LIBRARY OF CONGRESS
`
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`Duplication Services Section
`
`THIS IS TO CERTIFY that the collections of the Library of Congress contain a
`publication entitled HANDBOOK OF VLSI MICROLITHOGRAPHY, and that the attached
`photocopies — the back cover, the spine and the front cover, the inner cover, two blank pages, the
`preliminary title page, a blank page, the primary title page, the copyright page, two series pages,
`four preface pages, a Contributors page, a Notice page, ten Table of Contents pages, a blank
`page, and pages 41 thrdugh 147, - are a true representation from that work.'
`
`THIS IS TO CERTIFY FURTHER, that the spine bears a sticker with the Library of
`Congress call number “TK7874.H3404 1991, that the inner cover bears a stamp that reads
`“REVIEW COPY” and a printer’s mark depicting the seal of the Library of Congress,
`and that the copyright page has a penciled Library of Congress call number that reads “TK7874
`.H3494 1991” and an oval stamp that reads “LIBRARY OF CONGRESS 5 FEB — 3 1992
`COPY
`CIP”.
`
`IN WITNESS WHEREOF, the seal of the Library of Congress is at xcu hereto on
`May 1, 2017.
`
`@mtlmt
`
`Deirdre Scott
`
`Library of Congress
`
`Business Enterprises Officer
`Office of Business Enterprises
`
`101 Independence Avenue, SE Washington, DC 20540—4917 Tel 202.707.5650 www.10cyov; duplicationscrvices@loc.gov
`
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`

`p}§Cfihcn§1LrwU._.Wm»...
`
`.._.1.[_:{Maw.._.
`
`
`
`
`
`2000egaP87310.6102RPI
`
`IPR2016-01378 Page 0002
`
`

`

`HANDBOOK OF VLSI MICROLITHOGRAPHY
`
`IPR2016-01378 Page 0003
`
`IPR2016-01378 Page 0003
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`

`

`lleNDBOOK 0F
`
`VLSI MlCROLlTHOGRAPHY
`
`Principles, Technology
`
`and Applications
`
`Edited by
`
`William B. Glendinnlng
`
`Microlithography Consultant
`Nobleboro, Maine
`
`John N. Helberl
`
`Advanced Technology Center
`Motorola, Inc.
`Mesa. Arizona
`
`NOYES PUBLICATIONS
`Park Ridge, New Jersey, USA.
`
`IPR2016-01378 Page 0004
`
`IPR2016-01378 Page 0004
`
`

`

`
`
`Copyright 0 1991 by Noyes Publications
`No part of this book may be reproduced or utilized in
`any form or by any means. electronic or mechanical.
`including photocopying. recording or by any Informa-
`tion storage and retrieval system. without permission
`in writing from the Publisher.
`Library of Congress Catalog Card Number: 90-23646
`ISBN:
`[3-8155-1281-3
`Printed in the United States
`
`- 1 {‘3
`i
`i
`
`Published in the United States of America by
`Noyes Publications
`Mill Road. Park Ridge, New Jersey 07656
`
`1093765432!
`
`
`
`Library of Congress Cateloging~in-Publicafion Data
`
`Handbook of VLSI microlithography : principles, technology. and
`applications / edited by William B. Glendinning. John N. Herbert.
`p.
`cm.
`Includes bibliographical references and Index.
`ISBN 0—8155-123143 :
`
`1. Integrated circuits—Very large scale integration.
`2. Microlithography.
`l. Glendinning. William B.
`II. Helbert. John
`N.
`TK7874.H3494
`621.381‘531Hdc20
`
`1991
`
`90-23646
`ClF‘
`
`IPR2016-01378 Page 0005
`
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`

