(167k) Can Short Linear Block Copolymers Stabilize Perpendicular Lamellae in Linear-Cyclic Block Copolymer Blend Films?

Block copolymer (BCP) thin films with lamellar nanostructures oriented perpendicular to the substrate surface are a potential alternative to traditional photolithography for patterning nanoscale features for the semiconductor industry. Molecular cyclization can reduce feature sizes, but like linear BCPs, cyclic BCPs tend to form nanostructures oriented parallel to the substrate, which is undesirable for BCP-based nanolithography. Here, we use dissipative particle dynamics (DPD) simulations to study the relative stability of perpendicular (versus parallel or mixed) orientation for linear BCPs to that of cyclic BCPs. To mimic the experimental setup, BCP chains are confined between a substrate, modeled as a 2D lattice of DPD beads, and a bath of DPD beads acting as a dense “gas” to represent the atmosphere above the film. With non-selective surface interactions, we see that linear chains align parallel to the substrate and BCP-gas interfaces due an entropic effect, consistent with previous studies (Forrey et al., ACS Nano 2011, 5, 4, 2895–2907), thus favoring perpendicular lamellae. In contrast, cyclic chains also adopt parallel alignments but with more compact conformations. These findings suggest that the substrate neutrality condition for perpendicular lamellae is less stringent for linear BCPs than for cyclic BCPs. Thus, it should be easier to form perpendicular lamellae from linear BCPs than cyclic analogues. Currently, we are computing the free energy of the two competing orientations for linear and cyclic BCPs. Moreover, since shorter chains in a BCP blend tend to segregate near the surface due to the depletion effect, we are also exploring the possibility of adding a small amount of shorter linear BCPs to stabilize perpendicular lamellae in majority cyclic BCP blends. A previous study from our group has shown that the domain spacing of the linear-cyclic BCPs blend does not change significantly when linear chains constitute less than 10% of the blend (Goodson et al., ACS Appl. Polym. Mater. 2022, 4, 1, 327–337) making this a viable strategy from an application standpoint.