Determination of the maximum thickness for directed self-assembly of cylinder-forming PS-b-PMMA films on chemical patterns

Previous studies on directed self-assembly (DSA) of cylinder-forming PS-b-PMMA mainly use films with a thickness comparable to the natural period of the block copolymer, L-o. It is unclear how thick the cylinder-forming PS-b-PMMA film can be directed to assemble on chemical patterns. In this work, a feasible approach is developed to determine the maximum thickness for DSA of cylinder-forming PS-b-PMMA films. The chemical pattern with a controlled correlation length (xi) is fabricated by molecular transfer printing (MTP) by replicating the surface domain pattern of the template blend film and used to direct the self-assembly of the same blend film. The transition from substrate-controlled DSA to surface-controlled self-assembly is located in assembled films on MTP replica patterns with the thickness between 4.9L(o) and 5.7L(o) by comparing the xi of the assembled film with the of the original template. DSA of cylinder-forming PS-b-PMMA is achieved in films with thickness up to at least 4.9L(o). When the film is thicker than 5.7L(o), the substrate and surface effects decouple and the free surface controls the film surface morphology.