Wet chemical oxidation to improve interfacial properties of Al₂O₃/Si and interface analysis of Al₂O₃/SiO_x/Si structure using surface carrier lifetime simulation and capacitance-voltage measurement

A thin silicon oxide (SiO_x) layer (thickness: 1.5-2.0 nm) formed at an Al₂O₃/Si interface can enhance the interface properties. However, it is challenging to control the characteristics of thin SiO_x layers because SiO_x forms naturally during Al₂O₃ deposition on Si substrates. In this study, a ~1.5 nm-thick SiO_x layer was inserted between Al₂O₃ and Si substrates by wet chemical oxidation to improve the passivation properties. The acidic solutions used for wet chemical oxidation were HCl:H₂O₂:H₂O, H₂SO₄:H₂O₂:H₂O, and HNO₃. The thicknesses of SiO_x layers formed in the acidic solutions were ~1.48, ~1.32, and ~1.50 nm for SiO_x-HCl, SiO_x-H2SO4, and SiO_x-HNO3, respectively. The leakage current characteristics of SiO_x-HNO3 were better than those of the oxide layers formed in the other acidic solutions. After depositing a ~10 nm-thick Al₂O₃ on an SiO_x-acidic/Si structure, we measured the effective carrier lifetime using quasi steady-state photoconductance and examined the interfacial properties of Al₂O₃/SiO_x-acidic/Si using surface carrier lifetime simulation and capacitance-voltage measurement. The effective carrier lifetime of Al₂O₃/SiO_x-HNO3/Si was relatively high (~400 µs), resulting from the low surface defect density (2.35-2.88 × 10¹⁰ cm⁻²eV⁻¹). The oxide layer inserted between Al₂O₃ and Si substrates by wet chemical oxidation helped improve the Al₂O₃/Si interface properties.