Observation and Suppression of Nickel Germanide Overgrowth on Germanium Substrates with Patterned SiO[sub 2] Structures

We have investigated the reactions of thin Ni films on Ge-on-Si substrates with patterned SiO 2 structures. For rapid thermal anneals (RTAs) hotter than ∼300°C, an undesirable growth mode is observed whereby voids form in the Ge next to the SiO 2 and germanide grows over the SiO 2 . A model is proposed in which Ge is the dominant diffusing species during germanidation in the presence of topographies with Ge/SiO 2 boundaries. This undesirable growth is suppressed by the use of a 2-RTA process, preferably involving an RTA1 at ∼250°C, followed by a selective etch of the unreacted Ni, and an RTA2 at ∼330°C.