Mechanism of doping-dependent fixed charges in SiC/SiO2 structure: Defect formation related to the Fermi level during final annealing

Doping-dependent fixed charges, previously observed in SiC MOS capacitors with ion-implanted bodies and gate oxides formed by dry oxidation, were extensively investigated to reveal their formation mechanism through a series of control experiments, focusing on the fabrication process of MOS capacitors. A very similar relationship between the doping concentration and effective fixed charge density was observed, irrespective of SiO2 formation (oxidation or deposition) and doping control methods (ion implantation or epitaxial growth). On the other hand, the effective fixed charge density strongly depends not only on the doping concentration but also on the final annealing temperature. Based on these findings, the mechanism of doping-dependent fixed charges is discussed, focusing on the Fermi level during the final high-temperature annealing.