Advanced MEMS Packaging John H. Lau Chengkuo Lee C. S. Premachandran Yu Aibin Ш New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto
Contents Foreword Preface Acknowledgments xv xvii xxi 1 Introduction to MEMS 1 1.1 Introduction 1 1.2 Commercial Applications of MEMS 2 1.3 MEMS Markets 2 1.4 Top 30 MEMS Suppliers 5 1.5 Introduction to MEMS Packaging 5 1.6 MEMS Packaging Patents since 2001 6 1.6.1 U.S. MEMS Packaging Patents 6 1.6.2 Japanese MEMS Packaging Patents... 21 1.6.3 Worldwide MEMS Packaging Patents 27 References 43 2 Advanced MEMS Packaging 47 2.1 Introduction 47 2.2 Advanced 1С Packaging 47 2.2.1 Moore's Law versus More Than Moore (MTM) 47 2.2.2 3D 1С Integration with WLP 49 2.2.3 Low-Cost Solder Microbumps for 3D 1С SiP 52 2.2.4 Thermal Management of 3D 1С SiP with TSV 58 2.3 Advanced MEMS Packaging 67 2.3.1 3D MEMS WLP: Designs and Materials 68 2.3.2 3D MEMS WLP: Processes 72 References 76 3 Enabling Technologies for Advanced MEMS Packaging 81 3.1 Introduction 81 3.2 TSVs for MEMS Packaging 81 3.2.1 Via Formation 82 3.2.2 Dielectric Isolation Layer (SiO z ) Deposition 86 vii
viü Contents 3.2.3 Barrier/Adhesion and Seed Metal Layer Deposition 87 3.2.4 Via Filling 89 3.2.5 Cu Polishing by Chemical/ Mechanical Polish (CMP) 91 3.2.6 Fabrication of an ASIC Wafer with TSVs 92 3.2.7 Fabrication of Cap Wafer with TSVs and Cavity 93 3.3 Piezoresistive Stress Sensors for MEMS Packaging 93 3.3.1 Design and Fabrication of Piezoresistive Stress Sensors 93 3.3.2 Calibration of Stress Sensors 95 3.3.3 Stresses in Wafers after Mounting on a Dicing Tape 98 3.3.4 Stresses in Wafers after Thinning (Back-Grinding) 101 3.4 Wafer Thinning and Thin-Wafer Handling... 104 3.4.1 3M Wafer Support System 104 3.4.2 EVG's Temporary Bonding and Debonding System 105 3.4.3 A Simple Support-Wafer Method for Thin-Wafer Handling 108 3.5 Low-Temperature Bonding for MEMS Packaging Ill 3.5.1 How Does Low-Temperature Bonding with Solders Work? 112 3.5.2 Low-Temperature C2C Bonding... 113 3.5.3 Low-Temperature C2W Bonding... 122 3.5.4 Low-Temperature W2W Bonding... 124 3.6 MEMS Wafer Dicing 126 3.6.1 Fundamentals of SD Technology... 126 3.6.2 Dicing of SOI Wafers 129 3.6.3 Dicing of Silicon-on-Silicon Wafers... 130 3.6.4 Dicing of Silicon-on-Glass Wafers... 130 3.7 RoHS-Compliant MEMS Packaging 133 3.7.1 EURoHS 133 3.7.2 What Is the Definition of X-Free (e.g., Pb-Free)? 134 3.7.3 What Is a Homogeneous Material? 134 3.7.4 What Is the TAC? 135 3.7.5 How Is a Law Published in the EU RoHS Directive? 135
Contents jx 3.7.6 EU RoHS Exemptions 135 3.7.7 Current Status of RoHS Compliance in the Electronics Industry 138 3.7.8 Lead-Free Solder-Joint Reliability of MEMS Packages 138 References 149 Advanced MEMS Wafer-Level Packaging 157 4.1 Introduction 157 4.2 Micromachining, Wafer-Bonding Technologies, and Interconnects 158 4.2.1 Thin-Film Technologies 158 4.2.2 Bulk Micromachining Technologies 159 4.2.3 Conventional Wafer-Bonding Technologies for Packaging 168 4.2.4 Plasma-Assisted Wafer-Bonding Technologies 172 4.2.5 Electrical Interconnects 172 4.2.6 Solder-Based Intermediate-Layer Bonding 175 4.3 Wafer-Level Encapsulation 176 4.3.1 High-Temperature Encapsulation Process 177 4.3.2 Low-Temperature Encapsulation Process 178 4.4 Wafer-Level Chip Capping and MCM Technologies 180 4.5 Wafer-Level MEMS Packaging Based on Low-Temperature Solders: Case Study 182 4.5.1 Case Study: In/Ag System of Noneutectic Composition 183 4.5.2 Case Study: Eutectic InSn Solder for Cu-Based Metallization 193 4.6 Summary and Future Outlook 202 References 203 Optical MEMS Packaging: Communications 209 5.1 Introduction 209 5.2 Actuation Mechanisms and Integrated Micromachining Processes 211 5.2.1 Electrostatic Actuation 212 5.2.2 Thermal Actuation 215 5.2.3 Magnetic Actuation 219
