Challenges of photomask-based greyscale lithography with a highly-sensitive positive photoresist designed for>100µm deep greyscale patterns

Greyscale lithography is applied to manufacture complex 2.5D and freeform microstructures in photoresists which serve as master for the pattern transfer into materials for permanent applications, often used in micro-optics. We present the results and the challenges in reproducible generation of deep greyscale patterns in a highly sensitive greyscale positive photoresist, mr-P 22G_XP, when using photomask-based mask aligner greyscale lithography in contrast to laser direct writing on which resist development had been focused. Furthermore, we show the influence of resist aging on the resist response, and ways to correct it by process adaption, as well as we conclude requirements to greyscale photomasks suitable to make use of the full potential of the mr-P 22G_XP resist dedicated for >100μm deep greyscale patterns.