Materials Science Forum Vol. 1157

Abstract: At the high growth temperatures of the PVT method, thermal radiation from the graphite crucible surface to the seed region is the dominant mode of heat transfer. In this study, we propose a newly designed crucible structure with a thinner graphite wall compared to the conventional design for SiC crystal growth. The SiC ingot grown using the conventional crucible exhibited the smallest thickness variation (flat top surface) between the center and the edge of the ingot, accompanied by polytype inclusions, which led to an increase in defect density. In contrast, SiC ingots grown using the newly designed crucibles (Design A and Design B) showed a convex top surface and a significantly lower defect density due to the improved heat transfer efficiency. Thinning the graphite crucible wall helps maintain a relatively higher temperature at the seed edge region, thereby effectively enhancing thermal radiation in the radial direction inside the crucible. These results indicate that thermal radiation in the radial direction can be achieved through appropriate optimization of the graphite wall thickness.

Abstract: Thermoelastic stress generated within SiC crystals during the cooling process can induce various types of dislocation defects. In this study, a newly designed cooling protocol was proposed to investigate the correlation between cooldown rate and defect formation in 4H-SiC single crystals. Three distinct cooldown rates, 10~30 °C/min, 1~5 °C/min, and less than 1 °C/min, were applied to assess their impact on the development of thermoelastic stress and resulting crystal quality. Notable variations in ingot color and surface morphology were observed depending on the applied cooldown rate. Dislocation types, including basal plane dislocations (BPDs), threading edge dislocations (TEDs), and threading screw dislocations (TSDs), were quantified through etch pit density (EPD) measurements after molten KOH etching at 600 °C for 14 minutes. The results indicate that higher cooldown rates led to an increase in BPD density due to enhanced plastic deformation, while lower cooldown rates resulted in higher TED and TSD densities, likely due to increased thermal stress. These findings demonstrate that precise control of the cooldown rate is critical for suppressing thermoelastic stress and minimizing defect densities in SiC crystal growth.