The Modeling Routes for the Chemical Vapor Deposition Process
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ABSTRACT The purpose of this article is to present the modeling routes for the chemical vapor deposition process with a special emphasis to mass transport models with near local thermochemical equilibrium imposed in the gas-phase and at the deposition surface. The theoretical problems arising from the linking of the two selected approaches, thermodynamics and mass transport, are shown and a solution procedure is proposed. As an illustration, selected results of thermodynamic and mass transport analysis and of the coupled approach showed that, for the deposition of Sil-xGex solid solution at 1300 K (system Si-Ge-Cl-HAr), the thermodynamic heterogeneous stability of the reactive gases and the thermal diffusion led to the germanium depletion of the deposit.
INTRODUCTION - THE MODELING ROUTES High temperature CVD processes for producing thin films and coatings have found increasing applications in such diverse technologies as the fabrication of solid-state electronics devices and the manufacture of wear-or corrosion-resistant tools. Among the reasons for the growing adoption of CVD methods is the ability to produce a large variety of films and coatings of metals, semiconductors, and compounds in either a crystalline or vitreous form, possessing high purity and desirable properties. Furthermore, the capability of controllably creating films of widely varying stoichiometry makes CVD unique among deposition techniques. However, the interactions among deposition chemistry, transport processes and growth modes are complex and, consequently, poorly understood for most systems. It is the objective of CVD modeling to relate performance measures to operating conditions and reactor geometry. Besides the practical application of models in performance prediction, the models also provide insights into the underlying physicochemical processes. An accurate analysis should include homogeneous and heterogeneous chemical phenomena, heat transfer and multicomponent mass transport. Thermochemical and kinetic databases, mass transport models, together with computer codes have been developed to simulate different modeling approaches of the CVD process [1-3]. The modeling approaches are generally based (a) on kinetic computations, (b) on thermochemical equilibrium computations, (c) on mass transport computations linked with chemical kinetic data and (d) on mass transport linked with local thermochemical equilibrium. Thermodynamic analysis addresses several important issues with respect to CVD. Whether a given chemical reaction is feasible is perhaps the most important of these. Once it is decided that a reaction is feasible, thermodynamic calculations can frequently provide information on
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the partial pressures of the gaseous species and on the nature of the solid phases. Importantly, it provides an upper limit of what to expect under specified conditions. The complex chemical equilibrium involving gas and solid-phase can be computed by minimization of the Gibbs free e
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