Preparation of a chemically amplified photosensitive polyimide based on norbornene-end-capped poly(amic acid ethoxymethylester)

Abstract

A positive-working chemically amplified photosensitive polyimide (PSPI) developable with basic aqueous solutions was obtained from poly(amic acid ethoxymethylester) (PAAE) as a polyimide precursor and diphenyliodonium 5-hydroxynaphthalene-1-sulfonate (DINS) as a photoacid generator. The norbornene-end-capped PAAE based on 4,4'-oxydiphthalic anhydride and 4,4'-oxydianiline exhibited high transparency at 365 nm. The protection ratio of the ethoxymethyl groups was optimized to maximize the difference between the dissolution rates of the exposed and unexposed areas. The acid generated from DINS in the UV-exposed region effectively deprotected the ethoxymethyl groups of PAAE by a chemical amplification mechanism. A 10-flm-thick film of the PSPI precursor system containing 16 wt % DINS exhibited a sensitivity (D degrees) of 1100 mJ cm(-2) when developed with a 2.38 wt % aqueous tetramethyl ammonium hydroxide solution at room temperature. A fine, positive, 5-mu m line-and-space pattern was fabricated in a 15-mu m-thick film with 1500 mJ cm(-2) of UV exposure. This resolution is excellent in comparison with those previously reported for chemically amplified PSPIs, and such a film can thus be used as a buffer coating in semiconductor packaging. (c) 2005 Wiley Periodicals, Inc.