Influence of plasma excitation frequency fora-Si:H thin film deposition

The effect of plasma excitation frequency on the deposition rate and on the optical and electrical properties of amorphous silicon film is studied over the range 25–150 MHz. Deposition rates as high as 21 Å/sec are obtained at 70 MHz, which is a factor of 5–8 larger than typical rates obtained for the conventional 13.56-MHz silane glow-discharge system. Only minor changes occur in the defect density (as measured by the photothermal deflection spectroscopy method), the optical bandgap, and the electrical conductivity over this frequency range. In a preliminaryinterpretation given here, the large variation of the deposition rate as a function of excitation frequency is explained in terms of changes in the electron energy distribution function.