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.