The improved photosensitivity of photosensitive polyimides containing <i>o</i><i>‐</i>nitrobenzyl ether groups induced by the addition of photoacid generator
Gwang‐Sik Song, Youn‐Jung Heo, Jeong Ju Baek, Hyosun Lee, Geun Yeol Bae, Kyung Ho Choi, Won‐Gun Koh, Gyojic Shin
Abstract
Abstract In this article, photosensitive polyimides (PSPIs) with photosensitive groups, o ‐nitrobenzyl ether groups (Nb), were successfully synthesized based on 2,2′‐dihydroxy benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride and on diamine containing ethylene glycol chains (ODA). Also, a series of polyimide (PI), ODA‐1‐PI, ODA‐3‐PI, and ODA‐5‐PI with a number of ethylene glycol chains of 1, 3, and 5 were prepared to investigate the relationship between structure and solubility. Interestingly, ODA‐5‐PI, which possesses a large number of ethylene glycols, exhibited the most excellent solubility. Therefore, due to the good solubility of ODA‐5‐PI in organic solvents and alkaline solutions, a PSPI, poly(1,4‐phenyleneoxy‐3,6,9,12,15‐pentaoxaoctane‐1,4‐phenylene‐2,2′‐di[2‐nitrobenzyloxy]benzophenone‐3,3′,4,4′‐tetracarboxdiimide), named ODA‐5‐PSPI, was synthesized by linking Nb, which is a photosensitive group. Aiming at producing positive tone patterns, the synthesized ODA‐5‐PSPI was exposed to UV irradiation and then to a post‐exposure bake. Afterward, it was developed using a 2.38 wt% tetramethylammonium hydroxide solution. Furthermore, a photoacid generator (PAG) was additionally incorporated for a micropatterning process. Notably, in the presence of the PAG, the photocleavage of ODA‐5‐PSPI occurred not only by the intramolecular rearrangement of Nb but also by its hydrolysis reaction. As a result, due to the synergistic effect of photocleavage, the micropatterning of ODA‐5‐PSPI with PAG could be clearly obtained with less energy (2.0 J/cm 2 ) compared with that without PAG (3.6 J/cm 2 ). Therefore, through the addition of PAG, the photosensitivity was improved by 45%.