`

`MATERIALS SCIENCE AND PROCESS TECHNOLOGY SERIES
`
`Editors
`
`Fiointan F. Bunshah. University of California. Los Angeles (Series Editor)
`Gary E. McGuire, Microelectronics Center of North Carolina (Series Editor)
`Stephen M. Hossnagei,
`IBM Thomas J. Watson Research Center
`(Consulting Editor}
`
`Electronic Materials and Process Technology
`
`- DEPOSITION TECHNOLOGIES FOR FILMS AND (BATTING-S: by Rointan F. Bunshah et al
`
`CHEMICAL VAPOR DEPOSITION FOR MICFDEIECTFDNICS: by Author Sherman
`
`SEMICONDUCTOR MATERIALS AND PROCESS 'IEOI-INCXDGY HANDBOOK: edited by
`Gary E. McGuire
`
`HYBRID MICFDCIRCUH TECHNOIDGY HANDBOOIC by James J. Lioarl and Leonard Fl.
`Enlow
`
`HANDBOOKOF THIN FILM DB’OSUION PFDCBSSES AND TECHNIQUES: edited by Klaus
`K. Schuegraf
`
`WEED-CLUSTER BEAM DEPOSITION AND EPITAXY: by Toshinori Takagi
`
`DIFFUSION PHENOMWIN THIN FILMS AND MICFDEUECTHONIC MATERIALS: edited by
`Devendra Gupta and Paul 3. Ho
`
`HANDBOOK OF CONTAMINATION CONTROL IN MIGFDEIJEC'ITDNICS: Edited by Donald
`L Tolliver
`
`HANDBUJK 0F ION BEAM PMCESSING TECHNOLOGY: edited by Jerome J. Cuomo.
`Stephen M. Rossnagel. and Harold R. Kaufman
`
`CHARACTERIZATION OF SEMICONDUCTOR MAW—Mum 1: edited by Gary E.
`McGuire
`
`HANDBOOK OF PLASMA PROCESSING TECHNOLOGY: edited by Stephen M. Rossnagel,
`Jerome J. Cuorno. and William D. WesMood
`
`HANDBOOK OF SEMICONDUCTOR SILICON TECHNOLOGY: edited by William C. O‘Mara.
`Robert B. Herring. and Lee P. Hunt
`
`HANDBOOK OF POLYMER COATINGS Fm ELECTRONICS: by James .J. Lioari and Laura
`A. Hughes
`
`HANDBOOK OF SPUTTETI DEPOSITION TECHNOLOGY: by Kiyotaka Waea end Shigeru
`Hayakawa
`
`HANDBOOK OF VLSI MIOFDIJTI-IEERAPI-IY: edited by William B. Glendinning and John
`N. Helben
`
`CHEMISTRY OF SUPEFIOONDUCTOR MATERIALS: edited by Terrell A. Vande'rah
`
`CHEMICAL VAPOR DEPOSITION OF TUNGSTEN AND TUNGSTEN SILICIDES: by John E.J.
`SChmitz
`
`{continued}
`
`IPR2016-01378 Page 0006
`
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`
`

`

`vi
`
`Series Titles
`
`Ceramic and Other Materials—Processing and Technology
`
`SOL-GEL TECHNOLOGY FOR THIN FILMS-FIRES. PFEORMS, ELECTRONICS AND
`SPECIALTY SHAPES: edited by Lisa G. Klein
`.
`,
`FIBER REINFORCED CERAMIC COMPOSITES: by K.S. Mazdiyasni
`
`_
`
`ADVANCED CERAMIC PROCESSING AND TECI'NOLOGY—Voiume 1: edited by Jun GP.
`Binne:
`
`FRICTION AND WEAR THANSI'I'IONS OF MATERIALS: by Peter J. Blau
`
`SHOCK WAVES FDR INDUSITIIAL APPLICA‘I'IUNIS: edited by Lawrence E. Murr
`
`SPECIAL MELTING AND PFDCESSING TECHNOLOGIES: edited by G.K. Bhat
`
`0mm 0F cuss, owns mu Gamma sumoumons; edited by
`David E. Clark and Bruce K. Zoitas
`
`Related Titles
`
`ADHESIVE?» TECHNOLOGY HANDBOOK: by Arthur H. Landrock
`
`HANDBOOK OF THERMOSET PlASTICS: Edited by Sidney H. Goodman
`
`SURFACE PFEFAHMm TECHNIQUES FOR ADHESIVE BONDING: by Raymond F.
`Wegman
`
`TURMUM'I'ING PLAS'I'ICS AND HASTOMERS BY GOMPUIE by RaIph D. Hermansen
`
`I
`1'
`i
`
`I
`
`1
`!
`I
`
`IPR2016-01378 Page 0007
`
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`

