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The availability of relatively large (30 mm) SiC wafers has been a primary reason for the renewed high level of interest in SiC semiconductor technology. Projections that 75 mm SiC wafers will be available in 2 to 3 years have further peaked this interest. Now both 4H and 6H polytypes are available, however, the micropipe defects that occur to a varying extent in all wafers produced to date are seen by many as preventing the commercialization of many types of SiC devices, especially high current power devices. Most views on micropipe formation are based around Frank's theory of a micropipe being the hollow core of a screw dislocation with a huge Burgers vector (several times the unit cell) and with the diameter of the core having a direct relationship with the magnitude of the Burgers vector. Our results show that there are several mechanisms or combinations of these mechanisms which cause micropipes in SiC boules grown by the seeded sublimation method. Additional considerations such as polytype variations, dislocations and both impurity and diameter control add to the complexity of producing high quality wafers. Recent results at Cree Research, Inc., including wafers with micropipe densities of less than 1 cm—2 (with 1 cm2 areas void of micropipes), indicate that micropipes will be reduced to a level that makes high current devices viable and that they may be totally eliminated in the next few years. Additionally, efforts towards larger diameter high quality substrates have led to production of 50 mm diameter 4H and 6H wafers for fabrication of LEDs and the demonstration of 75 mm wafers. Low resistivity and semi‐insulating electrical properties have also been attained through improved process and impurity control. Although challenges remain, the industry continues to make significant progress towards large volume SiC‐based semiconductor fabrication.

Synchrotron white-beam X-ray topography studies, in conjunction with Nomarski optical microscopy, have been carried out on 6H-SiC single crystals grown by the sublimation physical vapour transport technique. Two kinds of dislocations were observed using topography: dislocations exhibiting bimodal images of various widths and with line directions approximately parallel to the (0001) axis and dislocations confined to the basal plane, which appear to have emanated from the former dislocations. The larger bimodal image width dislocations were found to have hollow cores, known as 'micropipes'. Detailed contrast analysis of topographic images obtained in transmission and back-reflection geometries establishes that 'micropipes' are Frank-type hollow-core screw dislocations with Burgers vectors typically equal to 3-7 times the c lattice parameter. X-ray topography also revealed many line defects approximately parallel to the (0001) axis that were determined to be screw dislocations with Burgers vectors equal to the c lattice parameter and there were no discernible 'micropipes' associated with these latter screw dislocations.