Plasma atomic layer etching of ruthenium with surface fluorination and ion bombardment

The plasma atomic layer etching (ALE) process for Ru was developed with surface fluorination and ion bombardment. We employed two methods for surface fluorination: (i) fluorocarbon deposition using CHF₃ or C₄F₈ plasmas and (ii) chemisorption and diffusion with CF₄ plasma. C₄F₈ plasma generated a more fluorine rich fluorocarbon layer on the Ru surface compared with CHF₃ plasma, and a higher etch per cycle (EPC) of 1.5 nm/cycle was achieved with C₄F₈ plasma, in contrast to the 0.6 nm/cycle achieved with CHF₃ plasma. Moreover, chemisorption and diffusion with CF₄ plasma yielded an EPC of 1.2 nm/cycle. The ALE process using CHF₃ plasma shows the lowest fluorine residue and lowest surface roughness compared with the ALE process using C₄F₈ and CF₄ plasmas.