Prediction of atomic layer deposition chemistry of Ru onto TaN for interconnect stack using the RuO₄ precursor

Interconnects are crucial for the operation of electronic devices and consist of a diffusion barrier, liner layer, and the metal copper. However, this trilayer stack is putting limits on the scaling down of interconnects and as a result is limiting future device miniaturization. Issues such as a pinch-off effect at the top of the via from PVD of the metal or the diffusion barrier-liner bilayer being too thick for the via dimensions means that a solution is required for interconnect downscaling. The proposed solution is a single combined barrier and liner material that can be grown using plasma enhanced atomic layer deposition (PEALD). The currently used barrier material is TaN and ruthenium can be used as a liner layer between TaN and copper. In this paper, the reactivity of ruthenium precursor RuO₄ on NH_x-terminated ɛ-TaN (110) surfaces was examined. We first report on the possible surface terminations of ɛ-TaN (110) post the N₂/H₂ plasma pulse. Reaction energies were endothermic after H₂O elimination for surfaces terminated with additional Ta—NH_x terminations. This shows that the TaN surface can be treated with just hydrogen plasma and surfaces such as 1ML (monolayer) N—H and 0.5ML N—H/0.5ML N—H₂ ɛ-TaN (110) can promote ligand elimination. RuO₄ adsorption along with H₂O formation via hydrogen transfer from the surface was highly exothermic and the risk of oxygen contamination is minimized by the favorable interaction of hydrogen plasma to remove remaining oxygen from the surface. This work will help guide experimental PEALD for the deposition of Ru onto TaN or combined barrier-liner materials composed of Ru incorporated into TaN for future interconnect stacks.