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

摘要

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 degrees C in N2 ambient. Ni3Si2 forms in the 100-130 nm wide nickel silicide nanowire without a Ti interlayer, while the presence of a Ti layer results in epitaxial NiSi2 formation. The Ti interlayer acts as a diffusion rate limiting barrier for Ni atoms, not only resulting in NiSi2 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., Ni3Si in the 15 nm nanowire for the Ni/Si reaction; and Ni3Si2 in the 25 nm nanowire for the Ni/Ti/Si reaction.