Effects of implanted arsenic on Ti-silicide formation

The influence of implanted arsenic on Ti-silicidation processes in TiN/Ti/Si-substrate structures was investigated. The Ti layers were deposited to 47-96 nm by ion sputtering, which was followed by reactive sputter deposition of 58-80 nm TiN layers. Complete structures were implanted with As+ ions at 300-500 keV, to the doses from 1×1015-1×1016 ions/cm2. After implantation the samples were annealed in vacuum, for 2-20 min at 650 °C-900 °C. The obtained structures were analyzed with RBS, EBS, XRD, SEM and TEM techniques, combined with thickness profile and sheet resistivity measurements. Direction implantation yields only local intermixing at Ti/Si interface and no other considerable redistribution of components. Post implantation annealing leads to formation of Ti-silicides, incomplete at 650 °C, almost complete formation of TiSi2 at 750 °C, and a complete consumption of the interposed Ti layer in formation of the C54 TiSi2 phase at 900 °C. The silicidation kinetics strongly depends on the dose of implanted arsenic. Low implantation dose, 1×1015 ions/cm2, enhances silicidation, resulting in a complete Ti-Si reaction, and in much sharper TiN/TiSi2 and TiSi2/Si interface compared to the unimplanted samples. The net result is a uniform silicidation front, preferred orientation of epitaxial TiSi2 crystal grains, and a low level of surface topography. Higher implanted doses, of 0.5-1×1016 ions/cm2, slow down the reaction due to high concentrations of arsenic, the excess arsenic being segregated towards the surface.