Mechanisms of the growth of nanocrystalline Si:H films deposited by PECVD

Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited using plasma-enhanced chemical vapor deposition from a SiF4/SiH4/H2 gas mixtures. Properties were examined of nc-Si:H films produced by decreasing the deposition temperature (Td) under two different hydrogen dilution ([H2]) conditions. For these films, the X-ray diffraction, the Raman scattering, the Fourier transform infrared absorption and the stress were investigated. Our results show that the decrease in Td has significant effects in the decrease of the average grain size (〈δ〉), the crystalline volume fraction (ρ) values, and an increase in the density of SiH-related bonds (NSiH) values. On the contrary, increases in [H2] decreased the 〈δ〉 and the NSiH, while the ρ were increased. Our experiments also confirmed that the increase in ρ corresponds with the decrease in NSiH. In view of these results, it may be concluded that the use of both low Td and high [H2] conditions might lead to growth of nc-Si:H films with small grains and high crystallinity. In this context, the surface processes (such as diffusion and etching) for the growth of nc-Si:H films were extensively discussed in this current work.