Commercial wafers and sublimation-grown epitaxial layers of 4H-SiC, with a thickness of 100µm, were studied. The substrates and the epitaxial layers were investigated separately by means of high-resolution X-ray diffraction and synchrotron white-beam X-ray topography. The results showed that the structural quality was improved in epitaxial layers, in the [11•0] and [¯11•0] directions, with regard to domain distribution, lattice-plane misorientation, mosaicity and strain; as compared with the substrates. Misoriented domains had merged together to form larger domains while the tilt between the domains was reduced. This resulted in non-splitting in diffraction curves. If the misorientation in the substrate was large, only a slight decrease in the misorientation in the epilayer could be detected. At some positions on the substrates, block structures (mosaicity) were observed. The ω-rocking curves revealed smaller full-width at half-maximum values and more uniform and narrow peaks, while the curvature was almost the same in grown epilayers as compared with the corresponding substrates. It was shown that threading edge dislocations along the c-axis in grown crystals transformed into deflected dislocations in the epilayer. A formation mechanism was presented for deflected dislocations. It was further shown that these deflected dislocations were one possible source for the creation of stacking faults that had been 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