Coarse grained molecular dynamics model of block copolymer directed self-assembly

A model has been developed for the simulation of block copolymer (BCP) directed self-assembly (DSA) based on a coarse grained polymer model that anneals using molecular dynamics. The model uses graphics processing units (GPUs) to perform the calculations; this combined with the coarse graining means simulations times approach the speed of other more commonly used simulation techniques for BCPs. The model is unique in how it treats the pure phase blocks interactions with themselves (i.e. A-A and B-B interactions) and their interactions with each other. This allows for simulations that can potentially more accurately capture the differences between the properties of each block such as density and cohesive energy. The model is fully described and used to examine some of the issues that are unique to DSA lithographic applications of BCPs. We describe a method to calculate χ for the off-lattice MD system based on observation of the order-disorder transitions (ODT) for different degrees of polymerization N. The model is used to examine the transient, complex, non-classical morphologies that can occur through film thickness during a DSA process. During the phase separation process from a mixed initial state, the BCPs first locally phase separate to form small aggregate type structures. These aggregates then coalesce into larger features that approach the size of the equilibrium domain. These features then shift to match the guiding pattern on the underlayer followed by the slow elimination of defects. We also studied how the guiding patterns work in chemo-epitaxy DSA. The guiding patterns have a strong immediate effect on the BCP film nearest the interface and induce locally aligned self-assembly. Over time, this induced pattern tends to propagate up through the thickness of the film until the film is uniformly aligned to the guiding pattern. We also clearly see that the observed morphology at the top of the film gives no indication of the morphology through the depth, especially during the transient portions of the self-assembly process.

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