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 HfO 2 and ZrO 2 using a novel NbF 5 /TiCl 4 precursor combination. HfO 2 films retained structural quality after ALE, with minimal impurity incorporation and preservation of density, roughness, and refractive index. In contrast, ZrO 2 etched more rapidly but showed surface degradation and higher impurity levels. Density functional theory calculations support these findings by indicating that ZrO 2 more readily undergoes the ligand-exchange step, which is consistent with its faster etching. ALE was further applied to HfO 2 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.