Investigation of Dislocation Behavior during Bulk Crystal Growth of SiC

Abstract

Dislocation behavior during physical vapor transport (PVT) growth of silicon carbide (SiC) single crystals has been investigated by defect selective etching and transmission electron microscopy (TEM). It was found that foreign polytype inclusions introduced a high density of basal plane dislocations at the polytype boundary, while in the polytype-transformed areas of the crystal, the density of medium size hexagonal etch pits due to threading screw dislocations was significantly reduced, indicating that the polytype transformation tended to cease the propagation of threading screw dislocations. Oval-shaped etch pit arrays observed on the etched vicinal (0001)Si surface, indicative of the dislocation multiplication in the basal plane, showed characteristic distribution around micropipes and low angle grain boundaries. Based on the results, we have argued dislocation behavior in PVT grown SiC crystals, suggesting that dislocation interaction and conversion are relevant processes to understanding the behavior. EXPERIMENTAL4H-SiC single crystals were grown by the physical vapor transport (PVT) growth (modified-Lely) method on a 4H-SiC (0001 -)C seed crystal. The growth conditions employed in this study were almost the same as those previously described [1], and the crystals were nitrogen-doped. The grown crystals were sliced approximately perpendicular to the growth direction into (0001)Si wafers off-oriented toward [11 -00] or [112 -0].Chemical wet etching in molten KOH was used to reveal the types and distribution of

Etching study of dislocations in heavily nitrogen doped SiC crystals

“…However, some dislocations disappeared or emerged, which can be explained by inter-conversion between threading and basal plane dislocations. TEM studies by Ohtani et al [10] showed some TEDs converted into BPDs during PVT growth of SiC. Nakamura et al [11] suggested that all types of threading and basal plane dislocations are capable to combine, dissociate and convert from one type into another.…”

Propagation and Density Reduction of Threading Dislocations in SiC Crystals during Sublimation Growth

“…The experimental measurement of dislocation density typically covers a range from a fraction of millimeter to a few centimeters, which corresponds to the region with steady slope in the simulation (10 2 to 10 6 steps). These differences may explain the discrepancies reported in the literature [7]. Each step in the calculation corresponds to the increase in the crystal thickness that allows a threading dislocation to transverse a maximum distance of D m .…”

Polytype inclusions and polytype stability in silicon-carbide crystals

“…CONTROLLED CHANGE IN THE POLYTYPE DURING GROWTH Technological parameters of the growth process can give rise both to the appearance of polytype inclusions and to a complete change in the growing polytype. It is known that transformation of the polytype leads to a stop in the propagation of threading screw dislocations already present in the crystal by varying the defect structure in the ingot [11,2]. In addition, a programmed change in the polytype can basically form (on the basis of silicon carbide) so-called heteropolytype compositions, i.e., unstressed epitaxial structures, including those with a two-dimensional electron gas [57,58].…”

“…In particular, cracking, the appearance of regions with a high density of micropores (penetrating extended defects with a hollow core) and dislocations [10,11] are from time to time observed at the boundaries of polytype inclusions. Thus, prevention of the appearance of polytype inclusions in SiC ingots is a priority tasks in the technology of this material.…”