Microelectronic Applications of Chemical Mechanical Planarization

Foreword xix

Contributing Authors xxiii

1 Why CMP? 1
Yuzhuo Li

1.1 Introduction 1

1.2 Preparation of Planar Surface 2

1.2.1 Multilevel Metallization and the Need for Planarization 2

1.2.2 Degrees of Planarization 4

1.2.3 Methods of Planarization 5

1.2.4 Chemical and Mechanical Planarization of Dielectric Films 7

1.2.5 Preparation of Planar Thin Films for Non-IC Applications Using CMP 8

1.3 Formation of Functional Microstructures 9

1.3.1 RC Delay and New Interconnect Materials 9

1.3.2 Damascene and Dual Damascene 12

1.3.3 Tungsten CMP 15

1.3.4 STI 16

1.4 CMP to Correct Defects 19

1.5 Advantages and Disadvantages of CMP 20

1.6 Conclusion 21

2 Current and Future Challenges in CMP Materials 25
Mansour Moinpour

2.1 Introduction 25

2.2 Historic Prospective and Future Trends 27

2.3 CMP Material Characterization 32

2.3.1 Thermal Effects 33

2.3.2 Slurry Rheology Studies 35

2.3.3 Slurry–Pad Interactions 38

2.3.4 Pad Groove Effects 42

2.3.5 Pad–Wafer Contact and Slarry Transport: Dual Emission Laser Induced Fluorescence 43

2.3.6 Dynamic Nuclear Magnetic Resonance 45

2.3.7 CMP Slurry Stability and Correlation with Defectivity 49

2.4 Conclusions 51

3 Processing Tools for Manufacturing 57
Manabu Tsujimura

3.1 CMP Operation and Characteristics 57

3.2 Description of the CMP Process 59

3.3 Overview of Polishers 60

3.3.1 CMP System 60

3.3.2 Brief History of CMP Systems 61

3.3.3 Diversity in CMP Tools 62

3.3.4 Polisher 62

3.3.5 Cleaning Module in a Dry-in/Dry-out System 64

3.4 Carriers and Dressers 65

3.4.1 Functions of Carriers and Dressers 65

3.4.2 Carrier 65

3.4.3 Profile Control by Carriers 68

3.4.4 Dressers 69

3.5 In Situ and Ex Situ Metrologies 72

3.5.1 Application 72

3.5.2 Representative Monitors 72

3.5.3 Other Applications for the Monitors 75

3.5.4 Communication 75

3.6 Conclusions 78

4 Tribometrology of CMP Process 81
Norm Gitis and Raghu Mudhivarthi

4.1 Introduction 81

4.2 Tribometrology of CMP 82

4.3 Factors Influencing the Tribology During CMP 85

4.3.1 Process Parameters During CMP 85

4.3.2 Polishing Pad Characteristics 88

4.3.3 Slurry Characteristics 90

4.3.4 Water Contour Characterists 92

4.4 Optimizing Pad Conditioning Process 92

4.4.1 PadProbe 92

4.4.2 Effect of Temperature 100

4.5 Conditioner Design 102

4.6 CMP Consumable Testing 105

4.6.1 Slurry Testing 105

4.6.2 Pad Testing 108

4.6.3 Retaining Rings 110

4.7 Defect Analysis 113

4.7.1 Coefficient of Friction and Acoustic Emission Signal 113

4.7.2 Advanced Signal Processing 114

4.8 Summary 117

5 Pads for IC CMP 123
Changxue Wang, Ed Paul, Toshihiro Kobayashi and Yuzhuo Li

5.1 Introduction 123

5.2 Physical Properties of CMP Pads and Their Effects on Polishing Performance 124

5.2.1 Pad Types 124

5.2.2 Pad Microstructures and Macrostructures 125

5.2.3 Polyurethane Pad Properties and Control 127

5.2.3.1 Hardness Young’s Modulus, and Strength 127

5.2.3.2 Pad Porosity/Density 128

5.2.3.3 Pad Thickness 128

