eric Eva, Laser Lab. Goettingen e.V., Goettingen,
            Germany.

Abstract: Absorption loss in DUV optics during 193 nm irradiation
       is investigated by employing a high-resolution
       calorimetric technique which allows determining both
       single and two photon absorption coefficients at energy
       densities of several 10 mJ/cm$+2$/, avoiding a
       significant thermal load on the samples. UV calorimetry
       is also employed to investigate laser induced aging
       phenomena, e.g. color center formation in fused silica
       or CaF$-2$/. A separation of transient and cumulative
       effects as a function of intensity can be achieved,
       giving insight into various loss mechanisms. Moreover,
       the influence of dielectric coatings on the absorption
       characteristics is discussed. !13 


Paper #: 3334-123
Reformulation for latent image formation model in
photolithography using numerical absorbing boundary condition,
pp.1062-1073
Author(s):  In-Ho Park, Univ. of Inchon, Inchon, South Korea;
            Hye-Keun Oh, Hanyang Univ., Ansan Kyunggido,
            South Korea;
            S. B. Hyun,
            Korea Advanced Institute of Science and Technology,
            Taejeon, South Korea.

Abstract: A method for simulating latent image formation in a
       photoresist illuminated by an arbitrary imaging system
       is presented. The perfectly matched layer absorbing
       boundary condition is applied to take wave propagation
       in the infinite region surrounding the photoresist into
       account. The validity of the method is examined by
       comparing the results with those made by the vertical
       propagation model and the previous two- dimensional
       models. !24 


Paper #: 3334-124
Modifications of polymeric ARC films by UV irradiation,
pp.1074-1084
Author(s):  Ronald A. Carpio, SEMATECH, Austin, TX, USA;
            Alan Stephen,
            SEMATECH and Advanced Micro Devices, Inc., Austin,
            TX, USA;
            Jeffrey A. Eisele, Eaton Corp., Cranston, RI, USA.

Abstract: Plasma etch studies as well as optical spectroscopic
       and contact angle measurements have been performed on a
       number of blanket spin-on organic antireflective
       coatings prior to and after being subjected to various
       UV photostabilization processes. Included in this study
       are antireflective coatings, which are in current use
       for 248 nm and 365 nm applications as well as others
       that are being evaluated for 193 nm lithography. The
       exposure dose, temperature, and blanketing atmosphere
       during the curing process were varied. The objective of
       these studies is to generate fundamental information
       regarding the impact of different UV photostabilization
       processes upon the structural, optical, and surface
       properties as well as upon the etch characteristics of
       these films. !7 

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