Nucleation and growth mechanisms of Al2O3atomic layerdeposition on synthetic polycrystalline MoS2.
Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of Al2O3(using Al(CH3)3/H2O ALD) on MoS2whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS2, we exclude the impact of surface contamination from a transfer process by direct Al2O3deposition on synthetic MoS2layers obtained by a high temperature sulfurization process. It is shown that Al2O3ALD on the MoS2surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS2crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS2top surface. During further deposition, the as-formed Al2O3nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous Al2O3film is obtained by lateral growth over the MoS2crystal basal plane, with the point of layer closure determined by the grain size at the MoS2top surface and the lateral growth rate. The created Al2O3/MoS2interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS2basal planes by using low deposition temperature in combination with short purge times. While this results in a more two-dimensional growth, additional H and C impurities are incorporated in the Al2O3layers. To conclude, our growth study reveals that the inherent reactivity of the MoS2basal plane for ALD is extremely low, and this confirms the need for functionalization methods of the TMD surface to enable ALD nucleation.
Department of Chemistry, KU Leuven, Leuven 3001, Belgium.
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Zhang
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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0000000185908269
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Chiappe
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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0000000324671784
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Meersschaut
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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Conard
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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Franquet
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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Nuytten
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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Mannarino
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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Radu
IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
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Vandervorst
Department of Chemistry, KU Leuven, Leuven 3001, Belgium.
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Delabie