Characterization of copper germanide as contact metal for advanced MOSFETs

The material and electrical characteristics of /spl epsiv/-Cu₃Ge as a contact metal were investigated. The samples were prepared by direct copper deposition on germanium wafers, followed by rapid thermal annealing. The /spl epsiv/-Cu₃Ge formed at 400 /spl deg/C has a resistivity of 6.8 μ/spl Omega//spl middot/cm, which is lower than typical silicides for silicon CMOS. Cross-sectional transmission electron microscopy showed smooth germanide/germanium interface, with a series of nanovoids aligning close to the top surface. These voids are believed to be the results of Kirkendall effect arising from the different diffusion fluxes of copper and germanium. The specific contact resistivity of Cu₃Ge, obtained from four-terminal Kelvin structures, was found to be as low as 8×10/sup -8/ /spl Omega//spl middot/cm² for p-type germanium substrate. This low resistivity makes Cu₃Ge a promising candidate for future contact materials.