Micropipes and the closure of axial screw dislocation cores in silicon carbide crystals

Micropipes in 6H, 4H, and 15R-SiC semiconductor wafers were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The screw dislocations intersecting wafers surface were located by etch pitting, and their Burgers vectors determined by x-ray topography. The etch pits were eroded into smooth craters by ion milling to expose levels of dislocation line from inside the samples bulk, so that the micropipes diameters were removed from the influence of prior surface treatments and surface relaxation effects. The bases of these craters were examined by SEM and AFM to determine whether hollow dislocation cores (micropipes) were present. In the case of 6H-SiC, hollow cores were never observed at the base of the craters whose screw dislocations had Burgers vectors of magnitude two multiples of the c-lattice parameter or less. In the 4H polytype, most 3c screw dislocations displayed hollow cores, but one was observed that did not. All axial screw dislocations in 15R-SiC crystals, because of this polytypes larger c-lattice parameter, had hollow cores.