Ultrashallow EUV and Soft X-Ray Gratings Fabricated by Broad-Beam Nitrogen Ion Irradiation

Controlled and precise fabrication of structures with heights in the range of single-digit nanometers 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 an 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 and 10 ± 0.5 nm and a pitch of 1 µm, which is suitable for both EUV and soft X-ray applications. A variation of ion energy from 20 to 40 keV further expands the foundations of this process and yields an additional parameter to control the resulting structure height and shape.