Wafer Manufacturing Shaping of Single Crystal Silicon Wafers

Presenting all the major stages in wafer manufacturing, from crystals to prime wafers.

This book first outlines the physics, associated metrology, process modelling and quality requirements and the goes on to discuss wafer forming and wafer surface preparation techniques.  The whole is rounded off with a chapter on the research and future challenges in wafer manufacturing.

Imin Kao, is Professor in the Department of Mechanical Engineering at the State University of New York in Stony Brook, USA. He is Faculty Director of the Undergraduate College in Information and Technology Studies. He holds three patents, and his research foci include robotic manipulation with soft contacts and smart contact surface technology using MEMS.

Chunhui Chung, is Associate Professor in the Department of Mechanical Engineering at the National Cheng Kung University in Taiwan.

Preface xi

1 Wafers and Semiconductors 3

1.1 Introduction 3

1.2 Semiconductor Revolution 3

1.2.1 Classification of materials 3

1.2.2 Semiconductor revolution today 6

1.2.3 Silicon wafers and solar cells 8

1.3 Silicon Wafers Used in Device Manufacturing (IC and MEMS) 8

1.3.1 Standard wafer diameters and sizes 9

1.3.2 Crystalline orientation of silicon wafers 11

1.3.3 The Moore’s Law 13

1.4 Surface Properties and Quality Measurements of Wafers 14

1.4.1 Surface waviness: TTV, bow, and warp 14

1.4.2 Discussion on warp 19

1.4.3 Automated measurements of TTV, warp, bow and flatness 20

1.4.4 Wafer flatness 21

1.4.5 Nanotopography or Nanotopology 27

1.4.6 Surface roughness 28

1.5 Other Properties and Quality Requirements of Silicon Wafers 34

1.5.1 Mechanical and material properties 34

1.5.2 Property of silicon with anisotropy 34

1.5.3 Gravity-induced deflection of wafers 38

1.5.4 Wafer edge properties 39

1.6 Economics ofWafer Manufacturing 41

1.6.1 Three categories of wafers 41

1.6.2 Cost of silicon wafers 43

1.7 Summary 45

References 46

2 WaferManufacturing: Generalized Processes and Flow 49

2.1 Introduction 49

2.2 Wafer Manufacturing: Generalized Process Flow 50

2.3 Crystal Growth 51

2.3.1 Melt growth 51

2.3.2 Vapor growth 61

2.3.3 Epitaxial growth 61

2.3.4 Casting polycrystalline crystal 63

2.3.5 Other crystal growth methods 64

2.4 Wafer Forming 64

2.4.1 Cropping 65

2.4.2 Trimming 65

2.4.3 Orientation identification 65

2.4.4 Slicing 65

2.4.5 Slicing using the Inner-diameter (ID) saw 66

2.4.6 Slicing using wiresaw 67

2.4.7 Other tools for slicing 68

2.4.8 Edge rounding 69

2.5 Wafer Polishing 71

2.5.1 Lapping 72

2.5.2 Grinding 72

2.5.3 Etching 73

2.5.4 Polishing 73

2.6 Wafer Preparing 74

2.6.1 Cleaning 74

2.6.2 Inspection 75

2.6.3 Packaging 75

2.7 Industrial Processes of Wafer Manufacturing 75

2.7.1 Crystal growth 76

2.7.2 Wafer forming 76

2.7.3 Wafer lapping and polishing 81

2.7.4 Wafer preparing 85

2.8 Summary 87

References 88

3 Process Modeling and Manufacturing Processes 91

3.1 Introduction 91

3.2 Wafer Manufacturing and Brittle Materials 92

3.3 Ductile Machining Versus Brittle Machining 94

3.4 Abrasive Machining in Wafer Manufacturing 95

3.4.1 Bonded abrasive machining (BAM) 96

3.4.2 Free abrasive machining (FAM) 97

3.5 Abrasive Materials 98

3.5.1 Classification of the grain size of abrasive materials 98

3.5.2 Hardness of abrasive materials 100

3.5.3 Commonly used abrasive materials in wafer manufacturing 102

3.6 Ductile Machining of Brittle Materials 105

3.6.1 Research on ductile machining and challenges 106

3.6.2 Opportunity and future research 106

3.7 Process Modeling of Manufacturing Processes 107

3.7.1 Rolling-indenting and scratching-indenting process models of FAM 108

3.7.2 Comparison between wiresawing and lapping 111

3.7.3 Other aspects of engineering modeling 113

3.8 Abrasive Slurry in FAM Processes 113

3.8.1 Composition of abrasive slurry 114

3.8.2 Comparison of water and glycol as carrier fluid for slurry 116

3.8.3 Recycling of abrasive grits in slurry 117

3.9 Summary 119

References 120

4 Wafer Slicing Using a Modern Slurry Wiresaw and Other Saws 125

4.1 Introduction 125

4.2 The ModernWiresaw Technology 126

4.2.1 Historical perspectives of saws using wire 127

4.2.2 The rise of PV industry and wafer slicing 129

4.3 The three categories of saws for wafer slicing 130

4.4 Inner-diameter (ID) saw 131

4.5 The modern slurry wiresaw 134

4.5.1 The control and program console 135

4.5.2 The wire management unit 135

4.5.3 Uni-directional versus bi-directional wire motion 140

4.5.4 The slicing compartment 144

4.5.5 Directions of ingot feeding 145

4.5.6 Consumables and other operations 147

4.6 Comparison between the ID saw and wiresaw 148

4.7 Research Issues in Wiresaw Manufacturing Processes 153

4.8 Summary 154

References 155

5 Modeling of the WiresawManufacturing Process and Material Characteristics 161

5.1 Introduction 161

5.2 The rolling-indenting model 164

5.3 Vibration modeling and analysis 167

