OPTICAL CHARACTERIZATION OF SILICON OXYNITRIDE THIN-FILMS BY VARIABLE ANGLE SPECTROSCOPIC ELLIPSOMETRY

Silicon oxynitride (SiOxNy) thin films were deposited on silicon substrates by ion-assisted deposition. Variable angle spectroscopic ellipsometry (VASE) was used to optically characterize the deposited film properties, such as layer thickness and composition, film surface and interface qualities, as well as the refractive index spectrum in the wavelength range 320-820 nm. The measured VASE spectra were analyzed by assuming SiOxNy to be a physical mixture of two distinct phases, silicon dioxide and silicon nitride, using the Bruggeman effective medium approximation. Remarkably good agreements between the measured spectra and model calculations were obtained over the entire spectral range for all the samples studied. Layer thicknesses of SiOxNy films determined by VASE were consistent with their corresponding nominal values. The ellipsometrically deduced refractive index spectrum was observed to be strongly dependent on the film composition. In addition, the film refractive index at each applied wavelength was found to be a linear function of its constituent relative volume fraction. The results from VASE analysis also indicated that all the sample films investigated exhibited smooth surfaces, sharp interfaces between the film and substrate and high packing density.