Characteristics of ultrathin HfO2 gate dielectrics on strained-Si0.74Ge0.26 layers

Abstract

The structural and electrical characteristics of HfO2 gate dielectrics along with the interfacial layers formed on strained-Si0.74Ge0.26 films have been investigated. The polycrystalline HfO2 film with a physical thickness of ∼4.0 nm and an amorphous Hf–silicate interfacial layer with a physical thickness of ∼4.5 nm have been observed by high-resolution transmission electron microscopy and time-of-flight secondary ion mass spectroscopy. The electrical properties have been studied using metal–oxide–semiconductor (MOS) structures. A dielectric constant of 26 for HfO2 film and 8.0 for Hf–silicate interfacial layer have been calculated from the accumulation capacitances of the capacitors. These dielectrics show an equivalent oxide thickness as low as 0.6 nm for HfO2 and 2.2 nm for the Hf–silicate layers. The fabricated SiGe MOS capacitors show a low leakage current density of ∼6.5×10−7 A/cm2 at a gate voltage of −1.0 V, breakdown field of 6.5 MV/cm, and moderately low interface state density of 5.5×1011 cm−2 eV−1.