Effect of Hf metal predeposition on the properties of sputtered HfO ₂/Hf stacked gate dielectrics

The electrical and physical properties of reactively sputtered HfO ₂ thin films on predeposited Hf metal layer were investigated. Compared with a conventional deposition process, i.e., direct deposition of HfO₂ on a Si substrate, the HfO₂/Hf stacked capacitor exhibits excellent electrical characteristics such as capacitance equivalent thickness (CET) as thin as 1.3 nm with lower leakage current of 2×10 ^-5(A/cm²) at -1 V gate bias. Based on the structural analysis as well as the electrical characteristics, the interfacial layer thickness is found to be controllable with minimum CET and higher permittivity by optimizing the thickness ratio between HfO₂ and Hf. This improvement in electrical characteristics can be explained by the blocking of oxygen diffusion through HfO₂ films into the Si substrate due to oxidation of the Hf metal layer itself.