Aqueous developable dual switching photoresists for nanolithography

Photon-mediated switching of polymer solubility plays a crucial role in the manufacture of integrated circuits by photolithography. Conventional photoresists typically rely on a single switching mechanism based on either a change in polarity or, molecular weight of the polymer. Here we report a photoresist platform that uses both mechanisms. The molecular weight switch was achieved by using a poly(olefin sulfone) designed to undergo photo-induced chain scission. The polarity switch was achieved using pendant groups functionalized with o-nitrobenzyl esters. These are hydrophobic photosensitive-protecting groups for hydrophilic carboxylic acids. On irradiation, they are cleaved, making the polymer soluble in aqueous base. Importantly, the resists do not contain photoacid generator, so do not suffer from problems associated with acid diffusion that are detrimental to pattern fidelity. The 193 nm photochemistry of polymer thin films was followed using grazing angle attenuated total reflectance Fourier transform infrared spectroscopy, variable angle spectroscopic ellipsometry, and measurements of solubility in aqueous base. The nanoscale patterning performance of the polymers was also assessed using 193 nm interference lithography and electron-beam lithography. The implications of using dual switching mechanisms are discussed. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012