1King Abdullah Univ. of Science and Technology (Saudi Arabia) 2Univ. of California, Santa Cruz (United States) 3NRC-Herzberg Astronomy & Astrophysics (Canada) 4Univ. of Victoria (Canada)
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Spatially-varying features with uniform depths in large areas are challenging to achieve with etching based lithography. Here we propose an additive lithographic fabrication process to realize simultaneous presence of micrometer and millimeter features with low surface roughness. The etching step is replaced by sputter deposition and bi-layer lift-off to form the microstructures. Instead of removing materials, our method grows materials onto the substrate. We demonstrate its effectiveness with a reflective Tilt-Gaussian-Vortex mask with aluminum deposited on a fused silica substrate. The center has a diameter of 130 microns with minimum spacing of 2 microns, and the background pattern is 3 mm by 3 mm, with the largest flat region spanning 1.5 mm. A preliminary 4-level prototype has been tested in the Gemini Planet Imaging calibration unit upgrading project, and an improved 16-level sample has been measured. The results show uniform depth and surface roughness control in the whole area.
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Qiang Fu, Hadi Amata, Benjamin Gerard, Christian Marois, Wolfgang Heidrich, "Additive lithographic fabrication of a Tilt-Gaussian-Vortex mask for focal plane wavefront sensing," Proc. SPIE 11889, Optifab 2021, 1188911 (28 October 2021); https://doi.org/10.1117/12.2602425