Chemoepitaxial guiding underlayers for density asymmetric and energetically asymmetric diblock copolymers

Abstract

Currently, high χ block copolymers (BCPs) are being investigated as a method to extend optical lithography due to their ability to microphase separate on small size scales. Typically, BCPs with larger Flory–Huggin’s χ parameters are composed of more dissimilar homopolymers. However, having dissimilar blocks changes how BCPs interact with their guiding underlayers. Several BCPs are simulated annealing on chemoepitaxial guiding underlayers using a coarse-grained molecular dynamics model to explore the effect that either energetic asymmetry or density asymmetry in the BCP have on the pattern registration. It is found that in varying the background region composition four regimes can be found. Minor variations in pinning stripe width are shown to have little effect on the window where well-aligned vertical lamellae form. For BCPs without an energetic mismatch, incommensurate films have the largest window for well-aligned vertical lamellae. However, with an energetic mismatch, the defectivity has a more complicated dependence on film thickness. Two different mixed lamellae (ML) morphologies can form depending on the film volume fraction and the relative compressibilities of the two blocks. It is found that more preferential background regions can be used when the BCP is transitioning between the two ML morphologies. This transition volume fraction shifts for a density asymmetric BCP, likely due to a difference in compressibilities of the two blocks.