Fundamental Principles of Optical Lithography The Science of Microfabrication

by Mack, Chris

• ISBN13: 9780470727300
• ISBN10: 0470727306
• Edition: 1st
• Format: Paperback
• Copyright: 2007-12-17
• Publisher: WILEY

Summary

The fabrication of an integrated circuit requires a variety of physical and chemical processes to be performed on a semiconductor substrate. In general, these processes fall into three categories: film deposition, patterning, and semiconductor doping. Films of both conductors and insulators are used to connect and isolate transistors and their components.By creating structures of these various components millions of transistors can be built and wired together to form the complex circuitry of modern microelectronic devices. Fundamental to all of these processes is lithography, i.e., the formation of three-dimensional relief images on the substrate for subsequent transfer of the pattern to the substrate.This book presents a complete theoretical and practical treatment of the topic of lithography for both students and researchers. This sole-authored text includes optional computer simulation exercises as well as problems at the end of each chapter.

Author Biography

Dr. Chris A. Mack is also an adjunct faculty member at the University of Texas at Austin

Table of Contents

Preface	p. xv
Introduction to Semiconductor Lithography	p. 1
Basics of IC Fabrication	p. 2
Patterning	p. 2
Etching	p. 3
Ion Implantation	p. 5
Process Integration	p. 6
Moore's Law and the Semiconductor Industry	p. 7
Lithography Processing	p. 12
Substrate Preparation	p. 14
Photoresist Coating	p. 15
Post-Apply Bake	p. 18
Alignment and Exposure	p. 19
Post-exposure Bake	p. 23
Development	p. 24
Postbake	p. 25
Measure and Inspect	p. 25
Pattern Transfer	p. 25
Strip	p. 26
Problems	p. 26
Aerial Image Formation - The Basics	p. 29
Mathematical Description of Light	p. 29
Maxwell's Equations and the Wave Equation	p. 30
General Harmonic Fields and the Plane Wave in a Nonabsorbing Medium	p. 32
Phasors and Wave Propagation in an Absorbing Medium	p. 33
Intensity and the Poynting Vector	p. 36
Intensity and Absorbed Electromagnetic Energy	p. 37
Basic Imaging Theory	p. 38
Diffraction	p. 39
Fourier Transform Pairs	p. 43
Imaging Lens	p. 45
Forming an Image	p. 47
Imaging Example: Dense Array of Lines and Spaces	p. 48
Imaging Example: Isolated Space	p. 50
The Point Spread Function	p. 51
Reduction Imaging	p. 53
Partial Coherence	p. 56
Oblique Illumination	p. 57
Partially Coherent Illumination	p. 58
Hopkins Approach to Partial Coherence	p. 62
Sum of Coherent Sources Approach	p. 63
Off-Axis Illumination	p. 65
Imaging Example: Dense Array of Lines and Spaces Under Annular Illumination	p. 66
Kohler Illumination	p. 66
Incoherent Illumination	p. 69
Some Imaging Examples	p. 70
Problems	p. 71
Aerial Image Formation - The Details	p. 75
Aberrations	p. 75
The Causes of Aberrations	p. 75
Describing Aberrations: the Zernike Polynomial	p. 78
Aberration Example - Tilt	p. 81
Aberration Example - Defocus, Spherical and Astigmatism	p. 83
Aberration Example - Coma	p. 84
Chromatic Aberrations	p. 85
Strehl Ratio	p. 90
Pupil Filters and Lens Apodization	p. 90
Flare	p. 91
Measuring Flare	p. 92
Modeling Flare	p. 94
Defocus	p. 95
Defocus as an Aberration	p. 95
Defocus Example: Dense Lines and Spaces and Three-Beam Imaging	p. 98
Defocus Example: Dense Lines and Spaces and Two-Beam Imaging	p. 100
