Trapping of Hydrogen in Hf-Based High Κ Dielectric Thin Films for Advanced CMOS Applications
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TRAPPING OF HYDROGEN IN Hf-BASED HIGH κ DIELECTRIC THIN FILMS FOR ADVANCED CMOS APPLICATIONS Vaishali Ukirde, B.E., M.S Dissertation Prepared for the Degree of DOCTOR OF PHILOSOPHY UNIVERSITY OF NORTH TEXAS December 2007 APPROVED: Mohamed El Bouanani, Major Professor Thomas Scharf, Committee Member Manuel Quevedos-Lopez, Committee Member Husam Al-Shareef, Committee Member Rick Reidy, Committee Member and Chair of the Materials Science and Engineering Department Nigel Shepherd, Graduate Programs Departmental Coordinator Oscar Garcia, Dean of the College of Engineering Sandra L. Terrell, Dean of the Robert B. Toulouse School of Graduate Studies Ukirde, Vaishali. Trapping of hydrogen in Hf-based high κ dielectric thin films for advanced CMOS applications. Doctor of Philosophy (Materials Science and Engineering), December 2007, 271 pp., 1 table, 93 illustrations, 225 references. In recent years, advanced high κ gate dielectrics are under serious consideration to replace SiO2 and SiON in semiconductor industry. Hafnium-based dielectrics such as hafnium oxides, oxynitrides and Hf-based silicates/nitrided silicates are emerging as some of the most promising alternatives to SiO2/SiON gate dielectrics in complementary metal oxide semiconductor (CMOS) devices. Extensive efforts have been taken to understand the effects of hydrogen impurities in semiconductors and its behavior such as incorporation, diffusion, trapping and release with the aim of controlling and using it to optimize the performance of electronic device structures. In this dissertation, a systematic study of hydrogen trapping and the role of carbon impurities in various alternate gate dielectric candidates, HfO2/Si, HfxSi1-xO2/Si, HfON/Si and HfON(C)/Si is presented. It has been shown that processing of high κ dielectrics may lead to some crystallization issues. Rutherford backscattering spectroscopy (RBS) for measuring oxygen deficiencies, elastic recoil detection analysis (ERDA) for quantifying hydrogen and nuclear reaction analysis (NRA) for quantifying carbon, X-ray diffraction (XRD) for measuring degree of crystallinity and X-ray photoelectron spectroscopy (XPS) were used to characterize these thin dielectric materials. ERDA data are used to characterize the evolution of hydrogen during annealing in hydrogen ambient in combination with preprocessing in oxygen and nitrogen. Copyright 2007 by Vaishali Ukirde ii ACKNOWLEDGEMENTS This gives me pleasant opportunity to express my thanks to all of them who had been a part in achieving an important goal in my life. The time when I joined UNT, and especially Laboratory of Electronics Materials Devices (LEMD) my aim was to work on new, exciting, challenging and unfamiliar research field. With Only after I started working in the lab did I realize that I was working in one of a few labs in the world with a complete setup to do real applied materials research. My motto was always "Difficult is easy and Impossible just takes a little more time” that came to be true under the guidance of my advisor Dr Mohamed El Bouanani. I feel short of words when it comes to express my sincere gratitude to my advisor Dr Mohamed El Bouanani, who showed me an elegant way to be successful. His quotes “You learn more from mistakes and criticism” and "Wait and hope attitude is not for those who are determined to shape their future” always kept me motivated. His unending encouragement was always there to offer me continuous support not only academic, but also as a friend. His way of approaching the different research problems was extremely helpful for me in almost every step till now. He helped me understand the strengths and weakness in me. His motivation towards research makes you feel that you “ALWAYS” have something to learn, new challenges, new problems to solve. I am extremely thankful to him for showing his extreme patience with me in completing this thesis. I would also like to thank my colleague Chang Duk Lim for all his help over past years. I always cherished his company and was a great colleague to work with. I would iii also like to thank , Jennifer Feng (TAMS), Ezekiel Walker (REU) and William Gustafson (REU) for their help during their course in LEMD.I am grateful and really appreciate the timely help I had from Dr. Manuel Quevedo-Lopez from University of Texas, Dallas for providing me with the samples for our experiments and for timely discussions. I thank the committee members Dr Husam Al-Shareef, Dr Rick Reidy and Dr Thomas Scharf for reading this dissertation, Thanks for your intelligent advice in making this dissertation more “reader friendly”. Thanks to Craig Collins, for their technical and logistic help. Personally, I owe lots of thanks to my “Dear Friends”. I feel extremely