Effects of junction profiles in bottom protection p-well on electrical characteristics of 1.2 kV SiC trench-gate MOSFETs

Abstract

Effects of junction profiles in bottom protection p-well (BPW) on electrical characteristics of 1.2 kV SiC trench-gate MOSFETs were investigated using simulation methods. Breakdown mechanisms of BPW in the device were also elucidated by energy-band diagram and electric-field distribution across trench-gate. Monte Carlo Al-implantation simulation on the trench structure for BPW formation was carried out with variations in peak depth (DBPW), concentration (NBPW), and thickness of SiO2 spacer (Tspacer) on trench sidewall. The SiC trench-gate MOSFETs with deep DBPW, high NBPW, and thin Tspacer are suitable for high drain voltage due to a shielded trench gate by BPW. However, specific on-resistance (Ron,sp) increased because of laterally penetrated Al into p-base and accumulation regions during ion implantation for BPW formation. In case of shallow DBPW, low NBPW, and thick Tspacer, however, the gate oxide at trench bottom corner is considerably vulnerable to the dielectric breakdown due to fully depleted BPW near trench bottom corner and electric-field crowding at gate oxide.