Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al2O3-ZrO2 composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO2 film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al2O3-ZrO2 film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO2-Al2O3 film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10−7 A/cm2 at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.