Quantitative hydrogen measurements in PECVD and HWCVD a-Si:H using FTIR spectroscopy

Abstract

A series of hydrogenated amorphous silicon films have been deposited using plasma enhanced chemical vapour deposition (PECVD) and hot-wire chemical vapour deposition (HWCVD) techniques. The total concentration of bonded hydrogen in the films was varied between 3% and 18% as determined by hydrogen effusion measurements. Fourier transform infra-red (FTIR) spectra of the PECVD and HWCVD samples exhibit strong absorption peaks that correspond to Si–H bend and stretch modes, and Si–H2 stretch modes. A quantitative fit of the FTIR peak areas to the hydrogen effusion concentrations reveals that there is reasonable agreement between the required proportionality constants in PECVD and HWCVD material for the Si–H bend and stretch modes. The uncertainty error for the FTIR proportionality constants is consistently greater for the HWCVD data set, however, which may indicate that the effective dynamical charge of the Si–H dipoles is perturbed in the HWCVD material by bonded impurities that are sourced from the tungsten wire.