3D and Circuit Integration of MEMS

Masayoshi Esashi is senior research fellow in the Micro System Integration Center at Tohoku University and Professor emeritus. He obtained his doctorate from Tohoku University and his research focuses on MEMS, integrated sensors, and MEMS packaging. He has published over 500 scientific papers and was the recipient of the IEEE Jun-ichi Nishizawa Medal in 2016.

• Part I Introduction 11 Overview 3Masayoshi EsashiReferences 10Part II System on Chip 132 Bulk Micromachining 15Xinxin Li and Heng Yang2.1 Process Basis of Bulk Micromachining Technologies 162.2 Bulk Micromachining Based on Wafer Bonding 202.2.1 SOI MEMS 202.2.2 Cavity SOI Technology 272.2.3 Silicon on Glass Processes: Dissolved Wafer Process (DWP) 292.3 Single-Wafer Single-Side Processes 342.3.1 Single-Crystal Reactive Etching and Metallization Process (SCREAM) 342.3.2 Sacrificial Bulk Micromachining (SBM) 382.3.3 Silicon on Nothing (SON) 40References 453 Enhanced Bulk Micromachining Based on MIS Process 49Xinxin Li and Heng Yang3.1 Repeating MIS Cycle for Multilayer 3D structures or Multi-sensor Integration 493.1.1 Pressure Sensors with PS3 Structure 493.1.2 P+G Integrated Sensors 523.2 Pressure Sensor Fabrication – From MIS Updated to TUB 543.3 Extension of MIS Process for Various Advanced MEMS Devices 58References 584 Epitaxial Poly Si Surface Micromachining 61Masayoshi Esashi4.1 Process Condition of Epi-poly Si 614.2 MEMS Devices Using Epi-poly Si 61References 675 Poly-SiGe Surface Micromachining 69Carrie W. Low, Sergio F. Almeida, Emmanuel P. Quévy, and Roger T. Howe5.1 Introduction 695.1.1 SiGe Applications in IC and MEMS 705.1.2 Desired SiGe Properties for MEMS 705.2 SiGe Deposition 705.2.1 Deposition Methods 705.2.2 Material Properties Comparison 715.2.3 Cost Analysis 725.3 LPCVD Polycrystalline SiGe 735.3.1 Vertical Furnace 735.3.2 Particle Control 755.3.3 Process Monitoring and Maintenance 755.3.4 In-line Metrology for Film Thickness and Ge Content 765.3.5 Process Space Mapping 775.4 CMEMS® Process 785.4.1 CMOS Interface Challenges 795.4.2 CMEMS Process Flow 805.4.2.1 Top Metal Module 805.4.2.2 Plug Module 845.4.2.3 Structural SiGe Module 855.4.2.4 Slit Module 855.4.2.5 Structure Module 855.4.2.6 Spacer Module 855.4.2.7 Electrode Module 855.4.2.8 Pad Module 865.4.3 Release 865.4.4 Al–Ge Bonding for Microcaps 875.5 Poly-SiGe Applications 885.5.1 Resonator for Electronic Timing 885.5.2 Nano-electro-mechanical Switches 92References 946 Metal Surface Micromachining 99Minoru Sasaki6.1 Background of Surface Micromachining 996.2 Static Device 1006.3 Static Structure Fixed after the Single Movement 1016.4 Dynamic Device 1036.4.1 MEMS Switch 1036.4.2 Digital Micromirror Device 1046.5 Summary 111References 1117 Heterogeneously Integrated Aluminum Nitride MEMS  Resonators and Filters 113Enes Calayir, Srinivas Merugu, Jaewung Lee, Navab Singh, and Gianluca Piazza7.1 Overview of Integrated Aluminum Nitride MEMS 1137.2 Heterogeneous Integration of Aluminum Nitride MEMS Resonators with CMOS Circuits 1147.2.1 Aluminum Nitride MEMS Process Flow 1157.2.2 Encapsulation of Aluminum Nitride MEMS Resonators and Filters 1167.2.3 Redistribution Layers on Top of Encapsulated Aluminum Nitride MEMS 1187.2.4 Selected Individual Resonator and Filter Frequency Responses 1197.2.5 Flip-chip Bonding of Aluminum Nitride MEMS with CMOS 1217.3 Heterogeneously Integrated Self-Healing Filters 1237.3.1 Application of Statistical Element Selection (SES) to AlN MEMS Filters with CMOS Circuits 1237.3.2 Measurement of 3D Hybrid Integrated Chip Stack 124References 1278 MEMS Using CMOS Wafer 