Effect of Silane Pressure on Silane-Hydrogen RF Glow Discharges

The intensity and time dependence of optical emission from silane and silane-hydrogen radio-frequency (RF) discharges have been measured as a function of silane pressure (0.05-1.0 torr). The rate of emission of H* and Si* resulting from dissociative excitation was found to decrease with increasing silane pressure in a manner consistent with a similar decrease in average electron energy. Results from a Monte Carlo plasma simulation code were used to compute the rate of optical emission. Comparison of theory and experiment shows good agreement for emission intensities and confirms for discharges operating at constant pressure and power density a decrease in electron density and average electron energy with increasing silane partial pressure in mixtures of silane and hydrogen. The time-dependent spatially averaged emission intensity of H* is experimentally nonsymmetric with a shape that is a systematic function of silane partial pressure. This systematic behavior is reproduced by the plasma simulation and is attributed to the change in the dc bias of the powered electrode, which becomes less negative with increasing silane partial pressure.