Influence of P+ Body on Performance and Ruggedness of 1.2 kV 4H-SiC MOSFETs

This article reports an investigation into the impact of P+ body design in 4H-silicon carbide (SiC) MOSFETs. Specifically, 1.2 kV SiC MOSFETs with various P+ body designs were fabricated and analyzed. MOSFETs with stripe pattern P+ body, orthogonal P+ body, and without P+ body were fabricated on the same wafer using the same mask set. A comprehensive comparison was conducted among the MOSFETs with different P+ body designs, focusing on their static characteristics, switching characteristics, and avalanche ruggedness. Two-dimensional simulations were also performed to support experimental results. The orthogonal P+ design was observed to provide improved conduction behaviors without adversely affecting the static characteristics, thanks to the reduced cell pitch. Conversely, MOSFETs without a P+ body exhibited reduced breakdown voltage due to the inability to extract holes during avalanche conditions. The presence of a large area of P+ body contact enhances the switching characteristics, whereas MOSFETs with a small area of P+ body contact exhibit a slow change of potential within the p-well during switching. Additionally, similar results are observed in unclamped inductive switching (UIS). The small area of P+ body contact causes a slow change of potential in the channel region during avalanche conditions. Consequently, the channel potential decreases, leading to higher avalanche current flow from the channel and a reduction in avalanche energy.