`

`
`
`PREFACE
`
`The chapter topics of this lithography handbook deal with
`the critical and enabling aspects of the intriguing task of printing
`very high resolution and high density integrated circuit
`(IO)
`patterns into thin resist process pattern transler coatings.
`Circuit pattern density or resolution drives Dynamic Random
`Access Memory {DRAM} technology. which is the principal circuit
`density driver for the entire Very Large Scale Integrated Circuit
`(VLSI)
`industry. The book's main theme is concerned with the .
`special printing processes created by workers striving to achieve
`volume high density IC chip production, with the long range goal
`being pattern features sizes near 0.25 pm or 256 Mbit DRAM
`lithography. The text is meant for a lull spectrum of reader types
`spanning university,
`industrial. and government research and
`development
`scientists
`and production-minded engineers,
`technicians, and students.
`Specifically. we have attempted to
`consider
`the needs of
`the lithography-oriented student and
`practicing industrial engineers and technicians in developing this
`handbook.
`The leadotf chapter focusses on the view that lithography
`methods (printing patterns) are pursued for the singular purpose
`of manufacturing 10 chips in the highly competitive commercial
`sector. and attempts to deiineate the factors determining
`lithographic tool selection. The reader's perspective is drawn to
`consider
`IC device electrical performance criteria versus
`plausible and alternative energetic. or circuit density limited.
`particle printing methods--visible or
`shorter UV optical.
`electron, X-ray, and ion beams. The criteria for high quality
`micrometer and submicrometer
`lithography is very simply
`defined by the three major patterning parameters:
`linerspace
`reSotution.
`line edge and pattern feature dimension control, which
`when combined with pattern to pattern alignment capability
`determine lithographic overlay accuracy.
`Patterning yield and
`throughput turther enter in as dependent economic factors.
`Resist technology has a logical, prominent, second-chapter
`position indicative of resist's overall
`importance in lithography.
`i.e.. the end product 0! any IC lithography process is the patterned
`resist masking layer needed to delineate the VLSI circuit
`level.
`Example coverage of optical resist process optimization assures
`the reader a grasp of the most commonly and widely used (world-
`
`Vii
`
`___———-'—_
`
`IPR2016-01378 Page 0008
`
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`

`

`viii
`
`Preface
`
`wide) lithographic process technologies The basic resist design
`concepts and definitions are thoroughly covered as well as
`advanced lithographic processes.
`Basic metroiogy considerations (Chapter 3) are' absolutely
`imperative to rendering a total description of
`lithography
`methodology. The task of precisely measuring printed Ilnewidth.
`or. space artifacts at submicron dimensions must be performed at
`present without the use of a traceable reference source-National
`institute of Standards and Technology. These desirable and
`necessary standards must be made available in the future.
`However, critical and sufficient physical modelling of varied
`resist and IC material
`topological structures requires funding
`support and completion. Nevertheless. elucidation of optical.
`scanning-electron-microscope (SEM), and electrical
`test device
`linewidth measurements data present
`the reader with key
`boundary conditions essential for obtaining meaningful linewidth
`characterization.
`The portrayal of energetic particle microlithography is
`totally incomplete without some detail of the actual printing tool
`concepts. design. construction. and performance. The printing
`tools are presented and described in chapters 4-7 as to their usage
`in the it) manufacturing world. Clearly optical
`lithography has
`been the backbone and mainstay of
`the world's microchip
`production activity and will most likely continue in this dominant
`role until about 1997.
`In the optical arena.
`it is found that 1X.
`5X. and 10X reduction printers of the projection scanned and
`unscanned variety must be described in subsets according to
`coherent and non-coherent radiation. as well as, by wavelengths
`ranging from visible to deep ultraviolet. Higher resolution or
`more energetic sourced tools are also well described.
`Next
`in world manufacturing usage. electron beam (8-
`beam) pattern printing has been vital. mostly because of
`its
`application in a pattern generation capacity for making photo
`masks and reticles. but also because of direct-write on-wafer
`device prototyping usage. The writing strategy divides e-bearn
`printers, in general. into two groups: Gaussian beam raster scan.
`principally for pattern generation. and fixed or variable-shaped
`beam vector
`scan for direct-write-on-wafer applications.
`Subsets of
`the latter groups depend upon site-by-site versus
`write-on-the—lly substrate movements. The sophistication and
`complexity of e-beam printers requires diverse expertise in
`many technical areas such as: electrostatic and electromagnetic
`beam deflection, high speed beam blanking.
`intense electron
`sources, precise beam shapers. and ultra fast data flow electronics
`and storage.
`interestingly.
`important special beam relationships
`
`I
`
`i
`.
`
`.
`
`.
`
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`

