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submitted on 14.08.2020 and posted on 10.09.2020by Ji Liu, hongliang lu, david wei zhang, Michael Nolan
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 NHx-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 NHx-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 NHx-terminated
Ru(001) surface and 2.02 Ru/nm2 on the NHx-terminated
Ru(100) surface. However, if the first H transfer barrier cannot be overcome,
leaving RuCp2 on NHx-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.