Nickel silicide nanowires formed in pre-patterned SiO2 trenches and their electrical transport properties

Nickel silicide (NiSi) nanowires with different linewidth (from 1000 to 32 nm) are formed in pre-patterned SiO2 trenches on a silicon substrate. SiO2 trenches are milled by focused ion beam (FIB) etching, and an electrical endpoint detection technique is used to control the FIB milling depth to just reveal the silicon surface. The formation is based on Ni thin film deposition and the subsequent annealing at 550 ◦C. Compared with the previously reported self-aligned formation process of NiSi nanowires, the present technique can form NiSi nanowires with controlled length and linewidth because of the pre-patterning of the SiO2 trenches. The as-formed NiSi nanowires show metallic transport characteristics with a rather low resistivity of about 15 μ cm, which exhibits very weak dependence on linewidth above 50 nm. The lowest resistivity of the nanowire is observed at a linewidth of about 100 nm. The low resistivity is thought to be due to the good crystalline structure of our as-formed NiSi nanowires. When the linewidth of NiSi nanowires is decreased to 32 nm, the resistivity increased abruptly to 22.7 μ cm, which can be explained by considering the short electron mean free path (about 5 nm), as well as the obvious effect of grain boundary on electron transport properties of NiSi.