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Alternative Growth and Interface Passivation Techniques ALTERNATIVE GROWTH AND INTERFACE PASSIVATION TECHNIQUES FOR SiO2 ON 4H-SiC Except where reference is made to the work of others, the work described in this dissertation is my own or was done in collaboration with my advisory committee. This dissertation does not include proprietary or classified information. _______________________________ Xingguang Zhu Certificate of Approval: _____________________________ _____________________________ Minseo Park John R. Williams, Chair Associate Professor Professor Physics Physics _____________________________ _____________________________ Jianjun Dong Yu Lin Associate Professor Professor Physics Physics ______________________________ George T. Flowers Dean Graduate School ALTERNATIVE GROWTH AND INTERFACE PASSIVATION TECHNIQUES FOR SiO2 ON 4H-SiC Xingguang Zhu A Dissertation Submitted to the Graduate Faculty of Auburn University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Auburn, Alabama December 19, 2008 ALTERNATIVE GROWTH AND INTERFACE PASSIVATION TECHNIQUES FOR SiO2 ON 4H-SiC Xingguang Zhu Permission is granted to Auburn University to make copies of this dissertation at its discretion, upon the request of individuals or institutions and at their expense. The author reserves all publication rights ____________________________ Signature of Author ____________________________ Date of Graduation iii VITA Xingguang Zhu, Son of Xi Zhu and Menghua Yang, was born on October 10, 1980, in Suzhou, Jiangsu Province, People’s Republic of China. He received a Bachelor of Science degree majoring in Solid State Physics from Physics Department of Nanjing University, Nanjing, P.R.China in July, 2003. He entered the graduate program in Physics Department of Auburn University in August, 2003 and worked as a Graduate Teaching Assistant and later as a Graduate Research Assistant in the Silicon Carbide Research Group under the supervision of Professor John R. Williams. During his graduate study at Auburn, he received a non-thesis Master of Science degree in August, 2005, and also taught the PHYS1500 General Physics I course during the summer semester, 2008. He married Linyun Han in Suzhou, P.R.China on May 28, 2007. iv DISSERTATION ABSTRACT ALTERNATIVE GROWTH AND INTERFACE PASSIVATION TECHNIQUES FOR SiO2 ON 4H-SiC Xingguang Zhu Doctor of Philosophy, December 19, 2008 (M.Sc., Auburn University, 2005) (B.Sc., Nanjing University, 2003) 256 Typed Pages Directed by John R. Williams Silicon Carbide is a novel wide band gap semiconductor material with excellent thermal, chemical and electrical properties. It also shares its natural oxide SiO2 with Si, which has been widely studied and optimized for decades. These properties make it a perfect candidate for applications in high-temperature, high-power MOS devices. Of over 200 polytypes, 4H-SiC is most commonly used, because it is among the only few commercially available polytypes that are known to be electrically and thermo -dynamically stable for making microelectronic devices. Unfortunately, the performance of such devices is limited by the poor SiO2/SiC interface quality after the standard dry O2 oxidation process. By far, the atomic understanding of the true physical structure and schematic of this interface still remains mystery. After applying most of the conventional v passivation techniques such as NO anneal and H2 anneal, improvements on the device performances can be clearly observed, however, the results are still far from satisfactory. In this work, two alternative passivation techniques are applied, in order to obtain better understanding of the interface properties and achieve improved electrical characteristics and higher performance. The first technique is the alumina enhanced oxidation, which by introducing metal impurities via the ceramic alumina during the oxidation, a decreased interface-trap density (DIT) and drastic increase in field effect channel mobility can be observed, however, this is also accompanied by a large amount of mobile ions inside the oxide. The results from electrical measurement of the devices as well as the possible cause and effect of those ions on the interface are discussed. Few other passivation techniques are also applied after this process for potential improvement and optimization, and the results are discussed. Another passivation technique is the nitrogen plasma anneal, which successfully creates atomic nitrogen by microwave induced plasma to achieve an oxygen-free nitridation annealing condition. This helps for further and better understanding of the passivation effect by the sole presence of nitrogen. All the electrical results obtained are discussed in detail and also compared with standard NO results. vi ACKNOWLEGEMENTS The author would like to express