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.
Bibliographical noteKAUST Repository Item: Exported on 2022-01-13
Acknowledgements: This work was supported in part by King Abdullah University of Science and Technology (KAUST) individual baseline funding and KAUST Visual Computing Center operational funding. The fabrication was done in the Nanofabrication Corlabs at KAUST. We also acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).