Mechanism of Depletion-Mode TDDB for 4H-SiC MOS Structure

The depletion-mode time-dependent dielectric breakdown (DM-TDDB) mechanism was investigated with n-type 4H-SiC MOS capacitors depleted by high-voltage dc bias. Under the DM-TDDB stress, the hole generation beneath the oxide/SiC interface and its injection into the oxide appeared in the current measurement results. The lifetime distribution was clearly divided into two groups: shorter and longer time to breakdown (t
_BD
). The breakdown point for the shorter t
_BD
was located close to a threading dislocation (TD) of the 4H-SiC, whereas the capacitors for the longer t
_BD
contained no dislocation. For the longer tBD, the charge-to-breakdown (Q
_BD
) decreased from approximately 4.5 to 0.1 C/cm
²
with an increase in the electric potential drop (V
_SiC
) below the interface at 503 K, demonstrating that the high-energy-hole injection lowers the lifetime. For the shorter t
_BD
, the TD was presumed to induce the additional hot-hole injection from the deeper depletion region into the local oxide and thereby precipitate the percolation path formation.