Thermal Atomic Layer Etching of Cobalt Using Sulfuryl-chloride and Hexafluoroacetylacetone

Thermal atomic layer etching (ALE) of cobalt was demonstrated using sulfuryl chloride (SO2Cl2) for chlorination and hexafluoroacetylacetone (hfacH) for ligand exchange. This etching chemistry is effective because CoCl2 has a low vapor pressure, whereas CoCl2(hfac) is volatile, facilitating efficient removal. Both the chlorination and ligand-exchange steps were self-limiting, yielding an etch per cycle (EPC) of 0.14 nm/cycle, approximately two-thirds of a Co monolayer thickness at 180°C. The EPC exhibited a temperature dependence of 0.11–0.17 nm/cycle in the 160–190°C range. This process offers a viable route for precise and selective thermal ALE of cobalt in advanced device fabrication.