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    Mechanistic Study of the Atomic Layer Deposition of Scandium Oxide Films Using Sc(MeCp)₂(Me₂pz) and Ozone

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    Date
    2019-01-02
    Author
    Rahman, Rezwanur
    Klesko, Joseph P.
    Dangerfield, Aaron
    Fang, Ming
    Lehn, Jean-Sebastien M.
    Dezelah, Charles L.
    Kanjolia, Ravindra K.
    Chabal, Yves J.
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    Abstract
    Abstract
    The atomic layer deposition (ALD) of scandium oxide (Sc₂O₃) thin films is investigated using Sc(MeCp)₂(Me₂pz) (1, MeCp = methylcyclopentadienyl, Me₂pz = 3,5-dimethylpyrazolate) and ozone on hydroxyl-terminated oxidized Si(111) substrates at 225 and 275 °C. In situ Fourier transform infrared spectroscopy reveals that 1 not only reacts with surface hydroxyl groups at 275 °C, as expected but also with the SiO₂ layer, as evidenced by losses in the SiO₂ longitudinal optical and transverse optical phonon modes, resulting in the partial transformation of near-surface SiO₂ to an ScSixOy interface layer. Ozone then combusts the MeCp groups of the O-Sc(MeCp)₂ chemisorbed species, yielding surface carbonates, and oxidizes some of the underlying silicon, evidenced by gains in the SiO₂ phonon modes. The Me₂pz group from the next pulse of 1 reacts with these surface carbonates, leading to Sc-O-Sc bond formation (Sc₂O₃ deposition) and the restoration of an O-Sc(MeCp)₂ surface. The reaction of the SiO₂ substrate with 1 and the oxidation of silicon by ozone are temperature-dependent processes that occur during the initial cycles of film growth and directly impact the changes in the intensities of the SiO₂ phonon modes. For instance, the intensity of the net gains in the phonon modes following ozone exposure is greater at 275 °C than at 225 °C. As the ALD cycle is repeated, the formation of an ScSiₓOᵧ interface layer and deposition of an Sc₂O₃ film result in the gradual attenuation of the reaction of the SiO₂ substrate with 1 and the oxidation of the underlying silicon by ozone. In addition to the ALD process, characterized by ligand exchange and self-limiting reactions, there are gas-phase reactions between 1 and residual water vapor near the substrate surface that lead to deposition of additional Sc₂O₃ and surface carbonates, the extent of which are also dependent on the temperature of the substrate. After 20 cycles of 1/ozone, the film thicknesses derived from ex situ X-ray photoelectron spectroscopy measurements are 2.18 nm (225 °C) and 3.88 nm (275 °C). This work constitutes the first mechanistic study of an Sc₂O₃ ALD process using ozone as the oxidant and emphasizes the significance of atypical reactions between the substrate and the reactants that influence the growth rate and near-surface stoichiometry during the initial cycles of film deposition. Published by the AVS.
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    Due to copyright restrictions and/or publisher's policy full text access from Treasures at UT Dallas is limited to current UTD affiliates (use the provided Link to Article).
    Supplementary material is available on publisher's website. Use the DOI link below.
    URI
    http://dx.doi.org/10.1116/1.5059695
    https://hdl.handle.net/10735.1/8700
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    • Chabal, Yves J.

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