An easy method to improve efficiency of multi-photon polymerization: Introducing solvents with nonlinear optical absorption into photoresist

Abstract

Understanding the photochemical mechanisms of multi-photon polymerization (MPP) is imperative to further improve the manipulation of photoresists and optimize the manufacturing of products via laser lithography. In this work, organic solvents with nonlinear optical absorption are employed to facilitate MPP in photoresists via enhancing the multi-photon absorption (MPA) of photo-initiator (PI). The nonlinear absorption (NLA) performance is characterized by the Z-Scan technique, and the verification of MPP is carried out using a single-pulse and long-focal-length exposure system, respectively. The Z-Scan measurements demonstrate that the NLA of the PI in nonlinear solvent is stronger than in “linear” solvent. Consequently, a photoresist with a nonlinear solvent requires less laser intensity (∼16%) to initiate polymerization, which could result in higher efficiency, smaller feature size, and higher resolution of MPP manufacturing. These nonlinear enhancements are ascribed to a superposition of the NLA of the PI and nonlinear solvent, derived from the enlargement of the multi-photon absorption cross section and the increase in solvated electrons liberated from the solvent. Introducing nonlinear solvents into photoresists is a simple and economical approach to optimize the efficiency and resolution of MPP fabrication. Furthermore, nonlinear solvents can be considered to strengthen the nonlinear performance in various solvated applications.