ULTRACONFORMAL CHEMICAL VAPOR DEPOSITION AND SYNTHESIS OF TRANSITION METAL NITRIDE FILMS BY ANDREW N. CLOUD DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Materials Science and Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 2013 Urbana, Illinois Doctoral Committee: Emeritus Professor John R. Abelson, Chair Professor Gregory S. Girolami Professor Paul V. Braun Adjunct Professor Andreas A. Polycarpou Professor Pascal Bellon ABSTRACT The miniaturization of devices places stringent demands on materials processing techniques. As device dimensions decrease, the aspect ratios (AR) of features tend to increase. Uniform coating of these features is required, but the difficulty scales with AR. I have demonstrated ‘static’ CVD in a simple, unpumped apparatus to conformally deposit stoichiometric and pure metallic films of hafnium diboride and iron in high AR features. By achieving high precursor pressure, growth rate saturation is maintained deeply into structures. CVD has a growth rate advantage over atomic layer deposition in high AR features. SCVD is highly scalable and conducive to batch processing. This is critical for the production of nanostructures assembled from pre-formed templates. Using SCVD, thermally stable hafnium diboride photonic crystals are fabricated. The combination of superior thermal stability and modified thermal emission has not been previously demonstrated. CVD of transition metal nitride films (where the metal is manganese, iron, cobalt, or nickel) is accomplished with newly developed di(tert-butyl)amide precursors M[N(t-Bu)2]2 and NH3 below 300 °C. Film growth likely proceeds via rapid transamination of the highly reactive precursors with NH3 to afford metal amido fragments with high sticking coefficients and low surface mobilities. Carbon contamination in the films is minimal for manganese, iron, and cobalt nitrides, but similar to the nitrogen concentration in nickel nitride. Thermal CVD at room temperature is highly unusual, but iron nitride grows rapidly at 25 °C. The di(tert-butyl)amido compounds are also able to serve as CVD precursors to cobalt and nickel nitride phases, for which very few other CVD methods have been described. The family of di(tert-butyl)amide precursors provides a useful synthetic pathway for late transition metal nitride films, which are difficult to produce by other means; the growth conditions are appropriate for deposition on temperature-sensitive substrates. To demonstrate the utility of HfB2 as a wear-resistant protective coating for nanoscale applications, polysilicon switches are coated with CVD HfB2 and evaluated. Functional devices demonstrate reproducible, sharp switching characteristics indicative of a stable contact. A critical factor in the efficacy of wear-resistant thin films is their adhesion and shear strength at the film-substrate interface. Poor adhesion can result in delamination and catastrophic failure. HfB2 thin films on Si(100) are studied to advance the understanding of adhesion and shear strength of this system. Hardness, elastic modulus, and friction coefficient are also measured. ii To my family and friends – current and future – and the countless people who had a hand in guiding me to where I am today. iii ACKNOWLEDGEMENTS The accomplishments memorialized in this thesis are products of the cumulative efforts of countless people who have had an impact on my professional and personal lives. It is impossible to acknowledge all of this in these few pages, but I shall try. Firstly, I am grateful for the professional relationships with my thesis advisor, Prof. John R. Abelson and my colleagues Shaista Babar, Pengyi Zhang, Wenjiao Wang, Tian Li, and Kristof Darmawikarta. John is an excellent supervisor; he patiently allowed me to pursue my own interests and provided incredibly insightful guidance whenever I asked. The content of this thesis is better for the comments and criticisms of John and the rest of the group members. As a thin film growth group, we are extremely dependent on our chemistry collaborators for their knowledge and invaluable supply of CVD precursors. Prof. Gregory S. Girolami and his students have been great partners over the years. In particular, the efforts of Justin L. Mallek and Luke M. Davis were critical. I must also acknowledge the efforts of former students of both groups, Drs. Teresa and Charles Spicer, who began the investigation of the transition metal nitride CVD that is discussed at length in this work. My interest in applications led me to rewarding collaborations with great groups here at the University of Illinois and other fine institutions. I greatly enjoyed collaborating with Prof. Paul Braun’s group on the solar thermophotovoltaic intermediate project, especially with his students Dr. Kevin Arpin and Hailong Ning and his post-doctoral researcher Dr. Mark Losego. The NEMS relay switch work was a collaboration with Dr. W. Scott Lee, Dr. J. Provine, Dr. Noureddine Tayebi, Dr. Roozbeh Parsa, Prof. Subhasish Mitra, Prof. H.