Simulation of the bulk and surface properties of amorphous hydrogenated silicon deposited from silane plasmas

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Abstract
A Monte Carlo simulation for the growth of amorphous hydrogenated silicon (a‐Si:H) thin films by plasma enhanced chemical vapor deposition is presented. The goal of the model is to predict the bulk and surface properties of films (e.g., hydrogen content, deposition rate, buried hydride/dihydride ratios, porosity, and surface roughness) having thicknesses of ≲2000 Å. The effects on the film properties of the composition of the radical flux incident on the surface are examined. Film properties were found to be critically dependent on the ratio of SiH3/SiH2 in the radical flux. High values for this ratio results in film properties resembling chemical vapor deposition. Film properties obtained with small values resemble physical vapor deposition. Rough films (roughness >10’s of Å) accordingly result from radical fluxes having high SiH2 fractions. We find that surface roughness and hydrogen fraction increase with increasing growth rate and increasing film thickness, though thin films (4 gas mixtures, we find that a decrease in the SiH3/SiH2 ratio in the radical flux, and an increase in the ion/radical ratio incident on the surface are largely responsible for the degradation of film properties observed with decreasing silane fraction.