Characterization of PECVD SiN films by spectroscopic ellipsometry

Plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films deposited on both GaAs and Si substrates have been characterized by spectroscopic ellipsometry. The results indicate that such films consist of three constituents: Si3N4, voids, and amorphous silicon (alpha-Si). In addition, it is also observed that for typical deposition conditions there is an intervening layer of alpha-Si (on the order of 50 - 100 Angstrom) between the nitride film and the semiconductor substrate. The thickness of this alpha-Si layer is found to depend on both the stoichiometry and the growth time of the nitride layer, leading to the conclusion that it is a result of excess Si diffusing from the growth surface through the nitride layer.