REFRACTORY-METAL BORIDE OHMIC CONTACTS TO P-TYPE 6H-SIC

Ohmic contacts have been fabricated on p-type 6H-SiC (1.3 x 10(19) cm( -3)) using CrB2, W2E, and TiB2. The boride layers (similar to 100-200 nm) were sputter-deposited in a system with a base pressure of 3 x 10( -7) Torr. Specific contact resistances were measured using the Linear transmission line method, and the physical properties of the contacts were examined using Rutherford backscattering spectrometry. All as-dep osited contacts exhibited rectifying characteristics. Ohmic behavior w as observed following short anneals (2-10 min) at 1100 degrees C and 5 x 10(-7) Torr. Current-voltage characteristics were linear for CrB2 a nd W2B and quasi-linear for TiB2. The lowest values of the specific co ntact resistance (r(c) in Omega-cm(2)) measured at room temperature fo r CrB2 and W2B were 8.2 x 10(-5) and 5.8 x 10(-5), respectively. The s pecific contact resistance for TiB, was not determined accurately. Lon ger anneals (30 min for W2B and 90 min for CrB2) reduced the room temp erature values of r(c) to 6.1 x 10(-5) for W2B and 1.9 x 10(-5) for Cr B2. Backscattering spectra revealed substantial concentrations of oxyg en in all as-deposited boride films. The short anneal cycle removed th e oxygen in the CrB2 films and reduced the concentration substantially in the W2B films; however, annealing had no affect on the oxygen conc entration in the TiB, films. The CrB2/SiC interface remained stable du ring annealing; i.e., Si and carbon were not, observed in the boride l ayers after annealing. In contrast, W2B and TiB2 reacted with the SiC epilayers, and after annealing, Si and carbon were observed at the sur face of each boride layer.