Interface properties of SiOxNy layer on Si prepared by atmospheric-pressure plasma oxidation-nitridation

SiOxNy films with a low nitrogen concentration (< 4%) have been prepared on Si substrates at 400 degrees C by atmospheric-pressure plasma oxidation-nitridation process using O-2 and N-2 as gaseous precursors diluted in He. Interface properties of SiOxNy films have been investigated by analyzing high-frequency and quasistatic capacitance-voltage characteristics of metal-oxide-semiconductor capacitors. It is found that addition of N into the oxide increases both interface state density (D-it) and positive fixed charge density (Q(f)). After forming gas anneal, D-it decreases largely with decreasing N-2/O-2 flow ratio from 1 to 0.01 while the change of Q(f) is insignificant. These results suggest that low N-2/O-2 flow ratio is a key parameter to achieve a low D-it and relatively high Q(f), which is effective for field effect passivation of n-type Si surfaces.