Structural and electronic properties of HfO2 films on Si through H2O2 wet oxidation with improved thermal stability

The thermal stability and material properties of HfO₂ thin films on Si substrates with and without H₂O₂ wet chemical oxidation were investigated. The HfO₂ samples were deposited through plasma-enhanced atomic layer deposition and subjected to thermal annealing. They were then examined using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, and conductive atomic force microscopy. For the Si substrate without H₂O₂ wet chemical oxidation, a native oxide (~1.8 nm) was formed on the substrate before HfO₂ deposition. After the annealing process at 600°C, the band gap (E_g) of the HfO₂ films increased from 6.0 to 6.2 eV due to the diffusion of Si into HfO₂. Furthermore, the conduction and valence band offsets (ΔE_c and ΔE_v, respectively) between HfO₂ and Si changed from 1.02 to 1.42 and 3.86 to 3.66 eV, respectively. After the H₂O₂ wet oxidation of the Si substrate, a 1.5-nm chemical oxide was formed instead of a native oxide. The band offset and E_g values of HfO₂ were similar before and after 600°C annealing (ΔE_v = 3.86 eV, ΔE_c = 1.02 eV, and E_g = 6.0 eV), implying the high thermal stability of the HfO₂ films. Accordingly, wet oxidation not only prevents diffusion from chemical oxide but also markedly improves the oxide leakage current, which is useful for developing highly efficient and thermally stable HfO₂ gate oxides in Si-based integrated circuit devices.