Self-aligned fabrication of high-aspect ratio high-resolution x-ray gratings

Abstract

High-aspect ratio x-ray absorption gratings are required for hard x-ray or high-resolution soft x-ray phasecontrast imaging (XPCi) applications. X-ray gratings play a central role in grating-based XPCi techniques, where visibility – image quality – is highly dependent on the quality of gratings. Although the fabrication process of x-ray gratings for soft x-ray imaging is well-developed, there are technological challenges in highresolution hard x-ray imaging that impede us from making high-aspect ratio large field-of-view fine x-ray gratings through conventional fabrication processes. Here we present a design and a fabrication process to fabricate highaspect ratio gratings that benefit from a self-aligned hard-mask – a patterned chromium-gold-chromium thin film deposited on a transparent ITO-on-glass substrate – which facilitates both lithography and electroplating processes. The repeatability of the proposed method makes it suitable for achieving high-aspect ratio fine structures as thick as desired through a multi-layer structure without any restraint or limitation on the aspect ratio of features. The multi-layer structure design overcomes the aspect ratio limitation associated with UVlithography. Although this method works well with X-ray lithography, the key advantage of this design is that it enables UV lithography for high-aspect ratio grating fabrication through a reliable yet simple process. To the best of our knowledge, self-aligned multi-layer SU-8 based grating design has not been previously reported. The proposed design and fabrication process help researchers further develop x-ray gratings performance to facilitate high-resolution coded-aperture and Talbot-Lau high-energy x-ray phase-contrast imaging.