Direct nitridation of silicon surface can be realized at a temperature as low as 430 degrees C by using high-density plasma above 10(12) cm(-3) featuring low ion bombardment energy below 7 eV. This study shows that stoichiometric silicon nitride can be obtained for the first time at a temperature of 400 degrees C by precise control of the nitrogen partial pressure to generate N-2(+) in the plasma. Moreover, hysteresis in the capacitance-voltage data that has been attributed to charge traps in silicon nitride film can be reduced dramatically by adding hydrogen to Ar/N-2 plasma for terminating dangling bonds with hydrogen. The dielectric strength of silicon nitride films is nearly equivalent to those of thermally grown silicon nitride and silicon oxide. The leakage current of silicon nitride film is dramatically reduced compared to that of thermally grown silicon oxide even if their equivalent thicknesses are equal. The silicon nitride films have almost no stress-induced leakage current and very little trap generation even in high-field stress.