Synchrotron White Beam X-ray Topography (SWBXT) is a powerful and versatile technique that enables rapid and non-destructive imaging of defects in thick and large-diameter wafers. Analysis of defect contrast facilitates determination of their configuration which, in turn, provides insight into their possible formation mechanisms. Here, we demonstrate the capabilities of SWBXT through the detailed characterization of a distinctive stacking fault pattern observed in 4H-SiC wafers. This fault has a shape of a six-pointed star comprised of rhombus-shaped stacking faults with three different fault vectors of the Shockley type. Transmission and grazing topography analysis reveals that the outline of the star is confined by 30° Shockley partial dislocations. Formation of the star fault is found to be associated with a micropipe at its center. It is well known that micropipes in SiC can act as nucleation sites for dislocation half-loops belonging to the primary basal (1/3<11-20> (0001)) slip system [1,2]. Occasionally, similar nucleation of slip on the secondary prismatic (1/3<11-20>{1-100}) slip system has also been reported [3,4]. In this case, the nucleation of the rhombus-shaped Shockley type stacking faults on the basal plane involves the reaction of 60° dislocations of a/3<-2110> Burgers vector on the basal plane and pure screw dislocations of a/3<11-20> Burgers vector on the prismatic plane and cross slip of the partial dislocation from prismatic plane to basal plane leading to the expansion of the faults [5]. The formation mechanism involves the operation of a double-ended Frank-Read partial dislocation source. Details of this mechanism will be discussed and we shall show that in the limit, this glide and cross-slip mechanism can lead to 4H to 3C polytype transformation in the vicinity of the micropipe by a mechanism similar to that proposed by Pirouz [6].

References:

[1] W. Vetter, Characterization of dislocation structures in silicon carbide single crystals, Ph.D. Thesis, Stony Brook University (1999).

[2] Jinwei Yang, SiC: Problems in Crystal Growth and Polytypic Transformation, Ph.D. Thesis, Case Western Reserve University (1993).

[3] S.Ha, N. T.Nuhfer, G. S.Rohrer, M. De Graef, M. Skowronski, J. Electron. Mater., vol. 29 L5-L8 (2000)

[4] H. Wang, S. Byrappa, F. Wu, B. Raghothamachar, M. Dudley, E. K. Sanchez, D. Hansen, R. Drachev, S. G. Mueller and M. J. Loboda, Mater. Sci. Forum, vols. 717-720, pp. 327-330, (2012).

[5] F. Wu, H. Wang, S. Byrappa, B. Raghothamachar, M. Dudley, P. Wu, X. Xu, I. Zwieback, J. Electron. Mater., doi: 10.1007/s11664-012-2379-9, (2012)

[6] P. Pirouz and J. W. Yang, Ultramicroscopy 51, 189-214 (1993)

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