Patterning of Mg-Based Oxide Semiconductors (MgZnO) at Sub-100 nm Pitches: Reactive Ion Etching versus Atomic Layer Etching

Magnesium-based oxide semiconductors (OSCs) are promising for applications in emerging memory and electronic devices. However, achieving precise and damage-free patterning of Mg-containing materials remains a critical challenge due to their complex etching mechanisms. In this work, we investigate the atomic layer etching (ALE) of Magnesium zinc oxide (MgZnO), a representative Mg-based OSC, using a controlled cyclic process with Cl₂ and CH₄ for surface modification and Ar plasma for removal of the formed byproducts. The ALE mechanism involves the formation of nonvolatile metal chlorides and volatile organometallic byproducts, which in turn enable controlled material removal with minimal surface damage. Compared to conventional reactive ion etching (RIE), the ALE approach offers improved etching controllability and reduces variations in the surface roughness and electrical breakdown fields in the as-deposited MgZnO film. To evaluate the ALE performance in patterned structures, Ruthenium (Ru) hard masks (HMs) were used to define MgZnO features at a 90 nm dense pitch. The ALE process on MgZnO line/space features enables effective feature definition without Zn or Mg redeposition along the feature sidewalls and maintains the stoichiometry of MgZnO within these patterned lines. These results demonstrate the potential of ALE as a scalable and precise etching technique for the fabrication of next-generation Mg-based OSCs, particularly in memory and logic applications.