Transfer of Direct and Moiré Patterns by Reactive Ion Etching Through Ex Situ Fabricated Nanoporous Polymer Masks

We present a conceptually simple approach to nanolithographic patterning utilizing ex situ fabricated nanoporous masks from block copolymers. The fabricated block copolymer (BC) masks show predictable morphology based on the correlation between BC composition and bulk properties, independent of substrates' surface properties. The masks are prepared by microtoming of prealigned nanoporous polymer monoliths of hexagonal morphology at controlled angles; they appear as 30-60 nm thick films of typical dimensions 100 μm × 200 μm. Masks cut perpendicular to the cylindrical axis show monocrystalline hexagonal packing of 10 nm pores with a principal period of 20 nm. We demonstrate the transfer of the hexagonal pattern onto silicon by means of reactive ion etching through the masks. In addition, patterns of elliptic and slit-like holes on silicon are obtained by utilizing masks cut at 45° relative to the cylinder axis. Finally, we demonstrate the first transfer of moiré patterns from block copolymer masks to substrate. The nanoporous masks prepared ex situ show outstanding long-range order and can be applied directly onto any flat substrate, eliminating the need for topographic and chemical surface modification, which are essential prerequisites for the conventional procedure of block copolymer directed self-assembly. The demonstrated elliptic and moiré pattern transfers prove that the proposed ex situ procedure allows us to realize nanolithographic patterns that are difficult to realize by the conventional approach alone.