5.2.3.4 Pad Stiffness/Stacked Pads 129

5.2.3.5 Pad Grooves 129

5.2.4 Effects of Pad Property on Polishing Performance 129

5.2.4.1 Pad Roughness Effects 130

5.2.4.2 Pad Porosity/Density Effects 131

5.2.4.3 Pad Hardness, Young’s Modulus, Stiffness, and Thickness Effects 136

5.2.4.4 Pad Groove Effects 138

5.3 Chemical Properties of CMP Pads and Their Effects on Polishing Performances 140

5.3.1 Polyurethane Pad Components 140

5.3.2 Polyurethane Property Control by Chemical Components 140

5.3.3 Chemical Effects on Polishing Performance 141

5.4 Pad Conditioning and Its Effect on CMP Performance 142

5.5 Modeling of Pad Effects on Polishing Performance 145

5.5.1 Review of Modeling of Pad Effects on Polishing Performance 145

5.5.2 Modeling of Pad Effects on Polishing Performance 148

5.5.2.1 Pads and Pressure 148

5.5.2.2 Pads and Abrasives 150

5.5.2.3 Pads, Dishing, and Erosion 154

5.6 Novel Designs of CMP Pads 159

5.6.1 Particle-Containing Pads 159

5.6.2 Surface-Treated Pads 162

5.6.3 Reactive Pad 164

6 Modeling 171
Leonard Borucki and Ara Philipossian

6.1 Introduction 171

6.2 A Two-Step Chemical Mechanical Material Removal Model 172

6.3 Pad Surfaces and Pad Surface Contact Modeling 175

6.4 Reaction Temperature 178

6.5 A Polishing Example 185

6.6 Topography Planarization 189

7 Key Chemical Components in Metal CMP Slurries 201
Krishnayya Cheemalapati, Jason Keleher and Yuzhuo Li

7.1 Introduction 201

7.2 Oxidizers 202

7.2.1 Nitric Acid 202

7.2.2 Hydrogen Peroxide 203

7.2.3 Ferric Nitrate 210

7.2.4 Potassium Permanganate, Dichromates, and Iodate 212

7.3 Chelating Agents 214

7.3.1 Ammonia 215

7.3.2 Amino Acids 216

7.3.3 Organic Acids 217

7.3.4 Thermodynamic Consideration and Quantitative Description 218

7.4 Surfactants 219

7.4.1 Structures and Physical Properties of Surfactants 219

7.4.2 Dispersion of Particles 221

7.4.3 Surface Modification of Wafer Surface 222

7.5 Abrasive Particles 225

7.5.1 Hardness 225

7.5.2 Bulk Particle Density 227

7.5.3 Particle Crystallinity and Shapes 227

7.5.4 Particle Size and Oversized Particle Count 228

7.5.5 Particle Preparation 230

7.5.6 Surface Properties 231

7.6 Particle Surface Modification 233

7.7 Soft Particles 234

7.8 Case Study: Organic Particles as Abrasives in Cu CMP 235

7.8.1 Particle Characterization 235

7.8.2 Material Removal Rate and Selectivity 235

7.8.3 Step Height Reduction Efficiency and Overpolishing Window 239

7.8.4 Summary on the Organic Particles 239

7.9 Conclusions 239

8 Corrosion Inhibitor for Cu CMP Slurry 249
Suresh Kumar Govindaswamy and Yuzhuo Li

8.1 Thermodynamic Considerations of Copper Surface 250

8.2 Types of Passivating Films on Copper Surface Under Oxdizing Conditions 252

8.3 Effect of pH on BTA in Glycine-Hydrogen Peroxide Based Cu CMP Slurry 257

8.4 Evaluation of Potential BTA Alternatives for Acidic Cu CMP Slurry 259

8.5 Electrochemical Polarization Study of Corrosion Inhibitors in Cu CMP Slurry 263

8.6 Hydrophobicity of the Surface Passivation Film 265

