4H-SiC commercial wafers and sublimation grown epitaxial layers with a thickness of 100µm were studied concerning crystalline structure. The substrates and the epitaxial layers were separately investigated by high-resolution X-ray diffraction and synchrotron white beam X-ray topography. The results showed that the structural quality was improved in the epitaxial layers in the [11•0] and [¯11•0] directions, concerning domain distribution, lattice plane misorientation, mosaicity, and strain, compared with the substrates. Misoriented domains have merged together to form larger domains while the tilt between the domains was reduced, which resulted in non-splitting in diffraction curves. If the misorientation in the substrate was large, only a slight decrease in the misorientation of the epilayer was seen. At some positions on the substrates block structures (mosaicity) were observed. Rocking curves showed smaller full width at half maximum values and more uniform and narrow peaks, while the curvature was almost the same in grown epilayers compared with the corresponding substrates. It was shown that threading edge dislocations along the c-axis in SiC grown crystals transform to deflected dislocations in the epilayer. A formation mechanism for deflected dislocations and supporting facts were presented. It was further shown that these deflected dislocations were one possible source for the creation of stacking faults that recently was reported to cause degradation in processed SiC bipolar diodes.

Dislocation Evolution in 4H-SiC Epitaxial Layers. H.Jacobson, J.Birch, R.Yakimova, M.Syväjärvi, J.P.Bergman, A.Ellison, T.Tuomi, E.Janzén: Journal of Applied Physics, 2002, 91[10], 6354-60