Block Copolymer Films Showing Dual Patterns Using Topographically-Defined Substrates

Directed self-assembly of block copolymers facilitates the creation of films with highly oriented domains over large areas. However, further enhancing our control over surface design requires the ability to create regions of a desired pattern which could be arbitrarily spaced.
We have recently discovered that the utilization of substrates with topographically-defined stripes leads to the formation of different morphologies in the trenches and on the plateaus in ultra-confined block copolymer films. This is explained by the fact that capillary action drives more material to deposit in the trenches than on the plateaus during spin coating. The high sensitivity of the patterns displayed by ultra-confined films to minute differences in film thickness and substrate selectivity gives rise to different patterns in the trenches and on the plateaus. Specifically, we were able to demonstrate the formation of hexagonally packed dots on the plateaus concomitant with featureless appearance of the slightly thicker films in the trenches, owing to the ability of the latter to accommodate lying lamellae. As the widths of the trenches are controlled by the lithographic design, this situation facilitates the creation of patterned domains that are spaced by featureless regions as needed.