Development and Validation of Mathematical Models for Chemical Vapor Deposition Processes.

In the past two decades, many researchers have modeled the transport phenomena in chemical vapor deposition (CVD) reactors. The purpose of this study is to present a generic mathematical model for describing the fundamental transport phenomena and for predicting the rate of deposition in CVD reactors. An extensive review of past effort has been presented. The detailed formulation of the mathematical model is outline together with the method of numerical solution. The development of the computer model to solve the problem is described in detail. The buoyancy force encountered in CVD systems is analyzed so that it can be taken into consideration properly. The model has been employed to predict the velocity field, temperature and concentration profiles of various gas species, and the rate of silicon deposition in a vertical CVD reactor with a rotating substrate by the reaction of silicon tetrachloride and hydrogen. The effects of inlet gas composition, reactor pressure, and substrate rotation on the silicon deposition have been studied. It is found that grid size, etching by HCl and thermal diffusion effect have to be considered to obtain rate of deposition predictions in good agreement with the experimental results. The model is used to optimize the design of a flow control device to obtain more uniform deposition rate. This illustrates that, once properly validated, mathematical models can be used to optimize the reactor design and other operating parameters. A three dimensional model has also been developed for a horizontal type of CVD reactor based on the understanding of the deposition process derived from the development of the model for the vertical CVD reactor. The flow field, temperature and concentration gradients in the horizontal reactor are obtained. Effects of different thermal boundary conditions and the tilt angle of the substrate on the flow filed and deposition rate are studied.