Base-Catalyzed Photosensitive Polyimide

A new scheme for photosensitive polyimide is described. This imaging scheme is based on the amine-catalyzed conversion of soluble polyamic esters to relatively insoluble, partially imidized polymers. The amine is generated photochemically from o-nitrobenzyl carbamate precursors which were made photochemically active at long wavelength either by using carbamate derivatives containing electron donating substituents or by using triplet photosensitizers. Imidization percentages ranging from 20-80% were obtained following irradiation and postexposure bake without any imidization in unexposed film. The imidization percentage of exposed and baked film was dependent on a number of factors including the polymer structure, the nature of the ester group, and the conditions of the postexposure bake. The differential solubility between polyamic esters and partially imidized polymer was greatest for polymers with relatively rigid polymer backbones and this resulted in significantly improved imaging properties (lithographic contrast of 3.0). A final cure of the patterned film results in fully imidized polymer.