Polyimide (6FDA-AHHFP) prepared from the polycondensation of fluorinated acid dianhydride (6FDA) and diamine (AHHFP) is soluble in an aqueous base due to the presence of a hydroxyl group in the phenyl group of the diamine segment. Easy acidolysis of the protecting groups of the hydroxyl group was demonstrated with several model compounds of the polyimide that were protected by a number of acyland (alkyloxy)carbonyl groups. The terf-butoxycarbonyl group showed the highest acidolysis rate in these tests. A polyimide (6F-t-BOC) with a terf-butoxycarbonyl (t-BOC) group was thus prepared. On the basis of the results obtained from the model compound, it was expected that 6F-t-BOC would have a high sensitivity because the t-BOC group, as the protecting group, showed the highest acidolysis rate. Although 6F-t-BOC is insoluble in an aqueous base, it is easily converted to an alkaline-soluble polyimide by the acidolysis of this t-BOC group. This implies that polyimide 6F-f-BOC acts as a positive-working photoreactive material in the presence of a photoacid generator. Actually, 6F-f-BOC in the presence of (p-nitrobenzyl)-9,10diethoxyanthracene-2-sulfonate (NBAS) as a photo acid generator showed excellent positive-working characteristics in an aqueous base developer because of the polarity change induced by removing the t-BOC group. The sensitivity and contrast after a postexposure bake at 120 °C for 10 min were 180 mJ/cm2 (365 nm) and 3.4. Resolution higher than 1.0 gm was obtained in the 5-jum-thick film. The kinetics of thermolytically deprotecting the 6F-1-BOC film, when catalyzed by p-toluenesulfonic acid (p-Tos), was studied further in its solid state. The results clearly indicated that the reaction was first order, suggesting it was a typical Aal-1 type reaction requiring no water. The activation energy for the acidolysis was 19.5 kcal/mol. It further became apparent that the diffusion radius of an acid in a 6F-f-BOC film containing p-Tos was ca.14.2 A when heated for 10 min at 80 °C. 6F-t-BOC has 2 mol of t-BOC groups per repeating unit. Examination of their thermolytic acidolysis showed that acidolysis of the first t-BOC group proceeded more slowly than that of the second one in each repeating unit. This was attributed to the fact that an acid could attack the second t-BOC group easier than the first one and was responsible for the steric inhibition of tert-butyl groups around the t-BOC that protected an acid.
Novel photoreactive polyimides with 1,2-naphthoquinone diazide (NQD) groups in the side chain were synthesized by esterification of the hydrophilic polyimide, which had been prepared by the polycondensation of a fluorinated acid dianhydride and diamine with various amounts of NQD. These polyimides showed unique lithographic behavior. Either positive behavior was observed with an aqueous base developer or negative behavior could be achieved with an organic solvent developer, depending on the content of NQD. The reaction leading to the negative-working mode resulted from the low content of absorbed water in the hydrophobic fluorinated polyimide film. The cross-linking reactions leading to insolubility were a coupling reaction of the ketene and the reaction of a ketocarbene and a ketene, which are unstable intermediates in the photochemical reaction of NQD. It was further found by the study of water diffusion in the fluorinated polyimide film that the time needed to reach equilibrium with the surrounding atmosphere is shorter than 1.3 s for a dry 5^m-thick film of the fluorinated polyimides.
Cyclized polyisoprene has been used as a photoresist by being sensitized with bisazides(l-3). Recently, H.Harada et al. have reported that a partially cyclized 1,2-polybutadiene showed good properties as a practical photoresist material in reproducing submicron patterns(4). S.Shimazu et al. have studied the photochemical cleavage of 2,6-di(4 ' -azidobenzal)cyclohexanone in a cyclized polyisoprene rubber matrix, and have reported that the principal photoreaction is the simultaneous cleavage of the both azido groups by absorption of a single photon with a 43% quantum yield(5). Their result does not support the biphotonic process in the photolysis of bisazide proposed by A.Reiser et al.(6).Even if a same azide is used as the sensitizer, such properties of the photoresist as photosensitivity, photocurability and adhesion to base surfaces differ depending on the property of the base polymer. That is, degree of cyclization, content of the unsaturated groups and molecular weight of the polymer affect the photoresist properties mentioned above. H.L.Hunter et al. have discussed the dependence of the sensitivity of polybutadiene photoresist on the polymer structure, and have concluded that a higher sensitivity was obtained when 1,2-and 3,4-isomers were used(7).It is known that aromatic azides are photodecomposed to give active nitrenes as the transient species, which react with the environmental binder polymers to crosslink them. However, the mechanism of these photocrosslinking polymers has not been studied in detail. L.S.Efros et al. have proposed that the rubber polymer is crosslinkes in such a way that the aromatic nitrene inserts into an unsaturated bond of the polymer to give an aziridine ring. The experimental evidence for this, however, has not been given (8).In the present experiment, we have studied the mechanism of photocrosslinking of 1,2-polybutadiene by aromatic azide, based on the reaction of aromatic nitrene with unsaturated hydrocarbon monomeric compounds. 0-8412-0540-X/80/47-121-185$05.00/0
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