131Weileun Fang, Sheng-Shian Li, Yi Chiu, and Ming-Huang Li8.1 Introduction: CMOS MEMS Architectures and Advantages 1318.2 Process Modules for CMOS MEMS 1398.2.1 Process Modules for Thin Films 1408.2.1.1 Metal Sacrificial 1408.2.1.2 Oxide Sacrificial 1428.2.1.3 TiN-composite (TiN-C) 1438.2.2 Process Modules for the Substrate 1458.2.2.1 SF6 and XeF2 (Dry Isotropic) 1458.2.2.2 KOH and TMAH (Wet Anisotropic) 1468.2.2.3 RIE and DRIE (Front-side RIE, Backside DRIE) 1468.3 The 2P4M CMOS Platform (0.35 μm) 1488.3.1 Accelerometer 1488.3.2 Pressure Sensor 1498.3.3 Resonators 1508.3.4 Others 1528.4 The 1P6M CMOS Platform (0.18 μm) 1548.4.1 Tactile Sensors 1548.4.2 IR Sensor 1568.4.3 Resonators 1588.4.4 Others 1608.5 CMOS MEMS with Add-on Materials 1648.5.1 Gas and Humidity Sensors 1648.5.1.1 Metal Oxide 1648.5.1.2 Polymer 1708.5.2 Biochemical Sensors 1738.5.3 Pressure and Acoustic Sensors 1758.5.3.1 Microfluidic Structures 1788.6 Monolithic Integration of Circuits and Sensors 1808.6.1 Multi-sensor Integration 1808.6.1.1 Gas Sensors 1808.6.1.2 Physical Sensors 1818.6.2 Readout Circuit Integration 1838.6.2.1 Resistive Sensors 1838.6.2.2 Capacitive Sensors 1848.6.2.3 Inductive Sensors 1888.6.2.4 Resonant Sensors 1908.7 Issues and Concerns 1918.7.1 Residual Stresses, CTE Mismatch, and Creep of Thin Films 1928.7.1.1 Initial Deformation – Residual Stress 1928.7.1.2 Thermal Deformation – Thermal Expansion Coefficient Mismatch 1958.7.1.3 Long-time Stability – Creep 1978.7.2 Quality Factor, Materials Loss, and Temperature Stability 1998.7.2.1 Anchor Loss 2018.7.2.2 Thermoelastic Damping (TED) 2018.7.2.3 Material and Interface Loss 2018.7.3 Dielectric Charging 2038.7.4 Nonlinearity and Phase Noise in Oscillators 2048.8 Concluding Remarks 205References 2079 Wafer Transfer 221Masayoshi Esashi9.1 Introduction 2219.2 Film Transfer 2239.3 Device Transfer (via-last) 2289.4 Device Transfer (Via-First) 2319.5 Chip Level Transfer 236References 24110 Piezoelectric MEMS 243T Takeshi Kobayashi (AIST)10.1 Introduction 24310.1.1 Fundamental 24310.1.2 PZT Thin Films Property as an Actuator 24410.1.3 PZT Thin Film Composition and Orientation 24610.2 PZT Thin Film Deposition 24610.2.1 Sputtering 24610.2.2 Sol–Gel 24810.2.2.1 Orientation Control 24810.2.2.2 Thick Film Deposition 24910.2.3 Electrode Materials and Lifetime of PZT Thin Films 25010.3 PZT–MEMS Fabrication Process 25110.3.1 Cantilever and Microscanner 25110.3.2 Poling 254References 255Part III Bonding, Sealing and Interconnection 25711 Anodic Bonding 259Masayoshi Esashi11.1 Principle 25911.2 Distortion 26211.3 Influence of Anodic Bonding to Circuits 26311.4 Anodic Bonding with Various Materials, Structures and Conditions 26511.4.1 Various Combinations 26511.4.2 Anodic Bonding with Intermediate Thin Films 26911.4.3 Variation of Anodic Bonding 27111.4.4 Glass Reflow Process 274References 27612 Direct Bonding 279Hideki Takagi12.1 Wafer Direct Bonding 27912.2 Hydrophilic Wafer Bonding 27912.3 Surface Activated Bonding at Room Temperature 283References 28613 Metal Bonding 289Joerg Froemel13.1 Solid Liquid Interdiffusion Bonding (SLID) 29013.1.1 Au/In and Cu/In 29113.1.2 Au/Ga and Cu/Ga 29413.1.3 Au/Sn and Cu/Sn 29713.1.4 Void Formation 29713.2 Metal Thermocompression Bonding 29813.2.1.1 Interface Formation 29913.2.1.2 Grain Reorientation 29913.2.1.3 Grain Growth 30013.3 Eutectic Bonding 30113.3.1 Au/Si 30213.3.2 Al/Ge 30213.3.3 Au/Sn 304References 30414 Reactive Bonding 309Klaus Vogel, Silvia Hertel, Christian Hofmann, Mathias Weiser, Maik Wiemer, Thomas Otto, and Harald Kuhn14.1 Motivation 30914.2 Fundamentals of Reactive Bonding 