Swift heavy ion induced modification of the Co/Si interface; cobalt silicide formation

Electron beam evaporated 60-nm Co films on Si (100) substrates were subjected to 120 MeV Au beam irradiation and subsequent thermal annealing to induce interdiffusion at the interface. Although low energy (keV/nucleon) ion beam induced mixing is known to produce cobalt silicides, the effect of MeV/nucleon radiation or swift heavy ions (SHIʹs), on the Co/Si system, has not been reported earlier. The irradiated and ex situ annealed samples were analyzed by Rutherford backscattering spectroscopy measurements. Respective crystalline cobalt silicide phases were identified by grazing incidence X-ray diffraction. Complete intermixing of Co and Si in the interfacial region to form CoSi was achieved following thermal annealing (at 400 °C) of the SHI irradiated Co/Si system. The radiation enhanced diffusion mechanism has been invoked to explain the SHI induced intermixing in the Co/Si system after annealing. Thermally assisted (ion generated) defect migration across the Co/Si interface enhanced defect mediated atomic mobility, which led to the formation of cobalt silicides, in accordance with the thermodynamically favored route. The post SHI irradiation annealing temperature required for the formation of crystalline phases (400 °C), is lower than that reported for low energy ion beam mixing cases where post irradiation annealing temperatures in excess of 700 °C are required for the occurrence of phases. Due to lower processing temperatures, SHI induced mixing may be considered as a promising silicidation technique in solid state technology.