X Contents 5.2.4 Piezoelectric Actuation 219 5.2.5 Integrated Micromachining Processes 221 5.3 Optical Switches 224 5.3.1 Small-Scale Optical Switches 225 5.3.2 Large-Scale Optical Switches 233 5.4 Variable Optical Attenuators 237 5.4.1 Early Development Work 238 5.4.2 Surface-Micromachined VOAs 240 5.4.3 DRIE-Derived Planar VOAs Using Electrostatic Actuators 242 5.4.4 DRIE-Derived Planar VOAs Using Electrothermal (Thermal) Actuators 252 5.4.5 3D VOAs 254 5.4.6 VOAs Using Various Mechanisms 258 5.5 Packaging, Testing, and Reliability Issues... 261 5.5.1 Manufacturability and Self-Assembly 264 5.5.2 Case Study: VOAs 269 5.5.3 Case Study: Optical Switches 275 5.6 Summary and Future Outlook 285 References 286 6 Optical MEMS Packaging: Bubble Switch 297 6.1 Introduction 297 6.2 3D Packaging 297 6.3 Boundary-Value Problem 302 6.3.1 Geometry 302 6.3.2 Materials 302 6.3.3 Boundary Conditions 305 6.4 Nonlinear Analyses of the 3D Photonic Switch 306 6.4.1 Creep Hysteresis Loops 306 6.4.2 Deflections 307 6.4.3 Shear-Stress Time-History 307 6.4.4 Shear-Creep-Strain Time-History... 307 6.4.5 Creep-Strain Energy-Density Range 308 6.5 Isothermal Fatigue Tests and Results 309 6.5.1 Sample Preparation 309 6.5.2 Test Setup and Procedures 309 6.5.3 Test Results 312 6.6 Thermal Fatigue Life Prediction of the Sealing Ring 314
Contents xi 6.7 Appendix A: Package Deflection by Twyman-Green Interferometry Method... 314 6.7.1 Sample Preparation 315 6.7.2 Test Setup and Procedure 316 6.7.3 Temperature Conditions 317 6.7.4 Measurement Results 317 6.8 Appendix B: Package Deflection by Finite-Element Method 317 6.9 Appendix C: Finite-Element Modeling of the Bolt 320 6.9.1 Description of the Bolted Model 320 6.9.2 Responses of the Bolted Photonic Switch 322 References 325 Optical MEMS: Microbolometer Packaging 327 7.1 Introduction 327 7.2 Bolometer Chip 329 7.3 Thermal Optimization 330 7.3.1 Final Temperature Stability Testing 334 7.4 Structural Optimization of the Package... 335 7.5 Vacuum Packaging of Bolometer 340 7.5.1 Ge Window 342 7.6 Getter Attachment and Activation 344 7.7 Outgassing Study in a Vacuum Package... 346 7.8 Testing Setup for Bolometer 347 7.8.1 Package Testing 347 7.8.2 Image Testing 350 References 352 Bio-MEMS Packaging 353 8.1 Introduction 353 8.2 Bio-MEMS Chip 355 8.3 Microfluidic Components 357 8.3.1 Microfluidic Cartridge 357 8.3.2 Biocompatible Polymeric Materials 359 8.4 Microfluidic Packaging 362 8.4.1 Polymer Microfabrication Techniques 362 8.4.2 Replication Technologies 362 8.4.3 Overview of Existing DNA and RNA Extractor Biocartridges 363 8.5 Fabrication of PDMS Layers 364 8.6 Assembly of PDMS Microfluidic Packages... 364
