Advanced MEMS Packaging This page intentionally left blank Advanced MEMS Packaging John H. Lau Chengkuo Lee C. S. Premachandran Yu Aibin New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto Copyright © 2010 by The McGraw-Hill Companies, Inc. All rights reserved. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. ISBN: 978-0-07-162792-4 MHID: 0-07-162792-8 The material in this eBook also appears in the print version of this title: ISBN: 978-0-07-162623-1, MHID: 0-07-162623-9. All trademarks are trademarks of their respective owners. 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Under no circumstances shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise. AbouttheAuthors John H. Lau earned a Ph.D. in theoretical and applied mechanics from the University of Illinois. He has also earned three master’s degrees. He currently is a visiting professor at the Hong Kong University of Science & Technology (HKUST). His research interests cover a broad range of enabling technologies for 3D IC and system-in-package integration for RoHS-compliant electronics, optoelectronics, photonics, and MEMS packaging. Prior to joining HKUST, Dr. Lau was the director of the Microsystems, Modules, and Compo- nents Laboratory at the Institute of Microelectronics in Singapore for 2 years and a Senior Scientist/MTS at Agilent/Hewlett-Packard in California for more than 25 years. With more than 35 years of R&D and manu- facturing experience, he has authored or co-authored more than 400 peer-reviewed technical publications, books, book chapters, and papers. Dr. Lau has received awards from ASME and IEEE, and is a Fellow of both organizations. Chengkuo Lee received a Ph.D. in precision engineering from the University of Tokyo, and has also earned two master’s degrees. He worked as a researcher in several labs and then managed the MEMS device division at the Metrodyne Microsystem Corporation in Taiwan. Dr. Lee co-founded Asia Pacific Microsystems, Inc., in Taiwan, and served as vice president. He is now an assistant professor in the Department of Electrical and Computer Engineering at National University of Singapore and a senior member of the technical staff at the Institute of Microelectronics in Singapore. He has authored or co-authored about 200 conference papers, extended abstracts, and peer-reviewed journal articles, and holds eight U.S. patents in the MEMS and nano- technology fields. C. S. Premachandran earned a master of technology degree in solid state technology from the Indian Insti- tute of Technology, Madras. He has held managerial/ executive positions at Indian Telephone Industries, Sun Fiber Optics, and Delphi Automotive Systems. Since 1998 he has worked as a member of the technical staff in the Microsystems, Modules, and Components Labo- ratory at the Institute of Microelectronics, Singapore. He has authored or co-authored more than 50 conference papers and journal articles and holds 10 U.S. patents. He is a Senior Member of IEEE. His research interests are in MEMS and biosensor, optical, and advanced packaging. Yu Aibin received a Ph.D. in electrical and electronic engineering from Nanyang Technological University in Singapore. He is a senior research engineer in the Microsystems, Modules, and Components Laboratory at the Institute of Microelectronics in Singapore. His research interests include advanced packaging and MEMS design, fabri cation, and packaging. Dr. Yu has authored or co-authored more than 60 technical publications. Contents Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 IC Packaging . . . . . . . . . . . . . . . . . . 47 2.2.1 Moore’s Law versus More Than Moore (MTM) . . . . . . . . . . . . . . . . . . . 47 2.2.2 3D IC Integration with WLP . . . . . . . 49 2.2.3 Low-Cost Solder Microbumps for 3D IC SiP . . . . . . . . . . . . . . . . . . . . 52 2.2.4 Thermal Management of 3D IC 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) 2 Deposition . . . . . . . . . . . . . . . . . . . . . . 86 vii viii 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 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 EU RoHS . . . . . . . . . . . . . . . . . . . . . . . . 133 3.7.2 What Is the Defi nition 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 ix 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 4 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 5 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