TiW/TiWN/Pt Ohmic Contacts to n -Type 3C-SiC
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0911-B11-06
TiW/TiWN/Pt Ohmic Contacts to n-Type 3C-SiC Kirk Hofeling, Loren Rieth, and Florian Solzbacher Electrical and Computer Engineering, University of Utah, Salt Lake City, UT, 84112
ABSTRACT TiW(40 nm)/TiWN(80 nm)/Pt(500nm) was investigated as a new high-temperature compatible contact stack to 3C-SiC for harsh environment applications. Performance of TiW/TiWN/Pt contacts deposited on unintentionally doped (8.85×1018 cm-3) 3C-SiC grown by LPCVD to a thickness of ~1µm on (100) Si are reported. The linear transmission line method was used to determine specific contact resistance (ρc) at room temperature and for long-term tests at 300 οC. As deposited contacts were Ohmic with a ρc range of 1×10-4 to 1×10-3 Ωcm2. These contacts were annealed for five minutes in forming gas (8% H2 92% Ar), at temperatures from 450 to 950 οC and all retained Ohmic character. Annealing samples at 450, 550 and 950 οC decreased ρc while anneling between 650 and 850 οC generally increased ρc. Auger Electron Spectroscopy (AES) analysis was performed on a sample annealed at 750 ο C. The as-received surface was composed of Si and O; after a brief sputter etch a characteristic Pt peak became visible and the O peak decreased substantially. Depth profiles detected Si throughout the Pt capping layer but not in the TiW layers. We suspect that Si diffuses from the SiC substrate into the Pt capping layer and surface Si also reacts with O2 to from an oxide. These reactions, in combination with incomplete SiC/TiW interface reactions, are suspected to cause the increase of ρc for samples annealed between 650 and 850 οC. Annealing at 950 οC gave the lowest contact resistance of 2.3×10-5. Long-term testing at 300 οC for 190 hours, in atmosphere, was performed on contacts annealed at 450 οC. When heated, the contacts initial ρc of 2.1×10-4 Ωcm2 increased to ~4×10-3 Ωcm2 which remained stable for the test duration. After long-term testing the sample ρc measured at room temperature decreased to 9.8×10-5 Ωcm2. INTRODUCTION Silicon Carbide (SiC) has excellent mechanical and chemical stability as well as electrical and thermal conductivity at temperatures well above 300 °C [1,2] making it an excellent material for high-temperature and harsh environment devices. The chemical inertness of SiC makes wet etching and bulk micromachining a very difficult process. Cubic silicon carbide (3C-SiC) epitaxially grown on Si substrates enables the excellent chemical and physical properties of SiC to be combined with current bulk micromachining techniques for Si simplifying the fabrication of harsh environment microsystems. There has been extensive research on Ohmic contacts to SiC [3-5]. However, the stability of SiC Ohmic contacts in harsh environments for extended time periods is less developed. The TiW/TiWN/Pt contact stack was selected based on the properties of the constituent metals. TiW (10/90 weight%) was selected because it has a high melting temperature (Ti 1660 ο C, W 3410 οC), is predicted to be thermally stable in contact with SiC up to 2700 οC, and had b
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