In this work, body diode stress has been carried out for 1700 V 25 mΩ planar SiC MOSFETs. The epitaxial wafers were mapped with Infra-Red photoluminescence (IR-PL) to determine and localize the exact number of basal plane dislocations present in the drift layers of each die. The SiC MOSFETs were then packaged in groups with individual BPD counts in different bins ranging from 0 up to more than 30 per device. Pulsed body diode measurements with high currents of 250-400 A (about 1000-1600 A/cm2) were then performed with electrical characterization before and after to check for drift in key electrical parameters. Significantly increased RDSon was found after high current stress from about 300 A for devices with BPDs. A physical analysis of the degraded devices by backside electroluminescence show the presence of several trapezoid-shaped patterns indicating the occurrence of bipolar degradation.
Bipolar degradation is a known problem in the development of SiC MOSFETs when the body diodes (p+ body/ n-drift layer) are forward biased. Mostly higher voltage classes like the 1.7 kV or 3.3 kV SiC MOSFETs have been studied in literature resulting with significant Rdson increase [1-2]. In this work, body diode stress was conducted for 1.2kV SiC MOSFETs, which were mapped with Infra-Red photoluminescence (IR-PL) to determine and localize the exact number of BPDs present in the drift layers of each die [3, 4] and grouped by this criterion. Devices were stressed at extremely high current densities (1200 – 1700 A/cm2) under pulsed conditions. The post-stress analysis shows non-negligible increase of Rdson and Vf. Bipolar degradation occurring from stressing the body diodes at high forward current densities was confirmed by electroluminescence analysis.
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