SiC Seeded Crystal Growth

Abstract

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.

High-Temperature Electronics in Europe

“…The material resistivity at room temperature can be estimated by high temperature resistivity measurements and was determined to be in the range of lO*-*« cm. Semi-insulating 4H-SiC crystals with comparable resistivities have also been reported (Tsvetkov, et al 1995;Glass, et al 1997).…”

Elastic Interaction of Micropipes in Crystals

“…To calculate w 1 and w 2 , we note that in the case b 1 ¼ Àb 2 the stress field (17) and (18) reduces to that of two image dislocations, b 1 and Àb 1 , at the points x ¼ w 1 and x ¼ w 2 , respectively. Such a stress field meets the free-traction boundary conditions at the free surfaces if the positions w 1 and w 2 of the image dislocations obey the relations [38]: w 1 w 2 ¼ r 2 1 and ðd À w 1 Þðd À w 2 Þ ¼ r 2 2 .…”

“…Their formation is attributed to different factors. One of them is the presence of large thermal stresses that act upon epitaxial film deposition [18,19]. Alternatively, micropipes can nucleate in the course of crystal growth at inclusions [20], voids [20,21] or surface steps [20,22].…”

Numerical simulation of the flow field and concentration distribution in the bulk growth of silicon carbide crystals

“…Large size bulk SiC crystals are commonly grown by the physical vapor transport (PVT) method [2][3][4][5][6][7][8]. The bulk growth process is associated with many important physical phenomena, such as electromagnetic field, radio frequency (RF) induction heating, conduction and radiation heat transfer, sublimation and condensation, mass transfer and so on.…”