Silicon-Carbide Devices and Technology

SiC JBS Power Diodes For Ultra Low Loss Power Switching Applications

Silicon Carbide is an extremely versatile semiconductor which is receiving renewed attention for use in high temperature, high power, and high frequency circuits. Specific applications include high frequency, high power radar systems, jet ignition systems, turbine engine monitoring and control, spacecraft power conditioning, nuclear power instrumentation, in-cylinder engine sensors, and numerous others. The Air Force is currently pursuing the more electric aircraft, which will replace traditional hydraulic and mechanical systems with lighter, more reliable electronic systems. To achieve this goal without cooling, wide bandgap semiconductor power devices and circuitry must be developed to be placed on fighter aircraft by 2005. Silicon, which becomes intrinsic about 325 degree C, will be unable to handle the high temperature (350 to 500 degree C), and high power requirements for the more electric aircraft application.

Auburn University has been active in Silicon Carbide research since 1989. The research efforts between the Electrical & Computer Engineering and Physics Departments include developing ohmic contacts, epitaxial growth of SiC, oxide/insulator studies, device fabrication and characterization over wide temperature ranges, reactive ion etching of SiC, hybrid SiC circuit fabrication, testing, and design, high temperature, high power, and high frequency packaging, as well as SiC/nitride heterostructure device development. Auburn's primary research partners in SiC are industrial partners in the Center for Commercial Development of Space within the NASA Space Power Institute at Auburn University. A close relationship with companies such as Westinghouse provide Auburn with insight into key problems which must be solved, and the alliance has proven fruitful for both Auburn and its industrial partners.

The progress in SiC development has been astounding. Since Auburn fabricated and tested the world's first SiC hybrid operational amplifier capable of 400 degree C operation in 1992, other research efforts elsewhere have generated monolithic SiC op-amps, 17 stage ring oscillators, digital logic gates (NAND, NOR, Inverter), flip-flops, and other circuits which have all been operated above 300 degree C. In addition power device development continues, with 1 A, 375 V thyristors operating up to 500 degree C demonstrated by Cree Research, Inc. MESFET's with fmax's of 30 GHz, 2.8W/mm power density at 1.8 GHz have also been fabricated and tested in 1995. Material defect densities have decreased from ~1000/cm2 in 1993 to ~27/cm2 in 1995 (research). The defect density continues to decrease by a factor of 2 every 8 to 12 months. Both 6H and 4H SiC substrates are commercially available.

Auburn's research program continues to attack the fundamental problems preventing commercialization of high power, high frequency, high temperature devices, including p-type ohmic contact development, packaging, etching, and insulator studies. The close collaboration between Auburn and Westinghouse continues as the rapid approach of high power, high frequency device commercialization approaches.

Fabrication Steps:

n+ starting wafer w/10-30mm n- epi
RIE alignment marks
Pattern Mo implant mask
High-T Al implant (30-300keV)
Implant anneal (1650C)
Surface RIE/sac oxide
Thermal oxide passivation
Poly deposition and conversion
Backside Ni Ohmic contacts
Contact anneal (2min 1150C)
Pattern Ni/Ti Schottky Metal
Ti-Al contact overlayer