Effects of various substrate materials on microstructural and optical properties of amorphous silicon oxynitride thin films deposited by plasma-enhanced chemical vapor deposition

Abstract

Plasma-enhanced chemical vapor deposition (PECVD) technique is well suited for fabricating optical filters with continuously variable refractive index profiles; however, it is not clear how the optical and microstructural properties of thin films differ when deposited on different substrates. Herein, silicon oxynitride films were deposited on silicon, fused silica, and glass substrates with two stoichiometric ratios by PECVD, using silane, ammonia, and nitrous oxide gasses, to investigate the effects of the substrate used on the optical properties and microstructures of the films. All the deposited films were amorphous. Further, the types and amounts of Si-centered tetrahedral Ox-Si-Ny bonds formed were based upon the substrates and stoichiometric ratios used; Ox-Si-Ny bonds with higher elemental nitrogen content were formed on Si substrates, which lead to obtaining higher refractive indices. The relationship between the surface roughness of the film and type of substrate was discussed. The extinction coefficients of all the films were very small, and the films exhibited low absorption. The refractive indices of the films formed on the different substrates had a maximum difference of 0.03. The deposition rates of the films increased in the order of fused silica, glass, and silicon.