Chemical Patterns for Directed Self-Assembly of Lamellae-Forming Block Copolymers with Density Multiplication of Features

• Published in: Macromolecules Vol. 46; no. 4; pp. 1415 - 1424
• Main Authors: Liu, Chi-Chun, Ramírez-Hernández, Abelardo, Han, Eungnak, Craig, Gordon S. W, Tada, Yasuhiko, Yoshida, Hiroshi, Kang, Huiman, Ji, Shengxiang, Gopalan, Padma, de Pablo, Juan J, Nealey, Paul F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.02.2013
• Subjects: Applied sciences; composite polymers; crosslinking; energy; Exact sciences and technology; Monte Carlo method; Organic polymers; Physicochemistry of polymers; polymethylmethacrylate; polystyrenes; Properties and characterization; scanning electron microscopy; Structure, morphology and analysis; styrene; Ultrathin films; Self assembly; Monte Carlo method; Patterning; Interface energy; Computer simulation; Polymer brush; Composition effect; Experimental study; Methyl methacrylate copolymer; Surface effect; Random copolymer; Interface properties; Lamellar structure; Domain structure; Diblock copolymer; Styrene copolymer
• DOI: 10.1021/ma302464n
• ISSN: 0024-9297; 1520-5835

Lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films, with bulk period L 0, were directed to assemble on lithographically nanopatterned surfaces. The chemical pattern was comprised of “guiding” stripes of cross-linked polystyrene (X-PS) or poly(methyl methacrylate) (X-PMMA) mats, with width W, and interspatial “background” regions of a random copolymer brush of styrene and methyl methacrylate (P(S-r-MMA)). The fraction of styrene (f) in the brush was varied to control the chemistry of the background regions. The period of the pattern was L s. After assembly, the density of the features (domains) in the block copolymer film was an integer multiple (n) of the density of features of the chemical pattern, where n = L s/L 0. The quality of the assembled PS-b-PMMA films into patterns of dense lines as a function of n, W/L 0, and f was analyzed with top-down scanning electron microscopy. The most effective background chemistry for directed assembly with density multiplication corresponded to a brush chemistry (f) that minimized the interfacial energy between the background regions and the composition of the film overlying the background regions. The three-dimensional structure of the domains within the film was investigated using cross-sectional SEM and Monte Carlo simulations of a coarse-grained model and was found most closely to resemble perpendicularly oriented lamellae when W/L 0 ∼ 0.5–0.6. Directed self-assembly with density multiplication (n = 4) and W/L 0 = 1 or 1.5 yields pattern of high quality, parallel linear structures on the top surface of the assembled films, but complex, three-dimensional structures within the film.