Electrical and structural evaluations of high-k gate dielectrics fabricated using plasma oxidation and the subsequent annealing for a Hf/SiO₂/Si structure

High-permittivity (high-k) dielectrics with HfO₂/Hf _xSi_1-xO_y/Si structures were fabricated using plasma oxidation and the subsequent annealing for a Hf/SiO ₂/Si structure. By changing a SiO₂ film in an initial structure from plasma oxidation at a low temperature to dry oxidation at a high temperature, the drastic decrease in the trap density in an interfacial layer (IL: Hf_xSi_1-xO_y) could be successfully achieved, which showed an interface state density of 1 × 10¹¹ eV^-1 cm^-2, an effective oxide thickness (EOT) of 1.2 nm and four orders decrease in the leakage current density relative to SiO₂ with the same EOT. The influence of post-annealing on structural and electrical properties of the IL was investigated by using x-ray photoelectron spectroscopy and a transmission electron microscope. It was clarified that the increase in EOT after post-annealing at 900 °C was caused by the decrease in Hf content in the IL and the increase in the IL thickness. The kinetics of the IL formation is discussed in detail. The effects of O ₂ gas ambience during post-annealing on EOT and flat-band voltage (V_fb) were investigated, which showed that the V_fb decreased with increasing O₂ gas pressure while maintaining a low EOT.