Nanostructure and optical properties of fluoride films for high-quality DUV/VUV optical components

Abstract

The persistent utilization of optical lithography at the DUV and VUV excimer laser wavelengths leads to extraordinary demands on the optical components involved (high throughput, low scattering, high mechanical stability, ...). Fluorides are the main or even the only candidates for film materials in these spectral regions because of their low absorption. There are several high-index and low-index fluoride materials. These materials, however, may significantly differ in their nanostructural properties leading to scatter losses crucially influencing the performance of the multilayers. In order to find optimal material combinations, HR multilayer mirrors were fabricated using several high-index fluoride film materials. Spectral photometry, atomic force microscopy, as well as total and angle resolved light scattering measurement and analysis were performed for comprehensive characterization

The determination of infrared optical constants of rare earth fluorides by classical Lorentz oscillator model

“…Moreover, they have good mechanical property, chemical stability and compatibility with other coating materials. In the ultra-violet, they have been widely used to construct optical multilayer components with other fluorides, such as AlF 3 [3,4], MgF 2 [5] and others.…”

Influence of substrate temperatures on the properties of GdF_3 thin films with quarter-wave thickness in the ultraviolet region

“…The extensive reported inhomogeneity of GdF 3 was undetectable during this first 27 nm growth [7][8][9][10]. The inhomogeneity of GdF 3 film is a result of the film porosity change as film thickness accumulatively increases; the growth mechanisms of cone-shaped columnar and polycrystalline microstructures may introduce gaps between the grains, leaving a discontinuous columnar structure with more voids between the microstructures.…”

“…Pioneering work has been done to evaluate the optical and structural properties of the evaporated GdF 3 ; however, the physical property results of GdF 3 thin films in the UV spectral range are dissimilar [7][8][9][10]. The value of the refractive index of GdF 3 film is usually thickness dependent because of its inhomogeneous structure.…”

Scattering reduction through oblique multilayer deposition

“…One approach to determine the roughness properties inside multilayer coatings is to measure the surface topography during different stages of the deposition process [16,17]. Since this enables 2D measurements of the surface topography, a detailed roughness analysis of the individual interface is possible.…”