Depletion-Mode TDDB for n-Type MOS Capacitors of 4H-SiC

TDDB for n-type 4H-SiC MOS capacitors depleted by DC bias (named as depletion-mode TDDB) has been investigated. The lifetime distribution can apparently be classified into two groups: shorter and longer tBD. Breakdown for the shorter tBD occurs at a point close to a threading dislocation. In contrast, the capacitors possessing longer tBD include no dislocation. An increase in the stress temperature and/or EOX leads to a decrease in tBD, indicating that the breakdown is caused by gate-oxide degradation. On the other hand, the tBD distributions acquired by accumulation-mode TDDB are relatively even, and the breakdown point is independent of dislocations. We presume that holes excited in the SiC layer by hot electrons play an important role at a threading dislocation for depletion-mode TDDB.