The structural and electrical properties of cobalt annealed on heteroepitaxial, strained-layer silicon-germanium were studied by transmission electron microscopy, four-point-probe and four-terminal resistor resistivity measurements, and junction diodes. The I50nm thick epitaxial p-Si0.87Ge0.13 was grown by UHV-CVD at 590°C. Cobalt was deposited by DC magnetron sputtering. The cobalt was rapid-thermally annealed at various temperatures in forming gas.
The cobalt film and the SiGe layer reacted, as illustrated by changes in their film thicknesses, and increased interfacial roughness. The roughness and reacted-film thickness increased with increasing temperature. The sheet resistances of the samples were dependant on the anneal temperature and time. Films formed by annealing at 700°C, 3 min, were 80nm thick, and had 2.8ω/sq sheet resistivity, corresponding to 20μω-cm resistivity. The contact was ohmic, with contact resistivity of l.6×10−4ω-cm2. SiGe/ Si heterojunction diodes contacted by the reacted film, containing Co, Si, and Ge, were compared to diodes contacted by aluminum.