Chemoepitaxial guiding underlayers for density asymmetric and energetically asymmetric diblock copolymers

Block copolymers, polymers composed of two or more homopolymers covalently bonded together, are currently being investigated as a method to extend optical lithography due to their ability to microphase separate on small size scales. In order to drive down the size that these BCPs phase separate, the BCPs with larger Flory-Huggin's χparameter needs to be found. Typically these BCPs are composed of more dissimilar homopolymers. However, changing these interactions also changes how BCPs interact with their guiding underlayers. In this paper, several block copolymers are simulated annealing on chemoepitaxial guiding underlayers using a coarse-grained molecular dynamics model in order to explore the effect that either energetic asymmetry or density asymmetry in the BCP have on the pattern registration. It is found that energetic asymmetry in BCPs causes one of the blocks to desire to skin, which shifts the composition of the background region that leads to well aligned vertical lamellae formation. It is hypothesized that moderate footing and undercutting at the underlayer or slight skinning at the free surface can increase the kinetics of defect annihilation by decreasing the distance that bridges must form. The density asymmetric BCPs simulated in this paper have different mechanical properties which lead to straighter sidewalls in the BCP film and potentially lead to better pattern registration. It is hypothesized that altering the compressibility of the blocks can alter equilibrium defectivity.