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Principles of Lithography, Second Edition PDF

435 Pages·2005·9.639 MB·English
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Principles of Lithography Second Edition Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Principles of Lithography Second Edition Harry J. Levinson Bellingham, Washington USA Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Library of Congress Cataloging-in-Publication Data Levinson, Harry J. Principles of lithography / Harry J. Levinson.—2nd ed. p. cm. Includes bibliographical references and index. ISBN 0-8194-5660-8 1. Integrated circuits—Design and construction. 2. Microlithography. I. Title. TK7874.L397 2004 621.3815'31—dc22 2004025977 Published by SPIE—The International Society for Optical Engineering P.O. Box 10 Bellingham, Washington 98227-0010 USA Phone: +1 360 676 3290 Fax: +1 360 647 1445 Email: [email protected] Web: http://spie.org Copyright © 2005 The Society of Photo-Optical Instrumentation Engineers All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means without written permission of the publisher. The content of this book reflects the work and thought of the author(s). Every effort has been made to publish reliable and accurate information herein, but the publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon. Printed in the United States of America. Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx TABLE OF CONTENTS Preface to the second edition / ix Preface / xi 1 Overview of lithography / 1 Problems / 6 2 Optical pattern formation / 7 2.1 The problem of imaging / 7 2.2 Aerial images / 10 2.3 The contribution of physics and chemistry / 24 2.4 Focus / 33 Problems / 49 References / 49 3 Photoresists / 53 3.1 Positive and negative resists / 53 3.2 Adhesion promotion / 57 3.3 Resist spin coating, softbake, and hardbake / 60 3.4 Photochemistry of novolak/DNQ g- and i-line resists / 70 3.5 Acid-catalyzed DUV resists / 72 3.6 Development and post-exposure bakes / 79 3.7 Operational characterization / 83 3.8 Line edge roughness / 84 3.9 Multilayer resist processes / 86 Problems / 89 References / 90 4 Modeling and thin film effects / 99 4.1 Models of optical imaging / 99 4.2 Aberrations / 105 4.3 Modeling photochemical reactions / 114 4.4 Thin film optical effects / 117 4.5 Post-exposure bakes / 123 4.6 Methods for addressing the problems of reflective substrates / 125 4.7 Development / 133 Problems / 133 References / 134 5 Wafer steppers / 139 5.1 Overview / 139 5.2 Light sources / 142 5.3 Illumination systems / 154 5.4 Reduction lenses / 159 v Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx vi PRINCIPLES OF LITHOGRAPHY 5.5 Autofocus systems / 176 5.6 The wafer stage / 179 5.7 Scanning / 183 5.8 Dual-stage exposure tools / 185 Problems / 186 References / 187 6 Overlay / 199 6.1 Alignment systems / 201 6.1.1 Classification of alignment systems / 205 6.1.2 Optical methods for alignment and wafer-to-reticle referencing / 206 6.1.3 Number of alignment marks / 212 6.2 Overlay models / 213 6.3 Matching / 222 6.4 Process-dependent overlay effects / 233 Problems / 235 References / 236 7 Masks and reticles / 243 7.1 Overview / 243 7.2 Mask blanks / 245 7.3 Mechanical optical-pattern generators / 248 7.4 Electron beam lithography and mask writers / 248 7.5 Optical mask writers / 258 7.6 Resists for mask making / 259 7.7 Etching / 261 7.8 Pellicles / 262 Problems / 268 References / 268 8 Confronting the diffraction limit / 273 8.1 Off-axis illumination / 273 8.2 Optical proximity effects / 282 8.3 The mask error factor / 292 8.4 Phase-shifting masks / 295 Problems / 307 References / 308 9 Metrology / 313 9.1 Linewidth measurement / 313 9.1.1 Linewidth measurement using scanning electron microscope / 313 9.1.2 Scatterometry / 320 9.1.3 Electrical linewidth measurement / 322 9.2 Measurement of overlay / 324 References / 327 Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx CONTENTS vii 10 The limits of optical lithography / 331 10.1 The diffraction limit / 331 10.2 Improvements in optics / 333 10.3 The shortest wavelength / 335 10.4 Improved photoresists / 336 10.5 Flatter wafers / 337 10.6 How low can k go? / 338 1 10.7 Immersion lithograpy and maximum numerical aperture / 339 10.8 How far can optical lithography be extended? / 345 10.9 Resist limits / 350 10.10 Interferometric lithography / 351 Problems / 352 References / 352 11 Lithography costs / 355 11.1 Cost of ownership / 355 11.1.1 Capital costs / 357 11.1.2 Consumables / 365 11.1.3 Mask costs / 366 11.1.4 Rework / 367 11.1.5 Metrology / 368 11.1.6 Maintenance costs / 369 11.1.7 Labor costs / 369 11.1.8 Facilities costs / 370 11.2 Mix and match strategies / 370 Problems / 373 References / 373 12 Alternative lithography techniques / 375 12.1 Proximity x-ray lithography / 375 12.2 Extreme ultraviolet lithography––EUV / 382 12.3 Electron-beam direct-write lithography / 392 12.4 Electron-projection lithography––EPL / 395 12.4.1 Small-field EPL systems / 395 12.4.2 Large-field EPL systems / 396 12.5 Ion-projection lithography—IPL / 398 12.6 Imprint