WALK-OUT PHENOMENA IN 6H-SIC MESA DIODES WITH SIO2 SI3N4 PASSIVATION AND CHARGE TRAPPING IN DRY AND WET OXIDES ON N-TYPE 6H-SIC/

The drift or ''walk-out'' of the breakdown voltage in 6H-SiC mesa diod es passivated by a double layer of 1000 Angstrom SiO2 and 3000 Angstro m Si3N4 was stud:ed and related to the charge trapping in the oxide. T he first-order trapping kinetics using four distinct electron traps wi th trapping cross-sections in the range 10(-16) to 10(-19) cm(2) were found to best describe the breakdown voltage drift curves. The wet oxi de trapping cross-sections are 2 to 10 times larger compared to the dr y oxide ones, resulting in about one order of magnitude faster chargin g of the traps. No significant differences in the amount of drift and saturation level of breakdown voltage were found between the different passivations. The influence of UV illumination, supplied by a HeCd la ser with wavelength 325 rim, on the walk-out characteristics and on th e reverse current was also Investigated. The build-up of the surface s tares was observed in wet oxide under UV illumination and DC stress. T he results are consistent with the coexistence of large concentrations of positive charge and acceptor type deep interface electron traps. T he walk-out is a result of the acceptor states being filled by hot ele ctrons supplied by the mechanism of avalanche injection. The suitabili ty of the walk-out measurements as a tool for characterisation of the charge trapping properties of the passivation is demonstrated. (C) 199 8 Elsevier Science Ltd. All rights reserved.