In situ UV-visible and Infrared ellipsometry study of the influence of silane dilution on the growth of hydrogenated amorphous silicon

The initial stages of hydrogenated amorphous silicon growth from the RF glow discharge decomposition of pure silane and mixtures of silane with H₂ or He has been studied using UV-visible and infrared ellipsometry. The substrate as well as the gas phase conditions strongly influence the early stages of a-Si:H growth. As compared to pure silane conditions, when using H₂ or He dilution of silane, thicker films must be deposited for SiH bonding to become dominant with respect to SiH₂. Moreover, in the case of high deposition rates from silane-helium mixtures, the SiH₂ band increases with film thickness, indicating that, contrary to low deposition rate conditions, SiH₂ is present in the bulk of the film.