Tetragonal WSi2 formation by 0.5–5 MeV Xe-ion-beam irradiation at 250 °C and 450 °C

Abstract

We studied two-step tungsten-silicidation processes, which consist of low-energy W implantation followed by high-energy Xe irradiation. The formation of silicides was studied by Rutherford backscattering spectroscopy, x-ray diffraction and transmission electron microscopy. The formed silicide layer is richer in Si than that formed by thermal annealing. The transformation from the hexagonal to tetragonal (usually formed by thermal annealing above 600 °C) WSi2 phase occurred and a tetragonal WSi2 layer was successfully formed by 1-MeV Xe+ and 5-MeV Xe++ ion irradiation at under irradiation temperatures of 410 and 450 °C. The transformation did not occur by 0.5-MeV Xe+ ions at the same substrate temperature. The tetragonal phase was also observed after irradiation by 1-MeV Xe+ at 250 °C. The phase transformation rate normalized to the nuclear energy deposition density En increases with the electronic energy deposition density Ee. This fact indicates that the phase transformation is enhanced by the inelastic electronic scattering of high-energy ion irradiation. The irradiation temperature dependence of the phase transformation was also studied. The mechanism of the silicidation by elastic nuclear scattering and that of the phase transformation by inelastic electronic scattering of high-energy heavy-ion-beam irradiation are qualitatively discussed.