Fabrication of diffractive optical components for an extreme ultraviolet shearing interferometer

We have constructed four optical components for use in an extreme ultraviolet shearing interferometer which will operate at a wavelength of 13.4 nm. The components that have been constructed include transmission diffractive optical components such as a Fresnel zone plate, angled gratings, and two‐frequency gratings, as well as pinhole apertures. All the components are fabricated in 110 nm of Ge, which is supported by a 0.5–0.7‐μm‐thick membrane of Si. The patterns were fabricated by first evaporating Ge and then spinning 100 nm polymethylmethacrylate (PMMA) onto the Si membranes. The desired patterns were exposed in the PMMA resist using electron beam lithography. Custom interative computer programs generated the patterns used to control the exposure. After developing the PMMA resist the Ge layer was etched using a reactive ion etching technique. Electron microscopy of the finished components show that the smallest features in our components are cleanly constructed, and the linewidths and placement of the...