Reaction mechanism and kinetics of silane pyrolysis on a hydrogenated amorphous silicon surface

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Abstract
Three regimes of pressure and temperature are identified in which silane pyrolysis has distinctly different initial kinetics: in two regimes the initial reactions are heterogeneous and in the third regime it is homogeneous. We report here a preliminary model for the heterogeneous reaction regime where the decomposition rate is nearly independent of pressure. In the model the silicon surface is saturated with hydrogen and hence is nonreactive. The rate limiting step for silane decomposition is the creation of reactive surface sites by release of hydrogen. These reactive sites are refilled by decomposition of SiH4 or reincorporation of H2. A new adsorbed state of SiH4 is proposed which is bound to the surface by a three-center bond. After making some simplifications to the full model the kinetics are solved for static- and flowing-gas hot wall reactor experiments. The implications of the proposed reactions for the other two pyrolysis regimes and for silane discharges are briefly discussed.