In this paper we will compare different UVPL imaging systems available on the market in terms of UV excitation parameters and their PL detectors and discuss their defect detection capabilities. We will present the visibility of structural defects in substrates and epiwafers with regard to their defect-specific PL wavelength as well as excitation wavelength and intensity. SiC epiwafers can be optically stressed by using high excitation intensity, i.e. the conversion of basal plane dislocations to stacking faults can be provoked in unprocessed material as shown in figure 1. This “optical stress test” can be used for material quality testing prior to device processing as well as for scientific questions such as the velocities of dislocations. Furthermore, we will present UVPL images of partially processed SiC wafers revealing technologically induced structural defects. In case of 6.5 kV PIN diodes, the UVPL measurements allow even for prediction of bipolar device degradation.
UVPL imaging provides fast, non-destructive defect characterization on full-wafer area and allows for targeted process optimization in epitaxial growth and device processing as well as for process control measurements. Defects can be tracked from substrate/epiwafer to different stages of device production. Hence, UVPL imaging is of great importance for cost reduction and reliability improvement of SiC power electronic devices.