Analytical model for reduction of deep levels in SiC by thermal oxidation

Abstract

Two trap-reduction processes, thermal oxidation and C+ implantation followed by Ar annealing, have been discovered, being effective ways for reducing the Z1/2 center (EC – 0.67 eV), which is a lifetime killer in n-type 4H-SiC. In this study, it is shown that new deep levels are generated by the trap-reduction processes in parallel with the reduction of the Z1/2 center. A comparison of defect behaviors (reduction, generation, and change of the depth profile) for the two trap-reduction processes shows that the reduction of deep levels by thermal oxidation can be explained by an interstitial diffusion model. Prediction of the defect distributions after oxidation was achieved by a numerical calculation based on a diffusion equation, in which interstitials generated at the SiO2/SiC interface diffuse to the SiC bulk and occupy vacancies related to the origin of the Z1/2 center. The prediction based on the proposed analytical model is mostly valid for SiC after oxidation at any temperature, for any oxidation time, and any initial Z1/2-concentration. Based on the results, the authors experimentally achieved the elimination of the Z1/2 center to a depth of about 90 μm in the sample with a relatively high initial-Z1/2-concentration of 1013 cm−3 by thermal oxidation at 1400 °C for 16.5 h. Furthermore, prediction of carrier lifetimes in SiC from the Z1/2 profiles was realized through calculation based on a diffusion equation, which considers excited-carrier diffusion and recombination in the epilayer, in the substrate, and at the surface.