Study of the oxidization of ns-SiNx:H thin films using FTIR phase modulated ellipsometry

The time evolution of the optical properties of nanostructured silicon nitride (ns-SiN_x:H) thin films was studied by FTIR phase-modulated ellipsometry. The samples were produced by RF-PECVD and ellipsometric measurements were performed after the deposition and at different time intervals in the spectral range between 950 and 3500 cm^-1. The experimental data show an evolution from an initial not-oxidized state to a final oxidized state. The oxidation process of ns-SiN_x:H films is modeled with two different approaches: i) assuming that the oxidation starts at the film surface and diffuses towards the substrate and ii) assuming a homogeneous oxidization through the entire volume of the film. The final best fitting of the data suggests that the oxidization occurs homogeneously in all the thickness of the film.