Characterization and formation mechanism of six pointed star-type stacking faults in 4H-SiC

Synchrotron white-beam x-ray topography (SWBXT) studies of defects in 100-mm-diameter 4H-SiC wafers grown using physical vapor transport are presented. SWBXT enables nondestructive examination of thick and large-diameter SiC wafers, and defects can be imaged directly. Analysis of the contrast from these defects enables determination of their configuration, which, in turn, provides insight into their possible formation mechanisms. Apart from the usual defects present in the wafers, including micropipes, threading edge dislocations, threading screw dislocations, and basal plane dislocations, a new stacking fault with a peculiar configuration attracts our interest. This fault has the shape of a six-pointed star, comprising faults with three different fault vectors of Shockley type. Transmission and grazing topography of the fault area are carried out, and detailed contrast analysis reveals that the outline of the star is confined by 30 Shockley partial dislocations. A micropipe, which became the source of dislocations on both the basal plane slip system and the prismatic slip system, is found to be associated with the formation of the star fault. The postulated mechanism involves the reaction of 60 dislocations of a/3 〈̄2110〉 Burgers vector on basal plane and pure screw dislocations of a/3 〈11̄20〉 Burgers vector on prismatic plane and cross slip of the partial dislocation from prismatic plane to basal plane leading to expansion of the faults.