Laser photolytic studies of sensitizers for negative photoresists: 2,7-diazidofluorene in poly (methyl methacrylate) films

Abstract

The time evolution of the transient absorption spectra of 2,7-diazidofluorene(DAF)(N₃–R –N₃) under excimer laser irradiation has been investigated in poly(methyl methacrylate)(PMMA) films and in inert cyclohexane solution and compared with the results for 4,4′-diazido-3,3′-dimethoxybiphenyl (DADMB), which has a similar biphenyl skeleton to DAF. The results from a DAF-cyclohexane solution containing diethylamine indicated that, in addition to the triplet azido nitrene (:N –R –N₃) which was the main intermediate, didehydroazepine derivatives were generated. The formation of these intermediates in solution and in PMMA films was completed within the duration of the laser pulse. The reaction of these intermediates in solution was completed within 10 ms and in PMMA films within 100 s, while the reaction related to the azido nitrene of DADMB in PMMA films continued up to 1200 s. The results for 1% w/w DAF-doped PMMA films irradiated with a high fluence indicated that the azido nitrene and the dinitrene (:N –R –N:) underwent dimerization and/or further polymerization, suggesting that DAF molecules form aggregates even in dilute PMMA films (1% w/w). The difference in the miscibility of DAF and DADMB in PMMA affected the photoreaction behaviour of these diazido compounds in polymer films.