Electrochemical Atomic Layer Etching (e-ALE) of Copper - Thermodynamic and Diffusion-Reaction Considerations of the Surface-Limited Sulfidization of Copper

Abstract

Deposition and etching of ultra-thin materials are critical to many technological applications including nano-electronics and electrocatalysis. Atomic layer etching (e-ALE) in particular is attractive because it can enable precise sub-nm control over the etching rate. Conventionally, atomic layer etching of materials is achieved using plasma-assisted techniques; however, when applied to metal etching, such techniques have several drawbacks including generation of volatile byproducts, low throughput and high cost. An alternative electrochemical atomic layer etching (e-ALE) approach, utilizing benign liquid-phase precursors and electrode potential control, is being developed in our group. The e-ALE process enables atomic layer-by-layer etching of metals such as Cu with unprecedented control over etching rate and surface smoothness. In our e-ALE approach, surface-limited sulfidization facilitates formation of a monolayer of cuprous sulfide (Cu2S) on Cu. The Cu2S monolayer is then selectively etched using a halide-containing etching solution. The two-step sequence (sulfidization + etching) can be repeated to achieve atomic layer-by-layer etching as confirmed using stripping coulometry measurements and atomic force microscopy. This talk will discuss the unique characteristics of the e-ALE chemistry and its applicability to a broader class of materials. Figure 1