Atomic Layer Etching of HfO ₂ and ZrO ₂ Using NbF ₅ and TiCl ₄ in High-Aspect-Ratio Three-Dimensional Nanohole Structures

Atomic layer etching (ALE) enables atomic-scale removal of thin films through self-limiting reactions, and robust ALE processes for high-κ oxides are essential for semiconductor applications. Here, we report the ALE of HfO2 and ZrO2 using a novel NbF5/TiCl4 precursor combination. HfO2 films retained structural quality after ALE, with minimal impurity incorporation and preservation of density, roughness, and refractive index. In contrast, ZrO2 etched more rapidly but showed surface degradation and higher impurity levels. Density functional theory calculations support these findings by indicating that ZrO2 more readily undergoes the ligand-exchange step, which is consistent with its faster etching. ALE was further applied to HfO2 films in 3D nanohole structures, revealing crystallinity- and location-selective etching in complex geometries. These results highlight the importance of developing selective ALE processes for high-κ oxides, underscoring their potential for precise patterning and integration in advanced semiconductor manufacturing.