Thermal atomic layer etching of copper via sequential chlorination and volatility-controlled hydration.

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Thermal atomic layer etching (ALE) of metals is limited by the low volatility of metal halides.
• Existing dry etching processes face challenges in scalability, selectivity, and temperature flexibility.

Purpose of the Study:

• To introduce a novel hydration-activated volatilization strategy for thermal metal ALE.
• To overcome the low volatility limitation of metal halides in dry etching.

Main Methods:

• A two-step thermal ALE process using copper (Cu) as a model system.
• Sequential chlorination with sulfuryl chloride (SO2Cl2) followed by controlled hydration with H2O vapor.
• Utilizing quartz crystal microbalance, X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, and scanning electron microscopy for analysis.

Main Results:

• Demonstrated a hydration-induced phase transformation of CuCl2 into volatile CuCl2·2H2O.
• Achieved self-limiting behavior in both chlorination and hydration steps with etch rates from 0.04 to 1.10 nm/cycle at 75-175 °C.
• Verified surface species formation/removal and morphology evolution, confirming the process's effectiveness.

Conclusions:

• Established a new paradigm for thermal metal ALE by decoupling halide formation from volatilization via hydration.
• The strategy provides a general framework for atomic-scale recess engineering of Cu and other interconnect materials.
• Offers new opportunities for scalable three-dimensional integration in future electronic devices.