The influence of a Ni interlayer on the formation of cobalt silicides is investigated. By substrate curvature measurements, x-ray diffraction, and Auger electron spectroscopy, a detailed reaction sequence for the Co(90 nm)/Ni(9 nm)/Si(001) system annealed at a ramp rate of 5 °C/min is revealed. For the relatively thick Ni interlayer, the reaction sequence began with the formation of Ni2Si and was followed by the formation of Co2Si on top of the Ni2Si. As the temperature rose, the layer of Ni2Si transformed into NiSi and the formation of CoSi occurred quickly. After, the occurrence of the (NixCo1-x)Si2 phase began at the interface of NiSi/CoSi. The initial phase formation of cobalt silicides occurred via the diffusion of Si through the layer of nickel silicides. It is only when the (NixCo1-x)Si2 phase formed that both Co and Si became mobile in the layer and a CoSi2–(NixCo1-x)Si2–CoSi2 structure developed. The structure exhibits a preferred (400) orientation for the bottom CoSi2 layer. © 2003 American Vacuum Society.