Atomic Layer Deposition of Ruthenium on Ruthenium Surfaces: A Theoretical Study

Atomic layer deposition (ALD) of ruthenium using two ruthenium precursors, i.e., Ru­(C₅H₅)₂ (RuCp₂) and Ru­(C₅H₅)­(C₄H₄N) (RuCpPy), is studied using density functional theory. By investigating the reaction mechanisms on bare ruthenium surfaces, i.e., (001), (101), and (100), and H-terminated surfaces, an atomistic insight in the Ru ALD is provided. The calculated results show that on the Ru surfaces both RuCp₂ and RuCpPy can undergo dehydrogenation and ligand dissociation reactions. RuCpPy is more reactive than RuCp₂. By forming a strong bond between N of Py and Ru of the surface, RuCpPy can easily chemisorb on the surfaces. The reactions of RuCp₂ on the surfaces are less favorable as the adsorption is not strong enough. This could be a factor contributing to the higher growth-per-cycle of Ru using RuCpPy, as observed experimentally. By studying the adsorption on H-terminated Ru surfaces, we showed that H can prevent the adsorption of the precursors, thus inhibiting the growth of Ru. Our calculations indicate that the H content on the surface can have an impact on the growth-per-cycle. Finally, our simulations also demonstrate large impacts of the surface structure on the reaction mechanisms. Of the three surfaces, the (100) surface, which is the less stable and has a zigzag surface structure, is also the most reactive one