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 (T_d) 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 T_d 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 (N_SiH) values. On the contrary, increases in [H₂] decreased the 〈δ〉 and the N_SiH, while the ρ were increased. Our experiments also confirmed that the increase in ρ corresponds with the decrease in N_SiH. In view of these results, it may be concluded that the use of both low T_d 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.