8.7 Competitive Surface Adsorption Behavior of Corrosion Inhibitors 266

8.8 Summary 270

9 Tungsten CMP Applications 277
Jeff Visser

9.1 Introduction 277

9.2 Basic Tungsten Application, Requirements, and Process 278

9.2.1 Basic Applications of Tungsten CMP 278

9.2.2 Basic W CMP Requirements and Procedures 281

9.3 W CMP Defects 282

9.4 Various W CMP Processing Options 285

9.4.1 Basic Considerations 285

9.4.2 Barrier Polishing 289

9.4.3 Oxide Buffing 289

9.4.4 Post-W CMP Cleaning 290

9.5 Overall Tungsten Process (Various Processing Design Options and Suggestions) 290

9.5.1 W CMP Process Controls 290

9.5.2 Platen Temperature Control 291

9.5.3 Slurry Selectivity 292

9.6 Conclusions 292

10 Electrochemistry in ECMP 295
Jinshan (Jason) Huo

10.1 Introduction 295

10.2 Physical and Chemical Processes in Electrochemical Planarization 297

10.2.1 Electrode/Electrolyte Interface 297

10.2.2 Electrochemical Reaction 298

10.2.3 Mass Transport 299

10.2.4 Anodic Polarization Curve and Conditions for Electrochemical Planarization 300

10.3 Mechanisms and Limitation of Electrochemical Planarization 304

10.3.1 Ohmic Leveling 304

10.3.2 Diffusion Leveling 305

10.3.3 Migration Leveling 307

10.4 In Situ Analysis of Anodic/Passivation Films 309

10.4.1 Impedance Measurement 309

10.4.2 Electrochemical Impedance Spectroscopy 310

10.4.3 Ellipsometry 311

10.5 Modified Electrochemical Polishing Approaches 312

11 Planarization Technologies Involving Electrochemical Reactions 319
Laertis Economikos

11.1 Introduction 319

11.2 CMP 321

11.3 ECP 322

11.4 ECMP 326

11.5 Full Sequence Electrochemical–Mechanical Planarization 334

11.6 Conclusions 340

12 Shallow Trench Isolation Chemical Mechanical Planarization 345
Yordan Stefanov and Udo Schwalke

12.1 Introduction 345

12.2 LOCOS to STI 346

12.3 Shallow Trench Isolation 349

12.4 The Planarization Step in Detail 351

12.5 Optimization Techniques 358

12.5.1 Dummy Active Area Insertion 359

12.5.2 Patterned Oxide Etch Back 359

12.5.3 Nitride Overcoat 360

12.5.4 EXTIGATE 361

12.5.5 Selective Oxide Deposition 363

12.5.6 Polysilicon-Filled Trenches 363

12.6 Outlook 364

13 Consumables for Advanced Shallow Trench Isolation (STI) 369
Craig D. Burkhard

13.1 Introduction 369

13.2 Representative Testing Wafers for STI Process and Consumable Evaluations 371

13.3 Effects of Abrasive Types on STI Slurry Performance 373

13.4 Effects of Chemical Additives to Oxide: Nitride Selectivity 379

13.5 Effect of Slurry pH 385

13.6 Effect of Abrasive Particle Size on Removal Rate and Defectivity 388

13.7 Conclusion 395

14 Fabrication of Microdevices Using CMP 401
Gerfried Zwicker

14.1 Introduction 401

14.2 Microfabrication Processes 402

14.3 Microfabrication Products 403

14.4 CMP Requirements in Comparison with IC Fabrication 404

14.5 Examples of CMP Applications for Microfabrication 412

14.5.1 Case Study I: Integrated Pressure Sensor 416

14.5.2 Case Study II: Poly-Si Surface Micromachining and Angular Rate Sensor 417

