Positive-type Photosensitive Polyimide with Low Modulus based on Soluble Block Copoly(imide-siloxane)

Abstract

A novel positive-type photosensitive polyimide with low modulus based on soluble block copoly(imide-siloxane) with hydroxyl group and diazonaphthoquinone as a photoreactive compound has been developed. The base block copoly(imide-siloxane) was prepared by a direct one-pot polycondensation of biphenyltetracarboxylic dianhydride(BPDA) 2,2-Bis(3-amino-4-methyl)phenylhexafluoropropane(Bis-AP-AF) and diamino(poly)siloxane in the presence of a γ-valerolactone and pyridine catalyst system using dipolar aprotic solvent such as N-methyl-2-pyrrolidone(NMP). The base block copoly(imide-siloxane) consists of aromatic polyimide unit as a hard segment, and polysiloxane unit as a soft segment.The polysiloxane unit contributed to the resulting poly(imide-siloxane) film with not only colorlessness and transparency which are the important factors for a photosensitive polyimide but also low modulus. Due to the low modulus, it can reduce the residual wafer stress caused by the CTE (coefficient of thermal expand) mismatch between silicon wafer (3ppm/K) and polyimide (30∼60ppm/K), and prevent semiconductor devices from physical and electric damage. Photosensitive block copoly(imide-siloxane) containing 20wt% Ester of 2,3,4,4'-trihydrobenzophenone with 1,2-naphthoquinone-(2)-diazide-5-sulfonic acid (4NT-300) showed a sensitivity of 350mj/cm2 and a contrast of 1.95 when it was exposed to UV light, followed by development with 2.38% tetramethylammonium hydroxide (TMAH) aqueous solution containing 10wt% isopropyl alcohol (IPA) at room temperature.