Superjunction MOSFET with an N-Dot Region in the P-Pillar for Soft Reverse Recovery

In this paper, a novel superjunction MOSFET with an N-dot region in the P-pillar is proposed and experimentally investigated. By taking advantage of the difference in diffusion rates of boron and arsenic, the N-dot region is naturally formed by implanting equal doses of arsenic and boron after the P-pillar implantation. Therefore, the charge balance condition between the N-pillar and the P-pillar remains unchanged, which allows an unaffected breakdown voltage of the proposed superjunction MOSFET. More importantly, the N-dot region increases the grounding resistance of the P-pillar located below the N-dot region, which reduces the extraction velocity of the non-equilibrium holes during the reverse recovery period. Consequently, a soft reverse recovery performance is obtained in the proposed one. The experiment results show that, in comparison with the conventional superjunction MOSFET, the softness factor of the proposed one could be improved by more than 2.5 times without side effects.