The improved photosensitivity of photosensitive polyimides containing o ‐ nitrobenzyl ether groups induced by the addition of photoacid generator

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%.