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Title:Role of growth inhibitors in nucleation and growth of thin film deposited by chemical vapor deposition in high aspect ratio structures
Author(s):Babar, Shaista
Director of Research:Abelson, John R.
Doctoral Committee Chair(s):Abelson, John R.
Doctoral Committee Member(s):Girolami, Gregory S.; Braun, Paul V.; Martin, Lane W.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):ultra-smooth thin film
Growth inhibition
Chemical Vapor Deposition
Abstract:The goal of this dissertation is to identify, and understand the role of, growth inhibitors in the nucleation and growth of thin films by chemical vapor deposition (CVD). We focus on steady state processing methods using stable molecules in order to change thin film surface morphology in a controlled manner in high aspect ratio structures. The results also provide insight into the interpretation of surface morphology using the power spectral density (Fourier transform) of AFM height data, in particular, the low- and high-k dependencies. In general, thin film morphology is highly sensitive to the processing conditions, which influence the precursor reactivity with the surface. It is possible to deposit a coating within a deeply recessed feature by chemical vapor deposition. However, when the goal is to obtain a very smooth film of very uniform thickness, there are two main problems: one is the lack of formation of mono-disperse nuclei, which leads to roughness, and the other is gas depletion due to limited diffusivity, which creates a tapering thickness. These factors both accentuate as a function of depth. I propose and demonstrate, for the growth of HfB2 films, a new approach that provides a solution to the nucleation problem: the use of a molecular inhibitor which decreases the growth rate of the already existing islands but permits continued nucleation on bare sites because the inhibitor, NH3, binds only weakly to the substrate surface. As a result, mono-disperse nuclei form everywhere inside the feature. The inhibitor eventually desorbs without decomposition and thus does not incorporate into the film. In addition, because the overall growth rate is significantly reduced, gas depletion effects are minimized. I show remarkably smooth HfB2 thin film deposition with constant morphology in a deep feature of aspect ratio ~ 500. Motivated by the results, I also explore the use of a growth inhibitor to control the surface morphology of copper thin film, ranging from extremely smooth to uniformly islanded. The precursor is Cu(hfac)VTMS and the inhibitor is additional VTMS. Interestingly, this system is very distinct from that of HfB2: the use of the inhibitor during nucleation creates a uniform dispersion of Cu islands. This is interpreted in terms of a large inhibitor effect on the bare substrate surface than on the Cu islands. However, by injecting the inhibitor only after the nucleation has proceeded to coalescence, the resulting Cu film is made very smooth. By carefully controlling the statistics of nucleation and growth, I show that the signature of initial nucleation layer morphology propagates in the roughness of thicker films grown on top of the nucleation layer: the long range statistical roughness in power spectral density analysis is strongly related between the nucleation layer and the thick film surface.
Issue Date:2015-01-21
Rights Information:Copyright 2014 Shaista Babar
Date Available in IDEALS:2015-01-21
Date Deposited:2014-12

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