Metal assisted chemical etching
Grating fabrication is the main bottleneck so far preventing grating-based X-ray phase-contrast interferometry (GI) from being applied at high energies and large field of view. Metal Assisted Chemical Etching (MacEtch) is an electroless chemical etching technique that has been largely used to create high aspect ratio nanostructures in silicon substrates. With respect to the other wet etching techniques, MacEtch showed better performance in terms of anisotropy and feature size. However, MacEtch still suffers from some limitations such as the control of the catalyst stability for etching high aspect ratio structures in the micro-scale and off-mask undesired porosity. We recently demonstrated the capability of etching structures in gas phase with aspect ratio up to 10000:1 with and feature size in the nanoscale (10 nm). This research project wants to answer the fundamental open questions about MacEtch in order to fully explore the range of application and the limits of this technique for grating fabrication and to point out the real performances in terms of etching selectivity, rate, aspect ratio, feature size and X-ray optical performances in combination with other proper technique for the realization of the absorber gratings. The main goal of this project is to use MacEtch for grating fabrication with characteristics that fulfill high energy and large field of view applications. Understanding how MacEtch works with the proper knowledge about semiconductor physics and metal nanostructures is the key to optimize this process and to make it reliable as a grating fabrication technology.