Hydrogen-free silicon nitride films were deposited at room temperature by microw ave electron cyclotron resonance (ECR) plasma source enhanced unbalanced magnetr on sputtering system. Fourier-transform infrared spectroscopy and X-ray photoele ctron spectroscopy were used to study the bond type, the change of bond structur es, and the stoichiometry of the silicon nitride films. Atomic-force microscopy and nano-indentation were used to study the morphological features and mechanica l characteristics of the films. The results indicate that the structure and char acteristics of the films deposited by this technique depend strongly on the dens ity of sputtered Si in plasma and the films deposited at 4 sccm N2 fl ow show excellent stoichiometry and properties.