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Title:Kinetic optimization of titanium silicide chemical vapor deposition
Author(s):Southwell, Robert Peter
Doctoral Committee Chair(s):Seebauer, Edmund G.
Department / Program:Chemical and Biomolecular Engineering
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Chemical
Engineering, Electronics and Electrical
Abstract:Titanium disilicide (TiSi$\sb 2$) has found widespread application as a material for transistor gate/source/drain contacts. Considerable interest has arisen in fabrication by chemical vapor deposition (CVD) because of scalability problems with the salicide process (a Ti-Si solid-phase reaction) that currently defines the state-of-the-art. Furthermore, the possibility of selective CVD on Si vs SiO$\sb 2$ offers the potential to eliminate masking and etching steps that are currently required for the salicide process. Numerous studies of thermal TiSi$\sb 2$ have been performed, but the results have been hampered by one or more of the following problems: excessive substrate consumption, high nucleation and growth temperatures, or selectivity loss.
In order to efficiently optimize TiSi$\sb 2$ CVD for industrial applications, a quantitative kinetic understanding of this process is required. Due to the complicated, non-linear behavior of the CVD process, trial-and-error optimization, utilized by other researchers, has proved to be extremely difficult. Therefore, a novel approach has been developed to study such a complicated system. This approach involves intensive experimental studies of both the deposition process itself, and the elementary surface reactions that control the reaction. This combined approach forms the foundation for a quantitative, predictive kinetic model necessary for process optimization. The roots of this methodology are quantitative kinetics obtained in parallel with ultrahigh vacuum (UHV) experiments and actual CVD experiments.
In UHV, techniques such as temperature-programmed desorption (TPD) are utilized to obtain quantitative kinetics for the elementary reaction steps (source gas adsorption and product desorption) that control the CVD process. Furthermore, advances in the existing TPD technology were required to obtain the necessary kinetics for a predictive model. For example, a new technique, differential-conversion TPD (DCTPD), is developed to yield the desorption kinetics for HCl which cannot be observed with conventional TPD.
To complement the reaction kinetics obtained in UHV, experiments involving the deposition of TiSi$\sb 2$ films are performed in a CVD chamber. These experiments provide confirmation of the important gas-phase reaction products observed with TPD experiments. Most importantly, reaction kinetics are measured for comparison with those calculated with the predictive model. Agreement provides confidence in these predictions and the ability of the model to optimize the process. Both steady-state and transient kinetics can be measured with the CVD apparatus. In short, with the use of a microbalance and a line-of-sight mass spectrometer, in-situ measurements of the rates of deposition, substrate consumption, and product desorption can be measured quantitatively. This information, not obtainable until this work, is necessary for accurate comparison with model predictions and to gain a full understanding of the deposition process, especially where transient behavior is observed.
A predictive model has been developed and found to be accurate using the experimental studies described above, and has been utilized to develop a new, industrially applicable TiSi$\sb 2$ CVD process.
Issue Date:1996
Rights Information:Copyright 1996 Southwell, Robert Peter
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9712442
OCLC Identifier:(UMI)AAI9712442

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