Conformal Growth of Nanometer-Thick Transition Metal Dichalcogenide TiSx‑NbSx Heterostructures over 3D Substrates by Atomic Layer Deposition: Implications for Device Fabrication

The scalable and conformal synthesis of two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures is a persisting challenge for their implementation in next-generation devices. In this work, we report the synthesis of nanometer-thick 2D TMDC heterostructures consisting of TiSx-NbSx on both planar and 3D structures using atomic layer deposition (ALD) at low temperatures (200−300 °C). To this end, a process was developed for the growth of 2D NbSx by thermal ALD using (tert-butylimido)-tris-(diethylamino)-niobium (TBTDEN) and H2S gas. This process complemented the TiSx thermal ALD process for the growth of 2D TiSx-NbSx heterostructures. Precise thickness control of the individual TMDC material layers was demonstrated by fabricating multilayer (5-layer) TiSx-NbSx heterostructures with independently varied layer thicknesses. The heterostructures were successfully deposited on large-area planar substrates as well as over a 3D nanowire array for demonstrating the scalability and conformality of the heterostructure growth process. The current study demonstrates the advantages of ALD for the scalable synthesis of 2D heterostructures conformally over a 3D substrate with precise thickness control of the individual material layers at low temperatures. This makes the application of 2D TMDC heterostructures for nanoelectronics promising in both BEOL and FEOL containing high-aspect-ratio 3D structures.