Impact of byproducts formed on a 4H–SiC surface on interface state density of Al₂O₃/4H–SiC(0001) gate stacks

The impact of byproducts formed on a 4H–SiC(0001) surface by substrate oxidation on the interface state density (D_it) of Al₂O₃/4H–SiC gate stacks was investigated in this study, because some C-related byproducts are predicted to have defect states near the conduction band minimum (E_C) of 4H–SiC. At first, by developing an in situ cyclic metal layer oxidation method, we realized the formation of an Al₂O₃/4H–SiC gate stack without substrate oxidation, which was verified using conventional X-ray photoelectron spectroscopy (XPS). Then, the amount of byproducts on the 4H–SiC surface was controlled by chemical etching of thermally oxidized 4H–SiC. The results showed that the D_it near the E_C of 4H–SiC for the Al₂O₃/4H–SiC gate stack increased with the amount of byproducts until it fully covered the 4H–SiC surface; thereafter, it did not increase. For the sample with byproducts below the detection limit of XPS, a D_it value as low as 5 × 10¹¹ cm⁻² eV⁻¹ at around E_C − 0.15 eV of 4H–SiC was obtained.