Synthesis and self-assembly of low χ block copolymers with large periodicity

Typically block copolymers (BCPs) are employed for their ability to phase separate at very small length scales (<20 nm) but rarely are the upper limits in pitch studied for BCPs. Large pitch forming BCPs show applications in extending cheap chip fabrication using older lithographic exposure tools as well as in light filtering as photonic crystals. For these large N BCPs, a low χ may be attractive as many suspect defects are kinetically trapped in phase separated BCPs due to high enthalpic penalties for defect annihilation to begin. Here, the authors synthesized and characterized the BCP poly(4-tertbutylstyrene)-block-poly(propyl methacrylate) (PtBS-b-PPMA) as a useful block copolymer for 248 nm lithography. Small angle x-ray scattering (SAXS) was used to calculate the χ value of PtBS-b-PPMA as well as to measure the pitch. The χ for PtBS-b-PPMA was measured and found to be roughly 2/3 that of PS-b-poly(methylmethacrylate), leading to a BCP that should permit less kinetically trapped defects. A neutral und...