The effects of implanted arsenic on Ti-silicide formation
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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 1x10(15)-1x10(16) ions/cm(2). After implantation the samples were annealed in vacuum, for 2-20 min at 650 degrees C-900 degrees C. The obtained structures were analyzed with RBS, EBS, XRD, SEM and TEM techniques, combined with thickness profile and sheet resistivity measurements. Direct ion 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 degrees C, almost complete formation of TiSi2 at 750 degrees C, and a complete consumption of the interposed Ti layer in formation of the C54 TiSi2 phase at 900 degrees C. The... silicidation kinetics strongly depends on the dose of implanted arsenic. Low implantation dose, 1x10(15) ions/cm(2), 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 0.5-1x10(16) ions/cm(2), slow down the reaction due to high concentrations of arsenic, the excess arsenic being segregated towards the surface.