Nanopatterning via Self-Assembly of a Lamellar-Forming Polystyrene-block-Poly(dimethylsiloxane) Diblock Copolymer on Topographical Substrates Fabricated by Nanoimprint Lithography

Abstract

The self-assembly of a lamellar-forming polystyrene-<i>block</i>-poly(dimethylsiloxane) (PS-<i>b</i>-PDMS) diblock copolymer (DBCP) was studied herein for surface nanopatterning. The DBCP was synthesized by sequential living anionic polymerization of styrene and hexamethylcyclotrisiloxane (D₃). The number average molecular weight (<i>M</i>_n), polydispersity index (<i>M</i>_w/<i>M</i>_n) and PS volume fraction (φ_ps) of the DBCP were <i>M</i>_n^PS = 23.0 kg mol^-1, <i>M</i>_n^PDMS = 15.0 kg mol^-1, <i>M</i>_w/<i>M</i>_n = 1.06 and φ_ps = 0.6. Thin films of the DBCP were cast and solvent annealed on topographically patterned polyhedral oligomeric silsesquioxane (POSS) substrates. The lamellae repeat distance or pitch (λ_L) and the width of the PDMS features (<i>d</i>_L) are ~35 nm and ~17 nm, respectively, as determined by SEM. The chemistry of the POSS substrates was tuned, and the effects on the self-assembly of the DBCP noted. The PDMS nanopatterns were used as etching mask in order to transfer the DBCP pattern to underlying silicon substrate by a complex plasma etch process yielding sub-15 nm silicon features.