-S. Philip Wong, and Prof. Roger T. Howe at Stanford University. I also am thankful for the efforts of Prof. Andreas Polycarpou and his students Dr. Jungkyu Lee, Dr. Kyriaki Polychronopoulou, and Shahla Chowdhury. They conducted extensive mechanical testing of films I provided at a level I could never approach. I am grateful to those collaborators who kept me supplied with interesting and challenging substrates, including Matt Goodman and Neil Krueger from UIUC and Professor Anna Fontcuberta i Morral from École Polytechnique Fédérale de Lausanne. Film characterization was carried out in the Frederick Seitz Materials Research Laboratory Central Facilities, University of Illinois. I benefited greatly from the analytical iv assistance of the staff of the MRL and the Beckman Institute at the University of Illinois. In particular, I give much thanks to Dr. Rick Haasch, Dr. Jim Mabon, Dr. Mauro Sardela, Dr. Julio Soares, Dr. Timothy Spila, and Dr. Leilei Yin. During my graduate studies, I was personally supported by fellowships provided by the National Defense Science and Engineering Graduate fellowship program (2008 - 2011) and National Science Foundation Graduate Research Fellowship Program (2011 - 2013). I am deeply grateful for the intellectual freedom these fellowships offered me. The work presented in this thesis would not have been possible without the broad support of these organizations. I also must acknowledge the incredible support of my family and dear friends. Without them, this work would be meaningless. The people of Illinois have been, on the whole, incredibly welcoming and gracious during my time here. In particular, I am grateful for the support of my committee members – Dr. Abelson, Dr. Girolami, Dr. Braun, Dr. Polycarpou, and Dr. Bellon – who are among the smartest and most impressive people I know. I also appreciate all the help and support I received from the wonderful staff in the Department of Materials Science and Engineering. I owe a great debt to all the people at the University of Arkansas who prepared me for graduate school. The faculty and staff of the Honors College and the College of Engineering provided an excellent education and critical one-on-one guidance. In particular, I must thank Dr. Matthew Gordon (now at the University of Denver) for exposing me to the research lab for the first time. I am constantly reminded of the great guidance provided by Dr. John A. White (Chancellor emeritus), Dr. Gary Standridge, Dr. Ashok Saxena, and Dr. Carol Gattis. I owe an enormous debt to Dr. Lee Bodenhamer and the Bodenhamer Foundation for financing my undergraduate education and giving me the freedom and support to follow my own path. It is an honor to be associated with these people and rarely does a day go by that I do not reflect on the advantages I have been allotted due to the kindness of those that came before me. v TABLE OF CONTENTS CHAPTER 1: OVERVIEW .................................................................................................. 1 1.1 Introduction ......................................................................................................... 1 1.2 Motivations ......................................................................................................... 2 1.3 Chapter summaries ............................................................................................ 5 1.4 References ......................................................................................................... 9 1.5 Figures ............................................................................................................... 12 CHAPTER 2: SUPERIOR INFILTRATION OF CONVOLUTED STRUCTURES BY STATIC CHEMICAL VAPOR DEPOSITION .................................................. 16 2.1 Introduction ......................................................................................................... 16 2.2 Experimental apparatus ...................................................................................... 17 2.3 Results ............................................................................................................... 17 2.4 Discussion .......................................................................................................... 20 2.5 Conclusions ........................................................................................................ 24 2.6 References ........................................................................................................