Hideaki Nakajima: conception and design various aspects of the study, acquisition of patients, analysis and interpretation of data, drafting of the manuscript; Arisa Kubota: analysis and interpretation of data, statistical analysis; Yasuhisa Maezawa: conception and design of the study, acquisition of patients; Shuji Watanabe: analysis and interpretation of data, statistical analysis; Kazuya Honjoh: analysis and interpretation of data, statistical
In the presence of a small amount of acid, 3-phenyl-3,3-ethylenedioxy-1-propyl ptoluenesulfonate autocatalytically decomposed to give p-toluenesulfonic acid both in solution and in a polymer matrix. Such a reaction was successfully applied for the improvement of sensitivity of several positive-working chemical-amplification photoresists. It was revealed that the diffusion of the acid plays the most essential role in the sensitivity enhancement, by determining the addition effect of the acid amplifiers with various arenesulfonates on photosensitivity characteristics.
The thickness of UV-irradiated films of poly [p-(tert-butoxycarbonyloxy)styrene] and poly-(tert-butyl methacrylate) containing a photoacid generator as a chemically amplified photoresist was reduced by the deprotection of the side chain residues as a result of the acidolysis reaction catalyzed by a photogenerated acidic species. It was observed that the reduction of film thickness is spread laterally on a millimeter scale to unexposed areas upon heating in the presence of 3-phenyl-3,3-ethylenedioxy-1-propyl p-toluenesulfonate as an acid amplifier that displays the autocatalytic acidolysis referred to as acid proliferation. The enlargement of areas showing the thickness reduction was suppressed effectively by covering the films with a glass plate or a polymer film. This observation suggested that the acidolysis reaction of the films is caused predominantly by the migration of acid molecules originated from the acid amplifier through the air. This was confirmed by the transfer of acid molecules to another acid-sensitive polymer layer placed on the acid-generating film through an air gap. The photosensitivity enhancement of the chemically amplified photoresists owing to the acid proliferation is discussed on the basis of these results.
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