Evaluation of grating realized via pulse current electroplating combined with atomic layer deposition as an x-ray grating interferometer

Abstract

In this work, the authors developed a simple and efficient two-step deposition process for the realization of an x-ray absorption grating: ALD (atomic layer deposition) of a conductive seed layer, followed by electroplating of the absorbing metal with a pulse current mode. An Si grating with a high aspect ratio of 1:40 was fabricated by deep reactive ion etching on an 8 in. Si wafer. In order to form a conductive seed layer on the Si grating with such a high aspect ratio over an area of 10 × 10 cm2, Ru was conformally deposited by a thermal ALD process with O2 reactant gas. The authors analyzed the results of electroplating performed in different bias modes to fill Au in a high aspect ratio Si grating structure. It was found that electroplating in the pulse current mode (duty cycle: 5%, current density: 1.7 mA/cm2) for 79 h allowed Au to uniformly fill the entire grating area, whereas in the direct current mode, severe step coverage on top of the grating was observed. The authors successfully tested the grating fabricated by the suggested two-step deposition process as an absorption grating (G2) for a high x-ray energy Talbot-Lau grating interferometer.