Processing factors impacting the leakage current and flicker noise of germanium p+-n junctions on silicon substrates

The impact of several processing factors, such as the n-well doping, the use of nickel-germanidation, and the postmetallization anneal (PMA) temperature, on the reverse current and flicker noise of p(+)-n junctions fabricated in epitaxial germanium-on-silicon substrates is investigated. It is shown that a higher well doping leads to a lower leakage current, in the range studied here, both for the perimeter and bulk. component. It is furthermore shown that there exists an optimal PMA temperature around 450 degrees C, depending on the leakage current component and the process details. The use of NiGe contacts improves the series resistance (forward current) but may deteriorate the perimeter leakage associated with surface-state generation, at the Ge-SiO2 interface. This is confirmed by the low-frequency noise results, showing a dominance of the perimeter component. It is demonstrated that these effects are related to the occurrence of Ni-germanidation-induced voids along the edge of the p(+)-n junctions. (c) 2007 The Electrochemical Society.