5.3.1 A historical perspective on the vibration of wire 168

5.3.2 Equation of motion of a moving wire 169

5.3.3 Modal analysis of a undamped moving wire 170

5.3.4 Response for point-wise harmonic excitation 171

5.3.5 Natural frequency of vibration and stability 172

5.3.6 Numerical solution by the Galerkin’s method 176

5.3.7 Response of multiple-point and distributed excitations 177

5.3.8 Frequency response of multiple excitations 179

5.3.9 Vibration responses of a moving wire with damping 181

5.3.10 Discussions 183

5.4 Damping factor of the slurry wiresaw system 185

5.5 Elasto-hydrodynamic process modeling 188

5.5.1 Approach of modeling of EHD in wiresawing process 189

5.5.2 TheoreticalModeling 190

5.5.3 Results of the EHD analysis 192

5.5.4 Implications related to floating machining and rolling-indenting

modeling of modern slurry wiresaws 194

5.5.5 Important conclusions from the elsto-hydrodynamicmodeling 197

5.6 Thermal Management 198

5.7 Wire, Wire Web, and Slurry Management 199

5.7.1 Real-time and on-line monitoring of wire wear 199

5.7.2 Monitoring the pitch of the wire web spacing 202

5.7.3 Mixing ratio of slurry consisting of abrasive grits and carrier fluid 205

5.8 Summary 206

References 207

6 Diamond-ImpregatedWire Saws and Sawing Process 213

6.1 Introduction 213

6.2 Manufacturing processes of diamond-impregnated wires 216

6.2.1 The resinoid wires 216

6.2.2 The electroplated wires 219

6.2.3 Machines and operations of diamond wire saws 221

6.3 Slicing Mechanism of DiamondWire Saw 223

6.4 Properties of Wafers Sliced by DiamondWire Saws 228

6.4.1 Wafer surface 228

6.4.2 Wafer fracture strength 229

6.4.3 Residual stress and stress relaxation 230

6.4.4 PV wafer efficiency 230

6.4.5 Cost of wafering 231

6.5 Slicing Performance with Different Process Parameters 231

6.5.1 Effect of wire speed 232

6.5.2 Effect of feed rate 232

6.5.3 Effect of grain density 232

6.5.4 Effect of wire tension 233

6.6 Summary 233

References 235

7 Lapping 239

7.1 Introduction 239

7.2 Fundamentals of Lapping and FAM 240

7.3 Various Configurations and Types of Lapping Operation 244

7.3.1 Single-sided lapping 251

7.3.2 Double-sided lapping 252

7.3.3 Soft-pad lapping 253

7.3.4 Further references 253

7.4 Lapping and Preliminary Planarization 253

7.4.1 Quality driven needs for preliminary planarization 254

7.4.2 Cost driven needs for preliminary planarization 255

7.5 Technical Challenges and Advances in Lapping 256

7.5.1 Technical Considerations 258

7.5.2 Advances in Lapping 259

7.6 Summary 259

References 260

8 Chemical Mechanical Polishing 263

8.1 Introduction 263

8.2 Chemical Mechanical Polishing (CMP) 264

8.2.1 Schematic illustration of CMP process and system 265

8.2.2 Measurement and evaluation of silicon wafer after polishing 268

8.2.3 Specifications for polished silicon wafers 269

8.2.4 Types of CMP processes 271

8.2.5 Challenges of CMP technology 271

8.3 Polishing Pad Technology 272

8.3.1 Polishing pad conditioning 273

8.4 Polishing Slurry Technology 273

8.5 Edge Polishing 274

8.5.1 Fundamentals of edge polishing 275

8.5.2 Challenges of edge polishing 276

8.6 Summary 276

References 277

9 Grinding, Edge Grinding, Etching and Surface Cleaning 279

9.1 Wafer Grinding for Surface Processing 279

9.1.1 Wafer grinding methods 280

9.1.2 Grinding wheel technology 284

9.1.3 Types of grinding operations 285

9.1.4 Technical challenges and advances in grinding 286

9.2 Edge Grinding 287

9.2.1 Fundamentals of edge grinding 288

9.2.2 Technical challenges in edge grinding 290

9.3 Etching 291

9.3.1 Acid etching 291

9.3.2 Caustic etching 292

9.3.3 Preferential etching 292

9.3.4 Technical challenges and advances in etching 296

9.4 Surface Cleaning 297

9.4.1 Impurities on surface of silicon wafer 297

9.4.2 Various cleaning steps in wafer process flow 298

9.5 RCA Standard Clean 300

9.5.1 Introduction 300

9.5.2 RCA cleaning protocol 300

9.5.3 Techniques and variations of RCA method 303

9.5.4 The evolution of silicon wafer cleaning technology 304

9.6 Summary 304

References 306

10 WaferMetrology and Optical Techniques 311

10.1 Introduction 311

10.2 Evaluation and Inspection ofWafer Surface 311

10.2.1 Wafer surface specifications 312

10.3 Wafer Defects and Inspection 316

10.3.1 Defect classification 316

10.3.2 Impacts of wafer defects on device yield and performance 319

10.3.3 Defect inspection techniques and systems 320

10.4 Measurement ofWafer Surface Using Moir´e Optical Metrology 324

10.4.1 Measurement of wafer surface using shadow moir´e with Talbot effect 325

10.4.2 Enhancing the resolution of shadow moir´e with “phase shifting” 331

10.4.3 Wire web management using optical metrology technology 345

10.5 Summary 346

References 347

11 Conclusion 353

11.1 (I) From Crystal to Prime Wafers 353

11.2 (II)Wafer Forming 355

11.3 (III)Wafer Surface Preparation and Management 356

11.4 Final Remarks 357

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