The nitrogen-rich silicon oxynitride thin film for gate insulator application has been studied in this work. The Plasma Enhanced Chemical Vapour Deposition (PECVD) process was carried out at 350 degree(s)C with a low power density (0.011 W/cm2). The Auger Electron Spectroscopy (AES) depth profiling and infrared absorption spectra show the film is composed of nitrogen-rich silicon oxynitride. MOS C-V measurements demonstrated that a pre-deposition plasma nitridation may result in a higher dielectric breakdown. The post- deposition densification can be used to remove the plasma induced damages, and the post-metallization annealing is effective in reducing the irradiation damage and obtaining a low interface state density.