Effects of oxygen flow rate on the properties of HfO ₂ layers grown by metalorganic molecular beam epitaxy

The investigations on the properties of HfO ₂ dielectric layers grown by metalorganic molecular beam epitaxy were performed. Hafnium-tetra-tert-butoxide, Hf(C ₄ H ₉ O) ₄ was used as a Hf precursor and pure oxygen was introduced to form an oxide layer. The grown film was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), and capacitance-voltage (C-V) and current-voltage (I-V) analyses. As an experimental variable, the O ₂ flow rate was changed from 2 to 8 seem while the other experimental conditions were fixed. The XPS spectra of Hf 4f and O 1s shifted to the higher binding energy due to the charge transfer effect and the density of trapped charges in the interfacial layer was increased as the oxygen flow rate increased. The observed microstructure indicated the HfO ₂ layer was polycrystalline, and the monoclinic phases are the dominant crystal structure. From the C-V analyses, k = 14-16 and EOT = 44-52 were obtained, and the current densities of (3.2-3.3) × 10 ^-3 A/cm ² were measured at - 1.5 V gate voltage from the I-V analyses.