Abstract
Initial transient phenomena in the plasma deposition of hydrogenated amorphous silicon (a-Si:H) film from SiH4 has been studied in terms of an origin and an influence on the device fabrication. The initial transient state (ITS) of plasma over the time ranging from 2 to 40 s is observed as variations of optical emission intensities from SiH and H rather than as double probe currents. A simple model shows that this is caused mainly by the variation of the SiH4 concentration at relatively high rf power as well as at a low SiH4 flow rate. The variation of electron energy distribution is also discussed as a dominant origin at low rf power and high SiH4 flow rate. The predischarge method by which the SiH4 concentration is controlled just before a main discharge is proposed in order to reduce the ITS. A strong influence of the ITS on the field-effect response of the thin-film transistor is observed and can be avoided by the predischarge method.
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