Characterization of single LaF3 and MgF2 films on spherical substrate by planetary deposition

• LaF3 and MgF2 films prepared on spherical lens by planetary deposition are characterized.
• Column slanting angles are analyzed with flux vector theory.
• Refractive index inhomogeneities of the films are reversely engineered from optical spectra.
• Influence of film properties on spectral uniformity of 193 nm AR coatings is demonstrated.

LaF3 and MgF2 films were prepared upon witness plates distributed on a steep spherical substrate by thermal evaporation and planetary deposition. Micro-structures and optical properties of the films at different locations of the spherical substrate were comprehensively investigated. Column slanting angles of the films are experimentally revealed to increase from the center to the brim of spherical substrate, as interpreted by a flux vector theory. Accompanied by the increased column slanting angles, the average refractive indices of the films decrease while the refractive index inhomogeneities increase from the substrate center to the brim. Influence of the position-dependent refractive index and refractive index inhomogeneity on the optical spectra of 193 nm interference antireflective coatings is experimentally demonstrated. This investigation is helpful for optimizing the spectral uniformity and minimizing the wave-front aberration of 193 nm interference coatings used in micro-lithography systems.