Effect of composition inhomogeneity in a-SiOxNy thin films on their optical properties

The variation of optical properties of amorphous silicon oxynitride (a-SiOxNy) thin films was studied as function of their elemental composition and the deposit homogeneity was checked by Auger profiling. The optical gap, determined from the transmission spectra, showed high values increasing with the oxygen concentration. The Urbach energy was also estimated and linked to the film structure and composition. Their refractive index was found to decrease linearly from 1.94 to 1.46 when the layer composition varies between silicon nitride and silicon oxide. Spectroscopic ellipsometry showed that all samples were transparent over the visible range and that the layer with intermediate composition exhibited interface inhomogeneity. These results were confirmed by Auger profiling.