RuAl intermetallic compound of low resistivity scaling and high thermal stability as potential interconnect metallization

Abstract

Thin films of single-phase ruthenium aluminide (RuAl) intermetallic compound were deposited by magnetron co-sputtering. An ordered B2 body-centered cubic structure of high crystallinity was formed after rapid thermal annealing at 800 °C for 1 min. Data fittings using the Fuchs–Sondheimer and Mayadas–Shatzkes models suggested the very short mean free path of electrons of below 5 nm and the high specularity parameter of 0.9. The short mean free path and the much reduced diffuse scattering of electrons at the interface effectively suppressed the resistivity scaling of the B2 RuAl intermetallic compound as compared to ruthenium metal. At an ultra-small film thickness of below 5 nm, the reflection of electrons by grain boundaries or domain walls might alternatively dominate the increase in resistivity. The RuAl intermetallic compound with an ordered B2 structure and a high cohesive energy (a large negative mixing enthalpy) also demonstrated a superior thermal stability at an extreme temperature up to 900 °C. It could be a promising candidate for potential use as the next-generation interconnect metallization without the need of a diffusion barrier.