Infrared spectroscopy of hydrogenated amorphous silicon nitride films

PECVD grown Hydrogenated amorphous silicon nitride (a:SixHyNz) films are studied by infrared spectroscopy at ambient and different low temperatures in the region 4000-400 cm(-1) to understand the formation of nitrogen and hydrogen bonded groups in the amorphous film. The vibrations pertaining to NH, SiH2, Si-N-Si, Si-NH, Si-Si species of HSiNSi2, NSi3, HNSi2, Local bonding groups in a:SixHyNz network are observed and assigned. The different local bonding arrangements are characterized by the inplane antisymmetric stretching and breathing modes of Si-N-Si bond and stretching vibrations of Si-H and NH groups. Infrared studies revealed the three fold coordination of nitrogen atom at planar site with three silicon atoms and one hydrogen atom bonded to any one of the silicon atom as second nearest neighbor. At low temperatures, the removal of degeneracy, shift in peak position with gain in Intensity of some bands and appearance of new bands are observed due to reorientational ordering of local bonding groups through dynamical and chemical changes caused by hydrogen bonding.