Fundamnetal chemistry of silicon CVD

Model CVD reactor studies and UHV surface adsorption kinetic measurements are a powerful combination for investigation of the chemical mechanisms active in thermal silicon CVD from silane. We use the model reactor to separate two regimes of pressure and temperature in which SiH₄ heterogeneous decomposition or homogeneous pyrolysis chemistry dominate the observed silicon film growth kinetics. Residence time of SiH₄ in the reactor hot zone and total pressure are essential quantities distinguishing the two regimes. Growth rates are controlled by surface SiH₄ adsorption kinetics in the heterogeneous regime. The regime we call the homogeneous regime is dominated by adsorption kinetics of higher silanes Si_nH_2n+2. UHV adsorption kinetic measurements comparing SiH₄, Si₂H₆, and Si₃H₈ chemisorption on clean, well defined single crystal surfaces are useful in understanding the two regimes. The UHV studies also demonstrate the necessity of considering the competitive adsorption of SiH₄ with the higher silanes in film growth rate measurements because of homogenous reactions forming higher silanes from SiH₄ under certain reactor conditions, and because of trace disilane impurities commonly present in commercially available SiH₄.