Editors’ Choice—Atomic Layer Etching of Tungsten Disulfide Using Remote Plasma-Induced Oxidation and Wet Etching

Abstract

WS 2 is an emerging semiconductor with potential applications in next-generation device architecture owing to its excellent electrical and physical properties. However, the presence of inevitable surface contaminants and oxide layers limits the performance of WS 2 -based field-effect transistors (FETs); therefore, novel methods are required to restore the pristine WS 2 surface. In this study, the thickness of a WS 2 layer was adjusted and its surface was restored to a pristine state by fabricating a recessed-channel structure through a combination of self-limiting remote plasma oxidation and KOH solution etching processes. The reaction between the KOH solution and WO X enabled layer-by-layer thickness control as the topmost oxide layer was selectively removed during the wet-etching process. The thickness of the WS 2 layer decreased linearly with the number of recess cycles, and the vertical etch rate was estimated to be approximately 0.65 nm cycle −1 . Micro-Raman spectroscopy and high-resolution transmission electron microscopy revealed that the layer-by-layer etching process had a nominal effect on the crystallinity of the underlying WS 2 channel. Finally, the pristine state was recovered by removing ambient molecules and oxide layers from the surface of the WS 2 channel, which resulted in a high-performance FET with a current on/off ratio greater than 10 6 . This method, which provides a facile approach to restoring the pristine surfaces of transition-metal dichalcogenide (TMDC) semiconductors with precise thickness control, has potential applications in various fields such as TMDC-based (opto)electronic and sensor devices.