Directed self-assembly of ternary blends of block copolymer and homopolymers on chemical patterns

Abstract

In this work ternary blends of symmetric lamellae-forming poly(styrene-block-methyl methacrylate) block copolymer and polystyrene and PMMA homopolymers were prepared for the directed self-assembly (DSA) on chemically nanopatterned substrates using 2× density multiplication. Homopolymers with comparable molecular weights to that of the corresponding blocks in the block copolymer were used to adjust the periods of the blends. The periods of the blends increased from 38.5 to 50 nm as the volume fraction of homopolymers increased from 0 to 30%. The periods were analyzed by grazing-incidence small-angle X-ray scattering, direct measurement from and fast Fourier transform of scanning electron microscopy images. DSA results indicate that the perfection and registration of the assembled films were mainly determined by the commensurability between the periods of the blends and the chemical patterns. Patterns with relatively small w/LS (guiding stripe width/period of chemical pattern) led to mixed structures of dots and parallel structures. The process window of LS where the block copolymer alignment shows a high degree of perfection was estimated at ±3.6% to ±4.6% Lo.