Electrical characterization and material evaluation of zirconium oxynitride gate dielectric in TaN-gated NMOSFETs with high-temperature forming gas annealing

The electrical, material, and reliability characteristics of zirconium oxynitride (Zr-oxynitride) gate dielectrics were evaluated. The nitrogen (∼1.7%) in Zr-oxynitride was primarily located at the Zr-oxynitride/Si interface and helped to preserve the composition of the nitrogen-doped Zr-silicate interfacial layer (IL) during annealing as compared to the ZrO₂ IL - resulting in improved thermal stability of the Zr-oxynitride. In addition, the Zr-oxynitride demonstrated a higher crystallization temperature (∼600°C) as compared to ZrO₂ (∼400°C). Reliability characterization was performed after TaN-gated nMOSFET fabrication of Zr-oxynitride and ZrO₂ devices with equivalent oxide thickness (EOTs) of 10.3 Å and 13.8 Å, respectively. Time-zero dielectric breakdown and time-dependent dielectric breakdown (TDDB) characteristics revealed higher dielectric strength and effective breakdown field for the Zr-oxynitride. High-temperature forming gas (HTFG) annealing on TaN/Zr-oxynitride nMOSFETs with an EOT of 11.6 Å demonstrated reduced D_it, which resulted in reduced swing (69 mV/decade), reduced off-state leakage current, higher transconductance, and higher mobility. The peak mobility was increased by almost fourfold from 97 cm²/V·s to 383 cm²/V·s after 600°C HTFG annealing.