Development of realistic potentials for the simulation of directed self-assembly of PS-PMMA di-block copolymers

Atomistic simulations of poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) were performed and used to develop a realistic interaction potential for use in a mesoscale model of the PS-PMMA block co-polymer (BCP) system. The resulting interaction potential includes an attractive PS-PMMA segmental interaction, which is due to the electron dispersion interaction between these polymers. This attractive PS-PMMA interaction is not included in typical simulations of PS-PMMA phase behavior which use repulsive PS-PMMA interactions. Use of such repulsive interactions hastens the convergence of simulations of BCP phase separation and should not change the average phase behavior of such systems. However, failure to include this attractive PS-PMMA interaction can affect a variety of important properties and behaviors of interest including: (1) the width of interfacial regions, (2) the stability and energetics of metastable states such as local defects, and (3) the energy of interaction of BCP phases and morphologies with surfaces. Given the importance of defects and surface interactions in the application of the directed self assembly in BCP lithography in the microelectronics industry such a realistic potential is important. The potential from this mesoscale model was applied to a simple lattice model and showed that it was able to predict the process window for the formation of a lamellar phase for PS-PMMA BCP. However, elimination of the attractive PS-PMMA component broadened this process window by a significant amount suggesting that this component is important in the accurate modeling of BCP films for directed self assembly.

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