Characterization of V-shaped Defects in 4H-SiC Homoepitaxial Layers

Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V-shaped stacking faults in the epilayer. KOH etching of the V-shaped defects reveals small oval pits connected by a shallow trench which correspond to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V-shaped defects prepared using focused ion beam milling show stacking sequences of (85), (50) and (63) at the faulted region using high resolution TEM. In order to study the formation mechanism of the V-shaped defects, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V-shaped defects. Simulation results of the contrast from the two partial dislocations associated with V-shaped defects in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V-shaped defects, which requires elimination of non-sequential c /4[0001] bilayers from the original structure to create the observed faulted stacking sequence.