ADVANCED GERMANIUM COMPLEMENTARY-METAL-OXIDE-SEMICONDUCTOR TECHNOLOGIES A DISSERTATION SUBMITTED TO THE DEPARTMENT OF ELECTRICAL ENGINEERING AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Chi On Chui August 2004 © Copyright by Chi On Chui 2004 All Rights Reserved ii I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. __________________________________________ Krishna C. Saraswat (Principal Advisor) I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. __________________________________________ Yoshio Nishi I certify that I have read this dissertation and that, in my opinion, it is fully adequate in scope and quality as a dissertation for the degree of Doctor of Philosophy. __________________________________________ Paul C. McIntyre Approved for the University Committee on Graduate Studies __________________________________________ iii This thesis is dedicated to my family iv Abstract Drive current saturation in scaled Si MOSFETs is fundamentally limiting the prospect of future scaling. To overcome this scaling bottleneck and allow further improvements on short-channel MOSFET drive current, Ge MOSFET channel with high carrier mobility and source injection velocity should be incorporated. However, the unstable Ge native oxide for gate insulation and field isolation, together with the high diffusivity and low solubility of n-type Ge dopants for source and drain junction formation are the two classical problems that have obstructed CMOS device realization in Ge for four decades. In this work, three types of nanoscale gate dielectric for Ge MOS applications are investigated. The scalability and stability of native Ge oxynitrides are first examined followed by a seminal investigation and demonstration of integration of the more scalable and stable high-k metal oxides for Ge MOS applications. The effects of different Ge surface cleaning and passivation strategies are discussed, leading to the demonstration of sub-1.0 nm equivalent SiO 2 thickness dielectric stack on Ge. Additionally, two techniques to form shallow junctions for Ge MOSFET source and drain applications are studied. The corresponding activation and diffusion of various p-type and n-type dopants in Ge are analyzed after either the ion implantation or solid source diffusion doping. Through monitoring the thermal stability of the out-diffused dopants, phosphorus deactivation in Ge is observed for the first time. Finally, two low thermal budget processes to fabricate Ge MOSFETs are developed using the above dielectric and junction technologies. Metal gate high-k Ge p- MOSFETs are fabricated without exceeding 400 °C that demonstrate effective hole mobility enhancement over the silicon universal mobility model. On the other hand, functional metal gate high-k Ge n-MOSFETs are built using an innovative self-aligned gate-last process, which could be used as a technology vehicle to expedite the evaluation of numerous novel materials integration for advanced MOSFET applications. v Acknowledgements The accomplishment of this Ph.D. would never be possible without the supports from many individuals. First and foremost, I would like to express my sincere gratitude to my principal advisor, Professor Krishna C. Saraswat, for all his guidance and support in my last 4 years in the group. I am particularly impressed by his deep insights on many apparently general problems as well as his vision on numerous future potential research areas of interest. His liberal style in supervising students and his unselfishness in sharing credit are the most valuable characteristics for me to learn from. In addition, I would like to thank the members of my reading and orals committee including Professor Yoshio Nishi for his useful advice and continuous encouragement, Professor Paul C. McIntyre for making possible my collaboration with his group on high-k dielectric issues, and Professor Piero A. Pianetta for enabling my interaction with his team on synchrotron radiation photoemission studies. The invaluable consultation from a number of experts is another key to success. Above all, I would like to pay my tribute to Dr. James P. McVittie, whose significant contributions are usually ignored as an un-named hero, for his hands-on experimental assistance. Secondly, I would like to acknowledge Dr. Baylor B. Triplett for his initial help on the high-k dielectric on Ge feasibility study and spreading his expertise on SiO 2 on Si interfaces. Thirdly, I am extremely grateful to Prof. Eugene E. Haller (from UC Berkeley) for our numerous phone discussions to check out his career-long experience on Ge. Also, other specialists’ advices