Process Variations in Microsystems Manufacturing (eBook)

Preface 7
Acknowledgments 10
Contents 11
Chapter 1: Introduction 18
1.1 From Vacuum Tubes to Microsystems 18
1.2 MEMS Microsystems 19
1.3 Some of the Important Attributes of MEMS Microsystems 21
1.4 Organization of This Book 23
References 25
Other Information 25
Chapter 2: An Overview of MEMS Microsystems 26
2.1 Introduction 26
2.2 Microsensors and Microactuators 26
2.2.1 MEMS Microsensors 27
2.2.1.1 Resistive 27
2.2.1.2 Piezoresistive 29
2.2.1.3 Capacitive 30
2.2.1.4 Piezoelectric 32
2.2.1.5 Tunneling 33
2.2.1.6 Magnetic 35
2.2.1.7 Photoconduction 36
2.2.1.8 Thermoelectric 37
2.2.1.9 Diodes 38
2.2.2 MEMS Microactuators 40
2.2.2.1 Electrostatic 40
2.2.2.2 Piezoelectric 41
2.2.2.3 Thermal 43
2.2.2.4 Shape-Memory Alloys (SMA) 44
2.2.2.5 Magnetic 45
2.3 Microsystems Manufacturing Processes 47
2.4 Batch Fabrication 49
2.5 Some Basics of Microsystems Manufacturing 51
2.5.1 Differences Between IC and MEMS Manufacturing 52
2.5.2 Microsystems Feature Sizes 54
2.6 Some Material Basics Regarding Semiconductors and Silicon 55
2.7 Summary 60
References 60
Chapter 3: Microsystems Manufacturing Methods: Integrated Circuit Processing Steps 62
3.1 Introduction 62
3.2 Basic IC Processing Steps 64
3.2.1 Thin-Film Growth and Deposition Techniques 64
3.2.1.1 Thermal Oxidation 64
3.2.1.2 Chemical Vapor Deposition 69
3.2.1.2.1 Atmospheric Chemical Vapor Deposition (ACVD) 72
3.2.1.2.2 Low-Pressure Chemical Vapor Deposition (LPCVD) 73
3.2.1.2.3 Plasma-Enhanced Chemical Vapor Deposition (PECVD) 75
3.2.1.2.4 Atomic Layer Deposition (ALD) 77
3.2.1.3 Physical Vapor Deposition (PVD) 79
3.2.1.3.1 Evaporation 79
3.2.1.3.2 Sputtering 82
3.2.2 Impurity Doping 84
3.2.2.1 Thermal Diffusion 85
3.2.2.2 Ion Implantation 88
3.2.3 Photolithography 93
3.2.4 Rapid Thermal Anneal (RTA) 98
3.2.5 Planarization 100
3.2.6 Etching 102
3.2.7 Clean and Strip 109
3.3 Summary 110
References 111
Chapter 4: Microsystems Manufacturing Methods: MEMS Processes 115
4.1 Introduction 115
4.2 MEMS Substrate Material Types 116
4.3 MEMS Materials Deposition Processing Steps 117
4.3.1 MEMS Thin-Film Materials Deposited on IC Equipment 117
4.3.1.1 Thin-Film Semiconductors 117
4.3.1.1.1 Silicon (Si) 117
4.3.1.1.2 Silicon-Germanium (SiGe) 119
4.3.1.1.3 Germanium (Ge) 120
4.3.1.1.4 Silicon Carbide (SiC) 120
4.3.1.1.5 Diamond 121
4.3.1.2 Metals 122
4.3.1.3 Thin-Film Metal Oxides 124
4.3.1.4 Dielectrics 125
4.3.1.4.1 Silicon Nitride (SiN) 125
4.3.1.4.2 Silicon Dioxide (SiO2) 126
4.3.1.5 Polymers 127
4.3.1.5.1 SU-8 127
4.3.1.5.2 PDMS 128
4.3.1.5.3 Polyimide 128
4.3.1.6 Ceramics 129
4.3.1.7 Special MEMS Materials 130
4.3.1.7.1 Piezoelectric Materials 130
4.3.1.7.2 Shape-Memory Alloys (SMAs) 132
4.3.1.7.3 Magnetic Materials 133
4.3.2 MEMS Specific Processing Steps 134
4.3.2.1 Electrochemical Deposition 134
4.3.2.2 MEMS Lithography 136
4.3.2.2.1 Contact Photolithography 137
4.3.2.2.2 Front-to-Back Contact Photolithography 137
4.3.2.2.3 Direct-Write Laser Photolithography 138
4.3.2.2.4 Grayscale Photolithography 138
4.3.2.2.5 X-Ray Lithography 140
4.3.2.2.6 E-Beam Lithography 140
4.3.2.2.7 Lithography on Large Topography 141
4.3.2.2.8 Lift-Off Patterning 142
4.3.2.2.9 Image Reversal Photoresists 143
4.3.2.2.10 Photolithography on Transparent Substrates 144
4.4 MEMS Micromachining Methods 144
4.4.1 Bulk Micromachining 145
4.4.1.1 Wet Chemical Etchants 145
4.4.1.1.1 Isotropic Wet Chemical Etchants 146
4.4.1.1.2 Anisotropic Wet Chemical Etchants 147
4.4.1.2 Gas-Phase Isotropic Chemical Etchants 153
4.4.1.3 Deep Reactive Ion Etching (DRIE) of Silicon 154
4.4.1.4 Deep, High-Aspect Ratio RIE of Fused Silica, Quartz, and Glass 157
