Phase formation sequence and cobalt behavior in the Ni0.9 Co0.1 system during the thin film solid-state formation

Abstract

In this work, the solid-state reaction between a 7 nm thick Ni0.9Co0.1 film and a silicon substrate has been studied. By combining various characterization methods (e.g. sheet resistance measurement, X-ray reflectivity, X-ray diffraction), a comprehensive phase sequence of the NiCo silicide formation has been proposed. At low temperature, we observed the formation of metal-rich Ni2Si-like phases: δ-(NiCo)2Si and θ-(NiCo)2Si. Contrary to Ni0.9Pt0.1 based silicides, the δ-Ni2Si phase appears before the θ-Ni2Si one. Beyond 320 °C, the (NiCo)Si monosilicide formation is initiated and this latter is complete at 400 °C. The presence of Co strongly decreases the NiSi2 formation temperature. This early formation of disilicide allows avoiding film agglomeration and enhances the thermal stability of NiSi silicide. Complementary studies using wavelength dispersive X-ray fluorescence allowed studying the cobalt behavior and highlighted the formation of a Co composition gradient into the metal-rich silicide phases at relatively low temperature (220–260 °C).