Defect control during femtosecond projection two-photon lithography

Kim, Harnjoo; Saha, Sourabh K.

Abstract Two-photon lithography (TPL) is a photopolymerization-based additive manufacturing technique that enables fabrication of millimeter scale complex three-dimensional (3D) structures with submicron features. Despite this unique capability, TPL has experienced limited industrial adoption due to its low throughput. The recently developed parallel projection technique, called femtosecond projection TPL (FP-TPL), is a promising approach to scale up this process as it increases the throughput up to three orders of magnitude. However, it requires tuning of process parameters, including photopolymer material properties, to minimize over-polymerization-based defects. Here, we show how a modification of the optical projection strategy can be used to control these over-polymerization defects without tuning the photopolymer composition. Through optical modeling of the projection technique, we show that these defects can be minimized by altering the density of the projected mask. In addition, the aspect ratio of the submicron features can by reduced from more than 2 to 1.2. Thus, this optimal projection strategy transforms FP-TPL into a more robust process suitable for high-throughput high-quality 3D printing of micro and nanoscale structures.