Formation of CoSi2 nanowires and nanochains in silicon by direct FIB writing

A Focused Ion Beam (FIB) equipped with a CoNd alloy liquid metal ion source was used for the formation of cobalt disilicide nanowires and nanochains by an ion beam synthesis process. Co ions at 60 keV were implanted into silicon (111) and (100) substrates at 400-450°C followed by a two-step annealing at 600°C and 1000°C. During the FIB patterning of the samples using a digital scanning system the dose, the pixel dwell time and the relaxation time between the irradiation cycles were varied. The FIB spot size was in the range of 40 nm. The formation of long, stable nanowires occurs along the favoured <110>-crystal direction. The misalignment of the FIB trace relative to this direction leads to a decay of the wire into shorter ones or to the formation of chains of single-crystalline nanoparticles. Nanowires of 20-80 nm diameter and lengths up to 50 microns were obtained. Imaging of nanostructures was done in-plane by SEM, AFM and TEM. Cross-sections through nanowires were prepared by conventional Ga FIB milling across the nanowire. Further efforts will be concentrated in a better control of the nanowires growth, in the characterization of the electrical properties and in the fabrication of nanodevices.