Effect of the interfacial SiO2 layer thickness on the dominant carrier type in leakage currents through HfAlOx∕SiO2 gate dielectric films

Abstract

The carrier conduction mechanism of leakage current in n+-gate p-channel metal-insulator-semiconductor field-effect-transistors with HfAlOx (Hf:60at%,Al:40at%)∕SiO2 dielectric layers has been investigated using the carrier separation method. Since the gate current depends on the substrate voltage and both electron and hole currents are independent of temperature in the range of 25–150°C, the conduction mechanism for both currents is a tunneling process. It is shown that the dominant carrier in the leakage current depends on the structure of the high-k stack. When the interfacial SiO2 layer (IL) thickness increases at a fixed high-k thickness (Thigh-k), the dominant carrier in the leakage current changes from hole to electron at ∼2.0–2.3-nm-thick IL, because of asymmetric barrier height for electron and hole in the SiO2∕Si system. In contrast, for the case of a fixed IL thickness of 1.3nm, the hole current dominates in the leakage current, regardless of Thigh-k, due to symmetric barrier height of the conduction and valence bands in the HfAlOx∕Si system.