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Surface Analysis of Materials for Direct Wafer Bonding

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Surface Analysis of Materials for Direct Wafer Bonding SURFACE ANALYSIS OF MATERIALS FOR DIRECT WAFER BONDING SURFACE ANALYSIS OF MATERIALS FOR DIRECT WAFER BONDING By ARIF UL ALAM, B.Sc. A Thesis Submitted to the School of Graduate Studies In Partial Fulfillment of the Requirements For the Degree Master of Applied Science McMaster University © Copyright by Arif Ul Alam, October 2013 MASTER OF APPLIED SCIENCE (2013) McMaster University (Electrical and Computer Engineering) Hamilton, Ontario, Canada TITLE: Surface Analysis of Materials for Direct Wafer Bonding AUTHOR: Arif Ul Alam, B.Sc. (Electrical and Electronic Engineering) Islamic University of Technology (IUT), Bangladesh. SUPERVISOR: Dr. Matiar R. Howlader CO-SUPERVISOR Dr. Thomas E. Doyle NUMBER OF PAGES: xi, 118 ii ABSTRACT Surface preparation and its exposure to different processing conditions is a key step in heterogeneous integration of electronics, photonics, fluidics and/or mechanical components for More-than-Moore applications. Therefore, it is critical to understand how various processing and environmental conditions affect the surface properties of bonding substrates. In this thesis, the effects of oxygen reactive-ion etching (O2 RIE) plasma followed by storage in ambient and 98% relative humidity on some key surface properties such as roughness, water contact angle, hardness, and the elemental and compositional states of three materials – silicon (Si), silicon dioxide (SiO2) and glass – are investigated to analyze their influence on bondability. Lower O2 RIE plasma activation times cause low surface roughness, high surface reactivity and high hydrophilicity of Si, SiO2 and glass. Although, the surface reactivity iii of plasma- and ambient-humidity-treated Si and SiO2 is considerably reduced, their reduction of roughness and increase of hydrophilicity may enable good bonding at low temperature heating due to augmented hydroxyl groups. The decrease of hardness of Si and SiO2 with increased activation time is attributed to higher surface roughness and formation of amorphous layers of Si. While contact angle and surface roughness results show correlation with bondability, the role of hardness on bondability requires further investigation. The high-resolution X-ray Photoelectron Spectroscopy (XPS) spectra of O2 RIE treated Si, SiO2 and glass showed the presence of Si(-O)2 resulting in highly reactive surfaces. A considerable shift in the binding energy of Si(-O)2 was observed only in Si. The ambient and 98% relative humidity storage of plasma-activated Si and SiO2 increased Si(-OH)x due to enhanced sorption of hydroxyls. The variation in the amounts of Si(-O)2 and Si(- OH)x in the ambient- and 98% relative humidity-stored Si were attributed to the crystal- orientation dependent surface roughness and oxidation of Si. The surface roughness, contact angle and hardness measurement results and their correlation with the XPS results give useful insights into the direct wafer bonding of Si, SiO2 and glass. Based on the analysis, the bondability of Si, SiO2 and glass can be summarized. The high surface reactivity of Si, SiO2 and glass obtained from oxygen plasma activation at lower activation times can result in better bondability. Also, the ambient humidity-induced Si(-OH)x plays an important role in the hydrophilic wafer bonding of Si and SiO2 which may require a low temperature heating. iv ACKNOWLEDGEMENTS This thesis would not have been possible without the cooperation, encouragement and support of many people. First of all, I would like to express my sincere gratitude to my supervisor Dr. Matiar R. Howlader, who has introduced me to the field of nanotechnology and provided me with thorough training and guidance in research, and helped me with learning the equipment in Micro- and Nano- Systems Laboratory (MNSL). His excellent supervision, utmost cooperation and incessant encouragement contributed greatly to this thesis. I also greatly appreciate my co-supervisor Dr. Thomas E. Doyle for his guidance. I acknowledge Dr. M. Jamal Deen for his encouragements and suggestions. I would like to extend my appreciation to Fangfang Zhang for her assistance in the experiments. Without her help, the experiments presented in this thesis would have been very difficult v for me. I am indebted to Dr. Moon J. Kim, University of Texas at Dallas for his contribution to review and comment on my experimental results. I am especially grateful to Dr. Peter Cruse, Department of Chemistry at McMaster University for his critical comments and suggestions on X-ray Photoelectron Spectroscopy (XPS) results. I would like to acknowledge Mubeen Mashroor, Engineer, JEOL Canada for his special training in XPS instrument and his continuous support throughout my experimental works. This research is supported by a discovery grant (#327947) from the Natural Science and Engineering Research Council (NSERC) of Canada and an infrastructure grant (#12128) from the Canada Foundation for Innovation (CFI). At last but not the least, I would like to thank my wife Kanij Sakara Nasrin, and my parents and brothers and sisters, for their eternal love, patience, and continuous encouragement throughout my study in Canada. vi TABLE OF CONTENTS ABSTRACT ................................................................................................................................. III ACKNOWLEDGEMENTS ......................................................................................................... V TABLE OF CONTENTS .......................................................................................................... VII LIST OF FIGURES ...................................................................................................................... X LIST OF TABLES ..................................................................................................................... XII CHAPTER 1. .................................................................................................................................. 1 INTRODUCTION ....................................................................................................................... 1 1.1 SURFACE ANALYSIS FOR WAFER BONDING .................................................................. 1 1.2 DIRECT WAFER BONDING ............................................................................................. 2 1.2.1 What is Direct Wafer Bonding? ................................................................................. 2 1.2.2 High Temperature Wafer Bonding ............................................................................ 3 1.2.2.1 Hydrophilic Wafer Bonding .......................................................................................... 3 1.2.2.2 Hydrophobic Wafer Bonding ........................................................................................ 5 1.2.2.3 Anodic Bonding ............................................................................................................... 6 1.2.3 Low Temperature Wafer Bonding .............................................................................. 7 1.2.3.1 Plasma Activated Wafer Bonding ................................................................................. 7 vii 1.2.3.2 Sequential Plasma Activated Wafer Bonding ............................................................ 11 1.3 SURFACE PROPERTIES IN BONDING ............................................................................ 12 1.3.1 Role of Surface Morphology on Wafer Bonding ..................................................... 12 1.3.2 Role of Surface Hydrophilicity on Bonding ............................................................. 17 1.3.3 Role of Surface Mechanical Properties on Bonding ............................................... 19 1.4 SURFACE CHEMICAL STATE IN BONDING ................................................................... 20 1.5 CONTRIBUTIONS ........................................................................................................... 24 1.6 OBJECTIVES AND OUTLINE OF THE THESIS ................................................................ 24 CHAPTER 2. ................................................................................................................................ 26 EXPERIMENTAL PROCEDURES .......................................................................................... 26 2.1 SPECIMEN PREPARATION ............................................................................................. 26 2.2 HYBRID PLASMA BONDER ............................................................................................ 28 2.3 ATOMIC FORCE MICROSCOPY .................................................................................... 29 2.4 DROP SHAPE ANALYSIS ................................................................................................ 32 2.5 NANOINDENTATION HARDNESS ................................................................................... 34 2.6 X-RAY PHOTOELECTRON SPECTROSCOPY ................................................................. 37 2.7 HUMIDITY AND RELIABILITY CHAMBER ..................................................................... 42 CHAPTER 3. ................................................................................................................................ 44 SURFACE ROUGHENSS, CONTACT ANGLE AND HARDNESS ...................................... 44 3.1 SURFACE ROUGHNESS .................................................................................................. 44 3.2 WATER CONTACT ANGLE ...........................................................................................
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