Electron Beam Lithography of Fresnel Zone Plates Using A Rectilinear Machine And Trilayer Resists

We describe the use of a commercial e-beam lithography system (JEOL JBX-6000FS) to fabricate Fresnel zone plates for x-ray microscopy. The machine is capable of controlling the pitch of optical gratings with sub-nanometer precision, so its beam placement properties are more than adequate for zone plate fabrication. The zone plate pattern is written into a thin top layer (PMMA or Calixarene) of a trilayer resist, and transferred into thick nickel zones using reactive ion etching (RIE) followed by electroplating. Zone plates with outermost zone widths of 30 nm have exhibited efficiencies up to 10.0% at a 390 eV photon energy and with diameters in the range 80 to 120 μm. Zone plates with outer zones of 18 to 20 nm were also fabricated in thinner Ni with correspondingly lower efficiencies of 2.6%. Zone plates with outermost zone widths of 45 nm have been fabricated with larger diameters up to 160 μm. All results reported were obtained with a 50 kV system with 80 μm field deflection size; future efforts will make use of a 100 kV, 500 μm field size system.