Negative-Working Photosensitive Polybenzoxazoles Based on Hyperbranched Poly(o-hydroxyamide)s

The negative-working photosensitive polybenzoxazole (PSPBO) composed of hyperbranched poly(o-hydroxyamide) (HBPHA), 2,6-bis(hydroxymethyl)-p-cresol (BHMP) as a cross-linker and diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) as a photoacid generator (PAG) was developed and evaluated. The HBPHA as a precursor of PSPBO was prepared by self-polycondensation of an AB2 type monomer. The acid-catalyzed cross-linking of the BHMP in the presence of strong acid such as p-toluenesulfonic acid (p-TsOH) was investigated by using DSC and TGA. The cross-linking of BHMP was accelerated in the presence of p-TsOH, whereas cross-linking was not observed until it reached 140 °C without acid. The photolithographic performance of the resist (XPR-721) formulated with 70 wt% of HBPHA, 20 wt% of BHMP, and 10 wt% of DIAS was evaluated. The resist showed high sensitivity (Eth1/2 = 56 mJ cm-2) and good contrast (γ1/2 = 4.6) with 365 nm light when it was developed in 1.19 wt% tetramethylammonium\-hydroxide (TMAH) aqueous solution at room temperature. The fine negative pattern was obtained at the 200 mJ cm-2 of i-line exposure. The patterned film was successfully converted to polybenzoxazole without any distortion by thermal treatment at 350 °C for 1 h.