The origin of micro-pipe defects was investigated in 6H-type single crystals which had been grown in normal or Si-enhanced atmospheres. The micro-pipe densities were equal to 0 and 22.5/cm2 for typical areas of crystals grown under normal and Si-enhanced atmospheres, respectively. A new technique, involving Vickers indentation, was used to expose an inner surface of a micro-pipe for Auger electron spectroscopic analysis. The results revealed that no specific evidence for Si droplets was to be found at the starting point of the micro-pipes in 6H-type single crystals that were grown in Si-enhanced atmospheres. Although a large number of low-angle boundaries and screw dislocations were observed in the regions around micro-pipes, even for low (1/cm2) micro-pipe densities, the screw dislocation density was of the order of 600/cm2 in other regions. Further investigations suggested that transitively formed Si droplets on the growing surface could be responsible for the generation of micro-pipes. The existence of other micro-pipe formation mechanisms could not be ruled out. The presence of low screw dislocation densities in the representative area showed that it would eventually be possible to produce SiC wafers having a very low density of screw dislocations.

Investigation of the Origin of Micropipe Defect. A.Okamoto, N.Sugiyama, T.Tani, N.Kamiya: Materials Science Forum, 2000, 338-342, 441-4