14.5.3 Case Study III: Infrared Digital Micromirror Array 422

14.5.4 More Representative Applications 425

14.6 Outlook 426

15 Three-Dimensional (3D) Integration 431
J. Jay McMahon, Jian-Qiang Lu and Ronald J. Gutmann

15.1 Overview of 3D Technology 431

15.2 Factors Motivating Research in 3D 432

15.2.1 Small Form Factor 432

15.2.2 Heterogeneous Integration 433

15.2.3 Performance Enhancement 434

15.3 Approaches to 3D 435

15.3.1 Singulated Die 3D 435

15.3.2 Wafer-Level 3D 436

15.3.2.1 Wafer-Level 3D Using Oxide–Oxide Bonding 436

15.3.2.2 Wafer-Level 3D Using Copper–Copper Bonding 438

15.3.2.3 Wafer-Level 3D Using Adhesive Bonding 439

15.3.2.4 3D Integration Using Redistribution Layer Bonding 440

15.3.2.5 Summary of Wafer Level 3D Approaches 440

15.4 Wafer-Level 3D Unit Processes 442

15.4.1 Wafer-to-Wafer Alignment 442

15.4.2 Wafer-to-Wafer Bonding 444

15.4.2.1 Oxide–Oxide and Silicon–Oxide Wafer Bondings 444

15.4.2.2 Copper–Copper Wafer Bonding 444

15.4.2.3 Polymer Adhesive Wafer Bonding 446

15.4.3 Wafer Thinning for 3D 447

15.4.3.1 Timed Removal Thinning Approaches 448

15.4.3.2 Thinning to Either an Etch or Polish Stop 448

15.4.4 Through-Silicon Vias 449

15.5 Planarity Issues in 3D Integration 450

15.5.1 CMP Planarity Capabilities 451

15.5.1.1 Nano- and Microscale Planarization 451

15.5.1.2 Wafer-Scale Planarity 451

15.5.2 Planarity Issues for Various 3D Approaches 452

15.5.2.1 CMP for Via-Last Approach to 3D Using Oxide-to-Oxide Bonding 452

15.5.2.2 CMP for Via-Last Approach to 3D Using Polymer Adhesive Bonding 454

15.5.2.3 CMP for Via-First Approach to 3D Using Copper-to-Copper Bonding 455

15.5.2.4 CMP for Via-First 3D Using Redistribution Layer Bonding 455

15.6 Conclusions 456

16 Post-CMP Cleaning 467
Jin-Goo Park, Ahmed A. Busnaina and Yi-Koan Hong

16.1 Introduction 467

16.2 Types of Post-CMP Cleaning Processes 468

16.2.1 Wet Bath Type Cleaning 468

16.2.2 Single Wafer Cleanings 469

16.2.2.1 Immersion-Type Single-Wafer Post-CMP Cleaning System 469

16.2.2.2 Single-Wafer Spin Cleaner 469

16.2.2.3 Brush Cleaning 473

16.2.2.4 Drying 475

16.3 Post-CMP Cleaning Chemistry 477

16.3.1 Conventional Wet Cleanings 477

16.3.2 Chemicals Used in Post-CMP Cleaning and their Roles 478

16.3.2.1 NH₄OH 478

16.3.2.2 HF 478

16.3.2.3 Organic Acids 479

16.3.2.4 Surfactants 479

16.4 Post-CMP Cleaning According to Applications 480

16.4.1 Post-Oxide CMP Cleaning 480

16.4.2 Post-W CMP Cleaning 481

16.4.3 Post-STI CMP Cleaning 481

16.4.4 Post-Poly-Si CMP Cleaning 482

16.4.5 Post-Cu/Low-k CMP Surface Cleaning 484

16.4.5.1 Corrosion 486

16.4.5.2 Organic Residue 487

16.4.5.3 Low-k Materials 489

16.4.5.4 Effect of Other Additives on Cleaning 491

16.5 Adhesion Force, Friction Force, and Defects During Cu CMP 492

16.5.1 Adhesion Force of Silica and Alumina on Cu 493

16.5.2 Friction Force in Cu CMP Process 494

16.5.3 Removal Rates of Cu Surface in Cu CMP 494

16.5.4 Surface Quality of Cu After Cu CMP Process 496

