Reactions of Ruthenium Cyclopentadienyl Praecursor in the Metal Precursor Pulse of Ru Atomic Layer Deposition

Ruthenium is a promising material in the semiconductor industry and is investigated as the interconnect metal or as a seed layer for Cu interconnects. Non-oxidative reactants are required in a plasma-enhanced atomic layer deposition (PE-ALD) process for metals to avoid oxygen contamination. The PE-ALD of Ru has been explored experimentally, but the growth mechanism is not clear. In this paper, the reaction mechanism of the cyclopentadienyl (Cp, C₅H₅) precursor RuCp₂ and NH_x-terminated Ru surfaces that result from the plasma cycle is studied in detail by first-principle calculations. The Cp ligands are eliminated by hydrogen transfer and desorb from metal surface as CpH. The results show that on the NH_x-terminated Ru surface at typical ALD operating condition (temperature range 550K to 650K), the first hydrogen transfer is the rate-limiting step and has high barriers, which are -1.51eV for Ru(001) and 2.01eV for Ru(100). Assuming that the initial activation barrier for the first hydrogen transfer can be overcome, the two Cp ligands will be completely eliminated completely on Ru(100) surface during the metal precursor pulse, resulting in Ru atoms on the surface, binding to N atom. But at most only one Cp ligand is eliminated on Ru(001) surface, resulting in an RuCp termination on (001) surface. Investigating the precursor coverage, the final surface coverages of final terminations after the metal precursor pulse are 0.85 RuCp/nm² on the NH_x-terminated Ru(001) surface and 2.02 Ru/nm² on the NH_x-terminated Ru(100) surface. However, if the first H transfer barrier cannot be overcome, leaving RuCp₂ on NH_x-terminated Ru surfaces, the maximum coverages of RuCp₂ on Ru(001) and Ru(100) surfaces are 2.54 RuCp₂/nm² and 2.02 RuCp₂/nm². These structures are vital to model the following N-plasma step.