30914.3 Material Systems 31114.4 State of the Art 31214.5 Deposition Concepts of Reactive Material Systems 31314.5.1 Physical Vapor Deposition 31314.5.1.1 Conclusion Physical Vapor Deposition and Patterning 31514.5.2 Electrochemical Deposition of Reactive Material Systems 31514.5.2.1 Dual Bath Technology 31614.5.2.2 Single Bath Technology 31814.5.2.3 Conclusion DBT and SBT 31914.5.3 Vertical Reactive Material Systems With 1D Periodicity 31914.5.3.1 Dimensioning 32014.5.3.2 Fabrication 32114.5.3.3 Conclusion 32314.6 Bonding With RMS 32314.7 Conclusion 326References 32615 Polymer Bonding 331Xiaojing Wang and Frank Niklaus15.1 Introduction 33115.2 Materials for Polymer Wafer Bonding 33215.2.1 Polymer Adhesion Mechanisms 33215.2.2 Properties of Polymers for Wafer Bonding 33515.2.3 Polymers Used in Wafer Bonding 33715.3 Polymer Wafer Bonding Technology 34115.3.1 Process Parameters in Polymer Wafer Bonding 34115.3.2 Localized Polymer Wafer Bonding 34815.4 Precise Wafer-to-Wafer Alignment in Polymer Wafer Bonding 35015.5 Practical Examples of Polymer Wafer Bonding Processes 35115.6 Summary and Conclusions 354References 35416 Soldering by Local Heating 361Yu-Ting Cheng and Liwei Lin16.1 Soldering in MEMS Packaging 36116.2 Laser Soldering 36216.3 Resistive Heating and Soldering 36516.4 Inductive Heating and Soldering 36816.5 Other Localized Soldering Processes 37016.5.1 Self-propagative Reaction Heating 37016.5.2 Ultrasonic Frictional Heating 371References 37417 Packaging, Sealing, and Interconnection 377Masayoshi Esashi17.1 Wafer Level Packaging 37717.2 Sealing 37817.2.1 Reaction Sealing 37817.2.2 Deposition Sealing (Shell Packaging) 38017.2.3 Metal Compression Sealing 38517.3 Interconnection 38817.3.1 Vertical Feedthrough Interconnection 38817.3.1.1 Through Glass via (TGV) Interconnection 38817.3.1.2 Through Si via (TSiV) Interconnection 39317.3.2 Lateral Feedthrough Interconnection 39517.3.3 Interconnection by Electroplating 401References 40418 Vacuum Packaging 409Masayoshi Esashi18.1 Problems of Vacuum Packaging 40918.2 Vacuum Packaging by Anodic Bonding 40918.3 Packaging by Anodic Bonding with Controlled Cavity Pressure 41418.4 Vacuum Packaging by Metal Bonding 41618.5 Vacuum Packaging by Deposition 41718.6 Hermeticity Testing 417References 42019 Buried Channels in Monolithic Si 423Kazusuke Maenaka19.1 Buried Channel/Cavity in LSI and MEMS 42319.2 Monolithic SON Technology and Related Technologies 42519.3 Applications of SON 435References 43920 Through-substrate Vias 443Zhyao Wang20.1 Configurations of TSVs 44420.1.1 Solid TSVs 44420.1.2 Hollow TSVs 44520.1.3 Air-gap TSVs 44520.2 TSV Applications in MEMS 44520.2.1 Signal Conduction to the Wafer Backside 44620.2.2 CMOS-MEMS 3D Integration 44620.2.3 MEMS and CMOS 2.5D Integration 44720.2.4 Wafer-level Vacuum Packaging 44820.2.5 Other Applications 45020.3 Considerations for TSV in MEMS 45020.4 Fundamental TSV Fabrication Technologies 45020.4.1 Deep Hole Etching 45120.4.1.1 Deep Reactive Ion Etching 45120.4.1.2 Laser Ablation 45220.4.2 Insulator Formation 45420.4.2.1 Silicon Dioxide Insulators 45420.4.2.2 Polymer Insulators 45520.4.2.3 Air-gaps 45520.4.3 Conductor Formation 45520.4.3.1 Polysilicon 45620.4.3.2 Single Crystalline Silicon 45620.4.3.3 Tungsten 45720.4.3.4 Copper 45720.4.3.5 Other Conductor Materials 45920.5 Polysilicon TSVs 46020.5.1 Solid Polysilicon TSVs 46020.5.2 Air-gap Polysilicon TSVs 46320.6 Silicon TSVs 46420.6.1 Solid Silicon TSVs 46520.6.2 Air-gap Silicon TSVs 46720.7 Metal TSVs 46920.7.1 Solid Metal TSVs 47020.7.2 Hollow Metal TSVs 47420.7.3 Air-gap Metal TSVs 480References 481Index 493