Materials Science Forum Vols. 821-823

Abstract: Solution growth of SiC has attracted significant attention due to its potential for the production of high-quality SiC wafers. We have recently investigated the dislocation propagation behavior during SiC solution growth with the aim of reducing the dislocation density. Threading dislocations were found to be converted to defects on the basal planes during solution growth. Utilizing this dislocation conversion phenomenon, we have proposed a dislocation reduction process during solution growth and achieved high-quality 4H-SiC crystal growth. Here we confirm the potential of SiC solution growth for the production of high-quality SiC wafers.

Abstract: We have investigated the solution growth under various Al-N co-doping conditions. Both p-type and n-type 4H-SiC were successfully grown under Al-N co-doping conditions, while using the effect of Al-addition to stabilize both growth surface and polytype. The doping and electrical properties were investigated systematically. Interaction between Al and N in the incorporation process and electrical property under heavily co-doped conditions were discussed.

Abstract: In solution growth of 4H-SiC, we have investigated changes in macrostep height with addition of the Group III (B, Al, Ga), Group IV (Ge, Sn), Group V (N) elements, and transition metals (Ti, V, Cr, Ni) to Si solvents, in order to find additives improving severe step bunching which often occurs during growth. The addition of Al, B, Sn, N, and V decreased the average macrostep height compared with the crystal grown with Si solvents. The addition of Al, B, Sn, N, and V suppressed the generation of trench-shaped surface defects in long-term growth of 10 hours. This result demonstrated that the addition of Al, B, Sn, N, and V has an advantage to achieve high quality bulk crystal growth from solution.

Abstract: We achieved the convex growth interface shape in top-seeded solution growth of SiC applying non-axisymmetric solution convection induced by non-axisymmetric temperature distribution. The detailed solution flow, temperature distribution and carbon concentration distribution were calculated by 3-dimensional numerical analysis. In the present case, the solution flow below the crystal was unidirectional and the supersaturation was increased along the solution flow direction. By the rotation of the crystal in the unidirectional flow and the temperature distribution, we successfully obtained the crystal with the convex growth interface shape.

Abstract: In this paper, we will discuss how to cope with the smoother growth front and higher growth rate by the forced convection. When the rotation rate of the upper part of the solution is different from that of the lower part in the crucible, the centrifugal force of the upper part is different from that of the lower part. As a result, a forced convection occurs in the solution. This kind of convection was achieved with accelerating/decelerating rotation of crucible and a plate fixed on the bottom of the crucible. By optimizing conditions of rotation program patterns and the crucible design for the forced convection, the growth rate could almost be doubled while maintaining smooth morphology.

Abstract: The off-axis solution growth of 4H-SiC was studied focusing on the morphological instabilities by using conventional TSSG technique. The morphology depends strongly on the crystalline polarity, and that on Si surface can be characterized by wandering while that on C surface is characterized by strong step-bunching. By raising the temperature gradient, step bunching on Si surface is considerably suppressed which can be consistent to the constitutional super cooling scheme. However, C surface exhibits strong step bunching as the temperature gradient increase. These behaviors can be explained by the difference in Ehrlich-Schwoebel barrier and diffusion behavior of adatoms.

Abstract: The solution growth of SiC on an off-axis seed is effective on the reduction of threading dislocations. We proposed a novel method to grow a SiC crystal on an off-axis seed by top-seeded solution growth (TSSG). In our previous study, a unidirectional solution flow above a seed crystal is effective to suppress surface roughness in the growth on the off-axis seed. However, it is difficult to apply the unidirectional flow in an axisymmetric TSSG set-up. In this study, the unidirectional flow could be achieved by shifting the rotational axis away from the center of the seed crystal. As a result, the smooth surface was obtained in the wider area where the solution flow direction was opposite to the step-flow direction.

Abstract: The influences of solution flow and lateral temperature distribution on the surface morphology of the 4H-SiC single crystal grown from solution was investigated. A flat surface region was enlarged by the seed-rotation rate. The solution flow simulation indicated that the higher rotation rate made the outward solution flow ordered beneath the solution surface. Such a solution flow was thought to be effective to enlarge the flat region of growth front. Furthermore, a full-flat surface was obtained with a hollow-type graphite rod at a seed-rotation rate of 60 min^-1. The simulated results of temperature distribution showed the hollow-type graphite rod reduced the lateral temperature gradient at the SiC-solution interface. The ordered solution flow and the small temperature gradient at the growth front were found to be effective to make the growth front flat in the solution-growth method.

Abstract: Surface morphology of the SiC crystal grown on the C face of the 4H-SiC seed crystal by TSSG method using pure Si, Si-1at%Ti-C, Si-5at%Ti-C and Si-20at%Ti-C solvents was investigated. The surface morphology of the crystal grown from pure Si solvent was smooth. By the addition of Ti to the solvent, the surface morphology became rougher. The RMS value is not proportional to the concentration of Ti. The formation of macrosteps with several micrometers was observed when the addition of Ti increased to 5at% indicating the possibility of the threading screw dislocation conversion on the C face of the 4H-SiC crystal.