New base-soluble positive-working photosensitive polyimides havingo-nitrobenzyl ester group

A new positive-working polyimide having photosensitive o-nitrobenzyl ester group as side substituent, poly{1,4-phenyleneoxy-1,4-phenylene-3,6-di[4-(o-nitrobenzyloxy)carbonylphenyl]pyromellitimide} (ODA-PI-Nb), was prepared and its aqueous alkali-developability and photosensitivity were investigated. ODA-PI-Nb was synthesized by the esterification reaction of poly[1,4-phenyleneoxy-1.4-phenylene-3,6-di(4-carboxylphenyl)pyromellit imide] (ODA-PI) with o-nitrobenzyl bromide in the presence of triethylamine (Et3N). ODA-PI-Nb obtained was characterized by FT-IR and 1H-NMR spectroscopy. The degree of esterification reaction was found from 1H-NMR absorption of CH2 proton to be over 95 mol%. Upon photo-irradiation ODA-PI-Nb transformed to the freely aqueous alkali-soluble ODA-PI under formation of o-nitrosobenzaldehyde. The thickness loss of thin ODA-PI-Nb films upon post-baking at 400°C was in the 10–15% range. ODA-PI-Nb showed positive-tone behavior in characteristic sensitivity curve and positive patterns were obtained using a typical lithographic process using aqueous tetramethylammonium hydroxide developer. The patterns with excellent resolution were observed and evaluated by optical microscopy and scanning electron microscopy.