The deposition of SiN_x thin films were prepared on SiO₂/Si substrate at room temperature by reactive dc magnetron sputtering. The deposition rate of SiN_x thin films were studied as a function of dc power, working gas and chamber pressure. As the dc power increases, the deposition rate linearly increases. However the deposition rate decreases with increasing chamber pressure and N₂ flow rate in Ar/N₂ mixture. The crystallization of Si dot in the SiN_x thin films was investigated by using x-ray diffraction and photoluminescence