Thermochemistry and kinetics of silicon hydride cluster formation during thermal decomposition of silane

Product contamination by particles nucleated within the processing environm ent often limits the deposition rate during chemical vapor deposition proce sses. A fundamental understanding of how these particles nucleate could all ow higher growth rates while minimizing particle contamination. Here we pre sent an extensive chemical kinetic mechanism for silicon hydride cluster fo rmation during silane pyrolysis. This mechanism includes detailed chemical information about the relative stability and reactivity of different possib le silicon hydride clusters. It provides a means of calculating a particle nucleation rate that can be used as the nucleation source term in aerosol d ynamics models that predict particle formation, growth, and transport. A gr oup additivity method was developed to estimate thermochemical properties o f the silicon hydride clusters. Reactivity rules for the silicon hydride cl usters were proposed based on the group additivity estimates for the reacti on thermochemistry and the analogous reactions of smaller silicon hydrides. These rules were used to generate a reaction mechanism consisting of rever sible reactions among silicon hydrides containing up to 10 silicon atoms an d irreversible formation of silicon hydrides containing 11-20 silicon atoms . The resulting mechanism was used in kinetic simulations of clustering dur ing silane pyrolysis in the absence of any surface reactions. Results of th ose simulations are presented, along with reaction path analyses in which k ey reaction paths and rate-limiting steps are identified and discussed.