Fabrication and characterization of single-crystalline CoSn (10-10) kagome metal thin films for interconnect applications: structure and anisotropic electrical resistivity

TL;DR

This study demonstrates the fabrication of single-crystalline CoSn kagome metal thin films with anisotropic electrical resistivity, highlighting their potential for interconnect applications and discussing growth challenges.

Contribution

It reports the successful epitaxial growth of CoSn(10-10) films with significant resistivity anisotropy, advancing understanding of their structure and electrical properties for technological use.

Findings

Achieved epitaxial growth of CoSn(10-10) films on Ru buffer layers.

Observed low resistivity along the c-axis (~13 μΩ·cm) in thick films.

Identified surface roughness and crystal growth challenges affecting resistivity evaluation.

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 for films thickner than 50 nm, and an approximately tenfold anisotropy of \r{ho} between [0001] and [2-1-10] (a-axis), 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.