Fabrication of microlens array using backside exposure and DMD-based grayscale lithography

This paper explores the fabrication of aspherical microlens arrays using a grayscale ultraviolet (UV) exposure system based on a digital micromirror device (DMD). The proposed DMD-based lithography system employs an oblique stepping method, where the DMD array is slightly tilted in the stepping direction to perform step-by-step grayscale UV exposure. This approach assigns the DMD pixels to a group of exposure points that are uniformly distributed over a large area with high spatial resolution. Consequently, the desired UV dose distribution for accurately shaping microlens array profiles after photoresist (PR) development is achieved. Unlike many previous approaches, this technique utilizes backside UV patterning on a transparent substrate, allowing direct use of negative-tone PR materials for microlens fabrication. Comprehensive theoretical analysis and numerical modeling are provided, alongside detailed experimental procedures and measurement results.