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 × 1012 eV−1 cm−2. The electrical characteristics and surface morphology of HfO2 films are affected by O2/Ar gas flow ratio. Finally, post-metallization annealing (PMA) was carried out to reduce the interface state density.