Image Isofocal Point	p. 102
Focus Averaging	p. 103
Reticle Defocus	p. 104
Rayleigh Depth of Focus	p. 105
Imaging with Scanners Versus Steppers	p. 106
Vector Nature of Light	p. 108
Describing Polarization	p. 111
Polarization Example: TE Versus TM Image of Lines and Spaces	p. 113
Polarization Example: The Vector PSF	p. 114
Polarization Aberrations and the Jones Pupil	p. 114
Immersion Lithography	p. 117
The Optical Invariant and Hyper-NA Lithography	p. 118
Immersion Lithography and the Depth of Focus	p. 120
Image Quality	p. 121
Image CD	p. 121
Image Placement Error (Distortion)	p. 123
Normalized Image Log-Slope (NILS)	p. 123
Focus Dependence of Image Quality	p. 125
Problems	p. 126
Imaging in Resist: Standing Waves and Swing Curves	p. 129
Standing Waves	p. 130
The Nature of Standing Waves	p. 130
Standing Waves for Normally Incident Light in a Single Film	p. 131
Standing Waves in a Multiple-Layer Film Stack	p. 135
Oblique Incidence and the Vector Nature of Light	p. 137
Broadband Illumination	p. 141
Swing Curves	p. 144
Reflectivity Swing Curve	p. 144
Dose-to-Clear and CD Swing Curves	p. 148
Swing Curves for Partially Coherent Illumination	p. 149
Swing Ratio	p. 151
Effective Absorption	p. 154
Bottom Antireflection Coatings	p. 156
BARC on an Absorbing Substrate	p. 157
BARCs at High Numerical Apertures	p. 160
BARC on a Transparent Substrate	p. 164
BARC Performance	p. 165
Top Antireflection Coatings	p. 167
Contrast Enhancement Layer	p. 170
Impact of the Phase of the Substrate Reflectance	p. 170
Imaging in Resist	p. 173
Image in Resist Contrast	p. 173
Calculating the Image in Resist	p. 177
Resist-Induced Spherical Aberrations	p. 179
Standing Wave Amplitude Ratio	p. 181
Defining Intensity	p. 183
Intensity at Oblique Incidence	p. 183
Refraction into an Absorbing Material	p. 184
Intensity and Absorbed Energy	p. 187
Problems	p. 188
Conventional Resists: Exposure and Bake Chemistry	p. 191
Exposure	p. 191
Absorption	p. 191
Exposure Kinetics	p. 194
Post-Apply Bake	p. 199
Sensitizer Decomposition	p. 200
Solvent Diffusion and Evaporation	p. 205
Solvent Effects in Lithography	p. 209
Post-exposure Bake Diffusion	p. 210
Detailed Bake Temperature Behavior	p. 214
Measuring the ABC Parameters	p. 217
Problems	p. 219
Chemically Amplified Resists: Exposure and Bake Chemistry	p. 223
Exposure Reaction	p. 223
Chemical Amplification	p. 224
Amplification Reaction	p. 225
Diffusion	p. 227
Acid Loss	p. 230
Base Quencher	p. 232
Reaction-Diffusion Systems	p. 233
Measuring Chemically Amplified Resist Parameters	p. 235
Stochastic Modeling of Resist Chemistry	p. 237
Photon Shot Noise	p. 237
Chemical Concentration	p. 239
Some Mathematics of Binary Random Variables	p. 241
Photon Absorption and Exposure	p. 242
Acid Diffusion, Conventional Resist	p. 246
Acid-Catalyzed Reaction-Diffusion	p. 247
Reaction-Diffusion and Polymer Deblocking	p. 251
Acid-Base Quenching	p. 253
Problems	p. 254
Photoresist Development	p. 257
Kinetics of Development	p. 257
A Simple Kinetic Development Model	p. 258
Other Development Models	p. 261
Molecular Weight Distributions and the Critical Ionization Model	p. 264
Surface Inhibition	p. 265
Extension to Negative Resists	p. 267
Developer Temperature	p. 267
Developer Normality	p. 268
The Development Contrast	p. 270
Defining Photoresist Contrast	p. 270
Comparing Definitions of Contrast	p. 274
The Practical Contrast	p. 276
