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 nextgeneration 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