Effects of combined NO and forming gas annealing on interfacial properties and oxide reliability of 4H-SiC MOS structures

The effects of NO and forming gas post oxidation annealing treatments on the interfacial properties and reliability of thermal oxides grown on n-type 4H-SiC (0001) Si face have been investigated in this study. The results show that forming gas annealing (FGA) treatment has limited effect on interface trap density (Dit) while it results in an improvement of the insulating properties of thermal oxide with uniform high FN barrier height (2.56 eV), high field-to-breakdown (10.71 MV/cm) and charge-to-breakdown (0.078 C/cm2). On the other hand, NO annealing causes a drastic reduction in Dit in the entire energy level, but in the case of reliability, it is not so effective as FGA, with lower barrier height (2.52 eV), field-to-breakdown (10.08 MV/cm), charge-to-breakdown (0.025 C/cm2) and worse uniformity of oxide. The combined NO&FGA treatment was also studied. It leads to a significant reduction in interface trap density further, especially in deep energy level (EC-ET ≥ 0.4 eV). As for reliability, it brings about uniform barrier height (2.69 eV), field-to-breakdown (10.15 MV/cm) and charge-to-breakdown (0.024 C/cm2). Taking interfacial properties and reliability into account, combined NO&FGA treatment is a promising POA technique for fabrication of high-quality SiC MOS devices.