Low-Energy Path to Dense HfO₂ Thin Films with Aqueous Precursor

Abstract

New, stable aqueous solutions have been developed for the deposition of high-quality HfO2 thin films. The low ionic strength of the solution relative to a stoichiometric salt provides the means to directly spin coat a film without organic additives. Peroxide mediates particle interaction in the solution, while enabling relatively low-energy pathways for condensation of the precursor species to a film. Film structure, chemistry, and density are investigated by X-ray diffraction, FT-IR, electron-probe microanalysis, SEM, and X-ray reflectivity. Results from these measurements collectively reveal that smooth and dense HfO2 films are readily produced from the precursors with annealing at moderate temperatures. Optical properties of the films are studied by spectroscopic ellipsometry and transmission/reflection measurements. The observed refractive indices (1.89−1.93) are comparable to those achieved via vapor deposition techniques. Dielectric properties are evaluated through integration of the films into capacitors and thin film transistors. Performance as capacitor dielectrics is characterized by leakage current densities <10 nA/cm2 (at 1 MV/cm) and breakdown fields up to 5.5 MV/cm. As gate dielectrics in thin film transistors with amorphous indium gallium zinc oxide channels, the films exhibit small gate leakage, enabling transistor performance with incremental mobilities near 13 cm2/V·s.