Comparative Study of the Optical and Vibrational Properties of a-SiNx:H Films Prepared from SiH4-N2 and SiH4-NH3 Gas Mixtures by rf Plasma

Abstract

ABSTRACTThe properties of amorphous silicon nitride films (a-SiNx:H) prepared by PECVD from SiH4-NH3 and SiH4-N2 gas mixtures have been determined by spectroscopie ellipsometry and FTIR spectroscopy as a function of the nitrogen concentration measured by XPS. The films are transparent for silane ratios [SiH4]/([SiH4] + [NH3]) < 20% and [SiH4]/([SiH4] + [N,]) < 1.5%. The refractive index shows a wide range of progressive variation from 3.2 for high silane concentrations to 1.8 for low silane concentrations. The hydrogen content of the low-absorbing films has much lower values for those obtained by SiH4 + N2 plasma than for those obtained by SiH4 + NH3 plasma. The results are discussed in terms of growth models of PECVD a-SiNx:H films from SiH4-NH3 and SiH4-N2 mixtures.