Preparation and optical properties of sputtered-deposition yttrium fluoride film

• Yttrium fluoride thin films have been prepared by magnetron sputtering method.
• Sputtering action causes non-stoichiometric yttrium fluoride films.
• Yttrium fluoride films have orthorhombic phase with (1 1 1) growth orientations.
• The film at 400 °C has desirable optical properties with low n and k.

Yttrium fluoride films were grown on silicon wafers by magnetron sputtering at different substrate temperatures (ST). The composition, structure and optical properties have been investigated systematically. X-ray photoelectron spectroscopy (XPS) analysis shows that the films mainly contain Y and F elements. The deficiency of F element in yttrium fluoride films is generally inevitable by magnetron sputtering. Glancing incident X-ray diffraction (GIXRD) analysis demonstrates that the films have the orthorhombic structure with different growth orientations. Spectroscopic Ellipsometer (SE) analysis on films exhibits that the refractive index of yttrium fluoride film grown at 400 °C posses lower value than these of ones under other temperatures. The absorption of films gradually diminishes as the substrate temperature increases. It has been convinced that the YF3 films with optimal optical properties can be achieved by adjustment of substrate temperature for desirable optical design and applications.