Synthesis and Properties of a Biophenolic End-Capped Polyimide Photoresist with High Film Retention and Sensitivity

A gallic acid derivative, methyl gallate, derived from renewable resources, was used as a starting material to synthesize 3,4,5-trihydroxy- N -(2-hydroxyethyl)benzamide (GEA). GEA was employed as an end-capping agent and incorporated into a poly(amic acid) copolymer based on 4,4′-oxydiphthalic anhydride (ODPA) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP). Subsequent esterification of the carboxylic acid groups with dimethylformamide dimethyl acetal (DMFDMA) yielded the final polymer, designated as OFPAE-G. The structure and properties of the polymers were characterized using Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance ( 1 H NMR), ultraviolet–visible spectroscopy (UV–vis), and gel permeation chromatography (GPC). UV–vis analysis indicated excellent optical transmittance of the polymer at 365, 405, and 436 nm. The lithographic performance of a positive-tone photoresist formulated from the gallic acid-end-capped, photosensitive polyimide (PSPI) was evaluated. Results demonstrate that the formulated photoresist exhibits high sensitivity (E th < 100 mJ/cm 2 ) at a 2 μm film thickness, with a development retention rate >95% and a curing retention rate >85%. Well-defined patterns were achieved, with a maximum resolution of 5 μm line/space (L/S). Even at an 11.5 μm film thickness, the photoresist maintained good photosensitivity, achieving a development retention rate >90% and a curing retention rate >75%. The photoresist showed good application prospects in OLED displays, MEMS, and chip packaging.