Phosporus diffusion in nanocrystalline 3C-SiC

Phosphorus diffusion in nanocrystalline 3C silicon carbide (nc-SiC) with a grain size of 4-7 nm is studied using polycrystalline silicon (poly-Si) as the phosphorus source. Diffusion is much faster than in monocrystalline SiC and proceeds exclusively via grain boundaries (GBs). The poly-Si deposition step, alone or followed by a 1000 °C drive-in step, is sufficient to create a shallow phosphorus profile <100 nm deep, while drive-in steps above 1100 °C lead to phosphorus penetrating the 200 nm thick films and reaching the Si substrate. In the bulk of the films, GB diffusion is Fickian, and thermally activated with an activation energy of 5.2 ± 0.3 eV, which is substantially lower than in the monocrystalline case. Boltzmann-Matano analysis corroborates the analysis of the phosphorus profiles in the bulk of the films using error functions and shows that the high near-surface concentrations observed can be explained in terms of a concentration-dependent diffusivity. The concentration dependence is stronger and begins at higher concentrations for higher drive-in temperatures.