Photo-sensitive bio-based copolymer containing cholic acids: novel functional materials for 248nm photoresist

Cholic acid is a class of biological compounds that exhibit valuable properties, and have been applied in many fields due to its special chemical structures for many areas. In this study, poly[(methacrylic acid tert-butyl cholate ester)- co -(acetoxy styrene)] [P(MATC- co -AS)] was synthesized from cholic acid, then the final copolymer poly[(methacrylic acid tert-butyl cholate ester)- co -(p-hydrostyrene)] [P(MATC- co -HS)] was obtained after P(MATC- co -AS) was hydrolysized. The structure and properties of the copolymers were determined through nuclear magnetic resonance, gel permeation chromatography, UV spectrometry, thermogravimetric analysis, and differential scanning calorimetry. The ultraviolet spectra of the copolymers indicate that they exhibit excellent optical transmittance at 248 nm. Moreover, the photolithography performance of a positive-tone photoresist based on the copolymers were evaluated using an KrF laser exposure system. The results indicate that a resolution of 0.25 μm could be achieved at a low exposure dose.