Nickel (Ni) and its aluminides are key materials in extreme ultraviolet lithography masks and nanoscale interconnects, where precise patterning is essential. However, the engineering of Ni-based intermetallics poses significant challenges due to their high physical stability and chemical inertness. This study introduces a plasma-enhanced atomic layer etching (ALE) method for Ni, relying on a surface modification by a N2/H2 plasma mixture followed by selective removal of the modified layer with hexafluoroacetylacetone vapor. Optimizing plasma chemistry, power, and exposure time promotes a controlled surface modification, which minimizes surface roughness and enhances process control. Half-reactions are shown to be self-limited, leading to an etch per cycle of 0.21 ± 0.03 nm at 350 °C. Periodic O2 plasma steps are incorporated to eliminate carbon residues from the surface. X-ray photoelectron spectroscopy reveals a mechanism involving surface nitridation and subsequent removal of the NixN layer. The ALE process is demonstrated on blanket substrates and assessed on prepatterned 3D nanostructures to examine the etching directionality. Transmission electron microscopy studies conducted on the blanket and 3D-structured Ni demonstrate the damage-free characteristics and anisotropic nature of the ALE process. The proposed method represents a significant advance in ALE technology and paves the way for anisotropic Ni patterning, which is essential for the fabrication of future nanoscale devices.
Ali et al. (2026) studied this question.