Nano-structured silicide formation by focused ion beam implantation and integration of silver metallization with thin film silicide layers

Nano-structured silicide formation was mediated through ion implantation. Silicide structures with dimensions of 170 nm were produced on (100) silicon substrates by ion implantation of 200 KeV As++ through a thin cobalt film on SiO₂/Si structure. A selective reaction barrier at the Si/Co interface comprising of a thin (∼2 nm) oxide (SiO ₂) prevents unwanted reactions. Ion-beam mixing was instrumental in the fracturing of the oxide layer, thereby allowing the migration of metal atoms across the SiO₂/Co boundary for the silicidation reaction to proceed during subsequent rapid thermal anneal (RTA) treatments. A threshold dose of 3 × 1015 cm−2 was required for process initiation. Four-terminal resistance test structures were formed for electrical measurements. Resistivity values obtained ranged from 12 to 23 μΩ-cm, improving with increased ion dose. Application of this method can facilitate a wide variety of silicide structures.; Part two of this study focused on the reliability study of silver metalization with silicides. Silicide thin films of CoSi₂ and NiSi were prepared by solid phase reactions utilizing the bi-layer technique. Silver thin films were then deposited on the silicides to evaluate the thermal stability of the films during vacuum annealing. Rutherford backscattering spectrometry of annealed films revealed Ag film changes to occur at 700°C. No changes in the silicide thin films could be detected. Scanning electron microscopy of annealed films shows grain coarsening of the Ag film with increasing anneal temperature. At 650°C, voids begin to appear in the film. Increasing anneal temperature up to 700°C agglomerates the film. X-ray diffraction glancing angle scans revealed no phase changes in annealed films. The as-deposited case and 700°C both show the same reflection peaks being present. Secondary ion mass spectroscopy depth profiling revealed trace amounts of Ag at the silicide/silicon interface following a heat treatment. This occurrence appears to be temperature-independent, since equal amounts of Ag were discovered at the silicide interface for all samples annealed from 450°C up to 700°C. A TiON reaction barrier showed marginal effectiveness against Ag diffusion to the silicide/silicon interface. Attainable temperature with no Ag diffusion for CoSi₂ and NiSi was 500 and 400°C, respectively.