Electron temperature control in silane plasma for fabricating highly stabilized hydrogenated amorphous silicon

We have attempted to fabricate stable hydrogenated amorphous silicon (a-Si:H) films against light exposure under high growth rate conditions by using silane plasma with low electron temperature, which is effective to reduce di-hydride density in the film responsible for photo-induced degradation. We have employed three methods of third electrode insertion, xenon addition and cathode heating, in order to reduce electron temperature. The negatively charged particle is effectively reduced by insertion of the positively biased third electrode. When proper positive bias was applied to the third electrode, electron temperature in the plasma is reduced due to modification of plasma potential. When xenon gas was added to silane plasma, the measure of electron temperature, observed by using optical emission spectroscopy, monotonically decreases with increasing xenon flow rate due to a decrease in the ambipolar-diffusion-electron-loss rate. To heat up gases in the plasma, cathode heating method is additionally employed, leading to a decrease in the di-hydride density and the degree of photo-induced degradation. As a result, di-hydride density and degree of photo-induced degradation in the resulting films are reduced, with decreasing of electron temperature in silane plasma.