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Spie Press Book

Principles of Lithography, Second Edition
Author(s): Harry J. Levinson
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Book Description

Out of print 05/10/2012. Replaced by PM198, the 3rd edition. Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. 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.

Book Details

Date Published: 14 February 2005
Pages: 438
Volume: PM146

Table of Contents
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Preface / ix
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 / 34
Problems / 49
References / 50
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 / 73
3.6 Development and post-exposure bakes / 79
3.7 Operational characterization / 83
3.8 Multilayer resist processes / 87
Problems / 90
References / 90
4 Modeling and thin film effects / 101
4.1 Models of optical imaging / 101
4.2 Aberrations / 107
4.3 Modeling photochemical reactions / 116
4.4 Thin film optical effects / 119
4.5 Post-exposure bakes / 126
4.6 Methods for addressing the problems of reflective substrates / 128
4.7 Development / 136
Problems / 136
References / 137
5 Wafer steppers / 141
5.1 Overview / 141
5.2 Light sources / 144
5.3 Illumination systems / 157
5.4 Reduction lenses / 161
5.5 Autofocus systems / 180
5.6 The wafer stage / 182
5.7 Scanning / 187
5.8 Dual-stage exposure tools / 189
Problems / 190
References / 191
Color Plates /
6 Overlay / 203
6.1 Alignment systems / 205
6.1.1 Classification of alignment systems / 209
6.1.2 Optical methods for alignment and wafer-to-reticle referencing / 210
6.1.3 Number of alignment marks / 216
6.2 Overlay models / 217
6.3 Matching / 226
6.4 Process-dependent overlay effects / 237
Problems / 239
References / 240
7 Masks and reticles / 247
7.1 Overview / 247
7.2 Mask blanks / 249
7.3 Mechanical optical-pattern generators / 252
7.4 Electron beam lithography and mask writers / 252
7.5 Optical mask writers / 263
7.6 Resists for mask making / 265
7.7 Etching / 267
7.8 Pellicles / 267
Problems / 273
References / 273
8 Overcoming the diffraction limit / 279
8.1 Off-axis illumination / 279
8.2 Optical proximity effects / 287
8.3 The mask error factor / 297
8.4 Phase-shifting masks / 301
References / 313
9 Metrology / 319
9.1 Linewidth measurement / 319
9.1.1 Linewidth measurement using scanning electron microscope / 319
9.1.2 Electrical linewidth measurement / 327
9.2 Measurement of overlay / 329
References / 331
10 The limits of optical lithography / 335
10.1 The diffraction limit / 335
10.2 Improvements in optics / 337
10.3 The shortest wavelength / 339
10.4 Improved photoresists / 340
10.5 Flatter wafers / 341
10.6 How low can k1 go? / 342
10.7 Immersion lithograpy and maximum numerical aperture / 343
10.8 How far can optical lithography be extended? / 348
10.9 Resist limits / 354
10.10 Interferometric lithography / 355
Problems / 356
References / 356
11 Lithography costs / 359
11.1 Cost of ownership / 359
11.1.1 Capital costs / 361
11.1.2 Consumables / 369
11.1.3 Mask costs / 371
11.1.4 Rework / 372
11.1.5 Metrology / 372
11.1.6 Maintenance costs / 373
11.1.7 Labor costs / 374
11.1.8 Facilities costs / 374
11.2 Mix and match strategies / 374
Problems / 377
References / 377
12 Alternative lithography techniques / 379
12.1 Proximity x-ray lithography / 379
12.2 Extreme ultraviolet lithography--EUV / 386
12.3 Electron-beam direct-write lithography / 398
12.4 Electron-projection lithography--EPL / 400
12.4.1 Small-field EPL systems / 401
12.4.2 Large-field EPL systems / 401
12.5 Ion-projection lithography-IPL / 403
12.6 Imprint lithography / 405
12.7 The ultimate future of lithography / 407
Problems / 408
References / 409
Appendix A: Coherence / 419
Problems / 423
References / 423
Index / 425

PREFACE

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 microlithogra-phy for people who are unfamiliar with the subject. Most papers written for jour-nals or conference proceedings assume that the reader is familiar with the topic and possesses 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 foun-dations 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 edition, I would like to thank several people who contributed to this update. These include 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 f�r 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 publication 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.


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