Silicon nitride and silicon oxynitride are materials used extensively in mechanical and electronic devices due to their outstanding properties. Thin films of silicon nitride and silicon oxynitride can be deposited on a silicon surface. In this study, nitridation of silicon wafers by a rapid thermal heating process with both nitrogen and ammonia as precursors was investigated by transmission electron microscopy, electron energy loss spectroscopy, and ellipsometry analyses. It was found that, under ammonia gas, the growth of nitride film was limited to 0.5 nm, whilst under the nitrogen atmosphere, a nitride film of 5-10 nm could be formed at 1200 • C. The limited growth in ammonia suggests formation of high-quality passivating layer.