Effects of wet oxidation on the electrical properties of sub-10 nm thick silicon nitride films

Abstract

Capacitors with sub- 10 nm thick oxidized nitride layers formed by wet oxidation of 8 nm thick silicon nitride films deposited on a polysilicon substrate were prepared. The effects of the wet oxidation time on the electrical properties of the silicon nitride film itself have been investigated with oxide/nitride composite film and oxidized nitride film by removing the top oxide from the oxide/nitride composite film. The capacitance of the capacitors consisting of oxide/nitride composite film decreases sharply and their breakdwon fields increase with increasing thickness of the top oxide layer. On the contrary, the capacitance and breakdown fields of silicon nitride layer, which was created by removing the top oxide layers grown thermally on silicon nitride, increase with increasing wet oxidation time. The reduction of thickness and the improved quality of silicon nitride are responsible for the improved capacitance and increased breakdown fields of nitride layer, respectively. In addition, wet oxidation improves the intrinsic TDDB characteristics and the early breakdown failure rate of silicon nitride film itself, probably due to the reduction of defects in the silicon nitride. Consequently, silicon nitride film created by removing top oxide is suitable for dynamic memories as a thin dielectric film.