This study investigated the effect of oxidation on the chemical bonding structures of silicon nitride thin films synthesized by a low-temperature plasma-enhanced chemical vapor deposition (PECVD) method. These films were heat treated to different temperatures up to 1373 K. The bonding structures were studied by means of x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. It was found that the amorphous PECVD SiNx films were subjected to oxidation in air at elevated temperatures. The oxidation caused the formation of crystalline silicon dioxide within the matrix of amorphous silicon nitride, conforming to the "random mixing" model. The crystalline silicon dioxide formed is believed to be stoichiometric SiO2, whereas the remaining matrix is believed to be a nonstoichiometric silicon oxynitride with a structure conforming to the "random bonding" model. (c) 2006 American Institute of Physics.