Cyclic Atomic Layer Etching of PdSe₂

The unique characteristic of 2D transition-metal dichalcogenide (TMD) semiconductor materials such as PdSe₂ is the ability of the bandgap to vary on the basis of the number of layers present. This variation results in a broad bandgap range spanning from semi-metallic to semiconducting materials, underscoring the significance of precisely controlling the material thickness. In this study, the thicknesses of chemical vapor deposited PdSe₂ films are precisely controlled layer-by-layer via cyclic atomic layer etching (ALE), which comprised a radical adsorption step generated by oxygen and chlorine plasmas, followed by a desorption step with an organic solvent vapor such as formic acid. Cyclic etching with one monolayer of PdSe₂/cycle is achieved using both types of adsorption gases while maintaining the ratio of Se/Pd underlying PdSe₂ at ≈2. This cyclic ALE method is also applicable for smoothing TMD material surfaces by isotropically removing individual rough surface layers. Because this etching method only utilizes chemical reactions with radicals generated by plasmas and organic vapors, it is not only unaffected by the physical damage caused by the irradiation of energetic particles such as ions in plasmas, but also is applicable to 3D structure processing.