Prediction of ALD Chemistry for the Incorporation of Ru into TaN using the RuO4 Precursor

Interconnects are crucial for the operation of electronic devices and consists of a diffusion barrier, liner layer and the metal copper. However, this tri-layer 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 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 NHx-terminated ε-TaN (110) surfaces was examined. We first report on the possible surface terminations of ε-TaN (110) post the N2/H2 plasma pulse. Reaction energies were endothermic after H2O elimination for surfaces terminated with additional Ta-NHx terminations. This shows that the TaN surface can be treated with just hydrogen plasma and surfaces such as 1 ML N-H and 0.5 ML N-H/0.5 ML N-H2 ε-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 favourable 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.