Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

The effects of reactive and sputtering oxygen partial pressure on the structure, stoichiometry and optical properties of hafnium oxide (HfO2) thin films have been systematically investigated. The electron cyclotron resonance ion beam deposition (ECR-IBD) technique was used to fabricate the films on to JGS-3 fused silica substrates. The amorphous structure of HfO2 films were determined by X-ray Diffraction. Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering Spectrometry were carried out for the composition and stoichiometry analysis, where this suggests the formation of over-stoichiometric films. The data suggests that the O:Hf ratio ranges from 2.4 – 4.45 to 1 for the ECR-IBD fabricated HfO2 films in this study. The transmission and reflectance spectra of the HfO2 films were measured over a wide range of wavelengths (λ = 185 – 3000 nm) by utilizing a spectrophotometer. The measured spectra were analyzed by an optical fitting software, which utilizes the model modified by O'Leary, Johnson and Lim, to extract the optical properties, refractive index (n) and the bandgap energy (E0). By varying the reactive and sputtering oxygen partial pressure, the optical properties were found to be n = 1.70 – 1.91, and E0 = 5.6 – 6.0 eV. This study provides a flexible method for tuning the optical properties of HfO2 coatings by controlling the mixture of reactive and sputtering gas.