Measurement of critical thickness for the formation of interfacial dislocations and half loop arrays in 4H-SiC epilayer via X-ray topography

Synchrotron X-ray Beam Topography (SWBXT) and KOH etching observations are presented of interfacial dislocations (IDs) and half-loop arrays (HLAs) which can form under certain growth conditions during homoepitaxy of 4H-SiC on off-cut substrates. The HLAs and IDs are observed to form from pairs of opposite sign screw oriented basal plane dislocations in the substrate which replicate into the epilayer and glide opposite directions once critical thickness has been exceeded. Critical thickness can be determined by extending the line of the HLA to intersect the original threading dislocation line direction, and then measuring the distance between this point and the ID along the line direction of the original BPD. Calculation shows that the critical thickness in this case is heavily influenced by the mutual attractive force between the pairs of opposite sign threading BPDs in the substrate. In addition we observed both interfacial dislocations and HLA's generated from: (a) surface sources of BPDs; (b) micropipes; (c) 3C inclusions; and (d) substrate/epilayer interface scratches.