Off c-Axis Bulk Crystal Growth of Silicon Carbide

The development of a process to produce bulk silicon carbide (SiC) boules with alternate crystallographic orientations, specifically the a-orientation, which is perpendicular to the normally-grown c-orientation crystal, offers significant improvements inthe SiC semiconductor electronic properties. Specifically, the electron mobility will increase by a factor of five for 4H-SiC, and the thermal conductivity will improve by a factor of 1.25. In addition to increments in the above key material properties,the nature of defects present in the a-face material are expected to be markedly different from those in c-face wafers; for example, the device-killing micropipes are expected to be absent in a-face wafers. Further, the availability of a-face wafersproduced by a bulk growth process will significantly add to the versatility of SiC as a high temperature and high power electronic material. The improvements in material properties are expected to result in SiC-based devices with greatly improvedcharacteristics and performance. In the Phase I SBIR program, the feasibility of growing SiC boules seeded from an a-orientation wafer was convincingly demonstrated. The objective of the proposed Phase II program is to take the Phase I demonstration ofthis radical approach to the systematic development of a process to produce a -orientation bulk crystals of approximately 35 mm in diameter and to improve the material quality. Further, in Phase II, the a-face growth process will be optimized for costeffectiveness, yield, and crystal quality, especially a significant improvement in polytype homogeneity, to develop a commercial product. Further, the wafers derived from the boules will be characterized for micropipes and other defects.