Fresnel zone plates (FZP) are diffractive photonic devices used for high-resolution imaging and lithography at short wavelengths. Their fabrication requires nano-machining capabilities with exceptional precision and strict tolerances such as those enabled by modern lithography methods. In particular, ion beam lithography (IBL) is a noteworthy method thanks to its robust direct writing/milling capability. IBL allows for rapid prototyping of high-resolution FZPs that can be used for high-resolution imaging at soft X-ray energies. Here, we discuss improvements in the process enabling us to write zones down to 15 nm in width, achieving an effective outermost zone width of 30 nm. With a 35% reduction in process time and an increase in resolution by 26% compared to our previous results, we were able to resolve 21 nm features of a test sample using the FZP. The new process conditions are then applied for fabrication of large arrays of high-resolution zone plates. Results show that relatively large areas can be decorated with nanostructured devices via IBL by using multipurpose SEM/FIB instruments with potential applications in FEL focusing, extreme UV and soft X-ray lithography and as wavefront sensing devices for beam diagnostics.
Keywords: Fresnel zone plate; extreme ultraviolet (EUV) radiation; focused ion beam (FIB); ion beam lithography (IBL); nanopatterning; soft X-rays.