sincere appreciation to Dr. John R. Williams, for all his invaluable advice, guidance, and academic and moral support. His encouragement, knowledge and enthusiasm continuously enlightened and guided him during the entire research work. The author is also very grateful to all the committee members, Dr. Minseo Park, Dr. Jianjun Dong, Dr. Yu Lin and Dr. Guofu Niu for their support, instruction and participation in the evaluating of his work. In addition, the author is also deeply in debt to Dr. Ayayi, C. Ahyi, for inspiration, collaboration, attention, discussion and help that he kindly provided at all times. Special thanks to Tamara Isaacs-Smith and Max Cichon for their valuable assistance all along, and to Dr. Shurui Wang for her instruction and time during the early part of the work. The author would also like to take this opportunity to thank Zengjun Chen, Mingyu Li, all the collaborators in the research group and the alumni in Physics Department of Auburn University for their help and contributions during the past five years. Last but not least, the author extends special thanks to his wife Linyun Han for all her patience, understanding and moral support. This dissertation is also dedicated to all his family members and friends. This work is supported by ARL under contract ARMY-W911NF-07-2-0046 and TARDEC under contract W56H2V-06-C-0228. vii Style manual or journal used: APA Computer software used: Microsoft® Office Word 2003, Microsoft® Office Excel 2003, Microsoft® Office Powerpoint 2003, Origin® 7.0, SRIM 2006, ICS, Labview® viii TABLE OF CONTENTS LIST OF FIGURES ………………………………………………………………….. xiv LIST OF TABLES …………………………………………………………………. xx CHAPTER 1 Introduction ……………………………………………………………. 1 1.1 General Introduction …………………………………….…………………... 1 1.2 General Information for SiC ...……………………………………….………. 5 1.2.1 Historical Review ……………………………………………………… 5 1.2.2 Polytypism ……………………………………………………………... 7 1.2.3 Bulk Crystal and Epitaxial Growth …………………………………… 13 1.2.4 Physical and Electrical Properties …………………………………….. 18 CHAPTER 2 Characteristic and Theoretical Parameters for 4H-SiC MOS Devices .………………………………………………………………………………………….. 22 2.1 MOS Structures ……………………………………………………………... 22 2.2 MOS Capacitor ………………………………………………………...….... 23 2.2.1 General Introduction ………………………………………………….. 23 2.2.2 Operating Modes and Surface Potential under Gate Bias …………….. 27 2.2.3 High-Low Frequency Capacitance-Voltage Measurement …………… 34 ix 2.2.4 Non-ideal Characteristic of MOS Capacitor .……………………….… 38 2.3 MOSFET ……………………………………………………………………. 60 2.3.1 General Introduction ………………………………………………….. 60 2.3.2 Basic Structure of MOSFET ………………………………………….. 61 2.3.3 Threshold Voltage VT ………………………………………………… 63 2.3.4 Channel Mobility ……………………………………………………... 66 CHAPTER 3 Equipments and Processes …………………………………………….. 76 3.1 Furnaces …………………………………………………………………….. 76 3.2 Photolithography ……………………………………………………...……. 78 3.3 Sputtering System …………………………………………………………... 80 3.4 Lift Off Process ……………………………………………………………... 84 3.5 Rapid Annealing System ……………………………………………………. 85 3.6 Reactive Ion Etching (RIE) System .……………………………………...… 90 3.7 Simultaneous High-low Frequency C-V Probe Station ….…………………. 96 3.8 I-V Probe Station and Measurement ………………………………………. 101 3.9 MOSFET Mobility Measurement …………………………………………. 105 CHAPTER 4 Current Oxidation and Passivation Procedures ……………………… 109 4.1 General Introduction ………………………………………………………. 111 4.2 Standard Dry O2 Oxidation ………………………….…………………….. 113 4.2.1 General Procedure for Standard Dry Oxidation …………….……………. 113 4.2.2 Electrical Characteristics of Standard Dry Oxidation …...……….………. 113 x 4.2.3 Summary for Standard Dry Oxidation …………………………………… 119 4.3 Nitric Oxide (NO) Anneal ………………………………………………. .. 119 4.3.1 General Introduction and Procedure for Standard NO Anneal ……… 119 4.3.2 Nitrogen Profile from Standard NO Anneal ………………………… 120 4.3.3 Electrical Characteristics Following Standard NO Anneal …………. 123 4.3.4 Summary for Standard NO Anneal ………………………………….. 130 4.4 Hydrogen Passivation ……………………………………………………... 133 4.4.1 General Introduction and Procedure for H2 Anneal …………………. 133 4.4.2 Electrical Characterizations of Standard H2 Anneal ………………… 134 4.4.3 Summary for Standard H2 Anneal …………………………………... 139 CHAPTER 5 Alumina Enhanced Oxidation (AEO) Process .……………………… 140 5.1 General Introduction .……………………………………………………… 140 5.2 Characteristics of Oxides Following Alumina Enhanced Oxidation .……... 143 5.2.1 Growth Rate …………………………………………………………. 143 5.2.2 C-V Characteristics and Interface Trap Density (DIT) ………………. 144 5.2.3 BTS Measurement and Mobile Ion Concentration ………………….. 147 5.2.4 Channel Mobility for N-channel MOSFETs ………………………… 150 5.2.5 I-V Characteristics and Breakdown Field …………………………… 153 5.3 Oxidation with Intentional Metal Contamination
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