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

Abstract

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-1and 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-1and fPS= 0.74. This ultra-small feature size can be used for next-generation lithography. © 2022 American Chemical Society. All rights reserved.