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

Abstract

WS2 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 WS2-based field-effect transistors (FETs). In this study, the thickness of a WS2 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 WOX enabled layer-by-layer thickness control as the topmost oxide layer was selectively removed during the wet-etching process. The thickness of the WS2 layer decreased linearly with the number of recess cycles, and the vertical etch rate was estimated to be approximately 0.65 nm/cycle. Finally, the pristine state was recovered by removing ambient molecules and oxide layers from the surface of the WS2 channel, which resulted in a high-performance FET with a current on/off ratio greater than 106. 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.

Layer-by-layer thinning of two-dimensional materials

“…14c and Table 1). 80 Following ten recess cycles, the current–voltage output curves displayed characteristics of n-type behavior, with a noticeable increase in the number of electrons being induced into the channel as the gate bias was incremented in the positive direction (Fig. 14d).…”

“…161 In another report, the layer-by-layer thinning of WS 2 is applied to CMOS devices, which is witnessed with very encouraging properties. 80 The WS 2 surface was treated by using remote O 2 plasma, leading to the formation of WO x oxidation. Subsequently, a layer-by-layer removal of the target material is achieved through a selective reaction between the KOH solution and WO x .…”

“…The O 2 plasma treatment, conducted for 30 s using a plasma cleaner in remote mode with a radio-frequency power of 50 W and a flow rate of 5 sccm, played a crucial role. 80 Throughout the downstream plasma-based oxidation process, a protective WO x layer formed on the surface, acting as a passivation layer to impede further process. 81 Following this, the WO x layer was selectively oxidized.…”

“…12 and Table 1). 60,66,75,76,80,89,107,108,111,112,[120][121][122][123][124][125][126][127][128][129] These 2D materials possess a wealth of electronic and optoelectronic properties, encompassing light emission, optical modulation, saturable adsorption, and electrically modulated field effect characteristics. [130][131][132][133][134][135][136][137][138] Harnessing these unique properties, significant endeavors have been channeled towards the exploration of 2D materials-based on electronic and optoelectronic applications, capitalizing on the advantages that are offered by top-down thinning strategies.…”