Polyimide containing an acetal structure with a photoacid generator: a novel positive polyimide photoresist

A main-chain degradable photosensitive polyimide containing an acetal structure which degrades by the action of acid coming from a photoacid generator has been developed. Polyimides 4 were prepared by the reaction of bis(4-aminophenoxy)methane 1 and various tetracarboxylic anhydrides 2, followed by thermal treatment. In the resulting polyimides 4, 4f film derived from 4,4'-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) and 1 showed good solubility in organic solvents and transparency to UV light. The acid-catalysed degradation reaction was confirmed by the model imide compound in the presence of p-toluenesulfonic acid. The system of the polyimide 4f containing 30 wt% of diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS), which is a photoacid generator (PAG) showed a sensitivity of 150 mJ cm(-2) with 436 nm light, when it was post-exposure baked at 140 degrees C for 30 min, followed by development with 5% tetramethylammonium hydroxide solution at 45 degrees C.