from Dr. Michael Deal, Prof. Robert Dutton, Dr. Peter Griffin, Dr. Christoph Jungemann, Dr. Ann Marshall, Prof. James Meindl (from Georgia Tech) and Prof. James Plummer are undoubtedly gratefully acknowledged. Additionally, I would like to greet the prompt and fruitful collaborations with Stanford insiders like David Chi, Kailash Gopalakrishnan, Fumitoshi Ito, Hyoungsub Kim, Hai Lan, Dong-Ick Lee, Yang Liu, Eric Pop, Shriram Ramanathan, Andy Singh, and Shiyu Sun, as well as outsiders like Muhannad Bakir from Georgia Tech and Jungwoo Oh from UT Austin. vi Due to the inherent experimental nature of this work, the helps from many SNF lab members should not be forgotten. Dr. Eric Perozziello, Pat Castle and Hector Cavazos have been my life-savers for years. Moreover, my processing time would not have been such enjoyable and productive without the presence of Cesar Baxter, Len Booth, Dick Crane, Elmer Enriquez, Carl Faulkner, Dan Grupp, Jim Haydon, Sameer Jain, Paul Jerabek, Eun-ha Kim, Robin King, Nancy Latta, Frankie Liu, Yaocheng Liu, Mahnaz Mansourpour, Mike Martinez, Chang-man Park, Henry Phan, Gladys Sarmiento, John Shott, Maurice Stevens, Yayoi Takamura, Mario Vilanova, Dunwei Wang, and many others. Also, I would thank Tom Carver of the Ginzton Lab for running literally hundreds of metal evaporations for me. Throughout these years residing in CIS, I have gotten many times help from staff including Dr. Richard Dasher, Maureen Rochford, and Carmen Mriaflor. Besides, I am very grateful to numerous members of Prof. Saraswat’s group, past and present, who have provided me with help and advice including Amol Joshi, Rohit Shenoy, Albert Wang, Dan Connelly, Ting-Yen Chiang, Marci Liao, Ali Okyay, Ammar Nayfeh, and Abhijit Pethe. Thanks especially to Irene Sweeney for her prompt and untiring administrative assistance on my behalf. Last but not least, thanks go to my wonderful family for sharing their endless love and support with me. Thanks go to my parents and brother for their care and for being there whenever I need them. Thanks to my wife, Hoi Yan, for her creativity and skill in preparing delicious dishes, her love and smile, and always being a good listener to me. I pray for their happiness and good health, and I dedicate my work to them in the most sincere way I can think of. vii Table of Contents Abstract......................................................................................................... v Acknowledgments....................................................................................... vi Table of Contents...................................................................................... viii List of Tables............................................................................................... xi List of Figures............................................................................................. xii Chapter 1. Introduction............................................................................... 1 1.1 Drive Current Saturation in Scaled Si MOSFETs............................................... 1 1.2 Demand for Germanium Channel MOSFETs...................................................... 5 1.2.1 Physical and Historical Facts about Germanium...................................... 5 1.2.2 CMOS Performance Boost with Germanium............................................ 9 1.3 Thesis Objective and Organization.................................................................... 13 Chapter 2. Nanoscale Ge MOS Gate Dielectrics: From native GeOxNy to high-k MOx.............................................................................. 15 2.1 Introduction........................................................................................................ 15 2.2 Native Germanium MOS Dielectrics................................................................. 18 2.2.1 Germanium Oxidations........................................................................... 18 2.2.2 The Rapid Thermal Processing System................................................... 20 2.2.3 Germanium Oxynitride Synthesis........................................................... 21 2.2.4 Scaling and Electrical Characterizations of Oxynitride.......................... 23 2.2.5 Effects and Degree of Nitridation in Oxynitride..................................... 28 2.2.6 Oxynitride-Germanium Interface Trapped Charge................................. 29 2.3 High-k Dielectrics by Atomic Layer Deposition............................................... 31 2.3.1 High-k Dielectric Motivation and Selection..........................................