Structure of As‐Deposited LPCVD Silicon Films at Low Deposition Temperatures and Pressures

Abstract

In this work we studied the effect of the deposition temperature, total pressure, source gas dilution, and deposition rate on the structure of the as‐deposited silicon films. Depositions were performed by low pressure chemical vapor deposition (LPCVD) in the temperature range of 530 to 600°C and in the pressure range of 2 to 300 mTorr. For a fixed deposition temperature a phase transition from polycrystalline to amorphous silicon was shown to occur when the deposition rate exceeded a critical value. The critical value for the deposition rate was found to depend only upon the deposition temperature and to decrease as the temperature was decreased. By controlling the rate, as‐deposited polycrystalline silicon was obtained by conventional LPCVD at temperatues as low as 530°C. A relationship between the deposition rate and the partial pressure of the source gas was established via a kinetic model for the decomposition of silane and used to provide a simple model for the dependence of the structure of the as‐deposited silicon films upon the deposition parameters. This model was subsequently used to provide guidelines for both the expected structure of the as‐deposited films and the grain size of the as‐deposited polycrystalline silicon films over an extensive range of deposition conditions.