SIC SEEDED CRYSTAL-GROWTH

The availability of relatively large (30 mm) SiC wafers has been a pri mary reason for tile renewed high level of interest in SiC semiconduct or 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 pol ytypes are available, however, the micropipe defects that occur to a v arying extent in all wafers produced to date are seen by many as preve nting the commercialization of many types of SiC devices, especially h igh 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 th e magnitude of the Burgers vector. Our results show that there are sev eral mechanisms or combinations of these mechanisms which cause microp ipes in SiC boules grown by the seeded sublimation method. Additional considerations such as polytype variations, dislocations and both impu rity and diameter control add to the complexity of producing high qual ity wafers. Recent results at Cree Research, Inc., including wafers wi th micropipe densities of less than 1 cm(-2) (with 1 cm(2) areas void of micropipes), indicate that micropipes will be reduced to a level th at makes high current devices viable and that they may be totally elim inated in the next few years. Additionally, efforts towards larger dia meter 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 h ave 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.