Effects of alloying elements on cobalt silicide formation

Alloying elements can substantially affect the formation of cobalt silicide. A comprehensive study of phase formation was performed on 23 Co alloys with alloying element concentrations ranging from 1 at.% up to 20 at.%. Using in-situ characterization techniques in which x-ray diffraction (XRD) and elastic-light scattering are monitored simultaneously, we follow the formation of the silicide phases and the associated variation in surface roughness in real time during rapid thermal annealing. For pure Co silicide, we detect the formation of all stable silicide phases (Co₂Si, CoSi, and CoSi₂) as well as abnormal grain growth in the Co film and thermal degradation of the silicide layer at high temperatures. The effect of the various additives on phase formation was determined. The roughness of the interface was also measured using grazing incidence x-ray reflectivity (GIXR). We show that by selecting an alloy with a specific composition, we can change the phase-formation temperatures and modify the final CoSi₂ film texture and roughness.