Inhomogeneous optical SiOxNy thin films prepared by ion assisted deposition

Optical SiOxNy films with variable refractive indices were prepared by nitrogen ion assisted deposition at various oxygen backfill pressures or ion beam energies and their optical properties, chemical bonding states, and stresses were investigated. The result shows that the refractive index is able to be varied from that of silicon nitride to silicon oxide as the oxygen backfill pressure increases. Also the index of silicon nitride film can be varied by controlling the bombarding nitrogen ion beam energy. Variations of optical constants, chemical bonding stares, and compressive stresses depend on the composition of SiOxNy film. As an application a rugate filter with a step index profile was fabricated by varying the oxygen backfill pressure while nitrogen ion beam was bombarding the growing Si film.