Preferential Alignment of Incommensurate Block Copolymer Dot Arrays Forming Moire Superstructures

Block copolymer (BCP) self-assembly is of great interest as a cost-effective method for large-scale, high resolution nanopattern fabrication. Directed self-assembly can induce long-range order and registration, reduce defect density, and enable access to patterns of higher complexity. Here we demonstrate preferential orientation of two incommensurate BCP dot arrays. A bottom layer of hexagonal silica dots is prepared via typical self-assembly from a PS-b-PDMS block copolymer. Self-assembly of a second, or top, layer of a different PS-b-PDMS block copolymer that forms a hexagonal dot pattern with different periodicity results in a predictable moire superstructure. Four distinct moire superstructures were demonstrated through a combination of different BCPs and Afferent order of annealing. The registration force of the bottom layer of hexagonal dots is sufficient to direct the self-assembly of the top layer to adopt a preferred relative angle of rotation. Large area helium ion microscopy imaging enabled quantification of the distributions of relative rotations between the two lattices in the moire superstructures, yielding statistically meaningful results for each combination. It was also found that if the bottom layer dots were too large, the resulting moire pattern was lost. A small reduction in the bottom layer dot size, however, resulted in large-area moire superstructures, suggesting a specific size regime where interlayer registration forces can induce long-range preferential alignment of incommensurate BCP dot arrays.