Thin CoSi₂ formation on SiO₂ with low-energy ion irradiation

Cobalt suicides were formed by heat treatment and ion irradiation for stacked 7 nm Co and 25 nm Si layers on 20 nm SiO₂ films. Irradiation was performed with 25keV Ar⁺ ions to a dose of 5×10¹⁵cm^-2 at sample temperatures between room temperature and 700°C. The phase, atomic concentration profiles, and sheet resistance of the suicide layers were investigated as a function of the processing temperature. X-ray diffraction measurement showed that the phase of CoSi₂ was formed by irradiation at temperatures above 300°C, and X-ray photoelectron spectroscopy measurement revealed uniform distributions of Co and Si atoms with the atomic ratio of Co : Si = 1 : 2 for samples irradiated at temperatures above 200°C. Sheet resistance measurement showed that almost complete di-silicidation occurred by irradiation at 700°C. It is concluded that the energy deposited by ions contributes to the migration of the species for silicidation at a lower temperature, and Co/Si mixed layers with an atomic ratio of 1 : 2 are easily obtained by irradiation of the stacked thin films with low-energy ions. Since the suicide regions formed in the deposited thin films were decomposed during the irradiation at temperatures below 700°C, thermal annealing at 700°C is necessary to obtain completely uniform CoSi₂ layers after the irradiation.