An abnormal star-like defect was found on the failed SiC gate turn-off thyristor (GTO)\ndevices after metal removal and KOH etching at 450 degreeC in this work. It is of extraordinary larger size\nof 210â??580 microm, even much larger than the etch pit of a micropipe in 4H-SiC. In addition, the abnormal\nstar-like defect, exhibiting the consistent orientation with the six-fold symmetry of silicon carbide, was\nfound to consist of several penetrating dislocations with the help of a LEXT OLS4000 3D laser confocal\nmicroscope. These abnormal star-like etch pits can severely reduce the forward blocking characteristic\nof GTOs, while exerting insignificant influence on the forward current-voltage characteristics between\nanode and gate electrode of the 4H-SiC GTO devices. Interestingly, the relationship between forward\nvoltage drop and dislocation density is affected by the abnormal star-like defect. A regular increase of\nforward voltage drop at 100 A/cm2 was observed with the increasing dislocation density, while this\ncorrelation disappears in the presence of an abnormal star-like defect.
Loading....