Structural and dielectric characterization of atomic layer deposited HfO2 and TiO2 as promising gate oxides

Tetrakis (diethylamino) hafnium (TDEAH), tetrakis (diethylamino) titanium (TDEAT) and H₂O were used for the atomic layer deposition of HfO₂ and TiO₂ films on silicon substrates. X-ray Photoelectron Spectroscopy showed that after a short Ar⁺ sputtering for removing surface contaminants, both HfO₂ and TiO₂ films were found to be essentially carbon free. While HfO₂ remained at +4 chemical state after the surface sputtering, TiO₂ partially changed into Ti⁺³ (Ti₂O₃) and Ti⁺² (TiO), suggesting a preferential sputtering of O over Ti. Phase-shift interferometry (PSI) was applied to probe the surface morphology of both as-deposited and post annealed films, which were later examined by Grazing Incidence X-ray Diffraction (GIXRD). From both PSI and GIXRD results, as-deposited HfO₂ and TiO₂ films were found to be amorphous with smooth surfaces but began to crystallize with roughened surfaces after annealing at 600 °C, with HfO₂ crystallizing into a monoclinic structure and TiO₂ crystallizing into an anatase structure. C-V and I-V measurement were performed after electron beam evaporation of Al metal contacts on the dielectric layers. The calculated dielectric constant (k) value of TiO₂ is almost three times higher than that of HfO₂ and the measured leakage current densities for the metal oxides are below 10^-5 A/cm² at the applied voltage of 1 V.