Investigation of structure and anisotropic electrical resistivity in single-crystalline CoSn kagome metal thin films for interconnect applications

Abstract: CoSn kagome metal is a pseudo-one-dimensional electronic conductor, exhibiting low resistivity (\r{ho}) along the [0001] direction (c-axis) and significantly higher \r{ho} along other crystallographic directions. Such anisotropic conduction is expected to mitigate resistivity increases in narrow interconnect wires at advanced semiconductor technology process nodes, making CoSn a promising candidate for future interconnect applications. In this study, CoSn thin films were fabricated by magnetron sputtering, and their resistivity anisotropy was investigated with respect to crystallographic orientation. Epitaxial growth of single-crystalline CoSn(10-10) films was achieved on a Ru(10-10) buffer layer at deposition temperatures above 350 {\deg}C. The CoSn films exhibited relatively low \r{ho} along [0001], reaching 13 micro{\Omega} cm, and an approximately tenfold anisotropy of \r{ho} between [0001] and 2-1-10, consistent with previous reports on bulk CoSn single crystals. However, the CoSn(10-10) surface exhibited pronounced roughness, attributed to three-dimensional crystal growth during sputtering, which hinders accurate evaluation of the thickness dependence of resistivity. Scanning transmission electron microscopy revealed the growth of a CoSn(10-10) single-crystal with (11-20) and (01-10) side wall facets, as well as domain boundaries within the films. These results highlight both the potential and challenges of employing CoSn kagome metal in future interconnect technologies.