A coarse-grained molecular dynamics model was used to study the thin film self-assembly and resulting pattern properties of block copolymer (BCP) systems with various molar mass dispersities. Diblock copolymers (i.e. A-b-B type) were simulated in an aligned lamellar state, which is one of the most common patterns of potential use for integrated circuit fabrication via directed self-assembly of BCPs. Effects of the molar mass dispersity (Ð) on feature pitch and interfacial roughness, which are critical lithographic parameters that have a direct impact on integrated circuit performance, were simulated. It was found that for a realistic distribution of polymer molecular weights, modeled by a Wesslau distribution, both line edge roughness (LER) and line width roughness (LWR) increase approximately linearly with increasing Ð, up to ∼45% of the monodisperse value at Ð = 1.5. Mechanisms of compensation for increased A-A and B-B roughness were considered. It was found that long and short chain positions were not correlated, and that long chains were significantly deformed in shape. The increase in LWR was due to the increase in LER and a constant correlation between the line edges. Unaligned systems show a correlation between domain width and local molecular weight, while systems aligned on an alternating pattern of A and B lines did not show any correlation. When the volume fraction of individual chains was allowed to vary, similar results were found when considering the Ð of the block as opposed to the Ð of the entire system.
Molecular dynamics simulations of polymers are significantly limited because of the large time and length scales often required. In this paper, a simulation method known as Protracted Colored Noise Dynamics (PCND) is adapted to linear polymer simulations. This polymer PCND applies a time correlated random force (colored noise) along the backbone of the polymer chain, causing an increase in fluctuations on the length scale of individual chains. This form of PCND greatly increases the rate of diffusion of bulk homopolymers while not significantly altering chain conformation or crystal packing structure. It is then applied to a coarse‐grained polymer model to explore this method's ability to increase the rate at which equilibrium conformations are obtained. This polymer PCND drastically increases the kinetics of defect annihilation in block copolymer simulations with only small changes to the domain size. Application of molecular dynamics restores the correct domain size, indicating that the free energy landscape is not being significantly altered. The computational overhead associated with polymer PCND is minimal, and outweighed by the increased equilibration rate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.