The reaction of Ni films with a Si0.8Ge0.2 alloy is studied in the temperature range of 200-750 degreesC from the point of view of process window, morphology of the resulting silicide, and mechanisms of degradation at high temperatures. The effect on the reaction of substrate crystallinity (single crystal and polycrystalline Si0.8Ge0.2), dopants (arsenic and boron) and process parameters is investigated. Sheet resistance measurements, X-ray diffraction and scanning electron microscopy were used for film characterization. Ni-rich germanosilicide is formed at low (<350 degreesC temperatures, the Ni monogermanosilicide phase is then formed, which is stable up to 550-600 degreesC. At temperatures above 600 degreesC, segregation of Ge and morphological changes result in an islanded structure of germanosilicide, with at least partial expulsion of Ge from Ni(SiGe) grains. Formation of the low resistivity Ni monogermanosilicide phase is delayed by the addition of Ge in comparison to the pure NiSi case. Ni(SiGe) films have lower thermal stability than pure NiSi films. Activation energies of degradation of 1.65 +/- 0.2 eV for Ni on c-SiGe and of 1.56 +/- 0.2 eV for Ni on poly-SiGe were determined, which are significantly lower than those measured for pure NiSi films. These results suggest that segregation of Ge play a significant role in the mechanism of degradation of Ni(SiGe) films. The process window for a low resistivity film is narrower for the reaction of Ni with Si-Ge in comparison to the reaction of Ni with pure Si. (C) 2004 Published by Elsevier B.V.