Substrate temperature dependence of SiH concentration in silane plasmas for amorphous silicon film deposition

Abstract

Spatial distributions of SiH radicals were measured between capacitively coupled electrodes for various substrate temperatures (Ts = 20–300 °C) in RF glow discharges of pure silane. Laser induced fluorescence and optical emission spectroscopic techniques were applied to determine the relative SiH concentrations in the ground state (A2Δ, v = 0) and in the excited state (X2π, v = 0) respectively. Both concentrations increase near the substrate with increasing substrate temperature Ts. In their respective Arrhenius plots (the logarithm of signal intensity vs Ts−1), the concentrations increase slowly for Ts 180 °C. The increase in SiH concentrations for Ts > 180 ° C is due to the increase in current density of fast electrons which are responsible for gas ionization and silane dissociation. This effect can be explained by an increase in secondary electron emission efficiency of the film surface, which is caused by H2 gas desorption. The “elbows” in the Arrhenius plots suggest that the film surface undergoes a physical change around 180 °C.