Development of a World Class Silicon Carbide Substrate Manufacturing Capability

Silicon carbide (SiC) semiconductor substrates provide the foundation for revolutionary improvements in the cost, size, weight and performance of a broad range of military and commercial radio frequency (RF) and power switching devices. Due to the lack of a viable, native gallium nitride (GaN) substrate, semi-insulating (SI) SiC substrates are the substrate of choice for high power AlGaN/GaN High Electron Mobility Transistors (HEMTs) due to their near lattice-match to GaN, superior thermal conductivity and commercial availability. GaN has emerged as the technology of choice for RF power because of its superior output power capability compared to other semiconductors. Similarly, semi-conducting (N+) SiC substrates are required for fabrication of high voltage Schottky Diodes and Metal Oxide Semiconductor Field Effect Transistor (MOSFET) power switching devices. Critical to this realization is the availability of affordable, high quality, large diameter SI and N+ SiC substrates for production of GaN and SiC power semiconductors. SiC is unique in that bulk single crystals cannot be grown via traditional melt-based manufacturing processes such as Czochralski. Rather, a high temperature sublimation process is required. In the late 1980's, pioneering physical vapor transport research taking place at North Carolina State University ultimately led to the formation of Cree Research and subsequently the wide bandgap semiconductor industry. U.S. Department of Defense investment in wide bandgap semiconductor development has easily exceeded $1B spawning the creation of an entirely new industry. During the early 1990's, SiC physical vapor transport growth development was fraught with perceived insurmountable technical challenges associated with micropipes, polytype conversion, diameter expansion and crystalline defects. Despite these monumental crystal growth technology hurdles, SiC substrates are now manufactured at a cost and quality never thought possible. This article highlights more than 20 years of Air Force Research Laboratory (AFRL) sponsored development with II-VI aimed at positioning itself as a merchant, world-class manufacturer of SiC substrates.