A new negative-type photosensitive polyimide based on poly(hydroxyimide), a cross-linker, and a photoacid generator

A negative working photosensitive polyimide based on poly(hydroxyimide) (PHI), 2,6-bis(hydroxymethyl)-4-methylphenol (BHMP) as cross-linker, and photoacid generator diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) has been developed. The PHI was prepared by the ring-opening polyaddition of 4,4'-hexafluoroisopropylidenebis(phthalic anhydride) and 4,4'-diamino-4''-hydroxytriphenylmethane, followed by thermal cyclization in refluxing xylene. The PHI film showed excellent transparency to UV light. The photosensitive polyimide containing 70 wt % PHI, 20 wt % BHMP, and 10 wt % DIAS showed a sensitivity of 70 mJ/cm(2) and a contrast of 3.8 when it was exposed to 365 nm light and postbaked at 120 degrees C, followed by developing with a 2.5% aqueous tetramethylammonium hydroxide solution at 40 degrees C. The mechanistic study on the formation of images is also discussed.