Studies of Relaxation Processes and Basal Plane Dislocations in CVD Grown Homoepitaxial Layers of 4H-SiC

It is well known that basal plane dislocations (BPDs) that are replicated from Physical Vapor Transport (PVT) grown 4H-SiC substrates into Chemical Vapor Deposition (CVD) grown homoepitaxial layers can have a detrimental effect on device performance by inducing the expansion of Shockley faults in the epilayer which cause forward voltage drop.  As a result, significant advances have been made in engineering the processes by which BPDs are replicated into the epilayer. For example, the conversion of BPDs into less harmful threading edge dislocations (TEDs) at the substrate/epi interface can be enhanced by direct etching of the substrate surface intersections of the BPDs or by growth interrupts which induce etching. Conversion rates of BPDs into TEDs during epilayer growth have been studied in this paper. Secondly, the behavior of BPDs which are replicated into the epilayer has been studied using Synchrotron White Beam X-ray Topography (SWBXT), Monochromatic Beam X-ray Topography (SMBXT), KOH etching and other techniques on pre- and after- epilayer growth of the same substrate. It is observed that dislocation loops inside substrate can move towards interface and then produce interfacial dislocations (IDs) and half-loop arrays (HLAs) under certain growth conditions during homoepitaxy growth 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. Thirdly, we report on both interfacial dislocations and HLA’s generated from: (a) surface sources of BPDs; (b) micropipes; (c) 3C inclusions; and (d) substrate/epilayer interface scratches.It is also observed that some dislocations glide past the interface and into the substrate. This will also be discussed.