Fabrication of Sub‑3 nm Feature Size Based on Block Copolymer Self-Assembly for Next-Generation Nanolithography

For ultrahigh-density storage media and D-RAM, the feature size of lithography should be much reduced (say less than 10 nm). Though some research groups reported feature size of 5–6 nm, further reduced feature size is needed for next-generation lithography. We synthesized, via a reversible addition–fragmentation chain-transfer polymerization, polydihydroxystyrene-block-polystyrene (PDHS-b-PS) copolymers showing lamellar and cylindrical microdomains by adjusting the volume fraction of PS block (f_PS). We found that the Flory–Huggins interaction parameter (χ) between PDHS and PS was very large, 0.7 at 170 °C. Because of the huge χ, the lamellar domain spacing (L) of PDHS-b-PS with a total molecular weight of 2.1 kg mol^–1 and f_PS = 0.5 was only 5.9 nm; thus, a sub-3 nm feature size (half-pitch) was successfully obtained. Furthermore, PDHS-b-PS with a molecular weight of 4.2 kg mol^–1 and f_PS = 0.79 showed hexagonally packed cylinders with 4 nm diameter. We also obtained thin films of PDHS-b-PS with cylindrical microdomains, showing 8.8 nm center-to-center spacing. Furthermore, we fabricated ultrahigh-density ZrO₂ nanowire arrays from the cylindrical monolayer thin films via atomic layer deposition, indicating an applicability of PDHS-b-PS for next-generation lithography.