Resolving In Situ Exposure Dynamics in a Chemically Amplified EUV Photoresist Using Table-Top EUV Photoemission Spectroscopy

Extreme ultraviolet (EUV) lithography has revolutionized the high-volume manufacturing of nanoscale components. The use of EUV light leads to ionization-driven chemistry in the imaging materials of lithography, the photoresists. The complex interplay of ionization, generation of primary/secondary electrons, and the subsequent chemical mechanisms that lead to image formation in photoresists has been notoriously difficult to study. This is in particular true for the radiochemical transformations occurring during exposure. In this work, we deploy table-top EUV photoemission spectroscopy to observe in situ chemical changes occurring during exposure in a model chemically amplified photoresist and discover a surprising chemical reaction pathway, the EUV-induced breakdown of a perfluoroalkyl substance (PFAS) photoacid generator (PAG). This previously unobserved breakdown of the PFAS PAG, a critical component in the EUV exposure mechanism, manifests as changes in the intensity of the valence band peaks of the EUV photoemission spectrum, which are linked to degradation of the PFAS PAG via an advanced atomistic simulation framework. Our combined experimental and theoretical approach shows that EUV photoemission can simultaneously resolve chemical dynamics and the production of primary and secondary electrons, giving unique insights into the radiochemical transformation of photoresist materials. More generally, our approach also shows that EUV photoemission spectroscopy can provide a unique platform for tracking degradation pathways of PFAS molecules in thin films, owing to the high ionization cross section of fluorine at EUV wavelengths. Our results pave the way for utilizing accessible, table-top EUV spectroscopy systems for observing EUV photoresist chemical dynamics, with the potential for time-resolved measurements of photoemission processes in the future.