Optical properties of silicon oxynitride thin films determined by vacuum ultraviolet spectroscopic ellipsometry

We determined the optical constants of silicon oxynitride (SiOxNy) thin films using a vacuum ultraviolet spectroscopic ellipsometer. The SiOxNy layers with a nominal thickness of 25 nm ~ 35 nm were grown on silicon substrates by using plasma enhanced chemical vapor deposition (PECVD). The precursor gases were nitrous oxide (N2O) and silane (SiH4). The ratio r of N2O flow rate to SiH4 one in the deposition process was controlled from 1.16 to 3.05. The ellipsometric measurements were performed at the angle of incidence 75 deg for the spectral range from 0.75 eV to 8.75 eV. The complex refractive indices, optical band gaps, and thicknesses of the SiOxNy layers were determined by using Tauc-Lorentz dispersion model.