Fresnel Zone Plates with Zone Widths below 10 nm

The fabrication of nanostructures with small lateral sizes and high aspect ratios is one of the key challenges in developing highly resolving diffractive X-ray optics with good efficiencies. Moving towards smaller and smaller nanostructures, lithography methods such as electron beam lithography approach fundamental limitations in feature size. For application of nanodevices like diffractive X-ray lenses, feature sizes of below 10 nm are required to enter a new regime in high resolution X-ray microscopy. As such dimensions are difficult to obtain using conventional electron beam lithography, we pursue a line-doubling approach.

The fabrication process consists of several steps. Firstly, a template structure is written by electron beam lithography, which consists of a low-Z material. The template is then coated with iridium, due to its high refractive index, and sputtered with argon ions to remove the caps and bottom. The template can then be etched away using hydrofluoric acid.

We demonstrate that this method yields structure sizes as small as 6.4 nm. X-ray lenses fabricated in this way are currently tested for their efficiency and resulting resolution. First results will be presented at the X-ray Microscopy Conference in Saskatoon, Canada.