Gas phase and surface kinetics in plasma enhanced chemical vapor deposition of microcrystalline silicon: The combined effect of rf power and hydrogen dilution

A gas phase and surface simulator of highly diluted silane in hydrogen rf discharges used for the deposition of microcrystalline silicon has been developed. The model uses the spatial density distribution of SiH (X (2)Pi) radicals measured using laser induced fluorescence and the total silane consumption for estimating the primary electron induced silane dissociation, thus avoiding fluid or statistical approaches commonly used for the prediction of electron impact rate coefficients. A critical analysis is made for the relative importance of all the parameters involved either in the gas phase chemistry or in the surface processes. The model results are compared to experimental data concerning disilane production and film growth rate over a wide range of rf power densities in 2% and 6% SiH4 in H-2 discharges. The good agreement between experimental and model results allows for the extension of the discussion to the composition of the radical flux reaching the substrate, the relative contribution of each of the radicals to the film growth, and the most probable mechanism of microcrystalls formation under typical conditions of low and high microcrystalline silicon deposition rate. (C) 2001 American Institute of Physics.