Fabrication of soft x-ray Fresnel zone plate on ultrathin membrane

Fabrication of diffractive x-ray optics for the x-ray region requires a high lateral resolution (~100 nm) and a large thickness of the phase-shifting material (0.5-3 µm). The thickness of the phase shifting material depends upon the energy of the photons. We have optimized the exposure and developing processes for 996 K poly methyl methacrylate (PMMA) of different thicknesses and have worked on adhesion issues to develop a Fresnel zone plate (FZP) structure on polyimide membrane. We discuss the effects of these fabrication steps on the FZP's fabrication and aspect ratio. Preliminary evaluation of the FZPs was done by scanning electron microscopy. The FZP focusing performance will be characterized at Indus synchrotrons.