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Spie Press Book

Resolution Enhancement Techniques in Optical Lithography
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Book Description

Ever-smaller IC devices are pushing the optical lithography envelope, increasing the importance of resolution enhancement techniques. This tutorial encompasses two decades of research. It discusses theoretical and practical aspects of commonly used techniques, including optical imaging and resolution, modified illumination, optical proximity correction, alternating and attenuating phase-shifting masks, selecting RETs, and second-generation RETs. Useful for students and practicing lithographers.

Book Details

Date Published: 15 March 2001
Pages: 234
ISBN: 9780819439956
Volume: TT47

Table of Contents
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Foreword / v
Preface / vii
List of symbols / ix
1 Introduction / 1
1.1 Brief history of printing and lithography / 1
1.2 Optical lithography and integrated circuits / 2
1.3 Basics of optical lithography / 6
1.3.1 Illumination / 6
1.3.2 Reticle / 8
1.3.3 Exposure / 13
1.3.4 Photoresist / 18
1.3.5 Optical lithography system parameters / 23
1.4 Requirements of microlithography / 24
1.5 Nonoptical microlithography techniques / 26
1.6 Current challenges of optical microlithography / 27
1.7 Three parameters affecting resolution / 28
1.8 Scope of discussion / 30
2 Optical imaging and resolution / 31
2.1 Coherent imaging / 31
2.1.1 Principle / 31
2.1.2 Resolution / 34
2.2 Mask spectrum / 39
2.2.1 Pitch dependence / 42
2.2.2 Dependence on dimension / 42
2.2.3 Two-dimensional patterns / 44
2.3 Partially coherent imaging / 45
2.4 Complex degree of coherence / 55
2.5 Rayleigh's resolution limit / 58
2.6 Lithography resolution limit / 59
2.7 Quantification of image quality / 59
2.7.1 Modulation transfer function / 60
2.7.2 Contrast / 60
2.7.3 Exposure latitude / 60
2.7.4 Normalized image log slope / 61
2.7.5 Depth of focus / 62
2.7.6 Exposure-defocus window / 64
2.7.7 Total window / 66
2.7.8 Common window / 68
2.7.9 Line width variability / 69
3 Modified illumination / 71
3.1 Partial coherence factor / 71
3.1.1 Large s / 71
3.1.2 Small s / 79
3.1.3 Medium s / 79
3.2 Off-axis illumination / 80
3.2.1 Dipole / 80
3.2.2 Quadrupole / 84
3.2.3 Annular / 85
3.2.4 Implementation issues / 87
3.3 General guidelines / 90
4 Optical proximity correction / 91
4.1 Image distortion / 91
4.2 Optical proximity correction approaches / 91
4.2.1 Catastrophic OPC / 93
4.2.2 Line width variation minimization / 94
4.2.3 Line shortening / 100
4.2.4 Corner rounding / 100
4.3 Numerical techniques / 101
4.3.1 Rule-based / 102
4.3.2 Model-based / 103
4.3.3 Hybrid / 105
4.4 Implementation / 106
4.4.1 Correction function derivation / 106
4.4.2 CAD system / 110
4.5 Discussion / 115
5 Alternating phase-shifting mask / 117
5.1 Principle / 117
5.2 Mask making process / 121
5.3 Issues / 123
5.3.1 Intensity imbalance / 123
5.3.2 Aberration sensitivity / 126
5.3.3 Mask defect / 128
5.4 Implementation / 130
5.4.1 Dark-field application / 131
5.4.2 Light-field application / 133
5.5 Summary / 138
6 Attenuated phase-shift mask / 139
6.1 Principle / 139
6.2 Mask making / 147
6.2.1 Thin film / 147
6.2.2 Opaque border / 148
6.3 Discussion / 151
7 Selecting appropriate RETs / 153
7.1 Critical levels / 153
7.2 Methodology / 154
7.2.1 Include applicable approaches / 154
7.2.2 Select promising techniques / 155
7.2.3 Experimental quantification / 158
7.3 Optimization results / 158
7.3.1 Storage / 160
7.3.2 Isolation / 163
7.3.3 Word line / 164
7.3.4 Bit line contact 166
7.4 Summary and discussion / 168
8 Second-Generation RETs / 171
8.1 Multiple exposure / 171
8.1.1 Forming sharp corners / 172
8.1.2 Assembling patterns / 172
8.2 Pupil filtering / 175
8.3 Advanced illumination scheme / 176
8.3.1 Concurrent reticle-illumination optimization / 176
8.3.2 Dark-field illumination / 177
8.4 Compensating process / 180
8.5 Mask and photoresist tone / 180
Concluding remarks / 183
k1 conversion charts / 187
Bibliography / 189
Index / 209

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