Isotropic Atomic Layer Etching of ZnO Using Acetylacetone and O₂ Plasma

Area of Science:

• Materials Science
• Nanotechnology
• Plasma Physics

Background:

• Atomic layer etching (ALE) offers precise material removal for nanomanufacturing.
• Existing ALE methods include ion-driven anisotropic and thermally driven isotropic processes.
• There is a need for new plasma-based isotropic ALE techniques.

Purpose of the Study:

• To develop a novel plasma-based ALE process for isotropic etching of zinc oxide (ZnO).
• To investigate the self-limiting mechanisms and reaction pathways of the proposed ALE process.
• To demonstrate the applicability of the process on complex nanostructures and evaluate its selectivity.

Main Methods:

• Development of a radical-driven ALE process using acetylacetone (Hacac) and O2 plasma for ZnO.
• In situ spectroscopic ellipsometry to monitor etch rates and self-limiting behavior.
• Transmission electron microscopy (TEM) for analyzing etch profiles on nanowire arrays.
• In situ infrared spectroscopy to elucidate reaction mechanisms.

Main Results:

• Achieved self-limiting half-reactions with etch rates of 0.5–1.3 Å/cycle at 100–250 °C.
• Demonstrated isotropic and damage-free etching on planar and 3D ZnO-coated semiconductor nanowires.
• Identified carbonaceous species as key to self-limiting behavior in the Hacac step.
• Exhibited high etch selectivities (∼80:1) over SiO2 and HfO2.

Conclusions:

• The developed plasma-based ALE process enables precise, isotropic etching of ZnO.
• The process is suitable for conformal coating of nanostructures and shows potential for other oxides like Al2O3.
• This technique expands the toolbox for advanced nanomanufacturing requiring controlled material removal.