Reaction mechanism of the metal precursor pulse in plasma-enhanced atomic layer deposition of cobalt and the role of surface facets

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Date
2020-05-15
Authors
Liu, Ji
Lu, Hongliang
Zhang, David Wei
Nolan, Michael
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Publisher
American Chemical Society
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Abstract
Cobalt is a potential candidate for replacing copper for interconnects and has been applied in the trenches and vias in the semiconductor industry. A non-oxidizing reactant is required in plasma-enhanced atomic layer deposition (PE-ALD) of thin films of metals to avoid O contamination. PE-ALD of Co has been demonstrated experimentally, but the growth mechanism and key reactions are not clear. In this paper, the reaction mechanism of metal cyclopentadienyl (Cp, C5H5) precursors (CoCp2) and NHx-terminated Co surfaces is studied by density functional theory calculations. The Cp ligands are eliminated by CpH formation via a hydrogen transfer step and desorb from the metal surface. The surface facet plays an important role in the reaction energies and activation barriers. The results show that on the NHx-terminated surfaces corresponding to ALD operating conditions (temperature range 550 K to 650 K), the two Cp ligands are eliminated completely on the Co(100) surface during the metal precursor pulse, resulting in Co atoms deposited on the Co(100) surface. However, the second Cp ligand reaction of hydrogen transfer is thermodynamically unfavorable on the Co(001) surface, resulting in CoCp fragment termination on the Co(001) surface. The final terminations after the metal precursor pulse are 3.03 CoCp/nm2 on the NHx-terminated Co(001) surface and 3.33 Co/nm2 on the NHx-terminated Co(100) surface. These final structures after the metal precursor pulse are essential to model the reaction during the following N-plasma step.
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Keywords
Atomic layer deposition , Activation energy , Atoms , Cobalt , Density functional theory , Hydrogen , Ligands , Semiconductor device manufacture
Citation
Liu, J., Lu, H., Zhang, D. W. and Nolan, M. (2020) 'Reaction Mechanism of the Metal Precursor Pulse in Plasma-Enhanced Atomic Layer Deposition of Cobalt and the Role of Surface Facets', The Journal of Physical Chemistry C, 124(22), pp. 11990-12000. doi: 10.1021/acs.jpcc.0c02976
Copyright
© 2020 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry C copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.jpcc.0c02976