Deep-reactive-ion-etching in X-ray grating fabrication: a review

The development of grating fabrication shares its journey with the development of X-ray phase contrast imaging. Indeed, the fabrication of gratings with features of sufficiently high aspect ratio is one of the bottlenecks preventing the widespread application of phase contrast imaging in X-ray diagnostics, material science and security. The silicon platform that underlies modern manufacture of integrated circuits, with its well-established technologies for lithography, etching and metal deposition, has the potential to provide high yields and volumes for industrial fabrication of both phase and absorption gratings used in a grating-based X-ray imaging systems. This review article introduces recent developments in the fabrication of high aspect ratio X-ray gratings using ubiquitous clean-room manufacturing tools, focusing on deep reactive ion etching processes. It summarizes the most challenging issues for fabricating features with aspect ratios reaching 70:1, proposing approaches to overcome processing problems and improve product quality.