Positive-working alkaline-developable photosensitive polyimide precursor based on polyisoimide using diazonaphthoquinone as a dissolution inhibitor

Abstract

A positive-working photosensitive polyimide precursor based on polyisoimide (PII) and 2,3,4-tris(1-oxo-2-diazonaphthoquinone-4-sulfonyloxy) benzophenone (D4SB) as a photoreactive compound has been developed. The polyisoimide was prepared by the ring-opening polyaddition reaction of 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) and 3,3′-diaminodiphenylsulfone (3,3′-DDS), followed by treatment with trifluoroacetic anhydride-triethylamine in N-methyl-2-pyrrolidone (NMP). The polyisoimide film showed excellent transparency to u.v. light, and good solubility in a wide range of organic solvents. The dissolution behaviour of the polyisoimide film containing 20 wt% of D4SB after exposure and post-exposure bake (PEB) has been studied and it has been found that the dissolution rate of an exposed area was ∼80 times faster than of an unexposed area, due to the photochemical reaction of D4SB in the polymer film. The photosensitive polyimide precursor containing 20 wt% of D4SB showed a sensitivity of 250 mJ cm −2 and a contrast of 2.4 with 435 nm light, when it was post-baked at 150°C for 10 min, followed by developing with 5% tetramethylammonium hydroxide solution at 45°C.