Electrochemical Atomic Layer Etching of Ruthenium

Abstract

A novel process for the electrochemical atomic layer etching (e-ALE) of ruthenium (Ru) is described. In this process, the surface Ru is electrochemically oxidized to form a monolayer of ruthenium (III) hydroxide—Ru(OH)3. The Ru(OH)3 monolayer is then selectively etched in an electrolyte containing chloride (Cl–) species. This etching process is selective towards Ru(OH)3 and does not attack the underlying Ru metal. Adsorbed Cl– on the Ru electrode is then cathodically desorbed before the sequence of Ru oxidation and Ru(OH)3 etching is repeated. This e-ALE sequence is shown to etch Ru at approximately 0.5 monolayer per cycle while practically avoiding any surface roughness amplification. The proposed Ru e-ALE process uses a single electrolyte which eliminates the need for electrode transfer or electrolyte switching between process steps. In this report, we employ electrochemical, microscopic and spectroscopic techniques to gain insights into the various characteristics of the Ru e-ALE process.