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Title:Ultraconformal chemical vapor deposition and synthesis of transition metal nitride films
Author(s):Cloud, Andrew
Director of Research:Abelson, John R.
Doctoral Committee Chair(s):Abelson, John R.
Doctoral Committee Member(s):Girolami, Gregory S.; Braun, Paul V.; Polycarpou, Andreas A.; Bellon, Pascal
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):chemical vapor deposition
thin films
transition metals
hard coatings
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.
Issue Date:2014-01-16
Rights Information:Copyright 2013 Andrew Cloud
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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