Failure analysis of high-voltage power MOSFET in the three phase inverter

This paper presents a failure analysis procedure on a power MOSFET in a three phase inverter. The analyzed power MOSFET has been obtained from a chopper leg in a three phase inverter when an anomalous failure is detected. At first, the X-ray microscope is utilized to inspect the failed device. A hint of the burn-out area in the chip is observed in the cross-section X-ray microscopy image. After that, the device is decapped and the internal chip is inspected. Two burn-out cavities, together with some cracks and melted areas are observed on the silicon chip. The signature of the burn-out cavities suggests that the device failure is induced by the current filamentation induced by high operation temperature. Thanks to the Scanning Acoustic Microscope (SAM) analysis, large void spot was found in the solider layer. This indicate that the device's high operation temperature is due to the degradation of the solider layer.