Gallol-Based Block Copolymer with a High Flory–Huggins Interaction Parameter for Next-Generation Lithography

The self-assembly of block copolymers has potential applications for next-generation lithography with a small feature size of less than 10 nm. Though a feature size of ∼5 nm has been reported, the fabrication of ultra-small feature sizes (less than 5 nm) still remains a great challenge. In this study, we utilized a compound with three hydroxyl groups named gallol, which shows strong intermolecular interactions. We synthesized, via a reversible addition–fragmentation chain-transfer polymerization, a polytrihydroxystyrene-block-polystyrene copolymer (PTHS-b-PS) having lamellar and cylindrical microdomains by adjusting the volume fraction of the PS block (fPS). We found that the Flory–Huggins interaction parameter (χ) between the PTHS and PS segments was extremely large, 1.24 at 220 °C. By using a PTHS-b-PS with a total molecular weight of 1.4 kg mol–1 and fPS = 0.53, we obtained a lamellar domain spacing (L0) as small as 4.5 nm. Also, the diameter of hexagonally packed cylinders was reduced to 4.0 nm by employing another PTHS-b-PS with a molecular weight of 2.9 kg mol–1 and fPS = 0.74. This ultra-small feature size can be used for next-generation lithography.