Molecularly tailored SAMs for Ru interconnects: high-temperature stability, suppressed metal diffusion, and enhanced adhesion

Abstract

The miniaturization of integrated circuits (ICs) necessitates alternative diffusion barriers with reduced electrical resistance to mitigate the RC delay effect. Self-assembled monolayers (SAMs), with their molecular-scale thickness (1–2 nm), offer a promising solution for controlling Ru interdiffusion while preserving low resistivity. This study investigates the effectiveness of 2-hydroxybenzylimine-triethoxysilane (2-HBITES), benzyliminetriethoxysilane (BITES), and n-octyltriethoxysilane (OTS) as SAM-based diffusion barriers for Ru metallization. SAM functionalization was confirmed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), while barrier performance was evaluated through sheet resistance measurements, X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) following rapid thermal annealing (RTA). The results demonstrate that SAM-modified substrates effectively suppress Ru silicide formation, with 2-HBITES exhibiting the highest thermal stability, delaying Ru interdiffusion until 800 °C, compared to 775 °C for BITES, 725 °C for OTS, and 600 °C for non-functionalized Ru/Ox/Si. The superior performance of 2-HBITES is attributed to its salicylaldimine terminal group, which enhances Ru adhesion and diffusion suppression. Additionally, this study provides direct XPS evidence of SAM retention within a Ru/SAM/Ox/Si structure post-annealing at 700 °C, highlighting the potential of SAMs as thermally stable, ultrathin diffusion barriers for advanced interconnect technologies.

As microchips become smaller and faster, the materials used to connect electronic components face increasing performance and reliability challenges. This study introduces a molecular engineering strategy that uses self-assembled monolayers (SAMs)—extremely thin molecular films—to improve the stability and performance of metal wiring in advanced electronics. By tailoring the molecular structure of the SAM, the team developed a new interface material that enhances adhesion, reduces electrical resistance, and withstands high temperatures. Specifically, the engineered monolayer coating demonstrated strong bonding with ruthenium (a metal used in chip wiring), effectively blocking unwanted diffusion and preserving material integrity even at 700 °C. This work offers a new pathway for creating ultra-thin, high-performance materials critical for next-generation semiconductor devices.

This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.

This study demonstrates the use of molecularly tailored self-assembled monolayers (SAMs) as ultrathin diffusion barriers and adhesion liners for Ru interconnects. Compared to non-functionalized and methyl-terminated surfaces, hydroxylated arylimine SAMs such as 2-HBITES effectively suppress Ru interdiffusion, prevent film delamination, and significantly enhance thermal stability up to 700 °C. The SAM-functionalized interfaces exhibit improved adhesion and structural integrity, offering a promising strategy for future scaled interconnect technologies.