ORIGINS OF ATMOSPHERIC CONTAMINATION IN AMORPHOUS-SILICON PREPARED BYVERY HIGH-FREQUENCY (70 MHZ) GLOW-DISCHARGE

The authors have studied the effect of plasma power, reactor outgassin g rates, and of silane purity on the oxygen, carbon, and nitrogen cont ents of amorphous silicon material prepared by the very high frequency (70 MHz) glow discharge technique. The silane purity could be optiona lly enhanced by the application of a getter-based silane gas purifier. It was found that oxygen incorporation was enhanced at lower depositi on rates, whereas the nitrogen and carbon film contamination were unaf fected. The deposition rate dependence of the incorporation is in exce llent agreement with a proposed model. Apart from the effects of plasm a power on the incorporation probability? the reactor outgassing rate and the purity of the silane gas itself were identified as the main co ntamination sources for the atmospheric contaminants in the deposited films. At the low outgassing rate, at least around one-half of the oxy gen detected in the a-Si:H material originates from the silane gas. Du e to the reduced outgassing rate and an enhanced purity of the silane gas used, the authors have deposited a-Si:H-material with the lowest c oncentrations of atmospheric contaminants reported to date. Furthermor e, the present results exclude a contamination of the a-Si:H-material by a postoxidation after air exposure. (C) 1995 American Vacuum Societ y.