Mechanisms of metallization degradation in high power diodes

Under operation the topside metallization of power electronic chips is commonly observed to degrade and thereby affecta device's electrical characteristics. However, the mechanisms of the degradation process and the role of environmental factors are not yet fully understood. In this work, we investigate the metallization degradation by passive thermal cycling of unpackaged high-power diode chips in different controlled atmospheres. The electrical degradation of the metallization is characterized by sheet resistance measurements, while the microstructural damage is investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). To study the evolution of the chemical composition of the metallization, energy dispersive X-ray spectroscopy (EDX) is also applied. Since the degradation depends on the initial microstructure of the metallization, the film texture and grain size distribution is determined using electron backscatter diffraction (EBSD). The obtained data show that the type of atmosphere plays a minor role in the degradation process, with a slight tendency that cycling in dry nitrogen atmosphere accelerates the degradation compared to the experiments in ambient atmosphere with a controlled relative humidity of 50 and 95%.