Enabling large ferroelectricity and excellent reliability for ultra-thin hafnia-based ferroelectrics with a W bottom electrode by inserting a metal-nitride diffusion barrier

Abstract

Metal-nitride layers were used as tungsten (W)-diffusion barriers for ultra-thin (<5 nm) Hf0.5Zr0.5O2 (HZO)-based ferroelectric capacitors with W as the bottom electrode. The influence of various metal nitrides (e.g., TiN, HfN, and ZrN) on the leakage properties, ferroelectricity, and reliability of the HZO capacitors was systematically investigated to identify appropriate materials for use as diffusion barriers in TiN/HZO/W stack capacitors. All the metal-nitrides were observed to significantly suppress W diffusion, resulting in a reduced leakage current. A comparative study between diffusion barriers revealed that the TiN/HZO/W stack capacitor with a ZrN layer exhibited the largest remanent polarization (2Pr) of 23 μC/cm2, as well as the highest reliability. This was attributed to the ZrN forming a ZrO2 interfacial layer, which could contribute to polarization switching and improve reliability. We quantitatively calculated the interfacial capacitance by performing the pulse switching measurement. In addition, crystal structures and diffusion properties with various metal nitrides are evaluated by analyzing grazing-angle incidence x-ray diffraction and x-ray photoelectron spectroscopy. These results provide a guideline for the fabrication of ultrathin HZO-based capacitors with stable ferroelectricity, reduced leakage, and excellent reliability.