Ni reaction with amorphous SiGe. (a-SiGe) thin film on SiO2 substrate through rapid thermal annealing (RTA) was investigated. The amorphous SiGe thin film was deposited by ion beam sputtering. X-ray diffraction (XRD), Auger electron spectroscopy (AES) depth profiling, and four point probe (FPP) were used to check the phase formation, atom distribution, and sheet resistance during the reaction. It was found that the Ni reaction with a-SiGe was different from the Ni reaction with poly-SiGe. Besides an orthorhombic NiSi phase, a tetragonal eta-NiSi phase was formed during Ni reaction with an a-SiGe layer and remained stable after 800 degrees C annealing. A NiSi, phase was formed at temperature as low as 550 degrees C along with the crystallization of SiGe. When annealed at a higher temperature, Ge outdiffused to the surface and Ni diffused to the interface of SiGe/SiO2 where it formed a thin layer of Ni silicide. The cause of the reduced temperature for formation of NiSi2 from Ni reaction with amorphous SiGe is discussed. (c) 2006 American Vacuum Society.