FORMATION OF MACRODEFECTS IN SIC

4H- and 6H-SiC boules have been grown by a sublimation process in a RF-heated system. A temperature gradient transports the material from source to the seed which is positioned at the coolest place of the crucible. The single-crystalline boules sometimes have macrodefects in the region of the seed. These defects are hexagonal tubelike cavities (we call them channels) with a diameter of 10 to 50 micrometers and a length up to some millimeters. These channels are parallel to the growth direction. They start at the seed and end with an enlargement of the hollow. Several possibilities of formation of such hollows are discussed. The experimental results showed that they are probably originated by secondary evaporation of SiC after the crystal has been grown.