We present a compact setup for near-edge x-ray absorption spectroscopy at the carbon K-edge based on a laser-driven plasma source. To generate the required broad-band emission in the spectral range of the ‘water window’ (λ = 2.2–4.4 nm) a krypton gas puff target was used. The table-top setup consisting basically of the laser-plasma source and a flat-field spectrometer can be used for near-edge x-ray absorption fine structure experiments in transmission as well as reflection under grazing incidence conditions (ReflEXAFS). The latter method offers the advantage that thin film preparation is not necessary and that the surface sensitivity is strongly enhanced. The results obtained for thin polymer films show good agreement with synchrotron data. Furthermore, we use the ReflEXAFS method to investigate changes in the chemical composition of PMMA induced by extreme ultraviolet (EUV) radiation. The spectra indicate a loss of the carbonyl functional group upon irradiation as well as crosslinking effects at high EUV radiation doses.

In order to perform material interaction studies with intense extreme ultraviolet (EUV) radiation, a Schwarzschild mirror objective coated with Mo/Si multilayers was adapted to a compact laser-based EUV plasma source (pulse energy 3 mJ at λ=13.5 nm, plasma diameter ∼300 μm). By 10× demagnified imaging of the plasma a pulse energy density of ∼75 mJ∕cm2 at a pulse length of 6 ns can be achieved in the image plane of the objective. As demonstrated for poly(methyl methacrylate) (PMMA), photoetching of polymer surfaces is possible at this EUV fluence level. This paper presents first results, including a systematic determination of PMMA etching rates under EUV irradiation. Furthermore, the contribution of out-of-band radiation to the surface etching of PMMA was investigated by conducting a diffraction experiment for spectral discrimination from higher wavelength radiation. Imaging of a pinhole positioned behind the plasma accomplished the generation of an EUV spot of 1 μm diameter, which was employed for direct writing of surface structures in PMMA.

We present first damage threshold investigations on EUV mirrors and substrate materials using a table-top laser produced plasma source. A Schwarzschild objective with Mo/Si multilayer coatings for the wavelength of 13.5 nm was adapted to the source, generating an EUV spot of 5 microm diameter with a maximum energy density of approximately 6.6 J/cm(2). Single-pulse damage tests were performed on grazing incidence gold mirrors, Mo/Si multilayer mirrors and mirror substrates, respectively. For gold mirrors, a film thickness dependent damage threshold is observed, which can be partially explained by a thermal interaction process. For Mo/Si multilayer mirrors two damage regimes (spot-like, crater) were identified. Fused silica exhibits very smooth ablation craters, indicating a direct photon-induced bond breaking process. Silicon shows the highest damage threshold of all investigated substrate and coating materials. The damage experiments on substrates (fused silica, silicon, CaF(2)) were compared to excimer laser ablation studies at 157 nm.

In order to generate high-energy densities of 13.5 nm radiation, an extreme ultraviolet ͑EUV͒ Schwarzschild mirror objective with a numerical aperture of 0.44 and a demagnification of 10 was developed and adapted to a compact laser-based EUV source. The annular spherical mirror substrates were coated with Mo/ Si multilayer systems. With a single mirror reflectance of more than 65% the total transmittance of the Schwarzschild objective exceeds 40% at 13.5 nm. From the properties of the EUV source ͑pulse energy 3 mJ at 13.5 nm and plasma diameter approximately 300 m͒, energy densities of 73 mJ/ cm 2 at a pulse length of 6 ns can be estimated in the image plane of the objective. As a first application, the formation of color centers in lithium fluoride crystals by EUV radiation was investigated. F 2 , F 3 , and F 3 + color centers could be identified by absorption spectroscopy. The formation dynamics was studied as a function of the EUV dose. By imaging of a pinhole positioned behind the plasma, an EUV spot of 5 m diameter was generated, which accomplishes direct writing of color centers with micrometer resolution.

Articles you may be interested inDamage of multilayer optics with varying capping layers induced by focused extreme ultraviolet beam Direct photo-etching of poly(methyl methacrylate) using focused extreme ultraviolet radiation from a table-top laser-induced plasma source Formation and direct writing of color centers in LiF using a laser-induced extreme ultraviolet plasma in combination with a Schwarzschild objective Rev. Sci. Instrum.