Vibrational property of the slow N ⁺₂ ions deposited SiN_x films

Abstract

We have investigated vibrational properties of silicon-nitride films, SiN_x (0.3≤×≤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≤k≤331 N/M, larger than the theoretical value for a nitrogen atom imbedded in a pure Si crystal.