Accuracy of structure transfer in deep X-ray lithography

Deep X-ray lithography with synchrotron radiation (DXRL) constitutes the key microfabrication process step in the LIGA technology. Microcomponents with a height of some mu m up to several mm can be manufactured with sub-mu m precision. The pattern transfer accuracy is governed by technological constraints like thermal mask deformation as well as by various physical effects, e. g. Fresnel diffraction, emission of photo- and Auger electrons, fluorescence radiation, radiation scattering and divergence of the synchrotron radiation beam. A computer program has been developed to investigate the significance of these effects to the dose distribution in the resist material, which in turn determines the lateral structure resolution. The paper gives a brief introduction to the calculation procedure and outlines the weight of the different contributions with respect to transfer accuracy. It is shown that beam divergence and diffraction are much less important than the image blur caused by photoelectrons. Fluorescence radiation emitted from the mask membrane or the substrate contributes to the dose deposition in the resist if mask membrane or substrate consist of high atomic number material. Radiation scattering is negligible for resist layers which are less than some mm thick. A good agreement is found between calculated dose distributions and measured resist profiles. This allows a partial compensation of the above mentioned accuracy limiting effects in the mask design.