Development of a World Class Silicon Carbide Substrate Manufacturing Capability

John Blevins, Air Force Research Laboratory (AFRL), Wright-Patterson AFB, OH

Silicon carbide (SiC) semiconductor substrates are 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 presently 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 gallium arsenide.  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 1980s, 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 semiconductors, since the early 1990s, has easily exceeded $1B spawning an entirely new industry. The early days of SiC physical vapor transport growth research were fraught with perceived insurmountable technical challenges associated with micropipes, doping, polytype conversion, diameter expansion and crystalline defects. Despite this monumental crystal growth, technology hurdles, SiC substrates are presently manufactured at a cost and quality never thought possible. This paper highlights more than 20 years of AFRL sponsored development with II-VI aimed at positioning itself as a world-class manufacturer of SiC substrates.

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