(Invited) Growing Large Diameter 4H SiC Boules – Furnace, PVT Growth and Characterization

Silicon carbide (SiC) is a semiconductor material which is replacing and outperforming the conventionally used silicon crystal in power applications. The wide bandgap of SiC results in a low leakage current even at high temperatures. SiC single crystals are also becoming popular as Mossanite gem stones competing with diamond because of their excellent brilliance and other properties. However, at present, the production of large size and high quality 4H SiC single crystals is limited to a few industrial entities worldwide. The seeded physical vapor transport (PVT), commonly known as the modified Lely method, which exploits the sublimation at above 1800°C is the only proven method for the industrial production of SiC boules. However, fabrication of the PVT system for the growth of SiC is highly instrumentation oriented, and also due to its commercial importance, the know-how, and technical details are scarcely available in the literature. The complexity is due to the fact that the operating temperatures are extreme (2100–2500°C) and monitoring and controls are difficult. The growth process occurs in a nearly air-tight graphite crucible and it is not feasible to observe the growing boule or determine experimentally the exact thermal conditions in the growth zone due to high operating temperatures and the opacity of the graphite crucible. Seed mounting technologies are critical, and it is still kept as the industry secret. It is difficult to control the radial gradients when the diameter reaches close to 6 inches or beyond. With full modeling knowledge as well as outstanding expertise in equipment and the process technology, Aymont has developed precisely controllable SiC growth systems and process for growing large boule with independently controllable axial as well as radial gradients. The technical details on the design and fabrication of the SiC PVT system, hot zone, modeling, crystal growth and characterization results are presented.