4.4.1.5 Deep, High-Aspect Ratio RIE of Silicon Carbide (SiC) 159
4.4.2 Surface Micromachining 160
4.4.3 Wafer Bonding 163
4.4.4 LIGA 166
4.4.5 Hot Embossing 168
4.4.6 Other MEMS Micromachining Technologies 169
4.4.6.1 Electro-Discharge Micromachining 169
4.4.6.2 Laser Micromachining 169
4.4.6.3 Focused Ion Beam (FIB) Micromachining 170
4.4.6.4 Electrochemical Fabrication (EFAB) 171
4.5 Summary 171
References 173
Chapter 5: Metrology for Microsystems Manufacturing 188
5.1 Introduction 188
5.2 Fabrication Metrology Equipment and Methods 189
5.2.1 Optical Microscopy 189
5.2.2 Fluorescence Microscopy 192
5.2.3 Confocal Microscopy 194
5.2.4 Stereomicroscopy 195
5.2.5 Scanning Electron Microscope (SEM) 195
5.2.6 Automated Scanning Electron Microscope 198
5.2.7 Thin-Film Thickness 200
5.2.7.1 Interferometry 200
5.2.7.2 Ellipsometry 202
5.2.7.3 Stylus Profilometry 204
5.2.8 Four-Point Probe 206
5.2.9 Thin-Film Stress Measurement 208
5.2.10 Particle Measurements 212
5.2.11 Noncontact Optical Profilometry 213
5.2.12 Wafer Bonding Inspection 215
5.3 Specialized Metrology Equipment and Methods 218
5.3.1 Focused Ion Beam 218
5.3.2 Scanning Tunneling Microscopy (STM) 221
5.3.3 Atomic Force Microscopy (AFM) 223
5.3.4 Energy-Dispersive X-Ray Spectroscopy (EDXS) 225
5.4 Highly Specialized Material Analysis Methods 227
5.5 Electrical Material Properties Test Methods 232
5.5.1 Junction Depth Measurements 232
5.5.2 Spreading Sheet Resistance 233
5.6 Summary 236
References 238
Chapter 6: Microsystems Material Properties 241
6.1 Introduction 241
6.2 Residual Stress and Young´s Modulus 243
6.2.1 Young´s Modulus 244
6.2.2 Residual Stress 246
6.3 Mechanical Test Structures 248
6.3.1 Test Structures for Young´s Modulus 248
6.3.2 Thin-Film Residual Stress Test Structures 251
6.3.3 Stress Gradients 255
6.3.4 Tests for Other Mechanical Material Properties 256
6.4 Electrical Test Structures 257
6.5 Thin-Film Material Properties 264
6.5.1 Thermal SiO2 264
6.5.2 LPCVD Polysilicon 265
6.5.3 LPCVD Silicon Dioxide (SiO2) 269
6.5.4 LPCVD Silicon Nitride (SiN) 271
6.5.5 PECVD Silicon Dioxide (SiO2) 273
6.5.6 PECVD Silicon Nitride (SiN) 275
6.5.7 PECVD Polycrystalline Silicon 277
6.5.8 Evaporative Physical Vapor Deposition 277
6.5.9 Sputter Physical Vapor Deposition 280
6.5.9.1 Sputter-Deposited Silicon 280
6.5.10 Electrochemical Deposition 281
6.6 Summary 283
References 283
Chapter 7: Microsystems Process Integration, Testing, and Packaging 288
7.1 Introduction 288
7.2 What Is Process Integration? 289
7.3 How Is Process Integration Performed? 291
7.4 What Is an Integrated MEMS Process Sequence? 296
7.5 Examples of MEMS Microsystems Process Technologies 296
7.5.1 PolyMUMPS Process Technology 297
7.5.1.1 Some Important Elements About PolyMUMPS 302
7.5.2 Digital Light Processor (DLP) Technology 304
7.5.2.1 Some Key Elements About the DLP Process Technology 307
7.6 Process Integration and Manufacturing Variations 308
7.6.1 Causes of Device Parameter Variations in Process Sequences 308
7.6.2 An Example of Parameter Variations for a Process Technology: The PolyMUMPS Process 311
7.7 Microsystems Design Rules 314
7.7.1 MEMS Microsystems Design Rules 314
7.7.2 Design Rule Checking 316
7.8 MEMS Microsystems Testing 317
7.8.1 Example of MEMS Microsystems Testing 318
7.8.2 MEMS Microsystems Device Trimming 319
7.8.3 MEMS Microsystems Calibration 320
7.9 MEMS Microsystems Packaging 320
7.10 Summary 323
References 323
Chapter 8: Device Parameter Variations in Microsystems Manufacturing 325
8.1 Introduction 325
8.2 Manufacturing Variations 326
8.3 Measurement of Manufacturing Variations 327
