A Model of Growth Rate Nonuniformity in the Simultaneous Deposition and Doping of a Polycrystalline Silicon Film by LPCVD

Abstract

We describe a mathematical model of the coupled diffusion and chemical kinetics in the simultaneous deposition of a phosphorous dopant and polycrystalline silicon film, in a low pressure CVD reactor. The model is based on a kinetic mechanism originally proposed by Meyerson and Olbricht (1), in which it is assumed that film growth is inhibited by the preferential adsorption of the dopant precursor molecule at the deposition surface. A numerical analysis of this process has been presented by Jensen et al. (2) that is in quantitative agreement with experiment. We present a simple model, one that permits an analytical solution, in which the single rate limiting step is the gas‐phase decomposition of silane. From the analytical solution, it is possible to propose a simple algebraic criterion for radially uniform growth. The dependence on interwafer spacing of the growth rate and radial growth profiles are predicted by the model. The use of kinetic parameters that are consistent with values reported in the literature gives results that are in good agreement with experiment. The similarity between results for the silane‐phosphine system and the semi‐insulating polysilicon (SIPOS) system is discussed with reference to the model results.