Aligned double exposure in deep X-ray lithography

Deep X-ray lithography with synchrotron radiation is a powerful tool to generate threedimensional microstructures with high aspect ratios. In order to complement and enhance the normal shadow printing with methods to generate true threedimefisional structures, we investigated the aligned multiple exposure process to produce step-like LIGA structures also involving the sacrificial layer technique to obtain movable structures. Irradiations have been performed utilizing a newly developed X-ray Scanner (JENOPTIK GmbH) with internal optical alignment system. Multiple exposure requires the alignment of mask and substrate. We used silicon nitride mask membranes with 10 mu m thick gold absorber patterns, which show excellent transmission in the visible light range for alignment purposes and good X-ray transparency in the hard X-ray regime. The first results of double exposure experiments obtained with the scanner prototype are promising. With the exception of a systematic error an alignment accuracy of sigma(x) = 0.26 mu m and sigma(y) = 0.4 mu m (standard deviation) has been achieved. Present work concentrates on the improvement of the adjustment system. All the exposures have been carried out at the BESSY wavelength shifter (Berlin/Genmany).