Asymmetric Distribution of Charge Trap in HfO2-Based High-k Gate Dielectrics

Abstract

The time-dependences of leakage currents by electrons and holes flowing through HfO2-based high-k gate dielectric films under constant voltage stresses are investigated by a carrier separation method using field-effect transistor structures. The ratio of the electron current to the hole current depended on gate voltage and the type of transistors. In the case of unbalanced charge injection, the trapping of the major leakage current carriers controlled the time dependence of both leakage currents. However, in the case of balanced injection, some of the injected electrons were trapped near the gate, while some of the injected holes were trapped near the substrate, giving rise to the both current reduction. As a result, both leakage currents reduced. Capacitance change during the relaxation after the removal of the gate voltage stress was consistent with the leakage current change. The relationship between the electron-/hole-trapping centers and oxygen-related defects in high-k dielectric films is discussed.