Role of surface states and band modulations in ultrathin ruthenium interconnects

TL;DR

This study uses density functional theory to explore how surface states and band structure modulations affect the electrical resistivity of ultrathin ruthenium films, emphasizing surface engineering for improved interconnects.

Contribution

It reveals the critical role of surface states in resistivity trends of ultrathin ruthenium films, highlighting the impact of surface termination on conductivity.

Findings

Vacuum-terminated Ru slabs show decreasing resistivity with decreasing thickness.

Oxygen-terminated Ru slabs exhibit increasing resistivity as thickness decreases.

Surface states significantly influence the thickness-dependent resistivity in ultrathin Ru films.

Abstract

Mitigating the RC delay from transistor miniaturization is essential for next-generation devices, driving a focus on interconnect electrical performance. Current copper-based interconnects face a critical challenge, that their resistivity sharply increases at the nanometer-scale due to surface and grain boundary scattering. Therefore, there is a pressing need for techniques that reduce resistance in ultrathin metal films. In this study, we employ the density functional theory to investigate how the intrinsic electronic structure of thin films impacts conductivity as a function of thickness. Notably, our analysis of ruthenium slab structures shows that surface states significantly influence thickness-dependent resistivity. It reveals that vacuum-terminated Ru slab exhibits decreasing resistivity with the decrease in thickness, whereas oxygen-terminated Ru slab shows the opposite trend. This difference is fundamentally attributed to the presence or absence of surface states, highlighting the importance of surface engineering in optimizing interconnect performance.