A recent study published in Nanotechnology shows that precise, top-down, fabrication techniques can be used to control surfaces and defects such that fundamental conductivity parameters can be extracted from 23 nm-wide NiSi nanowires. Si nanolines and test structures (see Figure) were fabricated on special silicon-on-insulator wafers using a combination of electron beam lithography and anisotropic wet etching techniques. Through careful alignment of the electron beam lithography with the silicon crystal axes, the walls of the nanolines consisted of {111} Si facets that were nearly atomically smooth. When Ni was deposited on the Si nanolines and reacted to form metallic NiSi, the smoothness was inherited by the NiSi. This made it possible to (i) separate surface scattering from other possible causes of resistivity and (ii) demonstrate that NiSi can continue to be a viable conductor for microelectronic devices having line widths down to 23 nm.

The experimental data derived from this study consisted of the resistances of the ultra-smooth nanolines, as measured down to cryogenic temperatures, coupled with a complete microscopic characterization of the nanolines and test structures. In ensemble, these results enabled the researchers to deduce the mean free paths for thermal, defect and surface scattering, and to work out the specularity parameter for sidewall scattering. The high value (0.7) of the specularity parameter confirmed that the NiSi sidewalls were, indeed, much smoother than conventional Cu interconnect sidewalls for which roughness-induced diffuse scattering reduces the specularity parameter almost to zero. This work demonstrates that precisely prepared experimental specimens subjected to careful measurements can produce good quantitative measurements even at the nanometer scale.