16.5.5 Correlation Among Friction, Adhesion Force, Removal Rate, and Surface Quality in Cu CMP 498

16.6 Case Study: Megasonic Post-CMP Cleaning of Thermal Oxide Wafers 499

16.6.1 Experimental Procedure 499

16.6.2 The Effect of Megasonic Input Power 500

16.6.3 The Effect of Temperature 503

16.6.4 The Effect of Etching on Cleaning 503

16.7 Summary 505

17 Defects Observed on the Wafer After the CMP Process 511
Paul Lefevre

17.1 Introduction 511

17.2 Defects After Oxide CMP 512

17.2.1 Introduction 512

17.2.2 Scratches 513

17.2.3 Color Variation—Oxide Thickness Variation 516

17.2.4 Slurry Residues and Organic Residues 518

17.2.5 Other Particles 519

17.2.6 Crystal Formation 519

17.2.7 Traces Elements 519

17.2.8 Radioactive Contamination 519

17.2.9 Defects Existing Before Oxide CMP 520

17.2.10 Source of Defect-Causing Large Particles 520

17.3 Defects After Polysilicon CMP 520

17.3.1 Introduction 520

17.3.2 Scratches 521

17.3.3 Polysilicon Residues 521

17.3.4 Particles 522

17.3.5 Residues 522

17.3.6 Trace Elements 522

17.3.7 Polysilicon Pitting and Voids 523

17.3.8 Discoloration at the Edge of the Structure or Edge of the Arrays 523

17.3.9 Defects Existing Before and Revealed After Polysilicon CMP 523

17.3.10 Influence of Processing Temperature 524

17.4 Defects After Tungsten CMP 524

17.4.1 Introduction 524

17.4.2 Corrosion, Pitting, and Void 524

17.4.3 Tungsten Recess and Rough Tungsten Surface 525

17.4.4 Scratches 528

17.4.5 Discoloration—Edge Overerosion (EOE) 529

17.4.6 Tungsten and Metal Liner Residues 530

17.4.7 Particles, Slurry Residues, and Trace Metal 531

17.4.8 Delamination 531

17.4.9 Preexisting Defects Revealed After Tungsten CMP 531

17.5 Defects After Copper CMP 532

17.5.1 Introduction and Summary on Copper CMP Defects 532

17.5.2 Copper Corrosion 533

17.5.3 Copper Pitting 535

17.5.4 Trenching at the Copper Line Edge 537

17.5.5 Rough Copper and Copper Recess 539

17.5.6 Discoloration—Metals Thickness Variations and/or Dielectric Thickness Variation 540

17.5.7 Copper Electromigration 542

17.5.8 Scratches 544

17.5.9 Metal Residues 544

17.5.10 Particles, Residues, and Trace Metals 547

17.5.11 Delamination 548

17.6 Defect Observation and Characterization Techniques 551

17.6.1 Optical Microscope 551

17.6.2 Scanning Electron Microscope 552

17.6.3 Energy Dispersive X-Ray Spectroscopy (EDX) 552

17.6.4 Scanning Auger Microscope (SAM) 553

17.6.5 Atomic Force Microscopy 553

17.7 Ensemble Defect Detection and Inspection Techniques 554

17.7.1 Optical Scan of Flat Film Blanket Wafers 554

17.7.2 Optical Scan of Patterned Wafers 554

17.7.3 Defect Classification 555

17.8 Consideration for the Future 555

18 CMP Slurry Metrology, Distribution, and Filtration 563
Rakesh K. Singh

18.1 Introduction 564

18.2 CMP Slurry Metrology and Characterization 567

18.2.1 Slurry Health Monitoring and Control 568

18.2.2 CMP Slurry Blend Control 569

18.2.2.1 Two-Component Blend Control 570

18.2.2.2 Three-Component Blend Control 572

18.2.3 CMP Slurry Characterization 573

18.2.4 Summary 576

