Imaging zone plates for x-ray microscopy fabricated by electron-beam lithography

Abstract

Fresnel zone plates have been fabricated by electron‐beam lithography using a modified scanning transmission electron microscope. These microzone plates are designed to work as imaging elements in an x‐ray microscope. To achieve zone plates that are free of distortions, the deflection field of the lithography system has been calibrated by the aid of externally generated reference marks. Microzone plates with a minimum linewidth of 20 nm have been written into polymethylmethacrylate and etched into a 15‐nm‐thick titanium layer. Two methods of transfer into a gold absorber layer have been used, namely sputter etching of the gold layer with a reactively ion etched titanium mask, and electroplating of gold using a suitable trilevel resist system. By these techniques, Fresnel zone plates with 100 zones, a width of the outermost zones of 50 nm, and a thickness of the gold absorber layer of 80 nm have been fabricated. Imaging experiments have been performed at the electron storage ring BESSY in Berlin, and the results have been compared with images obtained by holographically fabricated zone plates.