Effect of Hf metal predeposition on the properties of sputtered HfO2/Hf stacked gate dielectrics

Abstract

The electrical and physical properties of reactively sputtered ${\mathrm{HfO}}_2$ thin films on predeposited Hf metal layer were investigated. Compared with a conventional deposition process, i.e., direct deposition of ${\mathrm{HfO}}_2$ on a Si substrate, the ${\mathrm{HfO}}_2/\mathrm{Hf}$ stacked capacitor exhibits excellent electrical characteristics such as capacitance equivalent thickness (CET) as thin as 1.3 nm with lower leakage current of ${\text{2×10}}^{\text{−5}}\mathrm{\hspace{0.17em}(}{\mathrm{A/cm}}^2)$ 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 ${\mathrm{HfO}}_2$ and Hf. This improvement in electrical characteristics can be explained by the blocking of oxygen diffusion through ${\mathrm{HfO}}_2$ films into the Si substrate due to oxidation of the Hf metal layer itself.