`

`Preface
`
`ix
`
`of maximum current, density, and writing pattern path-speed
`require the observance of unique boundary conditions in meeting
`printing criteria.
`'
`On a worldwide basis. X-ray printing does not yet have
`high volume IC device production background examples. but high
`density prototype CMOS devices have been fabricated by IBM and
`feasibility demonstrated.
`The X-ray chapter presents X~ray
`lithography as a system approach with source. mask. aligner. and
`resist components.
`Of
`the competing volume manufacturing
`printing methods (optical and X-ray).
`the X-ray process is
`unique as a proximity and 1:1 method. As such.
`in order to meet
`the IC patterning quality criteria. extreme demands are placed on
`the mask fabrication process. much more so than for masks or
`reticles prdduced tor the optical analogue.
`For economiCally
`acceptable lC production, laser/diode plasma and synchrotron ring
`X-ray sources must be presented as high density photon emitters.
`in the second part of Chapter 6. synchrotron is given special
`attention and presented as a unique X-rey generator with an X-ray
`flux collimation feature.
`In spite of the synchrotron's massive
`size and very large cost. it's multiport throughput capacity makes
`it viable for the very high production needs of certain industrial
`to houses or possibly for multi-company or shared-company
`situations.
`the
`In the last of the printing tool chapters, Chapter 7.
`energetic ion is depicted in a controllable, steerable. particle
`beam serial pattern writer performing lithography at a high mass
`ratio compared to an e-beam writer. The iocussed ion beam not
`only can deposit energy to form lC pattern latent resist images.
`but otters as another application the direct implant of impurity
`ions into semiconductor wafers, obviating completely the need for
`any resist whatsoever and greatly simplifying the IC chip
`processing sequence. The versatile energetic ion plays yet another
`and possibly its most significant role in a "steered-beam" tool.
`indispensable for optical and X—ray mask repair through the
`precise localized oblation andlor deposition oi mask absorber
`material.
`The goal of establishing 0.35 pm IC chip production by
`1995 is plagued by the constraints of yield-detect models.
`A
`small tractional-submicron mask defect population is adversely
`catastrophic to the mask-and-reticle-dependent
`energetic
`lithographies (optical. X-ray). and especially so for the case of
`1:1 parallel reduction printing. The modernization of photo mask
`and reticle fabrication methods and facilities paves the way for
`achieving extremely accurate and defect tree optical masks and
`
`
`
`IPR2016-01378 Page 0010
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`

`

`3:
`
`Preface
`
`fractiona|~submicron
`( <0.1rcm2). With defects of
`reticles
`sizes. mask and reticle repairs require fully automated "steered-
`beam“ inspectionlmapping equipment to work under full computer
`automation with compatible focussed ion beam repair tools.
`One of the editors' purposes in assembling this book has
`been to accurately disseminate the results of many and varied
`microlithography workers.
`Since it
`is not possible in any one
`book to satisfy enough detail for every reader's full curiosity, we
`consider at least that the reader is enabled to perform his own
`valid analysis and make some meaningful conclusions regarding
`the status and trends of
`the vital
`technical
`thrust areas of
`
`submicron [0 pattern printing technology. The editors wish to
`extend appreciation to various colleagues for helpful discussions
`and encouragement: A. Oberai. JP. Fleekstin. M. Peckerar, and
`many others as the lengthy lists of chapter references attest.
`In addition. many individuals
`representing industrial.
`government. and university sectors have been extremely helpful
`in providing technical discussions. data. and figures to the chapter
`authors of this book. Gratitude is further extended here to those
`
`persons and their organizations. Gratitude also has been expressed
`via courtesy annotations in the figure captions. Finally. we
`commend and thank Judy Walsh for her compilation and editing
`skills.
`
`Nobleboro. Maine
`
`Mesa. Arizona
`June, 1991
`
`William B. Glendinning
`
`John N. Helbert
`
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`
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`

`

`
`
`CONTRIBUTORS
`
`Phillip D. Blais
`Westinghouse Electric Corp.
`Advanced Technology Labs
`Baltimore, MD
`
`Franco Cerrina
`University of Wisconsin
`Madison. WI
`
`William B. Glendinning
`U.S. Army ETDL
`Fort Monmouth. NJ
`
`John N. Helbort
`Motorola. Inc.
`Advanced Technology Center
`Mesa. AZ
`
`Robert D. Larrabee
`National Institute of
`Standards and Technology
`Gaithersburg. MD
`
`Loren W. Linholm
`National Institute of
`
`Standards and Technology
`Gaithersburg. MD
`
`John Melngailis
`Research Laboratory of
`Electronics
`Massachusetts Institute
`of Technology
`Cambridge. MA
`
`Michael E. Michaels
`Westinghouse Electric Corp.
`Advanced Technology Labs
`Baltimore. MD
`
`Michael T. Postek
`
`National institute of
`Standards and Technology
`Gaithersburg. MD
`
`Lee H. Veneklasen
`
`KLA Instruments. Inc.
`San Jose. CA
`
`Whitson G. Waldo
`Motorola. Inc.
`
`Chandler. AZ
`
`—————-—-—_———_
`
`IPR2016-01378 Page 0012
`
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`
`

