The mechanism of plasma-induced deposition of amorphous silicon from silane

Time-resolved mass spectrometric data show that the concentration of di- and trisilane, which are formed from monosilane under discharge conditions typical for the deposition of high electronic quality amorphous silicon, correlate with the measured deposition rate of a-Si. The data can be quantitatively and self-consistently described by a simple set of consecutive reactions:

1. SiH₄ →-SiH₂ + H₂
2. SiH₂ + SiH₄ → Si₂H₆
3. SiH₂ + Si₂H₆ → Si₃H₈
4. Si _n H_{2(n + 1)} →n ·a-Si:H+(n+1)H₂,n=2,3

The only fitting parameter necessary for an excellent fit of the measured data over a wide range of experimental parameters is the value of the reactive sticking coefficient .for the decomposition of di- and trisilane (reaction 3). The resultant value agrees well with the published data of other authors and with those calculated from the measured deposition rate and Si₂H₆, concentration. We did not find and physically meaningful way to lit the measured data with the various “SiH₃ models” proposed by other authors who assumed that the dominant species responsiblefor the deposition of a-Si: H is the SiH₃, radical. For this and some additional reasons mentioned in the present paper. the SiH₃ model is in disagreement with available experimental data.