Pyrolyzed Photoresist as a Continuous-Tone Mask for Grayscale Lithography.

Grayscale lithography enables single-step fabrication of continuous 3D surface relief for complex optics, MEMS, and scalable replication templates. However, its broad adoption is hindered by the cost, complexity, and resolution constraints associated with fabricating high-quality grayscale masks. Here, we address this challenge by developing a method to produce continuous-tone photolithography masks/reticles through the pyrolysis of 2.5D photoresist structures fabricated using standard multiphoton lithography systems. During pyrolysis, the pattern densifies from micrometers in thickness in the resist state to nanometers in thickness in the carbon state. While the pyrolyzed patterns undergo significant vertical shrinkage, adhesion to the substrate is maintained, preserving overall lateral pattern fidelity despite a systematic in-plane expansion. The amorphous carbon is chemically inert and mechanically robust, enabling repeated exposure and mask cleaning steps, converting the single-use polymer pattern written via direct-write technology into an optical mask capable of repeated exposures.