Physics of SiC MOS interface and development of trench MOSFETs

An original method to accurately evaluate the MOS interface state density has been proposed. Characterization using this method has revealed that a high density of fast states is generated by interface nitridation of SiC(0001), though the density of slow interface states can be remarkably reduced by the nitridation. The generation of fast states is less pronounced on non-basal planes of SiC, and high channel mobilities over 100 cm²/Vs are obtained for MOSFETs fabricated on Al⁺-implanted SiC(11-20) and (1-100). We also proposed a novel design of “double-trench” MOSFET, which is effective to alleviate the electric field crowding at the gate oxide near the trench bottom. Based on these fundamental investigations combined with advanced device technology, we achieved a very low on-resistance of 0.79 mΩcm² for a 630 V SiC trench MOSFET (normally off).