Plasma-thermal atomic layer etching of molybdenum using CF4 surface fluorination and Ar plasma removal

초록

As semiconductor interconnect dimensions continue to scale down, atomic-level etching with minimal surface damage has become increasingly important for advanced patterning applications. In this study, a plasma-thermal atomic layer etching (ALE) process for molybdenum (Mo) was developed using sequential CF4 plasma fluorination and Ar plasma removal. The effects of process temperature and pressure on Mo surface fluorination were systematically investigated to promote surface fluorination via a chemisorption-diffusion mechanism while suppressing undesired fluorocarbon deposition. Under optimized conditions, the fluorinated Mo layer exhibited self-limiting behavior with a saturated fluorination depth of ∼ 0.65 nm, which closely matched the saturated etch per cycle (EPC) obtained during the Ar plasma removal step. Self-limiting characteristics were confirmed in both the modification and removal steps, enabling precise atomic-scale etch control. Compared with conventional reactive ion etching (RIE), the ALE process significantly reduced surface roughness and fluorine-related residues while preserving the initial surface morphology. These results demonstrate that plasma-thermal ALE based on the chemisorption-diffusion mechanism is a promising low-damage etching strategy for next-generation Mo interconnect integration.

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