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In recent years we have investigated the feasibility of deep X-ray lithography in SU-8 as a means of fabricating very high aspect ratio and densely packed arrays of square channels. We have demonstrated how to overcome the problems in adhesion and stiction accompanying the fabrication of such high aspect ratio structures. We have also examined how to calculate the development time of these structures and how this can be used to optimize the dimensional fidelity of the resulting structures. More recently we have considered the effect of the non-uniform dose deposition and beam hardening as a function of depth in the resist on factors such as the surface roughness and the sidewall taper. In this paper we describe our experimental program, review these results and discuss their implications for the operation of our target device-the lobster-eye telescope.

We describe a model that predicts sidewall slope in SU-8 high aspect ratio microstructures made using x-ray lithography. Our experimental results are in accordance with our model and we demonstrate that essentially zero sidewall taper can be obtained under certain conditions. We use our results to explore the feasibility of optimizing a structure simultaneously for slope and surface roughness.