Microstructure and characteristics of the HfO₂ dielectric layers grown by metalorganic molecular beam epitaxy

HfO₂ dielectric layers were grown on the p-type Si (100) by metalorganic molecular beam epitaxy. Hafnium tetra-butoxide, Hf(O·t-C₄H₉)₄ was used as a Hf precursor for its moderate vapor pressure. The properties of the layers were evaluated by X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), and capacitance-voltage (C-V) and current-voltage (I-V) analyses. As the O ₂ flow rate increased, XPS spectra of Hf 4f and O 1s shifted to the higher binding energy due to the charge transfer. The excess oxygen at higher oxygen flow rate contributed to increase the density of trapped charges, however, the dielectric constant was increased as the oxygen flow rate increased. The microstructure observed from the TEM images indicates that the grown layer was polycrystalline, and XRD analysis reveals that the monoclinic phases are the dominant crystal structure. From the C-V analyses, the dielectric constant k=13-16 and the equivalent oxide thickness (EOT)=43-52 were calculated, and leakage current densities of 2.5-2.7×10^-2 A/cm² were measured at -1.5 V gate voltage from the I-V analyses.