Fundamental studies on nano-scale zirconia dielectrics

High-dielectric-constant metal-oxides are currently being investigated for application as gate dielectric materials to replace SiO₂ in future complementary-metal-oxide-semiconductor devices. In particular, zirconia is considered to be a potential candidate owing to its high dielectric constant, relatively large conduction band offset with Si and predicted thermodynamic stability on silicon. It is hence important to develop processing science for growing ultra-thin (2–5 nm) dielectric films with good structural and electrical properties.; We have developed a technique to grow ultra-thin metal oxide films by ultraviolet (UV)-ozone oxidation. In this method, a thin metal film (of Zr) deposited on passivated Si surfaces by UHV sputtering is oxidized in-situ by oxygen in presence of UV light. The oxidation kinetics of Zr and Al films has been studied by the method of nuclear reaction analysis. We have performed detailed transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) studies to characterize the dielectric films and their interfaces. Capacitor structures have been fabricated to study the electrical properties of the dielectric films grown on different surfaces and have been directly correlated to their electronic structure using EELS and x-ray absorption spectroscopy.; It has been shown that partially-oxidized dielectrics show severe frequency dispersion in the capacitance-voltage characteristics and very high leakage currents while stoichiometric zirconia films do not. Electronic structure studies using both EELS and XAS have shown that oxygen-deficient zirconia dielectrics can be identified by investigation of the oxygen-K absorption near-edge fine structure. The frequency-dependence of the C-V curves has been explained by the Maxwell-Wagner-Sillars interfacial polarization mechanism.; We have also studied the electrical properties of zirconia/SiO₂ gate stacks grown in-situ by the UV-ozone method. Capacitors with an electrical thickness of ∼1.5 nm, with leakage current of only ∼1.8 × 10−4 A/cm2 at 1 V from flatband, and low hysteresis have been fabricated. Ultra-thin SiO ₂ films grown by the UVO method appear to be promising templates for growth of the high-dielectric-constant dielectrics. It is shown that in order to grow gate stacks of good electrical quality, it is important to understand the oxidation kinetics.