Effect of Nitrogen on Diffusion in Silicon Oxynitride

Abstract

The effect of nitrogen (N) on diffusion in silicon oxynitride was investigated through the simulation of silicon oxynitridation. We assumed that the incorporation of N reduces the SiO diffusivity in SiO2 because oxynitride layers retard B penetration, or B diffusion, which is enhanced by SiO. In order to validate this assumption, we simulated the thickness of thermally grown oxynitride. The simulation was based on our oxidation model in which SiO molecules emitted to the oxide during oxidation modulate the oxidation rate. The assumption that the SiO diffusivity exponentially decreases with increasing N concentration was introduced to our oxidation model. The simulation results fit the experimental oxynitride thickness, and this indicates the validity of our assumption of the N effect on diffusion. During oxynitridation, the diffusion of SiO molecules generated at the interface is strongly retarded by the N atoms, which are incorporated and piled up at the interface. This retardation increases the SiO concentration in SiO2 near the interface as oxynitridation proceeds, which decreases the oxynitridation rate with time. The formation of Si3≡N bonds, which should block the reconstruction of Si–O bonds, is most likely the cause of the retardation of SiO diffusion in SiO2.