`

`NOTICE
`
`To the best of the Publisher’s knowledge
`the
`information
`contained
`in
`this
`
`the
`publication is accurate; however.
`Publisher assumes no responsibility nor
`liability for errors or any consequences
`arising from the use of the intormation
`contained herein. Final determination of
`
`of
`
`information.
`any
`suitability
`the
`for
`use
`product
`procedure,
`or
`contemplated by any user, and the
`manner
`of
`that
`use.
`is
`the
`sole
`
`responsibility of the user.
`
`The book is intended for informational
`
`purposes only. The reader is warned that
`caution must always be exercised when
`dealing with
`VLSI microlithography
`chemicals. products. or procedures which
`might be considered hazardous. Expert
`advice should be obtained at all times
`
`implementation
`when
`considered.
`
`is
`
`being
`
`Mention of trade names or commercial
`
`constitute
`not
`does
`products
`endorsement or recommendation for use
`
`by the Publisher.
`
`xii
`
`IPR2016-01378 Page 0013
`
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`

`

`
`
`CONTENTS
`
`
`2.1.3
`
`1. LITHOGRAPHY TOOL SELECTION STRATEGY ............. 1
`Phillip Star's, Michael Michael's
`1.0 introduction .................................... 1
`2.0 Strategy ....................................... 1
`2.1
`Charter ................................... 3
`2.1.1
`Flesearch and Development Class .
`.
`.
`.
`.
`.
`.
`.
`. 3
`2.1.2
`Very Low VolumefMany Processes and
`Products Glass ....................... 4
`Low Volume/Multiple Processes and
`Products Glass ....................... 4
`2.1.4 Moderate Volume/Few Processes and
`Products Class ....................... 4
`High Volume/Few Products Class ......... 5
`2.1.5
`Very High Volurne/One Product Class ...... 5
`2.16
`2.2 Marketing ................................. 5
`2.3
`Product Development ........................ 7
`2.4
`Production Facility ........................... 8
`25
`Technical Capability .......................... 9
`2.6
`Types of Lithography ........................ 10
`2.6.1
`Optical Lithography ................... 10
`2.6.2
`Contact/Proximity Printing .............. 11
`2.6-3
`Full Water Scanning Projection Printing .
`.
`.
`. 11
`2.6.4
`Direct Step On a Water, Stepper ......... 12
`2.6.5
`X—Ray Lithography .................... 13
`2.6.6
`E-Beam Lithography .................. 16
`2.6.?
`Ion Beam Lithography ................. 18
`2.6.8
`Lithography Support Equipment .......... 19
`311.1
`
`_—————————-—————_—
`
`IPR2016-01378 Page 0014
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`IPR2016-01378 Page 0014
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`

`

`xiv Contents
`
`2.7
`
`. 22
`.
`.
`.
`.
`.
`.
`.
`.
`_
`.
`Technical Evaluation ofToois .
`2.6.9
`Economic Factors .......................... 29
`2.7.1
`Cost of Manufacturing ................. 29
`2.7.2
`Labor Cost ......................... 29
`2.7.3
`Capital Equipment Costs .
`.
`.
`.
`.
`.
`_
`.
`.
`.
`.
`.
`.
`.
`. 30
`2.7.4
`Overhead Cost ...................... 30
`2.7.5 Material Cost ........................ 30
`23.6
`Total Cost .......................... 31
`2.7.7
`Yield .............................. 32
`3.0 Implementation of Strategy ....................... 32
`4.0 Summary ..................................... 39
`References ....................................... 40
`
`PROCESSING AND
`2. RESIST TECHNOLOGY—DESIGN,
`APPLICATIONS .................................... 41
`John Heiben
`
`Introduction ................................... 41
`1.0
`2.0 Resist Design ................................. 44
`2.1
`Conventional Photoresists .................... 44
`2.1-1
`Positive Resists ...................... 44
`2.1.2
`PAC lnil uence ....................... 44
`2.1.3
`Influence of Resin Composition .......... 52
`2.1.4
`Positive Photoresist Summary ........... 54
`2.1.5
`Negative Toned Photoresist ............. 54
`Deep UV Resists ........................... 55
`Radiation Resists ........................... 57
`2.3.1
`lntrod uction ........................ 57
`2.3.2
`Energy Absorption Considerations ........ 5?
`2.3.3
`Positive Resists ...................... 53
`2.3.4
`Negative E-Beam Resists ............... 59
`Future Resists ............................. 67
`2.4
`3.0 Resist Processing .............................. 69
`3.1
`Resist Parameter Screening ................... 69
`3.1.1
`Sensitivity and Contrast ................ 69
`3.1.2
`Resist Image Edge Wall ................ 7'1
`3.1.3
`Resist CD Latitude .................... 74
`3.1.4
`Process Compatibility ................. 80
`Resist Adhesion Requirements ................. 80
`Resist Application .......................... 97
`Prebake/Exposure/Deveiopment Processing .
`.
`.
`.
`.
`. 99
`3.4.1
`Statistical Process Optimization
`Characterization Example ............. 101
`Background ....................... 102
`Experimental Designs ................ 102
`
`2.2
`2.3
`
`3.2
`3.3
`3.4
`
`3.4.2
`3.4.3
`
`IPR2016-01378 Page 0015
`
`IPR2016-01378 Page 0015
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`

