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