A study of greyscale electron beam lithography for a 3D round shape Kinoform lens for hard X-ray optics

For high quality imaging of materials in nanoscale by hard X-ray optics, high resolution lenses with high focusing/imaging efficiency are needed. Refraction based conventional Kinoform lenses with 1D linear configuration in Si has been attempted for decades, but there has still been no sign of success due to the enormous difficulty in fabrication. This paper proposes a novel configuration of golden Kinoform lenses with round shape on a plate, in which each zone maintains the typical 3D parabolic profile as seen in the traditional 1D counterpart. The major focus in this work is on the generation of the 3D profile in e-beam resist through greyscale electron beam lithography (EBL) as the template for the golden Kinoform lens. Systematic study of the greyscale lithography conditions, including the comparisons of resists, developers and charge distributions, has been conducted by using Monte Carlo simulation as well as e-beam lithography. Initial results have been achieved for replicating the desired 3D profile of the golden Kinoform lens in the resist. Using the generated profile in resist as templates, the golden Kinoform lens with 200 μm diameter and 3.5 μm height has been successfully fabricated, for the first time, which will hopefully replace the existing Fresnel zone plates for hard X-ray imaging with high resolution and high efficiency. [Display omitted] •A novel configuration of golden Kinoform lenses with round shape on a plate for hard X-ray focusing/imaging with high resolution and high efficiency has been fabricated by grayscale e-beam lithography, followed by Au electroplating.•The process condition has been optimized by comparing the developers, the developing time, e-beam resists (PMMA and SML2000) and the dose distributions.•The success of this work has established a solid background for further developing round shape Kinoform lenses to focus and image materials with nanoscale resolution and high efficiency by hard X-ray beyond 20 keV, which has never ever been available before.