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.
During the last decade the ever increasing demand for both high-quality optical coatings and virtually deterministic deposition processes has led to a large number of ion sources available for deposition purposes. For a successful implementation of an ion source the prime economic objectives process stability and production yield have to be considered. The economic efficiency is strongly dependent on the temporal stability and spatial distribution of the ion current density and ion energy spectrum. Retarding Field Analyzers have demonstrated their potential as a tool for the analysis of ion sources. However, deliberate evaluation of the measurements is required especially at a non-zero angle of incidence occurring during the examination of three dimensional ion emission profiles. The present study discusses the influence of different geometric Faraday-Cup designs on the resulting data as well as erroneous conclusions potentially drawn from measurements. Furthermore first results of the ion current density distribution characteristics of different ion sources, evaluated on the basis of data taken by a multicup array are presented.
The presented work is embedded in the research network “Integrative Ion Processes for Modern Optics”, called IntIon, consisting of 12 partners from the German optics industry and two research institutes. The main target of the IntIon network is the development of new process concepts on the basis of ion assisted deposition (IAD) for the industrial production of optical thin film components. Besides an improvement in efficiency, a major aim is concentrated on the optical characteristics for selected application fields with high economical potential. In this network, different ion and plasma sources are compared with regard to their qualification for ion assisted deposition processes. This work includes the characterization of the ion energy and ion current using Faraday-cup measurements. The selection of investigated coating materials includes a broad variety of standard and non-standard oxides. First results of the network will be presented for adapted deposition materials and different operation characteristics of ion sources.