`

`Contents
`
`xv
`
`Developer Process Characteristics ....... 104
`3.4.4
`Variable Screen T-Test ................ 107
`3.4.5
`Results and Analysis .
`.
`.' .............. 108
`3.4.6
`Conclusions ............ ............ 1 10
`3.4.?
`SP0 Methods of Process Control ........ 112
`3.4.8
`Resist Postbake and Removal
`. ......... 112
`3.4.9
`4.0 Applications and Special Processes ............... 114
`4.1
`Future Device Demands ..................... 114
`4.2
`Applications ............................. 115
`4.2.1
`Dyed and Thinned Single Layer Resist (SLR)
`Processes ......................... 115
`Image Reversal (lREV) ................ 117
`4.2.2
`Thermal image Reversal .............. 117
`4.2.3
`Base Reaction Process ............... 120
`4.2.4
`Base ToneReversaI Process Comparison .
`. 123
`4.2.5
`Process Tuning ..................... 123
`4.2.6
`Resist Image Edge Wall Angle .......... 124
`4.2.7
`Resist Contrast ..................... 124
`4.2.8
`Process Latitude and CD Reproducibility .
`. 12?
`4.2.9
`4.2.10 Mask Efiects ....................... 128
`4.3 Multilayer Applications ...................... 130
`4.3.1
`Summary of Need ................... 130
`4.3.2
`Tri-Iayer Gate Processes .............. 131
`Future Processes .......................... 13?
`4.4
`5.0 Summary and Future Predictions ................. 139
`References ...................................... 141
`
`3. MICROLITHOGRAPHY METROLOGY ................... 148
`Robert Larrabee, Loren Linhoim, Michael T. Posteir
`1.0 Submicrometer Critical Dimension Metrology ........ 148
`1.1
`introduction .............................. 148
`2.0 Optical Critical Dimension Metroiogy .............. 150
`2.1
`introduction .............................. 150
`2.2
`Precision and Accuracy ..................... 151
`2.3
`Optical Diffraction ......................... 154
`2.4
`Geometry of the Sample .................... 160
`2.5
`Extent of Understanding Required for Precision and
`Accuracy ................................ 162
`Equipment Requirements for Precision and
`Accuracy ................................ 165
`An Ideal Submicrometer Optical Dimensional
`Metroiogy System ........................ . 187
`Current Issues in the Utilization of Optical
`Submicrometer Metrology ................... 17'0
`
`2.6
`
`2.?
`
`2.8
`
`
`
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`xvi
`
`Contents
`
`Accuracy Not Available ............... 1?0
`2.8.1
`Precision Not Attained ................ 171
`2.8.2
`Improper Use of Standards ............ 171
`2.8.3
`2-8-4 - Motivation for Dimensional Measurements
`- 172
`2.9
`Conclusion .............................. 173
`3.0 Scanning Electron Microscope Metrology ........... 174
`3.1
`Introduction .............................. 174
`
`3.2
`
`. 17?
`.
`.
`.
`The Basics of Scanning Electron Microscopy .
`3.2.1
`SEM Resolution ..................... 180
`
`3.2.2
`
`Nondestmctive Low Accelerating Voltage
`SEM Operation ..................... 181
`Electron Beam/Specimen Interactions .
`.
`.
`. 186
`3.2.3
`Interaction Modeling ....................... 196
`3.3
`3.4 ‘ Current Problems in the use of the SEM for
`198
`Metrology ..............................
`3.4-1
`Defining the Meaning of a Linewidth ...... 198
`3.4.2
`Edge Detection ..................... 200
`3.4.3
`Environmental Factors ................ 200
`3.4.4
`Sample Charging Effects .............. 201
`3.4.5
`Signal Detection and Accelerating Voltage
`Effects ........................... 203
`
`3.4.6
`Sample Contamination Effects .......... 203
`3.4.?
`Sample Dimensional Changes .......... 205
`3.4.8
`The SEM As a 'Tcol" ................. 205
`NIST Scanning Electron Microscope SRM
`Development Program ...................... 206
`3.5.1
`Precision and Accuracy -
`.
`.
`.
`.
`.
`.
`.
`.
`.
`-
`.
`-
`.
`. 206
`3.5.2
`Certification Instrument ............... 208
`3.5-3
`Electron Beam Interaction Modeling ...... 209
`3.5.4
`SEM Standards Development ........... 209
`Conclusion .............................. 210
`
`3.5
`
`3.6
`
`4.0 Electrical Linewidth Metroiogy .................... 212
`4.1
`Introduction .............................. 212
`4.2
`Electrical Linewidth Measurement .............. 212
`
`4.3
`
`4.4
`4.5
`4.6
