Reliability and irradiation effects of 4H-SiC MOS devices

Abstract

Bias-temperature-instabilities (BTIs) and total ionizing dose effects are investigated for 4H-SiC MOS devices. Low frequency noise measurements are employed to help understand the nature of the defects that affect the reliability and radiation response of SiC MOS devices. Threshold voltage shifts due to BTI correlate strongly with the additional ionization of deep dopants in SiC at elevated temperatures. The charge that leads to BTI lies in interface traps that are more than 0.6 eV below the SiC conduction band, nitrogen related defects, and O vacancies in the SiO2. Switching bias between irradiation and annealing can lead to significant enhancement of degradation in SiC MOS devices. The pair of positive/negative gate bias during irradiation/annealing on p-substrate capacitors is found to be worst-case for degradation. The 1/f noise in 4H-SiC MOSFETs is dominated by the interaction of channel carriers with slow interface traps at temperatures below 360 K and with border traps above 360 K. The interface traps related to 1/f noise are identified as carbon vacancy clusters and nitrogen dopant atoms at or near the SiC/SiO2 interface through first-principle calculations and TCAD simulations.