High contrast synchrotron x-ray lithography by means of silicon based masks and magnesium beam windows

This paper deals with the investigation of novel beam line windows based on magnesium in combination with silicon X-ray masks. Mg enables, because of the distinct absorption edge at 10Å, an effective contrast enhancement in synchrotron lithography. In regard to BESSY radiation and PMMA resist the contrast of Si-masks can be increased more than sixfold by use of Mg-beam windows instead of silicon/kapton windows. In comparison to Be-beam windows the contrast can be threefold enhanced. The prospects of a one-to-one submicron mask technology based on a thin absorbing layer are being discussed in view of exposure experiments with only 0.3 mm thick Au patterns on Si-masks. It turned out that also by adjusting a reliable proximity distance of 30 mm between mask and wafer 0.1 mm features can be replicated in 1 mm thick resist. This offers the important possibility of copying Si master masks having very thin absorbing layers by means of synchrotron lithography after inspection and elimination of faults.