Designing Intrablock Attractions to Increase the χ Parameter of a Symmetric Diblock Copolymer

Block copolymer (BCP) lithography is capable of forming features on the order of tens of nanometers, and this size is desirable for numerous applications, including data storage devices, microprocessors, and membranes. BCPs must be oriented to form device-relevant structures, and poly(styrene-block-methyl methacrylate) (PS-PMMA) is the most widely studied BCP due to its ability to form perpendicularly oriented features when simply heated on an energetically nonpreferential substrate. However, the smallest practical feature sizes attainable by PS-PMMA are about 11 nm. In this work, we incorporate a self-interacting monomer, vinylnaphthalene, into the styrenic block of PS-PMMA to effectively increase its Flory-Huggins interaction parameter. Introducing 35 mol % of vinylnaphthalene into the BCP more than doubled its χ parameter, resulting in a BCP structure that is capable of forming features as small as 6.3 nm. We also demonstrate that like PS-PMMA, this new poly((styrene-random-vinylnaphthalene)-block-methyl methacrylate) (PSVN-PMMA) BCP can be oriented vertically with only thermal annealing.