18.3 CMP Slurry Blending and Distribution 577

18.3.1 Slurry Delivery Technologies 578

18.3.2 Continuous (On-Demand) Slurry Dispense and Metrology 578

18.3.3 Slurry Turnovers in Fab Distribution 580

18.3.4 Slurry Abrasive Settling and Dispersion 580

18.3.4.1 Slurry Settling Rate Quantification 580

18.3.4.2 Settling Behavior of Different Abrasive CMP Slurries 581

18.3.4.3 Required Minimum Flow Velocity for CMP Slurries 584

18.3.5 Summary 585

18.4 CMP Slurry Filtration 586

18.4.1 Slurry Filtration Methodology 587

18.4.2 Filter Design Consideration 588

18.4.3 Slurry Filter Characterization 591

18.4.4 CMP Process and Consumable Trends and Challenges 592

18.4.5 Slurry Filtration-Case Studies 595

18.4.5.1 Silica Dispersion Single-Pass High-Retention Filtration 595

18.4.5.2 Silica Slurry POU and Recirculation 596

18.4.5.3 Silica Ceria and Alumina Slurry Tighter Filtration 599

18.4.5.4 Polystyrene Latex (PSL) Bead Solution Filtration 602

18.4.6 Summary 602

18.5 Pump Handling Effects on CMP Slurry Filtration—Case Studies 603

18.5.1 Pump Technologies and Applications 604

18.5.2 Pump Shearing Effects on Slurry Abrasives 605

18.5.3 Pump Handling and Filtration Data 606

18.5.4 Test Cases 607

18.5.5 Summary 620

19 The Facilities Side of CMP 627
John H. Rydzewski

19.1 Introduction 627

19.2 Characterization of the CMP Waste Stream 628

19.3 Materials of Compatibility 629

19.4 Collection System Methodologies 631

19.5 Treatment System Components 632

19.5.1 Collection Tank and pH Adjustment 632

19.5.2 Oxidizer Removal 633

19.5.3 Organics Removal 635

19.5.4 Treatment of Suspended Solids 635

19.5.5 Removal of Trace Metals 638

19.6 Integration of Components—Putting It All Together 644

19.6.1 Solids Treatment Before Metals Removal 644

19.6.2 Solids Treatment After Metals Removal 645

19.6.3 No Solids Removal 646

19.7 Conclusions 647

20 CMP—The Next Fifteen Years 651
Joseph M. Steigerwald

20.1 The Past 15 Years 651

20.2 Challenges to Silicon IC Manufacturing 655

20.3 New CMP Processes 661

20.3.1 The Two-Year Development Cycle 661

20.3.2 Finfet Transistors 664

20.3.3 High-k Gate Oxides 665

20.3.4 Other Examples 670

20.4 CMP Challenges 673

20.4.1 Development Time of New CMP Materials 673

20.4.2 CMP Defect Reduction 675

20.4.3 CMP Process Control 677

20.4.3.1 CMP Film Thickness Control 678

20.4.3.2 Process Control Systems, Consumables Material Control, and Excursion Prevention 680

20.4.4 Cost of CMP 683

20.5 Summary 683

21 Utilitarian Information for CMP Scientists and Engineers 687
Yongqing Lan and Yuzhuo Li

21.1 Physical and Chemical Properties of Abrasive Particles 687

21.2 Physical and Chemical Properties on Oxidizers 690

21.3 Physical and Chemical Properties on Relevant Surfactants 690

21.3.1 Classification of Surfactants 690

21.3.2 Critical Micellar Concentration 692

21.3.3 Ternary Phase Diagrams Involving Surfactants 693

21.4 Relevant Pourbaix Diagram 696

21.5 Commonly Used Buffering Systems 703

21.6 Useful Web Sites 704

Index 725