J. Kolbe
H. Schink
D. Ristau

Optical losses of fluoride coatings for UV/VUV applications deposited by reactive IAD and IBS processes

Proc. Annual Technical Conference Society of Vacuum Coaters
44-50
1993
Type: Zeitschriftenaufsatz (non-reviewed)
Abstract
The deposition of high-reflecting dielectric coatings for the VUV spectral range requires the use of fluoride materials because oxide layers show strong absorption at wavelengths below 200 nm. As shown in a previous paper, the reflectances of fluoride mirrors deposited conventionally are limited by volume and interface scattering attributed to the polycrystalline microstructure of the layers; reduced scattering was observed in layers deposited by IAD or IBS. In these processes, oxygen was used as reactive gas in order to eliminate the stoichiometric defects of the condensed layer material which were attributed to fluorine deficiencies caused by preferential sputtering during deposition. The resulting oxide content in the layers, however, leaded to strong absorption losses at wavelengths below 200 nm. To obtain layers with improved stoichiometry by using IAD or IBS, these processes were performed with fluorine as reactive gas. Single layers and high-reflecting quarterwave stacks were deposited and investigated. Their optical properties are compared to data obtained for conventionally deposited coatings and for coatings deposited by IAD or IBS using oxygen as reactive gas. The results indicate that the ion processes are promising tools for the deposition of low-loss dielectric UV/VUV mirrors.