AES and XPS of silicon nitride films of varying refractive indices

AES and XPS measurements of silicon nitride films with refractive indices ranging from 1.93 to 2.08 have been made. The films studied were grown on silicon (100) substrates by CVD using varying mixtures of silane and ammonia. Earlier AES studies of similar silicon nitride films have suggested that these films are microscopic mixtures of Si and Si3N4. We present XPS data which show that there is no measurable ’’free’’ silicon (i.e. the level of ’’free’’ silicon is ≲3 at. %) in the silicon nitride films with refractive indices ≲2.02. AES data show an increase in oxygen content corresponding to a decrease in refractive index of the silicon nitride films. These AES measurements agree qualitatively with measurements of the physical properties of silicon oxynitride films.