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 (1H 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 (Eth < 100 mJ/cm2) 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.