Si containing block copolymers quickly assemble into sub-6 nm domains

Abstract

The directed self-assembly (DSA) of block copolymers (BCPs) is a potential patterning technology for sub-7 nm lithography. Series of styryl-polyhedral oligomeric silsesquioxane (POSS)-containing BCPs, poly(N-propyl-4-vinylbenzamide isobutyl POSS)-block-poly(heptafluorobutyl methacrylate) (PStNPOSS-b-PHFBMA) and poly(styrene-co-N-propyl-4-vinylbenzamide isobutyl POSS)-block-poly(heptafluorobutyl methacrylate) (poly(St-co-StNPOSS)-b-PHFBMA) were synthesized via reversible addition–fragmentation chain transfer polymerizations, compared with poly(trimethylsilyl styrene)-block-poly(pentadecafluorooctyl methacrylate) (PTMSS-b-PPDFMA) and poly(trimethylsilyl styrene)-block-poly(heptafluorobutyl methacrylate) (PTMSS-b-PHFBMA). The hexagonal or lamellar domain sizes of BCPs were precisely controlled. The minimum domain size of TMSS-type and POSS-type BCPs were 5.1 nm and 5.6 nm, respectively, whereas POSS containing BCPs exhibited ultra-fast self-assembly (1 min at 80 °C), similar to our polystyrene backbone fluorine-containing BCPs, vs the slow self-assembly of TMSS-type BCPs (10 h at 160 °C). Bearing the same polymer backbone, it was clearly seen that the siloxane side chain group slowed down the assembly, whereas the inorganic POSS cage side chain barely changed the fast assembly kinetics. Benefiting from the high Si content, the resulting POSS-containing block showed a higher etch resistance of up to 7 times that of PHFBMA. By introducing random styrene units into the styryl-POSS block, better film formation with variable etch selectivity of the poly(St-co-StNPOSS) block against PHFBMA was obtained.