Effect of Si or Al interface layers on the properties of Ta and Mo contacts to p-type SiC

We present our results on the role of Si or Al interface layers on the structure and electrical properties of tantalum and molybdenum contacts to p-type 6H-SiC. Thin films of Ta or Mo were deposited on p-type SiC with and without p-doped Si or Al interface layers. The Ta/p-SiC, Ta/p-Si/p-SiC, Ta/Al/p-SiC, Mo/p-SiC, and Mo/Al/p-SiC structures were annealed at high temperatures up to 1200°C using the rapid thermal annealing process, in Ar-H2 or N2-H2 ambient. X-ray diffraction analysis showed TaSi2 in both Ta/p-SiC and Ta/p-Si/p-SiC structures annealed in Ar-H2 ambient. For the N2-H2 ambient anneal tantalum nitride (TaN) was formed in Ta/p-SiC and Ta/Al/p-SiC, and TaN plus TaSi2 in Ta/p-Si/p-SiC. While there was evidence of interaction between Mo and Si or Al no intermetallic phases were observed. Electrical measurements revealed that both TaN in Ta/p-SiC and TaN + TaSi2 in Ta/p-Si/p-SiC structures made ohmic contacts, with specific contact resistances of about 2.13 × 10−3 and 1.47 × 10−1 Ω-cm2, respectively. The specific contact resistance for Ta/Al and Mo/Al layers on p-SiC decreases with increasing temperature and varies with anneal ambient. The values calculated for Ta/Al/p-SiC and Mo/Al/p-SiC were about 4.22 × 10−4 at 1100°C and 4.5 × 10−5 Ω-cm2 at 1200°C, respectively. The heavy surface doping provided by Al in Ta/Al/p-SiC and Mo/Al/p-SiC is responsible for the low specific contact resistance.