Investigating pathways for deep-UV photolithography of large-area nanopost-based metasurfaces with high feature-size contrast

A major challenge in photolithography-based nanofabrication is the patterning of large features next to small features. However, such arrangements of features are often required by nanofabricated devices such as metasurfaces. Oftentimes, electron-beam lithography is utilized to circumvent this problem, but at the expense of cost, fabrication time, and limited write-area, which, thus, limits fabrication throughput. In this work, we detail an aperiodic design framework for metasurfaces that can achieve 2π phase control in the near-infrared (NIR) and can be easily fabricated with deep-UV photolithography. We also explore several approaches by which we can achieve the fabrication of fixed pitch metasurfaces with a range of nanopost diameters as small as 220 nm and as large as 480 nm directly adjacent to one another by splitting each device into several photomask images based on a nanopost diameter and/or a pitch, a diluting photoresist developer, and tailoring photoresist thickness. We report on the effectiveness of each strategy individually and in combination with each other and characterize the optical behavior of metasurfaces fabricated with these techniques. Ultimately, we find that using a combination of all three strategies results in the best fabrication performance, allowing us to fabricate 1 mm2 NIR metasurfaces that can achieve 2π phase control within design tolerance specifications and can be scaled to large-area optics.