Oxidation of silicon nitride prepared by plasma-enhanced chemical vapor deposition at low temperature

Hydrogenated amorphous silicon nitride (a-SiNx:H) films have been fabricated by plasma-enhanced chemical vapor deposition at temperatures ranging from 50 to 250 °C. It is found that as soon as the samples are taken out from the reaction chamber and exposed to the atmosphere, the a-SiNx:H films start to oxide. The oxidation processes are monitored using infrared absorption spectroscopy. A model of porous ‘‘fractal-like network’’ structure, which is probably inherent in low-temperature deposition, is proposed to explain why moisture (H2O) in the air can percolate through numerous microvoids into these films. The H2O molecules which percolate into these porous films are active to react with the —Si—N—Si—, —Si—N—H, and —N—Si—-H bonds and to form more chemically stabilized —Si—O—Si—, —Si—O—H, and H—O—H bond configurations with the result of eventual oxidization of the entire nitride films.