Oxidation of silicon nitride films in an oxygen plasma

Abstract

The fabrication of oxynitrides using low thermal budget process technology is a key component in the production of advanced devices. This work focuses on the use of plasma anodization of low-pressure chemical vapor deposition (LPCVD) silicon nitride films to produce silicon oxynitride films, which are characterized structurally and electrically. The oxynitride dielectric films have a three layer structure, with “SiO2”-like layers at the surface and near the interface, and a “Si3N4”-like layer between them. Hence, nitrogen atoms are replaced by oxygen atoms at the surface of the film and near the Si/dielectric interface. The conductivity of the silicon nitride film was found to be higher than the silicon oxynitride film, whereas the conductivity of the oxynitride and, therefore, its trapping characteristics are more temperature dependent. Furthermore, the activation energy required to release an electron from a trap in the silicon oxynitride film (0.218 eV) is 1.7× that of the silicon nitride film (0.130 eV). Although oxidation of the LPCVD silicon nitride film did not reduce the interface trap density (≅1012 cm−2 eV−1 for both Si3N4 and SiON films), the density of traps, which are thought to be silicon dangling bonds in the form of an sp3 state near midgap, have reduced. A model to explain the conduction properties of the silicon oxynitride film—based on the Fowler–Nordheim conduction mechanism—was developed. Moreover, this model takes into account the trapping dynamics of the film. It was found that the best theoretical fit to the experimental current density data was obtained by assuming that the areal trap density, No,=5×1012 cm−2 and the trap capture cross section, σ=1×10−16 cm2.