The present study deals with the characterization of hafnia, alumina, and zirconia coatings as well as mixtures
thereof with respect to applications in the UV. Emphasis is placed on optical properties, particularly on the
relation between UV refractive index and absorption edge. The shift of the coatings is investigated as well as the
mechanical stress. Finally, we present the results of stress measurements performed for quarterwave stacks
deposited on different substrates in a broad range of deposition temperatures. In this study, no systematic
dependence of the result of the stress measurement on the substrate material and geometry could be identified.
The aim of this work is the optimization of the resonator optics of excimer laser systems to achieve longer lifetimes and
to reduce the cost of ownership. The degradation after long-term exposure to high photon fluxes (typically 80 mJ/cm2 at
the ArF laser wavelength of 193 nm was analyzed. Based on the investigations, a model describing the process of the
deterioration of the out-coupling partial reflector was developed. It was found that contamination of the optics by the
laser's discharge electrodes leads to absorption losses on the surface facing the inside of the resonator. As a consequence,
the laser irradiation causes a temperature gradient in the CaF2-substrates which leads to crystal cleavage and braking of
the optics. Defects on the outward surface are the origin for the growth of Calcite crystals and organic compounds by
photo induced chemical reactions of the substrate material and contaminations in the purge gas. It was demonstrated that
the lifetime of the resonator optics can be substantially increased by adapted optical designs and coatings.
In many applications of ArF - excimer lasers, a specific degradation effect is observed for the CaF2 outcoupling
windows which starts assumedly at the rear surface and results in a characteristic damage morphology.
In the present study, this degradation mechanism is examined in a measurement series involving a variety of
window samples and irradiation sequences in an excimer laser with typical numbers of up to 2×108 pulses for
each component. The irradiated samples were inspected by scanning spectrophotometry, TOF-SIMS, electron
microscopy and other analytical techniques in order to clarify the underlying degradation mechanisms. On the
basis of the experimental findings, coating strategies will be outlined to improve the lifetime of CaF2 - output
couplers in 193nm excimer lasers.
ArF lithography technology requires minimization of optical losses due to scattering and absorption. Consequently, it is necessary to optimize the coating process of metal fluorides. The properties of metal fluoride thin films are mainly affected by the deposition methods, their parameters (temperature and deposition rate) and the vacuum conditions. A substrate temperature of more than 300°C is a condition for high density and low water content of metal fluorides.
Therefore, a substrate temperature of 150°C results in inhomogeneous films with high water content. Until now, the best results were achieved by boat evaporation. This paper will demonstrate that most of the common metal fluorides like MgF2, AlF3, and even LaF3 can be deposited by electron beam evaporation. In comparison to other deposition methods, the prepared thin films have the lowest absorption in the VUV spectral range. Furthermore, metal fluoride thin films were prepared by ion assistance. It will be demonstrated, that they have less water content, high packing density, and low absorption in the VUV spectral range. In this study, single layers of LaF3 and AlF3 and antireflection coatings were prepared by electron beam evaporation with and without
ion-assistance. The mechanical, structural, and optical properties were examined and discussed.
Nowadays, chirped dielectric mirrors for ultrafast optics and laser applications are usually manufactured by sputtering techniques. The suitability of Advanced Plasma Source (APS) assisted electron beam evaporation with respect to such coatings is still under investigation. The purpose of this presentation is to show our first results of the deposition of chirped layers produced by plasma ion assisted electron beam evaporation and of the investigation of their properties. The aim was to design and prepare a NIR-mirror for the spectral range of 700 nm to 900 nm. It has been attempted to find a design that is robust with respect to errors of thickness and refractive index. The mirror consists of more than 26 layers composed of alternating high- (Nb2O5) and low-refractive index (SiO2) material. The deposited coatings were tested in terms of their group delay dispersion (GDD) and their reflectivity. We show, that in the wavelength range between 720 nm and 890 nm the GDD exhibits a value of about -50 fs2, whereas the reflectivity is above 99%. However, the subsequent reverse engineering operations show a relatively large thickness error of more than 1% - 2% regarding the particular layers. Nevertheless the effect on the GDD and the reflectivity is tolerable. Furthermore, we present our first experiments concerning the design and fabrication of a chirped mirror, which allows controlling the third order dispersion (TOD), whereas the relative thickness error of the particular layers should not exceed 1%.