High-carbon concentrations at the silicon dioxide-silicon carbide interface identified by electron energy loss spectroscopy

High carbon concentrations at distinct regions at thermally-grown SiO₂/6H-SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS). The thickness of these C-rich regions is estimated to be 10-15 Å. The oxides were grown on n-type 6H-SiC at 1100 °C in a wet O₂ ambient for 4 h immediately after cleaning the substrates with the complete RCA process. In contrast, C-rich regions were not detected from EELS analyses of thermally grown SiO₂/Si interfaces nor of chemical vapor deposition deposited SiO₂/SiC interfaces. Silicon-rich layers within the SiC substrate adjacent to the thermally grown SiO₂/SiC interface were also evident. The interface state density D_it in metal-oxide-SiC diodes (with thermally grown SiO₂) was approximately 9×10¹¹cm^-2 eV^-1 at E-E_v=2.0 eV, which compares well with reported values for SiC metal-oxide-semiconductor (MOS) diodes that have not received a postoxidation anneal. The C-rich regions and the change in SiC stoichiometry may be associated with the higher than desirable D_it's and the low channel mobilities in SiC-based MOS field effect transistors.