in this study, we investigated the effects of nitrogen doping on the structural properties of cluster or microcrystalline Si embedded in thin SiO2 films. Thermal annealing of Si-rich a-SiOx or a-SiOxNy (x > y) films prepared by the r.f. co-sputtering method produces Si clusters or microcrystallines in the films. The structure of the embedded Si grains is affected by nitrogen doping that is achieved by using Ar-N-2 mixed gas as the sputtering gas. Nitrogen doping decreases the size of the Si grains after the thermal annealing process. We were able to observe this decrease of the crystallite size clearly by using the Raman spectra as a peak shift. Our analysis of the IR absorption of the Si-O-Si bond revealed the prevention of the migration reaction of Si and O atoms by nitrogen doping. This effect of doped nitrogen decreases the size of the Si crystals after the annealing process.