High-temperature CO2 treatments for 4H-SiC(0001) surfaces and SiO2/SiC structures were investigated. A stoichiometric SiO2 insulating layer was found to be grown on SiC by thermal oxidation in atmospheric CO2 ambient with an activation energy of 7.5 eV. Post-oxidation annealing (POA) in CO2 at a temperature of 1200 °C or more was effective in reducing interface fixed charges, oxide traps, and defect precursors, which are intrinsically involved in SiO2/SiC system grown with O2 oxidant. Furthermore, modification of the SiO2/SiC interface promoted by oxidizing SiC with CO2 at 1400 °C or more reduced the amount of interface states, thus the SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) treated with CO2 at 1400 °C exhibited improved channel mobility with a stable threshold voltage.

The combination of NO annealing and subsequent post-nitridation annealing (PNA) in CO2 ambient for SiO2/SiC structures has been demonstrated to be effective in obtaining both high channel mobility and superior threshold voltage stability in SiC-based metal-oxide-semiconductor field-effect transistors (MOSFETs). N atoms on the SiO2 side of the SiO2/SiC interface incorporated by NO annealing, which are plausible cause of charge trapping sites, could be selectively removed by CO2-PNA at 1300°C without oxidizing the SiC. CO2-PNA was also effective in compensating oxygen vacancies in SiO2, resulting high immunity against both positive and negative bias-temperature stresses.