Selective directed self-assembly of coexisting morphologies using block copolymer blends
Stein, A.; Wright, G.; Yager, K.G.; Doerk G.S.; Black, C.T. "Selective directed self-assembly of coexisting morphologies using block copolymer blends" Nature Communications 2016
We demonstrate a new mode of directed self-assembly (DSA). In particular, we show how self-assembling thin films can be generated that are responsive to the underlying chemical template, and wherein the chemical template enforces not just positional registry, but also selects the morphology that the film exhibits. This is accomplished by blending together different block-copolymer materials. This enables one to locally select the self-assembled morphology, vastly increasing the complexity and diversity of self-assembled patterns.
Directed self-assembly (DSA) of block copolymers is an emergent technique for nano-lithography, but is limited in the range of structures possible in a single fabrication step. Here we expand on traditional DSA chemical patterning. A blend of lamellar- and cylinder-forming block copolymers assembles on specially designed surface chemical line gratings, leading to the simultaneous formation of coexisting ordered morphologies in separate areas of the substrate. The competing energetics of polymer chain distortions and chemical mismatch with the substrate grating bias the system towards either line/space or dot array patterns, depending on the pitch and linewidth of the prepattern. This is in contrast to the typical DSA, wherein assembly of a single-component block copolymer on chemical templates generates patterns of either lines/spaces (lamellar) or hexagonal dot arrays (cylinders). In our approach, the chemical template encodes desired local spatial arrangements of coexisting design motifs, self-assembled from a single, sophisticated resist.