Tailoring the index of refraction of nanocrystalline hafnium oxide thin films

Abstract

Hafnium oxide (HfO2) films were grown by sputter-deposition by varying the growth temperature (Ts = 25–700 °C). HfO2 films grown at Ts < 200 °C were amorphous, while those grown at Ts ≥ 200 °C were monoclinic, nanocrystalline with (1¯11) texturing. X-ray reflectivity (XRR) analyses indicate that the film-density (ρ) increases with increasing Ts. The index of refraction (n) profiles derived from spectroscopic ellipsometry analyses follow the Cauchy dispersion relation. Lorentz-Lorenz analysis (n(λ) = 550 nm) and optical-model adopted agree well with the XRR data/analyses. A direct Ts-ρ-n relationship suggests that tailoring the optical quality is possible by tuning Ts and the microstructure of HfO2 films.