Compositional characterization of a-SiC:H films by infra-red spectroscopy

Abstract

Amorphous Si1−xCx:H films (0 < x < 0.6) deposited on c-Si substrates by r.f. plasma-enhanced chemical vapour deposition were studied as functions of the material composition and hydrogen content by infra-red reflectivity and transmission spectroscopy. The films were prepared by glow discharge decomposition of SiH4 and CH4 gases at 50 W r.f. power, 20 Pa of pressure and 300°C of substrate temperature. From analysis of the CH and SiH stretching absorption bands it is shown that the content of hydrogen atoms bonded to Si is not appreciably affected by the precursor CH4/SiH4 flow ratio. On the contrary, the fraction of hydrogen incorporated in CH bonds increases with the relative CH4 to SiH4 flow rate. We analysed the evolution of the refractive index with the growth conditions. In particular, we found that the contribution of the hydrogen content to the minima of the interference fringes in the IR reflectivity spectra is negligible, and all changes in the absolute value are directly attributed to changes in the material composition. This gives a measure of the composition of the film, when comparing the refractive index and the carbon content obtained by X-ray photoelectron spectroscopy.