Negative-type Chemically Amplified Photosensitive Semi-alicyclic Polybenzoxazole via Acid-catalyzed Electrophilic Substitution

Abstract

A negative-type photosensitive semi-alicyclic polybenzoxazole (Nega-PSPABO) based on poly(o-hydroxy amide) containing an adamantyl unit (PAHA) and oxybis(3,4-dihydroxymethyl)benzene (OBHB) as a cross-linker, and a photoacid generator, (5-propylsulfonyloxyimino-5H-thiophen-2-ylidene)-(2-methylphenyl)acetonitrile (PTMA) 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-methyl pyrrolidinone (NMP) at 0 °C for 12 h. The photosensitive polymer based on 85 wt % PAHA, 10 wt % OBHB, and 5 wt % PTMA showed a sensitivity of D0.5=14.4 mJ/cm2 and a contrast of 2.4 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 negative image of 7 μm line-and-space pattern was also printed in the film which was exposed to 80 mJ/cm2 of i-line by contact-printing mode. The negative image in PAHA was converted to the corresponding PABO pattern image by thermal treatment without pattern deformation. The average refractive index of Nega-PSPABO was 1.542 from which the dielectric constant estimated was 2.62 at 1 MHz.