Controversies in the suggested mechanisms of plasma-induced deposition of silicon from silane

The originally proposed mechanism of plasma-induced deposition of silicon from silane via the SiH3 radical, as suggested by several research groups, was based on speculation rather than on facts. Critical consideration of the experimental facts which were published recently shows that there is no substantial evidence for this reaction channel, and that the possible contribution of the SiH3 radical to the generally observed deposition rate of amorphous silicon (a-Si) and crystalline silicon (c-Si) is negligible. Based on the experimental data available so far it is shown that the most probable dominant reaction channel involves, as a first step, the fragmentation of silane into SiH2 and H2. In the case of a-Si deposition, this is followed by rapid formation of disilane (and to lesser extent higher silanes) which then decomposes at the surface of the growing film. The deposition of c-Si involves a direct insertion of SiH2 into the surface of the growing film. The ion-impact-induced dehydrogenation of the surface is the rate-determining step for fast growth rates.