Quantitative comparison between dislocation densities in offcut 4H-SiC wafers measured using synchrotron X-ray topography and molten KOH etching

Molten KOH etching and x-ray topography have been well established as two of the major characterization techniques used for observing as well as analyzing the various crystallographic defects in both substrates and homoepitaxial layers of silicon carbide. Regarding assessment of dislocation density in commercial wafers, though the two techniques show good consistency in threading dislocation density analysis, significant discrepancy is found in the case of basal plane dislocations (BPDs). In this paper we compare measurements of BPD densities in 4-inch 4H-SiC commercial wafers assessed using both etching and topography methods. The ratio of the BPD density calculated from topographic images to that from etch pits is estimated to be larger than 1/sinθ, where θ is the offcut angle of the wafer. Based on the orientations of the defects in the wafers, a theoretical model is put forward to explain this disparity and two main sources of errors in assessing the BPD density using chemical etching are discussed.