`
`4.7
`4.8
`4.9
`
`Cross-Bridge Resistor and Electrical Measurement
`Method ................................. 213
`Cross-Bridge Geometrical Design Criteria ........ 215
`Parametric Testing ......................... 216
`Electrical Measurement Results and Comparison to
`Optical Measurements ...................... 216
`Additional Design Considerations .............. 221
`Cross-Bridge Modifications ................... 221
`Conclusion .............................. 226
`
`4.10 Appendix ............................... 226
`
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`Contents
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`xvii
`
`4.19.1 Test Chip Fabrication Process Description . 226
`Conclusion ...........................
`. 228
`5.0
`References ...................................... 231
`
`. TECHNIQUES AND TOOLS FOR OPTICAL LITHOGRAPHY .
`Whit Waldo
`
`. 239
`
`Introduction .................................. 239
`1.0
`2.0 Fraunhofer Diffraction .......................... 242
`2.1
`Diffraction Through a Rectangular Aperture ...... 242
`2.2
`Diffraction Through 3 Circular Aperture .......... 244
`2.3
`Airy Disk ................................ 245
`3.0 Theoretical Resolution Limit ..................... 248
`__ 4.0 Diffraction Gratings ............................ 252
`5.0 Fourier Synthesis ..................... ’........ 255
`6.0 Abbe’5 Theory of Image Formation ................ 259
`7.0 Introduction to Transfer Functions ................ 259
`7.1
`Spread Functions ......................... 259
`7.2 Modulation .............................. 262
`7.3 Modulation, Phase. and Optical Transfer Functions . 262
`7.4
`Cascading Linear Functions .................. 264
`7.5
`illumination Degree of Coherence ............. 264
`7.6 Wavelength Effect on MTF ................... 271
`7.?
`Depth of Focus ........................... 273
`7.8
`Diffraction Limited Resolution ................. 273
`79 Minimum MTF Requirement .................. 275
`8.0 Application of Transfer Functions ................. 276
`8.1
`The OTF as a Design Tool ................... 278
`8.2
`Laser Interferometry ....................... 281
`8.3 Wave Aberration Function Modeling ............ 281
`8.4
`Aerial image Intensity Distribution ............. 289
`9.0 Numerical and Statistical Methods ................ 290
`9.1
`Data Regression .......................... 293
`9.2
`F-Test and T-Test ......................... 295
`9.3 Multifactor Experiments ..................... 297
`9.3.1
`Blocking, Randomization, and Replicates .
`. 297
`9.3.2
`Experimental Designs ................ 297
`Analysis of Experiments ..................... 300
`Process Control .......................... 301
`9.5.1
`Pareto Charts ...................... 301
`9.5.2 Multivariate Studies .................. 301
`9.5.3 ControICharts..-.--..._.: .......... 304
`9.5.4
`CF and 0pk ....................... .304
`10.0 Practicat Imaging Duality ....................... 306
`10.1
`Field Diameter and Resolution ................ 306
`
`9.4
`9.5
`
`
`
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`Contents
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`10.2 Exposure-Defocue Diagrams ................. 307
`10.2.1 Mask Bias ......................... 30?
`
`10.2.2 Aspect Fiatio of Features .............. 309
`10.2.3 Conjugate Lithography ............... 309
`10.2.4 Proximity Effects and Degree of Coherence 309
`10.2.5 Numerical Aperture .................. 310
`10.3 Depth of Focus Issues ...................... 311
`10.3.1 Resolution Versus Defocus Plots ........ 313
`
`10.4
`
`10.3.2 Autofocus Systems .................. 316
`10.3.3 Nominal Focus ..................... 31?
`
`10.3.4 Depth of Focus Dependence Upon
`Exposure Duty ..................... 318
`10.3.5 Water Flatness ..................... 319
`10.3.6 Chucks .
`.
`.
`.
`2 .................... 2 . 319
`Illumination .............................. 319
`10.4.1 Sources .......................... 319
`10.4.2 Bandwidth ......................... 322
`
`10.4.3 Wavelength Limitations ............... 323
`10.4.4 Uniformity ......................... 324
`10.4.5 Partial Coherence ................... 325
`10.4.6 Flare ............................. 325
`
