Degradation by water vapor of hydrogenated amorphous silicon oxynitride films grown at low temperature

Abstract: We report on the degradation process by water vapor of hydrogenated amorphous silicon oxynitride (SiON:H) films deposited by plasma-enhanced chemical vapor deposition at low temperature. The stability of the films as a function of oxygen content and deposition temperature was investigated. The degradation by defects like pinhole was not found by transmission electron microscopy observation. However, we showed that the SiON:H is degraded by the reaction with water vapor through interstitial paths. To monitor degradation process, atomic composition, atomic density, and fully oxidized thickness were measured by using high resolution Rutherford backscattering spectroscopy and X-ray reflectometry. The film was rapidly degraded above ~27 at％ for oxygen composition, below ~150 oC for deposition temperature, and below ~2.15 g/cm3 for atomic density. We showed that this trend can be explained by the extents of porosity and percolation channel based on the ring model of network structure. In the case of high oxygen composition or low temperature, the SiON:H film becomes more porous because the film consists of network rings with small energy barrier.