Negative-Working Photosensitive Poly(phenylene ether) Based on Poly(2,6-dimethyl-1,4-phenylene ether), a Cross-Linker, and a Photoacid Generator

A novel benzyl cation type cross-linker, hex-1,6-ylenebis[oxy(2,4,6-tris(acetyloxymethyl)-3,5-dimethylbenzene)] (HOAD), that suppresses acid-catalyzed self-polycondensation has been developed. Furthermore, a negative-working, photosensitive poly(phenylene ether) (PSPPE) based on poly(2,6-dimethyl-1,4-phenylene ether) (PPE), HOAD, and diphenylidonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) as a photoacid generator (PAG) has been developed. This resist system does not contain a high thermal curing process. The resist consisting of PPE (83 wt %), HOAD (10 wt %), and DIAS (7 wt %) showed excellent sensitivity (D 0.5) of 43 mJ/cm2 and high contrast (γ0.5) of 11 when it was exposed to 365 nm wavelength UV light (i-line), postexposure baked (PEB) at 190 °C for 5 min, and developed by dipping in toluene at 25 °C. A fine negative-type pattern having 6 μm resolution on 2.4 μm thick film on a silicon wafer was obtained by exposure to 300 mJ/cm2 of the i-line by using a contact-printed mode. The resulting PSPPE film, cured at 220 °C for 1 h under nitrogen, had a low dielectric constant (ε: 2.61), good thermal stability, and low water absorption.