VIBRATIONAL PROPERTY OF THE SLOW N2+ IONS DEPOSITED SINX FILMS

We have investigated vibrational properties of silicon-nitride films, SiN(x) (0.3 less-than-or-equal-to x less-than-or-equal-to 1.33), produced by a non-thermal method using high-resolution electron energy loss spectroscopy. The results, based on a continuous random network model assuming a planar XY3 vibrational bond unit, show that the Si-N bonds in the films closely resemble those in typical thermal silicon nitride although nitrogens occupy some metastable binding sites. We estimate force constants of the restoring forces for a Si3N bond unit, which tend to increase gradually with increasing nitrogen content x. In particular, the central force constant k1 for the in-plane stretching mode of silicon atoms varies with x in the range 297 less-than-or-equal-to k less-than-or-equal-to 331 N/M, larger than the theoretical value for a nitrogen atom imbedded in a pure Si crystal.