Electrical And Structural Evaluations Of High-k Gate Dielectrics Fabricated Using Plasma Oxidation And The Subsequent Annealing For A Hf/sio_2/si Structure

摘要

High-permittivity (high-k) dielectrics with HfO_2/Hf_xSi_(1-x)O_y/Si structures were fabricated using plasma oxidation and the subsequent annealing for a Hf/SiO2/Si structure. By changing a SiO_2 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-x)O_y) could be successfully achieved, which showed an interface state density of 1 × 10~(11) eV~(-1) cm~(-2), an effective oxide thickness (EOT) of 1.2 nm and four orders decrease in the leakage current density relative to SiO_2 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 ℃ 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 O_2 gas pressure while maintaining a low EOT.