Investigation on Gate-Oxide Damage of SiC Power MOSFETs Induced by Heavy Ion

Recent studies have shown that silicon carbide (SiC) power MOSFETs experience failures at extremely low-drain stress levels following heavy-ion irradiation, with structural damage concentrated in the oxide layer. However, the damage mechanism has not been precisely analyzed. This study examined the gate damage mechanisms of devices under different drain bias conditions. The gate structure of a 1200-V SiC power MOSFET did not exhibit damage at a 200-V drain bias. Damage locations for devices under drain biases above 200 V were concentrated in the oxide layer above the channel region. In prior studies, the transient picosecond-scale electric field within the gate dielectric has been identified as the primary driver of oxide damage; however, this mechanism alone does not account for the observations reported herein. Therefore, the gate-oxide degradation mechanism is investigated herein by computing both the electric field induced within the oxide by heavy-ion traversal of the gate dielectric and the electric field generated in the semiconductor by heavy-ion incidence. The results show that, above the critical drain voltage, hole injection into the oxide layer causes severe damage. Below the critical voltage, electron injection into the oxide layer leads to increased traps. These findings were further validated through charge pumping (CP) measurements. In addition, we demonstrate that theoretical models can predict the conditions at which gate damage starts to appear as a function of linear energy transfer (LET) and the range of heavy ions used in the irradiation experiments.