8.4 Bias and Random Variations 328
8.5 Resolution, Precision, and Accuracy 331
8.6 Comparison of the Dimensional Parameter Variations in Manufacturing Technologies 333
8.7 The Nature of Random Parameter Variations 337
8.8 Discrete Probability Distributions 354
8.9 Some Examples of Statistical Analysis of Variations 357
8.9.1 Confidence Interval for Manufacturing Large Samples (N > 30)
8.9.2 Confidence Interval for Small Samples (N < 30)
8.9.3 Hypothesis Testing for Small Sample Sizes (N < 30)
8.9.4 Hypothesis Testing of Goodness of Fit 363
8.9.5 Sample Size Required to Estimate Population Mean 365
8.9.6 Example of Use of the Hypergeometric Distribution 366
8.9.7 Example of Poisson Distribution 366
8.10 Impact of Physics and Random Parameter Variations 367
8.11 Combination of Both Bias and Random Manufacturing Parameter Variations 371
8.12 Device Output Behavior Variation Due to Parameter Variations 373
8.13 Example of Device Output Behavior Variation Analysis 375
8.14 Simplified Variation Analysis 382
8.15 Important Generalizations 384
8.16 Review of Methods for Variation Analysis 387
8.16.1 Worst-Case Variation Analysis 389
8.16.2 Non-worst-Case Variation Analysis 393
8.16.2.1 Non-sampling, Non-worst-Case Variation Analysis 393
8.16.2.2 Monte Carlo Variation Analysis 394
8.17 Summary 398
References 399
Chapter 9: Yield Analysis and Quality Assurance and Control Methods Used in Microsystems Manufacturing 400
9.1 Introduction 400
9.2 Importance of Manufacturing Yield 401
9.3 Definitions of Microsystems Manufacturing Yield 402
9.4 Microsystems Manufacturing Yield Monitoring and Analysis 404
9.4.1 Functional Yield 405
9.4.1.1 Functional Yield Models Based on Point Defects 406
9.4.1.2 Functional Yield Measurement Tools 410
9.4.2 Parametric Yield 411
9.4.2.1 Parametric Yield Model 411
9.4.2.2 An Example of a Parametric Yield Model 419
9.5 Yield Estimations Using Sampling Methods 421
9.5.1 Yield Estimation Using Regionalization 422
9.5.2 Yield Estimation Using Simplicial Approximation 425
9.5.3 Monte Carlo Yield Estimation 428
9.5.3.1 Confidence Intervals for Monte Carlo Yield Analysis 429
9.6 Statistical Process Control (SPC) 431
9.6.1 Control Charts for Variables 435
9.6.2 Control Charts for Attributes 440
9.6.3 Identification of Non-random Patterns in Control Charts 445
9.6.4 Process Capability 446
9.6.5 Rational Subgroups 450
9.6.5.1 Sampling Methods for Rational Subgroups 454
9.7 Summary 456
References 456
Chapter 10: Managing Parameter Variations in Microsystems Device Design 458
10.1 Introduction 458
10.2 Relationships Between Process Sequence and Parameter Variations 460
10.3 Overview of MEMS Device Design and Modeling 462
10.4 Example of the Design Levels for a MEMS Device 465
10.5 MEMS Design for Manufacturability 469
10.5.1 MEMS Device Design for Manufacturability 470
10.5.2 MEMS Process Sequence Design for Manufacturability 471
10.5.3 MEMS Microsystems Partitioning 473
10.6 Overview of MEMS Development 474
10.7 MEMS Design for Manufacturability Recommendations 477
10.8 Managing Device Parameter Variations in MEMS Design 478
10.8.1 Design Centering 480
10.8.2 Parameter Variation Reduction 484
10.8.3 Device Size Scaling 486
10.8.4 Acceptance Range Increase 488
10.8.5 Best Practices in Layout Design 489
10.8.6 Further Comments About MEMS Design Methods 496
10.9 MEMS Design in Multidimensional Spaces 497
10.10 MEMS Design Methods Using Monte Carlo Techniques 502
10.10.1 Design Centering Using Monte Carlo 505
10.11 Sensitivity Analysis 509
10.11.1 Generalized Sensitivity Analysis Methods 512
10.11.2 Optimizing Manufacturing Cost Function 516
10.12 Summary 517
References 517
Index 519