CF₄ plasma-based atomic layer etching of Al₂O₃ and surface smoothing effect

Plasma-based Al₂O₃ atomic layer etching (pALE) has a reaction mechanism similar to thermal Al₂O₃ ALE (tALE). The main difference between the two methods is that pALE uses plasma instead of HF in tALE to fluorinate Al₂O₃ to AlF₃. In this study, the CF₄ plasma source commonly used for dry etching is combined with a self-developed low-ion-bombardment remote Al₂O₃ plasma-based ALE system to obtain Al₂O₃ plasma fluorination conditions, and then the AlCl(CH₃)₂ (dimethylaluminum chloride) precursor is used to develop the pALE Al₂O₃ process. In addition to using x-ray photoelectron spectroscopy to investigate ideal fluorination conditions of CF₄ plasma for Al₂O₃ films and establishing the linear etching rate curves of pALE at different process temperatures (250–400 °C), we used atomic force microscopy to analyze the surface morphology of the Al₂O₃ films after dry etching and pALE. We showed that pALE can smooth Al₂O₃ films with a root mean square surface roughness of 1.396–0.655 nm and used anodic aluminum oxide substrates with nanotrench structures to demonstrate that pALE can improve the surface roughness of nonplanar structures.