We show that high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) can be applicable to quantitative examination of Hf chemical distribution at a HfO
2/SiO
2 interface in a ultra-thin gate dielectric of an advanced MOS-FET. We examined how the annealing at 1000
oC changes the chemical composition distribution at the interface and analyzed the observed change in the chemical composition in terms of Hf diffusion in SiO
2. The estimated diffusion coefficient of Hf in SiO
2 was 2.5×10
-18 cm
2/s and the diffusion length was 1.6×10
-2 nm for annealing at 1000
oC for 1 s. These indicate that high-temperature annealing used to fabricate Si devices, such as conventional dopant activation process, hardly changes the chemical composition distribution at the interface.
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