A novel oxidation process for silicon nitride films of various compositions have been undertaken utilizing nitrous oxide (N2O) plasma. Careful studies using elastic backscattering (EBS) technique to determine the composition and capacitance-voltage (C-V) measurements to determine the insulator charge density (Q(o)) and the interface state density (D-it) have been made on the films before and after N2O plasma oxidation. The incorporation of oxygen into the silicon nitride films of various compositions due to the N2O plasma treatment is confirmed. The insulates charge density (Q(o)) as well as the minimum interface state density (D-it)(min) are observed to be more for the N2O oxidized samples compared with the corresponding virgin samples.