Focussed ion beam synthesis of nanostructures
Locally Focused Ion Beam (FIB) implantation and subsequent annealing were investigated to synthesize nanowires (NWs) with feature dimensions smaller than 100 nm. For example, silicide NWs are of great interest for low-resistivity interconnect lines in future highly integrated circuits and Si NWs for CMOS-compatible nanowire devices.
For example, cobalt FIB ion implantation is applied to study ion beam synthesis of cobalt disilicide nanowires in silicon. Two mechanisms of CoSi2 nanowire formation are investigated: (a) conventional synthesis by 60 keV Co++ FIB implantation at elevated temperatures into silicon along the in-plane <110>Si crystal direction and subsequent annealing, and (b) self-aligned CoSi2 nanowire growth in cobalt supersaturated silicon on FIB-induced defects at room temperature during subsequent annealing. The obtained CoSi2 nanowires are 20-100 nm in diameter and several micrometers long. The growth stability of long NWs embedded in Si sensitively depends on the accuracy of FIB trace alignment relative to the preferred growth directions, namely, the in-plane <110> Si crystal directions. A small misalignment of the FIB trace of a few degrees leads to the decay of the CoSi2 NWs into shorter parts and a larger deviation causes a periodic chain of CoSi2 nanoparticles. These observations of NW growth, their stability and decay are in good agreement with predictions of KLMC simulations, carried out in the theory group of our Institiute.
(a) NW formation in dependence on the implanted Co++ fluence, FIB trace aligned in <110>-direction, and
(b) with a misalignment angle of about 15° (Co++FIB implantation dose was 1x1017cm-2).
(c) result of KLMC simulations of CoSi2 NW growth and decay in dependence on the NW alignment in the Si crystal.