Facile Synthesis of Photosensitive Poly(semi-alicyclic benzoxazole) and Subsequent Low-Temperature Cyclization of Poly(o-hydroxy amide)

A positive-type photosensitive polybenzoxazole (PSPBO) based on partially tert -butoxycarbonyl ( t Boc) protected poly(semi-alicyclic o -hydroxy amide) (PAtBA) and a photoacid generator, (5-propylsulfonyloxyimino-5 H -thiophene-2-ylidene)−(2-methylphenyl)acetonitrile (PTMA), has been developed for a promising material in microelectronics. PAtBA was prepared from poly(semi-alicyclic o -hydroxy amide) (PAHA) and di- tert -butyl dicarbonate in the presence of catalytic diethylmethylamine in cyclohexanone and used directly for lithographic evaluation. The t Boc protection to PAHA and thermal behavior of PAtBA were characterized by thermogravimetric analysis (TG), 1 H NMR, UV−vis, and FTIR spectrometry. As a result of photolithographic evaluation, the PSPBO precursor, PAtBA-20 containing 10 wt % PTMA, showed a sensitivity of 35 mJ/cm 2 and a contrast of 12.8, when it was exposed to a 365 nm light ( i -line), postbaked at 110 °C for 5 min, and developed with a 2.38 wt % aqueous tetramethylammonium hydroxide solution (TMAHaq) at 25 °C. A fine positive image of 7.8 μm line-and-space pattern was printed in a film which was exposed to 50 mJ/cm 2 of i -line by contact-printing mode and fully converted into the corresponding polybenzoxazole (PABO) pattern upon heating at 250 °C, confirmed by SEM and FTIR spectroscopy. Thus, PTMA is effective as a thermoacid generator for low-temperature cyclization of PAtBA into the PABO as well to meet practical requirement in the industry.