Threshold Voltage Instability in 4H-SiC MOSFETs With Phosphorus-Doped and Nitrided Gate Oxides

Threshold voltage instability was investigated for 4H-SiC MOSFETs with phosphorus-doped (POCl3-annealed) and nitrided (NO-annealed) gate oxides. Threshold voltage shift observed in the bidirectional drain current-gate voltage characteristics was evaluated using various gate voltage sweeps at room and elevated temperatures up to 200 °C. The threshold voltage shift was also studied after applying positive and negative bias-temperature stress. Two types of MOSFETs showed different instability characteristics, depending on gate biases and temperatures. These features were found to originate from the difference in trap density and trap location at/near the oxide/SiC interface and in the oxide. It is apparent that the oxide traps in phosphorus-doped oxides and near-interface traps in nitrided oxides are the main origin of the threshold voltage instability via capture and emission (in the case of oxide traps, only capture) of both electrons and holes.