Frequency effects on plasma deposition and properties of fluorinated silicon nitride films.

Low hydrogen fluorinated PECVD silicon nitride films were grown using NF sub 3/ SiH sub 4/ N sub 2 feed mixtures with RF excitation below the ion transit frequency, at 200 kHs. Under these conditions higher energy ion bombardment is expected to enhance surface diffusion and chemical reconstruction. Compared to fluorinated silicon nitride deposited at 14MHz under otherwise comparable conditions, the 200kHz films had a lower Si-H bond concentration (~1x10 sup (21) cm sup (-3)), lower total hydrogen content (5-8x10 sup (21) cm sup (-3)), better resistance to oxidation, lower compressive stress (-0.7 to -1.5Gdyne/cm), higher density (3.1g/cm sup 3)) and better dielectric properties. Bandgaps of low frequency PECVD fluorinated silicon nitride films were between 5.3 and 6.4eV, which compare with 4.4 to 5.9eV for the high excitation frequency fluorinated material, and 3 to 4eV for conventional PECVD nitride. It is believed that the larger bandgap reflects better structure and fewer defects.