Relationship between [gamma] and r[subscript max]/r[subscript min]	p. 277
The Development Path	p. 278
The Euler-Lagrange Equation	p. 279
The Case of No z-Dependence	p. 280
The Case of a Separable Development Rate Function	p. 282
Resist Sidewall Angle	p. 283
The Case of Constant Development Gradients	p. 284
Segmented Development and the Lumped Parameter Model (LPM)	p. 286
LPM Example - Gaussian Image	p. 287
Measuring Development Rates	p. 292
Problems	p. 293
Lithographic Control in Semiconductor Manufacturing	p. 297
Defining Lithographic Quality	p. 297
Critical Dimension Control	p. 299
Impact of CD Control	p. 299
Improving CD Control	p. 303
Sources of Focus and Dose Errors	p. 305
Defining Critical Dimension	p. 307
How to Characterize Critical Dimension Variations	p. 309
Spatial Variations	p. 309
Temporal Variations and Random Variations	p. 311
Characterizing and Separating Sources of CD Variations	p. 312
Overlay Control	p. 314
Measuring and Expressing Overlay	p. 315
Analysis and Modeling of Overlay Data	p. 317
Improving Overlay Data Analysis	p. 320
Using Overlay Data	p. 323
Overlay Versus Pattern Placement Error	p. 326
The Process Window	p. 326
The Focus-Exposure Matrix	p. 326
Defining the Process Window and DOF	p. 332
The Isofocal Point	p. 336
Overlapping Process Windows	p. 338
Dose and Focus Control	p. 339
H-V Bias	p. 343
Astigmatism and H-V Bias	p. 343
Source Shape Asymmetry	p. 345
Mask Error Enhancement Factor (MEEF)	p. 348
Linearity	p. 348
Defining MEEF	p. 349
Aerial Image MEEF	p. 350
Contact Hole MEEF	p. 352
Mask Errors as Effective Dose Errors	p. 353
Resist Impact on MEEF	p. 355
Line-End Shortening	p. 356
Measuring LES	p. 357
Characterizing LES Process Effects	p. 359
Critical Shape and Edge Placement Errors	p. 361
Pattern Collapse	p. 362
Problems	p. 366
Gradient-Based Lithographic Optimization: Using the Normalized Image Log-Slope	p. 369
Lithography as Information Transfer	p. 369
Aerial Image	p. 370
Image in Resist	p. 377
Exposure	p. 378
Post-exposure Bake	p. 381
Diffusion in Conventional Resists	p. 381
Chemically Amplified Resists - Reaction Only	p. 383
Chemically Amplified Resists - Reaction-Diffusion	p. 384
Chemically Amplified Resists - Reaction-Diffusion with Quencher	p. 391
Develop	p. 393
Conventional Resist	p. 397
Chemically Amplified Resist	p. 399
Resist Profile Formation	p. 400
The Case of a Separable Development Rate Function	p. 400
Lumped Parameter Model	p. 401
Line Edge Roughness	p. 404
Summary	p. 406
Problems	p. 408
Resolution Enhancement Technologies	p. 411
Resolution	p. 412
Defining Resolution	p. 413
Pitch Resolution	p. 416
Natural Resolutions	p. 418
Improving Resolution	p. 418
Optical Proximity Correction (OPC)	p. 419
Proximity Effects	p. 419
Proximity Correction - Rule Based	p. 422
Proximity Correction - Model Based	p. 425
Subresolution Assist Features (SRAFs)	p. 427
Off-Axis Illumination (OAI)	p. 429
Phase-Shifting Masks (PSM)	p. 434
Alternating PSM	p. 435
Phase Conflicts	p. 438
Phase and Intensity Imbalance	p. 439
Attenuated PSM	p. 441
Impact of Phase Errors	p. 445
Natural Resolutions	p. 450
Contact Holes and the Point Spread Function	p. 450
The Coherent Line Spread Function (LSF)	p. 452
The Isolated Phase Edge	p. 453
Problems	p. 454
Glossary of Microlithographic Terms	p. 457
Curl, Divergence, Gradient, Laplacian	p. 491
The Dirac Delta Function	p. 495
Index	p. 501
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