Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS₂ from WF₆, H₂ Plasma, and H₂S

Two-dimensional (2D) transition metal dichalcogenides are potential low dissipative semiconductor materials for nanoelectronic devices. Such applications require the deposition of these materials in their crystalline form and with controlled number of monolayers on large area substrates, preferably using deposition temperatures compatible with temperature sensitive structures. This paper presents a low temperature plasma-enhanced atomic layer deposition (PEALD) process for 2D WS 2 based on a ternary reaction cycle consisting of consecutive WF 6, H 2 plasma, and H 2 S reactions. Strongly textured, nanocrystalline WS 2 is grown at 300 °C. The composition and crystallinity of these layers depends on the PEALD process conditions, as understood by a model for the redox chemistry of this process. The H 2 plasma is essential for the deposition of WS 2 as it enables the reduction of −W 6+ F x surface species. Nevertheless, the impact of subsurface reduction reactions needs to be minimized to obtain WS 2 with well-controlled composition (S/W ratio of 2).