Higher-k Scalability and Leakage Current Reduction of SiO₂-Doped HfO₂ in Direct Tunneling Regime

The dielectric constant scalability and leakage current reduction of ultrathin SiO₂-doped HfO₂ (SDH) films are demonstrated. A good linearity of capacitance–physical thickness relationship in metal–insulator–metal capacitors indicates that the high dielectric constant (∼27) of the SDH film is maintained down to 2 nm in the physical thickness. Hence, the capacitance equivalent thickness (CET) is effectively reduced with the higher-k SDH film and a significant leakage current reduction at a given CET is observed in SDH films. In this thickness region, the leakage current density is determined by the physical thickness and is independent of measurement temperature. Those facts indicate the direct tunneling mechanism should dominate the leakage current. In addition, the tunneling effective mass is evaluated to be about 0.2 m₀ (m₀: electron rest mass) by fitting the physical thickness dependence of leakage current to the theoretical calculation.