A New Positive-Type Photosensitive Alkaline-Developable Alicyclic Polyimide Based on Poly(amic acid silylester) as a Polyimide Precursor and Diazonaphthoquinone as a Photosensitive Compound

A new positive working photosensitive alicyclic polyimide precursor based on poly(amic acid tert -butyldimethylsilylester) ( 3 ) and 2,3,4-tris[2-diazo-1-(2 H )-naphthalenone-4-sulfonyloxy]benzophenone ( D4SB ) as a photosensitive compound has been developed. Polymer 3 was prepared by ring-opening polyaddition of bicyclo[2.2.1]heptane-2-methanecarboxylic-3,5,6-tricarboxylic-2,3:5,6-dianhydride ( 2 ) with 5- tert -butyldimethylsilylamino- N - tert -butyldimethylsilyl-1,3,3-trimethylcyclohexanemethylamine ( 1 ) in toluene/ N, N -dimethyl acetamide (DMAc) (2/1 weight ratio) at 20 °C for 3 h. The film of polymer 3 showed excellent transparency at the wavelengths above 250 nm. The dissolution behavior of polymer 3 containing 30 wt % D4SB after exposure was studied, and it was found that the difference of dissolution rate between the exposed and unexposed areas was enough to obtain a high contrast due to the photochemical reaction of D4SB in the polymer film. The photosensitive polyimide precursor containing 30 wt % D4SB showed a sensitivity of 60 mJ/cm 2 and a contrast of 1.7 when it was exposed to 365-nm light and developed with a 2.38 wt % aqueous tetramethylammonium hydroxide solution at 25 °C. A fine positive image of 10-μm-line and space patterns was also printed in a film which was exposed to 300 mJ/cm 2 by contact mode. The positive image in polymer 3 was converted to the positive image in the polyimide ( PI ) film by thermal treatment. The optically estimated dielectric constants of the polyimides with and without D4SB are 2.45 and 2.44, respectively. These values are significantly lower than those of conventional aromatic polyimides.