Rhenium ohmic contacts on 6H-SiC

Rhenium (Re) thin-film contacts (100-nm thick) were deposited on carbon-rich, nominally stoichiometric, and silicon-rich 6H-SiC surfaces, which were moderately doped with nitrogen (1.28x10(18) cm(-3)). Morphology (Dektak), phase formation (x-ray diffraction), chemistry (Auger electron spectroscopy), and electrical properties (I-V) were characterized for the as-deposited and annealed (120 min, 1000 degreesC, vacuum <1x10(-6) Torr) contacts. As-deposited films were nonohmic. Films grown on carbon-rich surfaces were nonspecular, granular, and often delaminated during characterization. At room temperature in air, the Re films on stoichiometric SiC remained optically specular reflecting for 3 h, but then became hazy from oxidation. The Re films on silicon-rich surfaces, stored in air at room temperature, resisted ex situ oxidation for approximately 24 h. The annealed samples remained specular without visible signs of oxidation. The annealing resulted in a reduction in surface roughness for all the films regardless of substrate chemistry. The phase separation between carbon and rhenium was observed based on the formation of interfacial Re clusters and a similar to10-nm graphite surface layer after annealing. Auger data showed that Si layers (5-10 nm) deposited to create Si-rich surfaces were partially consumed to form rhenium silicide during annealing, and the sharp Re/Si/SiC interface became more diffused with Re detected similar to50 nm deeper into the structure. The annealing of Re films on moderately doped (1.28x10(18) cm(-3)) SiC resulted in ohmic contacts with an average specific contact resistance of 7.0x10(-5) Omega cm(2) for stoichiometric and 1.6x10(-5) Omega cm(2) for silicon-rich samples. The annealed contacts on carbon-rich surfaces remained rectifying. (C) 2004 American Institute of Physics.