The present paper describes the fabrication sequence of a LIGA mold insert by electroforming after the patterning steps of the overall process. These tools are applied for large scale fabrication of microcomponents made by molding and embossing processes. The application of an intermediate layer system leads to optimized process performance and to a better surface quality of the mold insert. The plating processes are described and the materials properties, e.g. hardness, are used for the characterization of the recrystallization behavior of the electroformed nickel which yields the high temperature application limit of the tool.
LIGA-structures are known to have a lateral dimensional precision of 1 lm and below. These speci®-cations strongly depend on the process parameters. Fabrication of 400 lm tall nickel LIGA-structures by electroplating of X-ray patterned (DXRL) resist structures revealed much higher distortions. These are caused on the one hand by thermal expansion of the structured resist since the electroforming is usually performed at 52°C, but on the other hand to a higher degree by swelling of the resist in the aqueous electroplating bath. Reducing the electrolyte temperature not only eliminates the thermal expansion but also particularly reduces the swelling. At room temperature the latter is reduced by a factor of 3 in comparison to the usual 52°C-bath leading to an overall reduction of the deformation of up to 80%. In this paper the experimental data are presented and the results are explained. Furthermore ®rst microstructures electroplated at room temperature with optimized precision are shown.
Nickel refractive planar lenses generating line and point X-ray spots were fabricated by LIGA technology. The optimum parameters of the lenses were simulated for a kinoform lens profile and an X-ray energy range from 100 keV to 1 MeV. The focusing elements of the lens are characterised by an aspect ratio of about 200 and a sidewall roughness of less than 5 nm r.m.s. The optical characteristics of the lenses were tested at the ESRF using a photon energy of 212 keV. A focal spot of 10 lm size was measured using a X-ray sensitive film as a width at a half maximum of the darkening of this detector. A ratio of appr. 7 of the detector responses of the focused spot to the unfocused radiation was measured. The correspondent characteristics of the focal spot of the lens for the revealed photon flux are FWHM » 6 lm and $20 for the gain. IntroductionRefractive lenses made of aluminium, silicon and other light materials are studied intensively and are used usually for focusing X-rays of photon energy from 10 keV to 30 keV [1-7]. However, light materials can't be used for experiments with a photon energy of more than 100 keV because of the low values of the decrement of the refractive index [8]. The focal distance of such lenses would be several tens of meters. Although it is possible to apply Al parabolic lenses for energies above 100 keV their practical use is very limited because a large number of lenses is required and consequently a massive lens holder is needed to obtain a reasonable focus distance within 5-10 m range. Anyway, investigations with high energy photons would extend the range of applications of X-ray methods but synchrotron radiation (SR) intensity in the photon energy range above 100 keV is small due to an exponential decrease of the spectral function of the SR sources. For example, the density of the photon flux of the relatively bright SR sources of third generation like ESRF, Spring-8, APS falls by several orders of magnitude within the photon energy range of 50-500 keV, even though undulators are used [9]. Therefore, lenses for high energy photons are necessary. The decrements of the refractive index of suitable lens materials in this energy range have to be many times larger that of light materials, but also absorption of the lens material should not be too high.Among heavy materials for a hard X-ray lens formation, nickel is the most suitable as it is radiation and corrosion stable and it can be electroplated. Focusing parameters of parabolic Ni lenses had been estimated in the work [8] devoted to the testing of aluminium lenses which were made by hot pressing. Indeed, the decrements of the refractive index of Ni is $3.3 times that of Al. However, thermal pressing of Ni plates is not easy because of the relatively high rigidity and melting temperature as well as the recrystallization during phase transition.LIGA technology allowing a formation of microstructures with any given profile by means of X-ray lithography and nickel electroplating has been widely used within the last ten years for the fabric...
Sub-lm structured surfaces allow modifying the behavior of polymer films or components. Especially in micro-fluidics a lotus-like characteristic is requested for many applications. Structure details with a high aspect ratio are necessary to decouple the bottom and the top of the functional layer. Unlike to stochastic methods, patterning with a LIGA-mold insert it is possible to structure surfaces very uniformly or even with controlled variations (e.g., with gradients). In this paper we present the process chain to realize polymer sub-lm structures with minimum lateral feature size of 400 nm and up to 4 lm high.
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