`Standing Wave Interference .................. 323
`10.5
`10.5 Vibration ................................ 332
`
`11.0 Practical Image Placement ...................... 333
`11.1 Alignment ............................... 333
`11.1.1
`lnterfield Mode! ..................... 334
`
`11.1.2 Types ............................ 334
`11.1.3 Target Design ...................... 338
`11.1.4 Dependence on Field Errors ........... 340
`11.1.5 Mapping and Fieid-By-Field Alignment
`.
`.
`.
`. 340
`Field Errors .............................. 341
`11.2.1 Geometric Model .................... 341
`
`11.2
`
`11.2.2 Symmetric Errors ................... 345
`11.2.3 Asymmetric Errors ................... 348
`11.2.4 liluminator Issues ................... 343
`12.0 Mask Issues ................................. 349
`12.1
`Particulate Protection ...................... 349
`12.1.1 Peilicles .......................... 349
`
`12.1.2 Glass Coverplates ................... 351
`12.1.3 Voting Lithography .................. 352
`Phase-Shifting Masks and Serifs .............. 352
`12.2
`12.3 Excimer Laser Irradiation Damage ............. 355
`12.4 Registration Error Contributions ............... 355
`References ...................................... 35?
`
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`Contents
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`xix
`
`5. ELECTRON BEAM PATTERNING AND DIRECT WRITE ..... 365
`Lee Veneklasen
`
`1.0 Introduction .................................. 365
`2.0 The EBL Process .
`.
`.
`.
`........................... 366
`2.1
`Feature Definition ......................... 36?
`
`2.2
`2.3
`2.4
`2.5
`2-6
`2.?
`
`Figure Placement Accuracy .................. 368
`Throughput and Area Coverage Time ........... 369
`Defect Density ........................... 369
`Automation and Process Integration ............ 370
`EBL Applications .......................... 370
`Classification of EBL Equipment ............... 371
`2.7.1 Mask and Reticie Makers .............. 371
`
`212
`213
`
`Electron Beam Replicators ............. 372
`Direct Write Pattern Generators ......... 372
`
`3.0 EBL Strategies ................................ 373
`3.1
`Strategies for E-Beam Pattern Replication .
`-
`.
`.
`.
`.
`.
`. 373
`3.2
`Strategies for E-Beam Pattern Generation ........ 375
`3.2.1
`Gaussian Beam Raster Scan ........... 3?6
`3.2.2
`Fixed Beam Vector Scan .............. 378
`
`Variable Shaped Beam Vector Scan ...... 331
`3.2.3
`3.3 Muitibeam and Hybrid Strategies .............. 384
`3.4
`Summary ............................... 385
`4.0 Theory of Writing Strategy ....................... 386
`4.1
`Throughput .............................. 386
`4.2
`Pattern and Dose Parameters ................ 387
`4.3
`Pattern Fracture .......................... 391
`4.4
`Flash Word Content ....................... 392
`
`4.5
`4.6
`
`System Accuracy ......................... 393
`Coverage Time Model for Serial Pattern
`Generation .............................. 395
`
`. 398
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`.
`Raster Scan Fracture Optimization .
`4.7
`Fixed Beam Vector Optimization .............. 399
`4.8
`VSB Fracture Optimization ................... 401
`4.9
`4.10 Example of Strategy Model ReSults
`.
`.
`-
`.
`.
`.
`.
`.
`.
`.
`.
`. 403
`4.11 Writing Overheads ......................... 409
`4.12 Electron Optical Optimization ................. 410
`5.0 The Recording Medium ......................... 411
`5.1
`Sensitivity ............................... 412
`5.2
`Contrast ................................ 413
`5.3
`Resolution .............................. 41:3
`
`5.4
`5.5
`5.6
`
`5.?
`
`Edge Profile ............................. 414
`Proximity Effects .........................
`416
`Resist Defects ............................ 418
`
`Charging Effects .......................... 419
`
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`

`xx Contents
`
`5.8
`5.9
`
`Thermal Effects ........................... 419
`Fracture Optimization for Resist Limited
`Conditions .............................. 425
`6.0 .An EBL Direct Write Pattern Generator .......... ..
`_
`. 427
`7.0 The Future ................................. . 432
`References ...............