Effects of Reducing Annealing Temperature on Ni/Al Ohmic Contacts to n- and p-Type 4H-SiC

Effects of reducing annealing temperature on a technique for the simultaneous formation of Ni/Al ohmic contacts exhibiting ohmic behavior to both n- and p-type SiC were investigated. The Ni/Al contacts reacted with the SiC substrates at 900℃, leading to formation of δ-Ni_2Si(Al). There was no contact consisting of δ-Ni_2Si(Al) after annealing at 900℃ for 20 min exhibited ohmic behavior to both n- and p-type SiC. Since Al concentration in the δ-Ni_2Si(Al) grains increased as the annealing temperature decreased due to less evaporation of the Al layer during annealing, and thus it is difficult to control the narrow range of Al concentration appropriate to exhibit ohmic behavior to both n- and p-type SiC using a conventional deposition technique. The specific contact resistances of the contacts which exhibited ohmic behavior to n-type SiC after annealing at 900℃ for 20 min were higher than those after annealing at 1000℃ for 5 min. In contrast, those which exhibited ohmic behavior to p-type SiC did not vary with annealing temperature. On the other hand, the specific contact resistance of the Ni(50 nm)/Al(10 nm) contact consisting of δ-Ni_2Si(8 at%Al) to p-type SiC was reduced to be about 4.0 × 10＾–4 Ωcm²