Correlation of refractive index and silicon content of silicon oxynitride films

Abstract

The refractive index of plasma-deposited silicon nitride and silicon oxynitride films may be used to estimate the atomic per cent silicon in the films. This linear correlation is different from previously reported correlations and can even be applied to high temperature low pressure chemically vapour deposited silicon oxynitride films. While the refractive index can be used to monitor plasma nitride and plasma oxynitride films, it is important to remember that oxynitride films with different nitrogen and oxygen contents can have the same refractive index. The Bruggeman effective medium approximation with silicon and silicon dioxide as the two phases can be used to model the correlation. Although physically unreal, the model suggest that the large polarizability of silicon in the film controls the refractive index and that the polarizabilities of voids, hydrogen, nitrogen, oxygen and fluorine can be grouped together with an effective refractive index of 1.46.