Maskless Lithography with Holographic Feedback for the Fabrication of Optical Elements

Photolithography has become a powerful tool in the fabrication of micro-optical elements following the advancements in grayscale approaches. However, hitting tight design tolerance goals require precise control of all parameters such as temperature, resist nonlinearity or preventing vignetting. In this work we took an alternative route to these problems by combining maskless lithography with digital holography. Addition of digital holography enables the use of feedback by measuring the quantitative phase of specimen near real time and in situ nondestructively. After each near UV exposure, phase retardation map of exposed photopolymer is measured with digital holography part of the system. Any deviation from target phase is corrected by changing the pattern displayed on the mask. We showed that the proposed method reduces the standard deviation of resulting phase compared to traditional one-shot grayscale lithography. It also does not require any precalibration of photoresist and relaxes the constraints for uniform UV illumination in sample plane.