Dimensions and Shapes of Block Copolymer Domains Assembled on Lithographically Defined Chemically Patterned Substrates

Abstract

Thin films of a nearly symmetric lamellae-forming diblock copolymer of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) having a bulk repeat period, LO, were directed to assemble vertically away from chemically nanopatterned striped substrates (having a periodicity LS) that consisted of alternating stripes that were preferentially wet by the two blocks of the copolymer. The relative widths of the adjacent stripes were systematically varied such that the normalized line width of the chemical surface pattern, defined as the width of the stripe that was wet by the styrene block of the block copolymer, W, divided by the constant chemical surface pattern period, Ls had values between 0.30 and 0.65. On chemical surface patterns with LS ≈ LO the diblock copolymer domains formed defect-free perpendicular arrays if the normalized line width W/LS, was between 0.36 and 0.63. On chemical surface patterns with LS ≠ LO, the range of W/LS capable of inducing defect free arrays decreased as the difference between LS and LO increased. Single-chain-in-mean-field (SCMF) simulations provided information on the dimensions and shapes of the block copolymer domains. The SCMF simulations indicated that the widths of the lamellae at half film thickness were 0.47LS independent of W/LS and the angle of the interface between the vertically oriented domains remained within 11° of the substrate normal over the range of experimentally relevant values of W/LS.