Ultra-shallow EUV and soft X-ray gratings fabricated by broad-beam nitrogen ion irradiation

Abstract

Controlled and precise fabrication of structures with heights in the range of single digit nanometres is one of the challenges for diffraction gratings operating near-normal incidence in the extreme ultraviolet (EUV) and soft X-ray range. Here, we expand on previous research utilizing swelling of silicon after irradiation with ions as alternative to conventional dry etching. By irradiating silicon through a mask with a broad beam of nitrogen ions, we realized lamellar gratings in a precise and well controlled process. We were able to fabricate gratings with structure heights between (1.00 +/- 0.05) nm to (10.0 +/- 0.5) nm and a pitch of 1 micrometre, which is suitable for both EUV and soft X-ray applications. A variation of ion energy from 20 keV to 40 keV further expands the foundations of this process and yielded an additional parameter to control the resulting structure height and shape.