lithography / 400 12.7 The ultimate future of lithography / 402 Problems / 403 References / 404 Appendix A: Coherence / 413 Problems / 417 References / 417 Index / 419 Color Plates Section follows page 210 Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx PREFACE TO THE SECOND EDITION This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. First, and foremost, this book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Most papers written for journals or conference proceedings assume that the reader is familiar with pre-existing knowledge. The same can be said for compilations of chapters written by experts who are providing their colleagues and peers with useful summaries of the current state of the art and of the existing literature. Such papers and books, while quite useful to experienced lithographers, are not intended to address the needs of students, who first need to understand the foundations on which the latest advances rest. It is the intention of this book to fill that need. For the experienced lithographer, there are many excellent books written on specialized topics, such as photoresist and resolution enhancement techniques, and I have referenced many of those fine works. However, I have often felt that several topics have not been well addressed in the past; most notably those subjects directly related to the tools we use to manufacture integrated circuits. Consequently, this book goes into a few subjects in depth. These include such topics as overlay, the stages of exposure tools, and light sources. Finally, this text contains numerous references. These are resources for students who want to investigate particular topics in more detail, and they provide the experienced lithography with lists of references by topic. A wise leader once told me that one of the most challenging tasks is to transform complexity to simplicity; in other words, to make apparent the forest obscured by all of the trees. I hope that I have succeeded adequately on the subjects covered in this book. Of course, simplicity should never be confused with easiness or completeness. To assist the student in recognizing these distinctions, more problems have been added to the end of each chapter. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus. Lithography is a field in which advances proceed at a swift pace, and many new topics have been included in this second edition, commensurate with the learning that has taken place during the past few years, and several subjects are discussed in more detail. Optical proximity corrections and next-generation lithography are examples where the landscape looks quite different than it did just a few years ago. Other topics, such as immersion lithography, were ideas that few took seriously just a few years ago, yet today are considered quite mainstream. It has been my good fortune to work with a number of outstanding lithographers. In addition to the people acknowledged in the preface to the first ix Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx x PREFACE TO THE SECOND EDITION edition, I would like to thank several people who contributed to this update. These include Tim Brunner of IBM, Wolfgang Henke of Infineon, Margaret Conkling of Nikon Precision, Nigel Farrar, Vladmir Fleurov, Palash Das and Charles Hindes of Cymer, Andreas Erdmann of Fraunhofer-Institut für Integrierte Schaltungen, Doug Resnick and John Algair of Motorola, Wilhelm Maurer of Mentor Graphics, Christian Wagner and Robert Socha of ASML, Paul Graeupner of Carl Zeiss, Johannes Nieder of Leica, John Ricardi and Harry Rieger of JMAR, Ray Morgan of Canon, USA, Walter Gibson of XOS, and Sandy Burgan of DNS. Merry Schnell and Sharon Streams of the publications staff of SPIE have been very helpful and supportive. I apologize if I have failed to mention anyone who has helped me with this update. It has also been a privilege and joy to work on a more frequent basis with some exceptionally outstanding lithographers in my own department, as well as other lithography departments, at AMD. In particular, this includes manufacturing organizations, where the principles discussed in this book have been put skillfully applied and expertly enhanced to produce high performance non-volatile memory and the world’s most powerful Windows-compatible microprocessors. From AMD, I would like to thank Bruno La Fontaine, Jongwook Kye, Ivan Lalovic, Adam Pawloski, Uzodinma Okoroanyanwu, Rolf Seltmann, Wolfram Grundke, and Rick Edwards for useful and informative discussions on lithography. I would like to thank my wife, Dr. Laurie Lauchlan, and my daughters, Sam and Sarah, who continued to exhibit amazing patience while I worked on the second edition of this book. On September 11, 2001, the world witnessed the destructive power of the irrational mind. I hope that this book will be a small reminder of the tremendous capacity of the rational human mind to improve the world around us. Downloaded From: http://ebooks.spiedigitallibrary.org/ on 08/31/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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