Synchrotron X-ray Topography Studies of Dislocation Behavior During Early Stages of PVT Growth of 4H-SiC Crystals

摘要

With the increasing attention of 4H-silicon carbide (4H-SiC) crystals in the applications of high-power electronics, it has become necessary to further improve the development of the 4H-SiC crystal growth process, especially the initial stage of physical vapor transport (PVT) growth, which is a critical step to obtain high quality SiC crystals with polytype stability and low dislocation density. This paper describes a study on dislocation behavior of large diameter 4H-SiC crystals at the early stages of PVT growth. Synchrotron x-ray topography is applied to 6-inch PVT-grown crystals with a thickness of several hundred microns on 4H-SiC seeds. Grazing-incidence topographs in g = 11 (2) over bar8 and g = 1 (1) over bar 09 recorded from both the seed crystal and newly grown layer show the presence of screw-type basal plane dislocations (BPDs) with b = 1/3[11 (2) over bar0] at the inner region of the wafers, which is further confirmed by comparing with ray tracing simulated images of these dislocations. Their origins are likely from deflection of threading edge dislocations (TEDs) onto the basal plane by the overgrowth of macro-steps. Pairs of threading screw/mixed dislocations (TSDs/TMDs) are found to be newly generated at the initial growth stage and some are deflected onto the basal plane. A high density of newly generated TEDs is observed in the early-grown crystals, which are either nucleated in pairs at the seed/crystal interface or converted from BPDs in the seed crystal. Furthermore, dislocations with unique shapes are observed and found to be associated with deflection of TMDs and TEDs, which become the major source for BPD generation during the early PVT growth stage. Possible models to explain their formation mechanism are developed.