Chemically Amplified Photosensitive Polybenzoxazoles Based on tert-Butoxycarbonyl Protected Hyperbranched Poly(o-hydroxyamide)s

We describe the synthesis, characterization, and lithographic performance of positive-working chemically amplified photosensitive polybenzoxazoles (PSPBOs) composed of partially tert-butoxycarbonyl (t-BOC) protected hyperbranched poly(o-hydroxyamide)s (HB-tbocPHAs) and diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) as a photo-acid generator (PAG). The HB-tbocPHAs as precursors of PSPBOs were synthesized from hyperbranched poly(o-hydroxyamide)s (HBPHAs), which were prepared by self-polycondensation of an AB₂ type monomer. A series of HB-tbocPHAs having the t-BOC content of 8−100 mol % were successfully prepared by controlling the feed amount of di-tert-butyl dicarbonate (DTBDC). HB-tbocPHAs had adequate dissolution rate in tetramethylammonium hydroxide (TMAH) aqueous solution as well as excellent solubility in common organic solvents. HB-tbocPHA having 39 mol % t-BOC group showed the optimum dissolution rate in 2.38 wt % TMAH aqueous solution and good adhesion on a silicon wafer. The thermal deprotection of the t-BOC group and conversion to polybenzoxazole (PBO) of HB-tbocPHA in the presence of strong acid such as p-toluenesulfonic acid (p-TsOH) were investigated by using FT-IR, DSC, and TGA to examine the acid effect. Both the deprotection of t-BOC groups and the conversion to PBO were accelerated in the presence of p-TsOH. The photolithographic performance of the resist formulated with HB-tbocPHA and 20 wt % of DIAS was evaluated. The resist showed 115 mJ/cm² of sensitivity and 2.2 of contrast with 365 nm light when it was developed in 2.38 wt % TMAH aqueous solution at room temperature. The fine positive pattern was obtained at the 200 mJ/cm² of i-line exposure. The patterned film was successfully converted to polybenzoxazole without any distortion by thermal treatment at 300 °C for 1 h.