Macromolecules, Vol.47, No.10, 3520-3527, 2014
Control of Directed Self-Assembly in Block Polymers by Polymeric Topcoats
The morphology of a block copolymer thin film is particularly sensitive to its boundary conditions. Lithographic applications of block polymers in the microelectronics and memory device industries require formation of morphologies with perpendicularly oriented domains. Current fabrication targets envisage the creation of dense arrays of structures with domain sizes in the sub-10 nm regime. Such length scales can be reached by resorting to block polymers with highly incompatible blocks (and a large Flory-Huggins parameter, chi). High chi values, however, generally lead to large differences in the surface energies of the corresponding blocks, thereby interfering with formation of the sought-after perpendicularly oriented domains. In this work, a coarse grain model is used to develop a topcoat strategy that enables control of the orientation of block copolymer domains in highly incompatible block polymer materials. A systematic study of a wide range of polymeric material combinations is presented, and the conditions leading to optimal assembly of perpendicular morphologies are clearly identified. We consider the effect of molecular weight, block polymer film thickness and architecture, and degree of incompatibility. Our results are summarized in the form of generic phase diagrams that should serve as a guide for experimental deployment of the topcoat strategy put forth in this work.