In situ study of the growth kinetics and interfacial roughness during the first stages of nickel–silicide formation

Metal silicides are widely used as contacts and interconnections in very large-scale integrated circuits. With the continuous scaling down of devices, the silicide thickness should be decreased and it becomes important to understand and control the first stages of the silicide formation. In this work, the first stages of the nickel–silicide formation in 40 nm Ni deposited on Si(1 0 0) wafer have been investigated, together with the development of the roughness linked to this formation. Both crystalline and amorphous phase formations have been followed using in situ X-ray reflectivity (XRR) and X-ray diffraction (XRD). In situ XRR allows to determine the number of formed layers and their individual thicknesses. Combining XRR and XRD, we show that the first nickel–silicide phase that is formed is certainly a metastable amorphous alloy which slightly increases before the formation of the crystalline Ni2Si phase. We also suggest that the amorphous alloy crystallises to form the Ni3Si2 phase at the very beginning of the Ni2Si formation. After crystallisation, this phase disappears in favour of Ni2Si. In addition, the Ni31Si12 phase is observed before the end of the Ni2Si formation and seems to have formed a layer.