Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η4‐2,3‐dimethylbutadiene ruthenium(0)tricarbonyl (Ru(DMBD)(CO)3), a zero‐valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. The authors study the growth mechanism of this precursor by in situ quartz‐crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO)3produces high‐quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical chemical vapor deposition processes, with a strong dependence on both temperature and reaction timescale. The non‐self‐limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, it is suggested that the findings can be generalized to the broader class of zero‐oxidation state carbonyl‐based precursors used in thermal ALD, with insight into the design of effective saturation studies.
Ionic Liquid-Mediated Route to Atomic Layer Deposition of Tin(II) Oxide via a C–C Bond Cleavage Ligand Modification Mechanism
Atomic layer deposition (ALD) is a technologically important method to grow thin films with high conformality and excellent thickness control from vapor phase precursors. The development of new thermal ALD processes can be limited by precursor reactivity and stability: reaction temperature and precursor design are among the few variables available to achieve higher reactivity, unlike in solution synthesis where the use of solvent and/or a catalyst can promote a desired reaction. To bridge this synthesis gap between vapor and solution, we demonstrate the use of an ultrathin coating layer of a vapor-phase compatible solvent—an ionic liquid (IL)— onto our growth substrate to perform ALD of SnO. Successful SnO deposition is achieved using tin acetylacetonate and water, a process that otherwise would require a stronger counter-reactant such as ozone. The layer of IL allows a solvent-mediated reaction mechanism to take place on the growth substrate. We report a growth per cycle of 0.67 Å/cycle at a deposition temperature of 100 °C in an IL comprised of 1-ethyl-3-methylimidazolium hydrogen sulfate. Characterization of the ALD films confirms the SnO film composition, and 1H and 13C NMR are used to probe the solvent-mediated ALD reaction, suggesting a solvent-mediated addition-elimination type mechanism forming acetone and acetate. Density functional theory calculations show that the ionic liquid solvent is beneficial to the proposed solvent-mediated mechanism by lowering the C-C bond cleavage energetics of acetylacetonate compared to the vapor phase. A general class of ligand-modification reactions for thermal ALD is thus introduced in this work.
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- Award ID(s):
- 1904108
- NSF-PAR ID:
- 10477748
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 144
- Issue:
- 47
- ISSN:
- 0002-7863
- Page Range / eLocation ID:
- 21772 to 21782
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/jacs.2c10257
