Abstract :
High-k gate dielectric HfO2 thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The
optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and
capacitance–voltage (C–V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO2 films are basically
amorphous. Based on a parameterized Tauc–Lorentz dispersion mode, excellent agreement has been found between the experimental and the
simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically
extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation
of more closely packed thin films and the enhancement of scattering effect in the targeted HfO2 film. Change of the complex dielectric function and
reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies
from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 8C, respectively. It has been found from the C–V
measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with
lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing
Keywords :
Plasma oxidation , Optical properties , interfacial layer , HfO2 thin films , High-k gate dielectrics