Interfacial Design for Block Copolymer Thin Films

Top coat design, coating, and optimization methodologies are introduced that facilitate the synthesis, application, and identification of neutral top coats for block copolymer (BP) thin films. Polymeric top coat composition, controlled via synthesis, determines interfacial wetting characteristics. Trimethylammonium salts of top coats improve solubility and coating uniformity. A confined island and hole test conveniently establishes (non)preferential wetting at the top coat/BP interface, which depends upon top coat composition. The utility of these three concepts was demonstrated with two high-chi, lamella-forming BPs, poly(styrene-block-4-trimethylsilylstyrene) (PS-b-PTMSS) having two periodicities L-0 = 18 and 22 nm and poly(styrene-block-methyltrimethylsilylmethacrylate) (PS-b-PTMSM) with L-0 = 15 nm. The combination of neutral top and bottom interfaces resulted in a perpendicular orientation of lamellae independent of BP :Rim thickness (1-3 L-0) when thermally annealed for 60 s or less.