1.2 SiC Semiconductor Crystal Growth

SiC does not melt due to its high thermal stability, but instead gradually sublimes at the process temperature of typically $1800-2400$$~^{\circ}$C. Therefore, it is impossible to form large single-crystal ingots by pulling a seed crystal from a melt, as in the Czochralski process that produces 200 to 300mm diameter silicon ingots. Instead, SiC crystals are formed by a modified sublimation process that is presently limited to 100mm diameter ingots. The growth rate lies typically at $200-500$$\mu$m/h which is to first order a function of the source temperature, the pressure of inert gas, and the surface area of the source material. During growth, gaseous (N$_{2}$) as well as solid (B, Al, V) dopants can be used to adjust the electrical properties of the growing semiconductor crystal.

The temperature field inside the growth cell determines the interface shape and has an impact on faceting and defect generation. Up to now, all grown SiC crystals exhibit dislocations and micropipes. Lowering the density of these defects is an essential prerequisite for the industrial application as substrate material. Further typical defects in SiC crystals are planar voids, silicon and carbon inclusions, stacking faults and polytype changes. Polytypes form due to the ability of SiC to crystallize in a number of distinct stacking orders which can co-exist in the SiC crystals. The most common polytypes in commercially prepared crystals are 3C, 4H, 6H and 15R, (cf. Subsection 2.1.1) the names respectively reflecting their stacking order.

T. Ayalew: SiC Semiconductor Devices Technology, Modeling, and Simulation