High-voltage accumulation-layer UMOSFET's in 4H-SiC

Abstract

A novel silicon carbide UMOSFET structure is reported. This device incorporates two new features: a self-aligned p-type implantation in the bottom of the trench that reduces the electric field in the trench oxide, and an n-type epilayer under the p-base to promote lateral current spreading into the drift region. This UMOS structure is capable of supporting the full blocking voltage of the pn junction while keeping the electric field in the gate oxide below 4 MV/cm. An accumulation channel is formed on the sidewalls of the trench by epigrowth, and the gate oxide is produced by a polysilicon oxidation process, resulting in a uniform oxide thickness over both the sidewalls and bottom of the trenth. The fabricated 4H-SiC devices have a blocking voltage of 1400 V (10 μm drift region), a specific on-resistance of 15.7 mΩ-cm2at room temperature, and a gate oxide field of 3 MV/cm.