Preparation and characterization of reactively sputtered silicon nitride thin films

Abstract

Stoichiometric silicon nitride and silicon oxynitride thin films were deposited at low temperature using r.f. diode reactive sputtering. The dependence of film properties on the sputtering parameters was studied. Depth profiling by X-ray photoelectron spectroscopy of the film of a given composition indicated chemical integrity throughout the thickness. A linear relationship was found between the refractive index of the film and the oxygen content. IR absorption measurements showed a considerable shift of the main Si-N peak as a function of the oxygen content. When cross-sections of the films were examined with a scanning electron microscope, it was revealed that silicon nitride films prepared at low sputtering pressure were smooth and had a very dense microstructure without any visible columnar growth. X-ray diffraction and selected area electron diffraction confirmed those structures to be amorphous. Si-N film acts as an efficient barrier to oxygen diffusion and moisture penetration, and is resistant to (0.1 M) KCl-chloroacetate (0.1 M) buffer solution. The results indicate that Si-N coatings are promising for application as a protective overcoat for optical media.