proud and happy to have Sonam Shah, my boyfriend and I am short of words when it comes to the support, encouragement that he provided. I would like to thank him for ALWAYS being there besides me in this long journey. Last, but not the least, I would like to thank my family for always being very supportive and encouraging in every step. I really feel lucky to have such wonderful parents, an excellent university, and the chance to work in LEMD here at UNT. Thank you every one for being so kind and helpful to me. iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS ................................................................................................. iii LIST OF TABLES............................................................................................................. ix LIST OF ILLUSTRATIONS...............................................................................................x Chapters 1. INTRODUCTION .......................................................................................1 1.1 References........................................................................................6 2. LITERATURE REVIEW: ROLE OF HYDROGEN IN SILICON BASED ELECTRONIC DEVICES...........................................................................8 2.1 CMOS Devices: Introduction ..........................................................8 2.1.1 MIS or MOSFET Structure..................................................8 2.1.2 MOSFET Working Principle.............................................10 2.2 Gate Oxide Scaling........................................................................10 2.2.1 MOSFET Scaling...............................................................10 2.2.2 Alternate Gate Dielectrics..................................................12 2.3 Hydrogen in SiO2/Si Structure: CMOS Devices ...........................14 2.3.1 Types of Charges in SiO2 -Si System ................................17 2.3.2 Determination of Interface Trapped Charge and Fixed Oxide Charge .....................................................................20 2.4 Role of Hydrogen: Defect Mechanisms.........................................24 2.4.1 Incorporation and Release of Hydrogen: Passivation/Depassivation of Interfacial and Bulk Traps ............................................................................................24 2.4.2 Hydrogen Transport in SiO2 Films and Si-based Gate Stacks .................................................................................32 2.4.3 Migration and Redistribution of Hydrogen in Oxide.........36 v 2.4.4 Degradation: Electrical Behavior/ Characteristics.............38 2.4.5 Role of Hydrogen: High-κ Dielectric Films ......................44 2.5 References......................................................................................53 3. HYDROGEN INCORPORATION IN HfO2/Si STRUCTURES..............64 3.1 Introduction....................................................................................64 3.2 Experimental..................................................................................68 3.2.1 Sample Preparation............................................................68 3.2.2 Processing in O2, N2 and FG Anneals................................69 3.2.3 Characterization Techniques..............................................70 3.2.4 Irradiation of the Samples: Amorphization........................73 3.3 Results and Discussion..................................................................75 3.3.1 RBS Results: HfO2/Si ........................................................75 3.3.2 Effects of Forming Gas Anneal Temperatures ..................78 3.3.3 Effects of O2 Post Anneals.................................................84 3.3.4 Effects of N2 Post Annealing .............................................91 3.3.5 Comparison of Bulk Hydrogen Trapping upon Oxygen and Nitrogen Anneals ...............................................................94 3.3.6 Effects of Carbon Impurities on the Hydrogen Trapping: NRA ...................................................................................95 3.3.7 Effects of Crystallization: Ion Irradiation Induced Amorphization ...................................................................97 3.4 Conclusion ...................................................................................101 3.5 References....................................................................................101 4. ERDA STUDY OF HYDROGEN UPTAKE AND CRYSTALLIZATION EFFECTS IN HfxSi1-xO2/Si STRUCTURES...........................................105 4.1 Introduction..................................................................................105 4.2 Experimental................................................................................108 4.2.1 Sample Preparation..........................................................108