Plasma-material interactions during patterning of Mg-based oxide semiconductors

Abstract

Magnesium-based oxide semiconductors (OSCs), particularly Magnesium Zinc Oxide (MgZnO), are promising materials for next-generation memory devices due to their stability in stress conditions. However, precise, damage-free nanoscale patterning of these materials remains a significant challenge, owing to complex etching mechanisms and the resulting impact on their electrical characteristics.

This thesis investigates the etching behavior and patterning strategies for MgZnO using reactive ion etching (RIE), atomic layer etching (ALE), and pulsed plasma atomic layer etching (PALE) techniques. The RIE process with Ar/Cl2/CH4 chemistry revealed that MgZnO etching proceeds via both chemical and physical mechanisms, producing volatile organometallic by-products and non-volatile metal chlorides. Optimized RIE encountered challenges in high-density patterns, specifically for 90 nm dense line/space features, due to sidewall redeposition and residue formation. To address these issues, ALE was employed, enabling controlled etching and improved surface uniformity. It also reduced the standard deviation in electric-field breakdown in the as-deposited sample and preserved stoichiometry in 90-nm dense line/space features. Hard mask (HM) engineering was further explored, demonstrating that SiN/Ru masks, combined with PALE and controlled ion flux, preserve HM integrity and enable high-fidelity patterning at sub-100 nm pitches.

Overall, this work provides a comprehensive understanding of MgZnO etching mechanisms and demonstrates scalable strategies for precise, damage-free nanoscale patterning, applicable to other Mg-based OSCs. These findings advance the fabrication of next-generation high-density memory and BEOL-compatible integration.