Investigation of the atomic layer etching mechanism for Al2O3 using hexafluoroacetylacetone and H2 plasma

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Abstract

Atomic layer etching (ALE) is required to fabricate the complex 3D structures for future integrated circuit scaling. To enable ALE for a wide range of materials, it is important to discover new processes and subsequently understand the underlying mechanisms. This work focuses on an isotropic plasma ALE process based on hexafluoroacetylacetone (Hhfac) doses followed by H2 plasma exposure. The ALE process enables accurate control of Al2O3 film thickness with an etch rate of 0.16 ± 0.02 nm per cycle, and an ALE synergy of 98%. The ALE mechanism is investigated using Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) simulations. Different diketone surface bonding configurations are identified on the Al2O3 surface, suggesting that there is competition between etching and surface inhibition reactions. During the Hhfac dosing, the surface is etched before becoming saturated with monodentate and other hfac species, which forms an etch inhibition layer. H2 plasma is subsequently employed to remove the hfac species, cleaning the surface for the next half-cycle. On planar samples no residue of the Hhfac etchant is observed by FTIR after H2 plasma exposure. DFT analysis indicates that the chelate configuration of the diketone molecule is the most favorable surface species, which is expected to leave the surface as volatile etch product. However, formation of the other configurations is also energetically favorable, which explains the buildup on an etch inhibiting layer. The ALE process is thus hypothesized to work via an etch inhibition and surface cleaning mechanism. It is discussed that such a mechanism enables thickness control on the sub-nm scale, with minimal contamination and low damage.
Original languageEnglish
Pages (from-to)1345-1358
Number of pages14
JournalJournal of Materials Chemistry C
Volume13
Issue number3
Early online date22 Nov 2024
DOIs
Publication statusPublished - 21 Jan 2025

Funding

This work is part of the research program HTSM with project no. 17124, which is financed by the Netherlands Organization for Scientific Research (NWO). A. J. M. M. acknowledges support from European Research Council (ERC) under the European Union\u2019s Horizon 2020 Research and Innovation Programme (Grant Agreement 949202), and from Vidi project 18363 which is financed by NWO. The authors would like to thank J. J. A. Zeebregts, C. A. A. van Helvoirt, C. van Bommel, J. J. L. M. Meulendijks, and B. Krishnamoorthy for technical support. We would also like to thank Schr\u00F6dinger for providing access to their software which is utilized in this work, and to Dr Simon Elliott for useful discussions on the DFT simulations.

FundersFunder number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
H2020 European Research Council
European Union's Horizon 2020 - Research and Innovation Framework Programme18363, 949202

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