Comparison between the solid state reaction of ultrathin Ni and Ni/Ti with Si nanowire on silicon-on-insulator.

• A sharp interface can be obtained through Ni/Ti/Si reaction. • NiSi 2 is formed after 500 °C annealing through Ni/Ti reaction with 130 nm Si nanowires. • Fully silicided Ni-rich phases form in 15 and 25 nm nanowires. The morphology and phase transformation of nickel silicide nanowires with and without a titanium (Ti) interlayer have been studied. The Ni (10 nm) layers with or without 1 nm Ti film were sputtered onto the Si nanowires onto the silicon-on-insulator substrate and blanket Si wafers. Nickel silicide was formed by rapid thermal annealing at 500 °C in N 2 ambient. Ni 3 Si 2 forms in the 100–130 nm wide nickel silicide nanowire without a Ti interlayer, while the presence of a Ti layer results in epitaxial NiSi 2 formation. The Ti interlayer acts as a diffusion rate limiting barrier for Ni atoms, not only resulting in NiSi 2 formation, but also causing a smooth interface between the nickel silicide nanowire and the substrate. Fully silicided nanowire can be formed on narrow wires, where Ni is excess, leading to the formation of the Ni-rich phase, i.e., Ni 3 Si in the 15 nm nanowire for the Ni/Si reaction; and Ni 3 Si 2 in the 25 nm nanowire for the Ni/Ti/Si reaction. [ABSTRACT FROM AUTHOR]