Sustainable photoresists from Kraft lignin

Abstract Photoresists are important materials for modern societies as they are decisive components in the fabrication of integrated circuits for semiconductors. Typical materials in such applications are based on synthetic fossil-based polymers such as epoxy resins or novolac resins, demonstrating a need to explore alternative materials that could reduce the dependence on fossil resources. Lignin is a complex phenolic polymer and a major byproduct of the paper industry, which is largely underutilized despite its vast availability. We investigate the use of Kraft lignin-based thin films as photoactive layers for potential applications in photoresists, i.e. materials that change their solubility upon exposure to light. Thin films of lignin acetate and silyl ethers were prepared, spin coated on a substrate and then irradiated with UV light in the presence of a photoacid generator to cleave off the acetate and silyl groups, respectively. We further investigate the influence of UV lamp, illumination time, and dark reaction time to achieve the optimum photo-conversion efficiency. Using a photomask, UV illumination and subsequent development with chloroform, we successfully produce lignin-based micropatterns. This work demonstrates the potential of lignin-based thin films as a renewable alternative for photolithography and their use in photoresists. Graphical abstract