Sub-10 nm Feature Sizes of Disordered Polystyrene-block-poly(methyl methacrylate) Copolymer Films Achieved by Ionic Liquid Additives with Selectively Distributed Charge Interactions

Weak segregation of polystyrene-block-poly(methyl methacrylate) block copolymers (PS-b-PMMA BCPs) limits their utility for sub-10 nm lithography. Such limits could be overcome by including ionic liquids (ILs) as additives, which conveniently enhance the demixing between PS and PMMA blocks. Herein, we studied the distribution and interaction evolution of the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate (HMHF) in PS-b-PMMA BCPs. The segmental dynamics of the rigid, intermediate, and mobile molecular components in PS-b-PMMA/HMHF was characterized by solid state nuclear magnetic resonance spectroscopy, and the results suggested a selective interaction between PMMA and HMHF. The surface energies and interfacial behaviors of the polymer/HMHF mixtures indicated that HMHF was distributed underneath the PMMA surface during heat treatment. Because of this distribution, disordered PS-b-PMMA with HMHF added formed perpendicular sub-10 nm features through thermal annealing. In addition, the effective i...