Development of Negative-type Photosensitive Polyimide, Based on Poly(amic acid)s, Photo Base Generator and Thermal Base Generator

A negative-type photosensitive polyimide (PSPI) based on poly(amic acid) (PAA), a photo base generator (PBG), {[(4,5-dimethoxy-2-nitrobenzyl) oxy]carbonyl}2,6-dimethyl piperidine (DNCDP) and a thermal base generator (TBG), N-(p-nitrophenyl)-2,6-dimethylpiperidine (NDP) has been developed. The PAA was prepared from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 3,3'-sulfonyldianiline (SDA) in N,N-dimethylacetamide (DMAc) and used directly for lithographic evaluations. The TBG was easily prepared by the reaction of p-nitrophenyl chloroformate with 2,6-dimethylpiperidine. The PAA film containing 10 wt % NDP was converted the polyimide (PI) at 200 °C. The PSPI consisting of PAA (83 wt %), PBG (8.5 wt %) and TBG (8.5 wt %) exhibited a high sensitivity (D0.5) of 38 mJ/cm2 and a contrast (γ0.5) of 0.56 when it was exposed to a 365 nm line (i-line), post-baked at 170 °C for 2 min, and developed with 2.38 wt % TMAHaq. A clear negative image of 8 mu;m line and space pattern was printed in a film which was exposed to 500 mJ/cmup>2 of i-line by contact printing mode, fully converted to the corresponding PI pattern upon heating at 200 °C, and confirmed by SEM and FTIR spectroscopy.