Hydrogen-free silicon nitride (SiNx) with x varying from 0 to 1.3 were prepared by sputtering a Si target with concurrent nitrogen ion (N2+) assist at an energy of 250 eV. The value of x saturated at 1.3 when the assist N2+ beam current was higher than 25 mA. As x increases from 0 to 1.3, the hardness of the films increases from 12.2 to 21.5 GPa, the elastic modulus increases from 191 to 256 GPa, the friction coefficient drops from 0.65 to 0.37, the compressive stress rises from -0.52 to -1.4 GPa, and the etching rate in buffered hydrofluoric acid increases from a negligible small value to 7 nm min-1. Potassium hydroxide does not attack the film at any composition. Ion assist resulted in peening and densification of the film structure, causing the SiN1.3 films to have high hardness, high stability against oxidation in air, and great compressive stress. Ion bombardment also generated defects, thus giving rise to the moderate etching rate of SiN1.3 in BHF. The good mechanical and etching properties suggest that dual ion beam deposition SiNx films are potentially useful materials in microelectromechanical devices applications. © 2001 American Vacuum Society.