MoS2 Functionalization with a Sub-nm Thin SiO2 Layer for Atomic Layer Deposition of High-κ Dielectrics

4 years ago

MoS2 Functionalization with a Sub-nm Thin SiO2 Layer for Atomic Layer Deposition of High-κ Dielectrics

Inge Asselberghs, Thierry Conard, Marc Heyns, Johan Meersschaut, Goutham Arutchelvan, Iuliana Radu, Dennis Lin, Haodong Zhang, Wilfried Vandervorst, Hugo Bender, Annelies Delabie, Abhinav Gaur

Several applications of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) in nanoelectronic devices require the deposition of ultrathin pinhole free high-κ dielectric films on 2D TMDs. However, deposition of nm-thin high-κ dielectric films on 2D TMDs remains challenging due to the inert TMD surface. Here, we demonstrate that the surface of a synthetic polycrystalline 2D MoS₂ film is functionalized with SiO₂ to enable the atomic layer deposition (ALD) of thin and continuous Al₂O₃ and HfO₂ layers. The origins of nucleation, the growth mode, and layer coalescence process have been investigated by complementary physical characterization techniques, which can determine the chemical bonds, absolute amount, and surface coverage of the deposited material. SiO₂ is prepared by oxidizing physical vapor deposited Si in air. The surface hydrophilicity of MoS₂ significantly increases after SiO₂ functionalization owing to the presence of surface hydroxyl groups. SiO₂ layers with a Si content of only 1.5 × 10¹⁵ atoms/cm² enable the deposition of continuous 2 nm thin Al₂O₃ and HfO₂ layers on MoS₂ at 300 °C. This fast layer closure can be achieved despite the sub-nm thickness and discontinuity of the SiO₂ nucleation layer. On the basis of the experimental results, we propose a nucleation mechanism that explains this fast layer closure. Nucleation of Al₂O₃ and HfO₂ occurs on the SiO₂ islands, and fast layer closure is achieved by the lateral growth starting from the many nm-spaced SiO₂ islands. Finally, the dielectric properties of Al₂O₃ on the functionalized MoS₂ are confirmed in a top-gated capacitor that shows a leakage current of 3.8 × 10^–6 A/cm² at a 3.4 nm equivalent oxide thickness. To conclude, fast nucleation and layer closure in ALD can be achieved even for a sub-nm thin, discontinuous nucleation layer. We propose that this insight can also be applied to other ALD processes, materials, or applications where thin and fully continuous layers are required.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b01695

DOI: 10.1021/acs.chemmater.7b01695