Understanding the Surface and Interfacial Structure of N -Heterocyclic Carbenes on Ruthenium Substrates: An X-ray Photoelectron Spectroscopic Approach

N-Heterocyclic carbenes (NHCs) are exceptional σ-donors and bind strongly to a wide variety of transition metals. Their unique binding properties have expanded the potential applications of NHCs to area-selective atomic layer deposition (AS-ALD) for microelectronics fabrication. This new application area requires a deeper understanding of the NHC-to-metal interaction beyond the scale of small molecule NHC–metal complexes. Various surface characterization techniques have been applied to study the NHC-deposited metal surfaces, but to date, most studies have been limited to NHCs deposited on single crystals. Ru is an appealing material in the semiconductor industry because of its moderate resistivity and low electromigration rate. There remains a lack of understanding regarding the surface chemistry of NHCs on Ru metal, with the knowledge gained from NHCs on single crystals not necessarily transferable to NHCs on the polycrystalline substrates encountered in microelectronic devices. To bridge this gap, we report herein an in-depth X-ray photoelectron spectroscopic investigation into the interactions between NHCs and polycrystalline Ru surfaces. Two NHC derivatives with different wingtip and backbone groups were employed. Using different incident energies providing varied penetration depths, X-ray photoelectron spectroscopic measurements were conducted to provide insight into how changes in the NHC structure impact the surface coverage density, molecule-to-metal charge transfer, and the ability to protect Ru surfaces.