Optical characteristics of H2O-based and O3-based HfO2 films deposited by ALD using spectroscopy ellipsometry

Optical properties of thin atomic layer-deposited HfO 2 films grown by H 2 O and O 3 are analyzed by variable angle spectroscopic ellipsometry. By investigating the dielectric constant, it is found that a higher real part of the dielectric constant ( ε 1 ) value is observed for H 2 O-based film due to less silicate component in the film. Careful examination of the log scale of imaginary part of the dielectric constant ( ε 2 ) leads to the conclusion that the absorption features in the energy range of 3.2–5.35 eV originate from the interface layer between the silicon substrate and the native oxide. In particular, O 3 -based gate stacks have less sub-band gap defect states besides the silicon’s critical features. Moreover, a larger high-frequency dielectric constant, direct and indirect band gap values are obtained for O 3 -based film. Meanwhile, suitable valence band offsets (3.38 and 3.55 eV) and conduction band offsets (1.58 and 1.47 eV) are obtained for H 2 O- and O 3 -based HfO 2 gate stacks, respectively, indicating both type of dielectric films can provide sufficient tunneling barriers for both electrons and holes.