A Photosensitive Semi-Alicyclic Poly(benzoxazole) with High Transparency and Low Dielectric Constant

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Abstract

A photosensitive semi-alicyclic poly(benzoxazole) based on poly(o-hydroxy amide) containing adamantyl units (PAHA) and 1,3,5-tris[(2-vinyloxy)ethoxy]benzene (TVEB) as an acidolytic de-cross-linker and a photoacid generator, diphenyliodonium 9,10-dimethoxyanthracene-2-sufonate (DIAS), has been developed. PAHA with a weight-average molecular weight of 24 100 was prepared from 1,3-adamantanedicarbonyl chloride (ADC) and 4,4‘-(hexafluoroisopropylidene)bis(o-aminophenol) (6FAP) in the presence of lithium chloride in N-methylpyrrolidinone (NMP) at 0 °C for 12 h. By thermal treatment, PAHA was easily converted to semi-alicyclic poly(benzoxazole) (PABO) that was insoluble in organic solvents and showed high thermal stability (Td5 = 520 °C under N2). The UV−vis spectra of PAHA and PABO indicated excellent transparency at wavelengths above 320 and 400 nm, respectively. The average refractive index of PABO was 1.523, and the dielectric constant estimated from the refractive index was 2.55 at 1 MHz. This value is significantly lower than those of conventional wholly aromatic PBOs. The photosensitive PABO precursor, PAHA containing 15 wt % TVEB and 5 wt % DIAS, showed a sensitivity of 40 mJ/cm2 and a contrast of 4.0 when it was exposed to a 365 nm light (i-line) and developed with a 2.38 wt % aqueous tetramethylammonium hydroxide solution (TMAHaq) at 25 °C. A fine positive image of 10 μm line-and-space pattern was also printed in a film which was exposed to 70 mJ/cm2 of i-line by contact-printing mode. The positive image in PAHA was converted to the positive image in the PABO film by the thermal treatment without pattern deformation.

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