Silane pyrolysis

We show that silane pyrolysis is initiated by decomposition on the amorphous silicon surface, with an activation energy E_a of 56 kcal/mole. The observed surface decomposition rate is only weakly dependent on silane pressure. Much faster delayed decomposition rates, approximately independent of surface area and proportional to pressure, are shown to be initiated by surface reactons. A model for surface decomposition is given. Also a model for gas reactions is suggested based on H atom or SiH₃ release by surface decomposition, causing chain reactions that process the gas to higher silanes that decompose rapidly. This model can explain the previous observations that the initial disilane formation rate and the delayed decomposition rate were independent of the surface area to volume ratio A/V, which had misled previous investigators to suggest homogeneous initiation processes.