X-ray lithography fabrication of a zone plate for X-rays in the range from 15 to 30 keV

Progress on the fabrication of zone plates for hard X-rays is reported. The issue of achieving a high aspect ratio for lithographic structures has been addressed by developing a specific fabrication protocol based on the combined use of electron beam and proximity X-ray lithography. An example of a 1 mm diameter wide zone plate, optimized for a 23 keV X-ray beam, is presented, showing an aspect ratio of the outermost zone of up to 10. The most critical steps of the fabrication process are discussed on the basis of the results.