Homogeneous ZrO2 gate dielectrics with intermediate ozone oxidation for improved interface stability and leakage suppression in Ge-based MOS devices

Abstract

With recent advances in semiconductor technology, Ge has gained significant attention as a high-mobility channel material. However, integrating Ge with high-k dielectrics remains challenging owing to the formation of unstable Ge suboxides at the interface, which degrade the device performance by increasing the interface trap density and leakage current. This study explores the use of a ZrO₂ interlayer, replacing Al₂O₃, followed by ozone post-oxidation (OPO) and an additional ZrO₂ deposition to create a homogeneous ZrO₂ gate dielectric on Ge. The resulting ZrO₂/OPO/ZrO₂ structure effectively suppresses the formation of unstable Ge suboxides, blocks Ge diffusion, and reduces the number of polycrystalline ZrO₂ phases. These advantages have been confirmed through extensive material studies including high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The electrical characteristics were examined using capacitance-voltage and current density-voltage measurements. Moreover, the leakage current behavior was further analyzed using current conduction mechanism models. The ZrO₂/OPO/ZrO₂ stack exhibits a low equivalent oxide thickness (EOT) of 1.87 nm, an interface trap density (D_it) of 2.48 × 10¹² cm⁻¹ev⁻¹, and a reduced leakage current density of 7.05 × 10⁻⁷ A/cm² at 1 V. This study highlights the possibility of the ZrO₂/OPO/ZrO₂ stack as a high-performance gate dielectric for next-generation Ge-based MOS devices.