Fabrication of extremely smooth blazed diffraction gratings

Abstract

High efficiency diffraction gratings are important in a variety of applications, such as optical telecommunications, lithography, and spectroscopy. Special interest has been placed on blazed diffraction gratings for their ability to enhance diffraction intensity at the specular reflection angle off the blazed facets. In this thesis I will report a novel process for fabricating extremely smooth blazed diffraction gratings with 200 nm-period. The blazed grating is fabricated using interference lithography and anisotropic etching, then replicated using nanoimprint lithography. This process was developed for fabricating the off-plane blazed diffraction gratings for the NASA Constellation-X x-ray space telescope. In order for x-rays to reflect effectively through grazing incidence reflection, the gratings will be coated with high atomic number materials, such as gold. Deposition of thin metal film often develops residual stress that adds out-of-plane distortion. In this thesis the out-of-plane distortions due to thin metal films are analyzed using wavefront aberration functions known as the Zernike polynomials. The thin film stress is proved to be linearly related to the change of the Z₂₁ Zernike coefficient. The anisotropic material properties of silicon are taken into account in the derivation, and a prediction of lattice dependent distortion is proposed.