Photogenerated Base in Polymer Curing and Imaging: Cross-Linking of Base-Sensitive Polymers Containing Enolizable Pendant Groups

The ability of photogenerated amine catalysts to effect the insolubilization of polymers containing acidic methylene units is explored. Cross-linking of films of poly(2-acetoacetoxyethyl methacrylate)-co-(methyl methacrylate) or poly(2-cyanoacetoxyethyl methacrylate)-co-(methyl methacrylate) containing [[(2,6-dinitrobenzyl)oxy]carbonyl] cyclohexylamine as photobase generator and a bifunctional aldehyde molecule can be achieved upon exposure to deep-UV irradiation and subsequent heating. Polymers containing the cyanoacetate functionality displayed high resist sensitivities (ca. 20 mJ/cm²) in simple contact imaging experiments. Monitoring of the resist films using UV-vis spectroscopy suggested that cross-linking of the polymers in the presence of the aldehyde moiety proceeds via a Knoevenagel reaction. Photo-cross-linking and imaging can also be achieved in the absence of the added acceptor molecule and possible mechanisms for this insolubilization are discussed. Incorporation of the reactive cyanoacetate functionality into a phenolic polymer to provide aqueous base development is examined via the synthesis of poly[4-(2-cyanoacetoxymethyl)styrene]-co-[4-hydroxystyrene].