Characterization and process effects of HfO₂ thin films grown by metal-organic molecular beam epitaxy

HfO₂ dielectric layers were grown on the p-type Si(1 0 0) substrate by metal-organic molecular beam epitaxy (MOMBE). Hafnium-tetra-butoxide [Hf(O·t-C₄H₉)₄] was used as a Hf precursor and argon gas was used as a carrier gas. The microstructure and thickness of HfO₂ films were measured by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrical characteristics of the HfO₂ layers were evaluated by high frequency (HF) capacitance-voltage (C-V) and current-voltage (I-V) measurements. The surface morphology, crystal structure, and chemical binding states of HfO₂ films were also examined by atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. HF C-V and I-V measurements have shown that HfO₂ layer grown by MOMBE has higher dielectric constant (k) of 20-22 and lower leakage current density of ∼10^-8 A/cm² compared with the conventional SiO₂. In addition, it has been shown that the HfO₂ layer has fixed oxide charge of about 8 × 10¹¹ cm^-2 and interfacial state density of about 1 × 10 ¹² eV^-1 cm^-2. The electrical characteristics and surface morphology of HfO₂ films are affected by O ₂/Ar gas flow ratio. Finally, post-metallization annealing (PMA) was carried out to reduce the interface state density.