XÜ Contents 8.6.1 Microfluidic Package without Reservoirs 366 8.6.2 Development of Reservoir and Valve 370 8.7 Self-Contained Microfluidic Cartridge 371 8.7.1 Microfluidic Package with Self-Contained Reservoirs 371 8.7.2 Pin-Valve Design 374 8.7.3 Fluid Flow-Control Mechanism... 375 8.8 Fabrication 377 8.8.1 Substrate Fabrication 377 8.8.2 Material Selection for the Reservoir Membrane 381 8.9 Permeability of Material 381 8.10 Thermocompression Bonding 384 8.10.1 Bonding of PMMA to PMMA for the Channel Layer 385 8.10.2 Polypropylene to PMMA for Reservoir and Channel Layer 387 8.10.3 Tensile Test 390 8.11 Microfluidic Package Testing 391 8.11.1 Fluid Testing 391 8.11.2 Biologic Testing on a Biosample... 392 8.12 Sample Preparation and Setup 394 8.12.1 Pretreatment of the Cartridge 394 8.12.2 PCR Amplification 394 References 395 9 Biosensor Packaging 397 9.1 Introduction 397 9.1.1 Review of Optical Coherence Tomography (OCT) 398 9.2 Biosensor Packaging 401 9.2.1 Micromirror 401 9.2.2 Single-Mode Optical Fiber and GRIN Lens 401 9.2.3 Upper Substrate 403 9.2.4 Lower Substrate 404 9.3 The Package 404 9.3.1 Configuration of the Probe 404 9.3.2 Optical Properties and Theories... 406 9.3.3 Evaluations of Parameters 410 9.4 Optical Simulation 412 9.4.1 Optical Model of the Probe 412 9.4.2 Effect of Mirror Curvature on Coupling Efficiency 415
Contents 9.4.3 Effect of Lateral Tilt of a Flat Micromirror on a Curved Sample... 417 9.4.4 Effect of Vertical Tilt of a Flat Micromirror on a Curved Sample... 419 9.4.5 Effect of Vertical Tilt of a Flat Micromirror on a Flat Sample 420 9.5 Assembly of the Optical Probe 421 9.5.1 Fabrication of SiOB 421 9.5.2 Probe Assembly 422 9.5.3 Probe Housing 425 9.6 Testing of the Probe 427 9.6.1 Optical Alignment 427 9.6.2 Axial Scanning Test Result 427 9.6.3 Probe Imaging 429 9.6.4 Optical Efficiency Testing 431 References 433 Accelerometer Packaging 435 10.1 Introduction 435 10.2 Wafer-Level Package Requirements 437 10.2.1 Electrical Modeling 438 10.2.2 Package Structure 438 10.2.3 Extraction Methodology of the Interconnection Characteristics 442 10.3 Wafer-Level Packaging Process 448 10.3.1 Method 1: TSV with Sacrificial Wafer 450 10.3.2 Method 2: TSV without Sacrificial Wafer 450 10.3.3 Method 3: TSV with MEMS Wafer 452 10.4 Wafer Separation Process 458 10.4.1 Process Integration 460 10.5 Sacrificial Wafer Removal 462 10.6 Wafer-Level Vacuum Sealing 464 10.7 Vacuum Measurement Using a MEMS Motion Analyzer 467 10.8 Reliability Testing: Vacuum Maintenance... 469 10.9 Wafer-Level 3D Package for an Accelerometer 471 References 473 Radiofrequency MEMS Switches 475 11.1 Introduction 475 11.2 Design of RF MEMS Switches 475 11.2.1 Design of Capacitive Switches 475
ents 11.2.2 Design of Metal-Contact Switches 479 11.2.3 Mechanical Design of RF MEMS Switches 479 11.3 Fabrication of RF MEMS Switches 484 11.3.1 Surface Micromachining of RF MEMS Switches 484 11.3.2 Bulk Micromachining of RF MEMS Switches 488 11.4 Characterization of RF MEMS Switches... 489 11.4.1 RF Performance 489 11.4.2 Mechanical Performance 489 11.5 Reliability of RF MEMS Switches 492 11.5.1 Reliability of Capacitive Switches 492 11.5.2 Reliability of Metal-Contact Switches 492 11.6 Summary 492 References 493 RF MEMS Tunable Capacitors and Tunable Band-Pass Filters 495 12.1 Introduction 495 12.2 RF MEMS Tunable Capacitors 495 12.2.1 Analog Tuning of RF MEMS Capacitors 496 12.2.2 Digital Tuning of RF MEMS Capacitors 503 12.3 RF MEMS Tunable Band-Pass Filters 504 12.3.1 Analog Tuning of a MEMS Band-Pass Filter 505 12.3.2 Digital Tuning of an RF MEMS Filter 506 12.4 Summary 512 References 513 Advanced Packaging of RF MEMS Devices 515 13.1 Introduction 515 13.2 Zero-Level Packaging 515 13.2.1 Chip Capping 516 13.2.2 Thin-Film Capping 523 13.3 One-Level Packaging 525 13.4 ReHability of Packaged RF MEMS Devices... 526 13.5 Summary 528 References 528 Index 531