Three-Dimensional Surface Treatment of MoS₂ Using BCl₃ Plasma-Derived Radicals

The realization of next-generation gate-all-around field-effect transistors (FETs) using two-dimensional transition metal dichalcogenide (TMDC) semiconductors necessitates the exploration of a three-dimensional (3D) and damage-free surface treatment method to achieve uniform atomic layer-deposition (ALD) of a high-k dielectric film on the inert surface of a TMDC channel. This study developed a BCl₃ plasma-derived radical treatment for MoS₂ to functionalize MoS₂ surfaces for the subsequent ALD of an ultrathin Al₂O₃ film. Microstructural verification demonstrated a complete coverage of an approximately 2 nm-thick Al₂O₃ film on a planar MoS₂ surface, and the applicability of the technique to 3D structures was confirmed using a suspended MoS₂ channel floating from the substrate. Density functional theory calculations supported by optical emission spectroscopy and X-ray photoelectron spectroscopy measurements revealed that BCl radicals, predominantly generated by the BCl₃ plasma, adsorbed on MoS₂ and facilitated the uniform nucleation of ultrathin ALD-Al₂O₃ films. Raman and photoluminescence measurements of monolayer MoS₂ and electrical measurements of a bottom-gated FET confirmed negligible damage caused by the BCl₃ plasma-derived radical treatment. Finally, the successful operation of a top-gated FET with an ultrathin ALD-Al₂O₃ (∼5 nm) gate dielectric film was demonstrated, indicating the effectiveness of the pretreatment.