Positive-working photosensitive polyimide precursor based on polyisoimide using nifedipine as a dissolution inhibitor

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Abstract
A positive-working photosensitive polyimide precursor based on polyisoimide (PFII) and nifedipine (1,4-dihydro-2,6-dimethyl-4-(nitrophenyl)-3,5-pyridinedicarboxylic acid dimethylester) (DHP) as a photosensitive compound has been developed. P11 was prepared by the ring-opening polyaddition of oxydiphthalic anhydride (ODPA) and 3,3' diamino diphenylsulphone (3,3'-DDS), followed by the treatment of trifluoroacetic anhydridetriethylamine in N-methyl-2-pyrrolidone (NMP). PII film showed excellent transparency at 365 nm and 436 nm. The dissolution behaviour of PII film containing 20 wt% of DHP after exposure and post-exposure bake (PEB) has been studied. It was found that the dissolution rate of the exposed area was about six times faster than that of the unexposed area due to the photochemical reaction of DHP in P11 film. The photosensitive polyimide precursor containing 20 wt% of DHP showed a sensitivity of 45 mJ cm- 2 and a contrast of 2.4 with 365 nm light when post-baked at 150C for 10 min and developed with cyclohexanone at 50C.