Highly Ordered, Complex Morphologies in Block Copolymer Films Obtained by Spatial Confinement Using Topographical Substrates*

Block copolymers microphase separate into periodic arrays of nanostructures. Thin films of these self-assembled BCPs are finding increasing use as platforms for nanofabrication, either as lithography masks or as templates for the patterning of nanowires and particles. Directed self-assembly, using a chemical or topographical pre-pattern, increases the long range order of BCP thin films and can be used to introduce diversity to the BCP morphology. However, the ability to pattern BCPs in a variety of morphologies in close confinement usually requires multiple fabrication steps and is limited in scope.
We present a simple, one-step process for obtaining complex, highly ordered morphologies in ultra-confined films in a controlled fashion. Our approach utilizes topographically patterned silicon substrates to guide the assembly of block copolymer domains. Remarkably, different local morphologies of the block copolymer are observed on the plateaus and inside the trenches. This behavior is explained in terms of the variation in the local film thickness and the selectivity of the substrate towards one of the copolymer domains.