Enhanced transmittance of sapphire by silicon oxynitride thin films annealed at high temperatures

Abstract

Silicon oxynitride (SiON) and SiO2 thin films attracted considerable attention for various applications such as anti-reflection coatings and surface passivation layers. In this report, we present the enhancement of sapphire optical transmittance by over-layer deposition of the amorphous SiON by RF magnetron sputtering, and investigation on changes in microstructure and transmittance upon high-temperature annealing ∼1373 K. A thin layer of nanocrystalline SiO2 was formed at the sapphire/film interface induced by the annealing. Remarkably, the XPS spectra revealed that the silicon-nitrogen bonds disappear in the annealed films to form a non-stoichiometric silicon oxide (SiOx) phase. The films showed high visible transmittance ∼92%, which is comparable to that of soda-lime glass due to a significant reduction in the refractive index 1.41 of the films after annealing at 1373 K.