Titanium nitride and hafnium-zirconium oxide thin film plasma etching for ferroelectric nonvolatile memory applications. I. Etching mechanisms and processes development

Nonvolatile memories are crucial for reducing energy consumption in modern computing systems. Ferroelectric random-access memories (FeRAMs) enable data retention without power, offering a promising solution for low-power applications. Hafnium-zirconium oxide (HZO) exhibits robust ferroelectric properties; however, its crystallization requires the presence of a titanium nitride (TiN) top electrode during annealing. Recent studies showed that reducing HZO thickness below 10 nm but such scaling typically requires annealing temperatures above 400 °C, which is not compatible with back-end-of-line (BEOL) integration. In this work, we propose an alternative approach to achieve sub-10 nm ferroelectric HZO films within a BEOL-compatible thermal budget. A 10 nm HZO layer is first crystallized between TiN electrodes at 400 °C, followed by selective removal of the TiN top electrode and controlled plasma thinning of the HZO layer. The selective TiN removal process was developed combining a CH4/N2/Cl2 plasma etching process followed with a subsequent SC1 wet cleaning step, ensuring efficient etching with high selectivity toward HZO and minimal surface degradation. Controlled thinning of crystallized HZO films was optimized using an inductively coupled plasma (ICP) process based on BCl3/Cl2 chemistry. The etching mechanism is discussed and relies on ion-assisted reactions, involving oxygen scavenging by boron species and metal chlorination, leading to the formation of volatile etch products. Minimizing bias conditions further enable improved process control while limiting ion-induced damage. The whole results demonstrate that conventional plasma etching can be adapted for the controlled thinning of crystallized HZO films, enabling the fabrication of ultrathin (<10 nm) ferroelectric layers compatible with BEOL integration.