High-Aspect-Ratio Grating Microfabrication by Platinum-Assisted Chemical Etching and Gold Electroplating

Diffractive optics play a key role in hard X-rays imaging for which many scientific, technological, and biomedical applications exist. Herein, high-aspect-ratio microfabrication of gratings for X-ray interferometry is demonstrated using Pt as a catalyst for the metal assisted chemical etching of Si in a solution of HF and H2O2. The Pt layer is thermally treated to realize a porous catalyst layer that stabilizes the etching of a pattern with a pitch size from 4.8 to 20 μm in the direction perpendicular to the <100> Si substrate and an aspect ratio up to 60:1. The superior etching performance of Pt as a catalyst and its stability in a solution with high HF content are reported in direct comparison with the Au catalyst for the same grating parameters. The Si structure is then used as a template for filling with Au, as a high absorbing X-ray material. The Pt catalyst layer is used as a conductive seed for Au electroplating. The quality of the overall process is assessed by obtaining a visibility map using 30 μm-thick Au grating in an X-ray interferometric setup at 20 keV.