Poly(2-vinylpyridine)-<i>b</i>-poly(fluorinated methacrylate) Block Copolymers Forming 5 nm Domains Containing Metallocene
Xuemiao Li, Hai Deng
Abstract
Directed self-assembly (DSA) of thin films of a block copolymer (BCP) is a promising approach for sub-10 nm lithographic patterning. In this paper, a series of poly(2-vinylpyridine)-block-poly(pentadecafluorooctyl methacrylate) (P2VP-b-PPDFMA) and poly(2-vinylpyridine)-block-poly(heptafluorobutyl methacrylate) (P2VP-b-PHFBMA) BCPs are synthesized by living anionic polymerization. The molar ratio of the two blocks and the degree of polymerization enable precise control of the morphology and size of the microdomains of the BCPs. The resulting materials form sub-5 nm scale microphase-separated structures, as seen with small-angle X-ray scattering and transmission electron microscopy. The introduction of the fluorine-containing blocks leads to a significant increase in the Flory–Huggins interaction parameter (χ) between the two blocks, as determined with the mean-field theory. The temperature dependence of χ2VP/PDFMA is χ = 48.79/T + 0.272 (0.387 at 150 °C) and of χ2VP/HFMBA is χ = 2.29/T + 0.342 (0.347 at 150 °C). χ of each of these BCPs is 4 times higher than that of polystyrene-block-poly(2-vinylpyridine) (0.083 at 150 °C). The resulting smallest domain spacing of these BCPs is 8.3 nm in a lamellar morphology. The BCPs self-assemble into straight lines in a silicon trench template and the doping of the P2VP block with metal atoms can enhance their etch resistance, demonstrating the potential of these BCPs for advanced lithographic applications.