Numerical simulation of birefringence imaging for threading dislocations in 4H-SiC wafers

Abstract

Silicon carbide (SiC) offers superior physical properties for power device applications. Particularly in its 4H-SiC form, it has outstanding availability of high-quality wafers and further exceptional material characteristics. However, crystalline defects in SiC wafers can degrade their performance. Threading dislocations are the defects of particular interest because of their potential impact on power devices. Birefringence imaging is a promising non-destructive technique that visualizes dislocation-induced stress fields, exploiting the piezooptic effect of the stress fields. Nevertheless, it is difficult to theoretically calculate the birefringence effect of dislocations in crystals because of the complexity of the induced changes in optical properties. This study proposes a numerical simulation model for birefringence imaging of threading dislocations in 4H-SiC wafers to overcome these challenges. In this model, the wafer is discretized into microvolume elements, with light propagation and polarization changes simulated using the composition of Jones matrices. The proposed model accurately reproduces experimental birefringence images, allowing detailed analysis of dislocation characteristics from polarized imaging. Similar considerations can extend this theory to other SiC polytypes than 4H-SiC. This simulation model enables the assessment of dislocation features and improves device performance, productivity, and reliability by addressing the underlying causes of defects.