Jan 6, 2011
Block copolymer blends form tunable nanotemplates
Thin films of block copolymers can be assembled with graphoepitaxy to form templates with potential uses in fabricating microelectronics and high-density storage media. However, the pattern quality of the assembled morphology depends on the commensurability of the block copolymer domain spacing and the trench dimensions. Forming customized patterns with a range of domain sizes and lattice dimensions would require a number of different block copolymers. Now, researchers have demonstrated the use of block copolymer blends with graphoepitaxially directed assembly to form hexagonal lattices over a range of lattice spacings and domain sizes. The scientists have also found a way to stretch the template, such that the lattice spacing along the trench wall can be different from the lattice spacing perpendicular to the trench wall.
Researchers at the University of Wisconsin-Madison, the University College Cork, and CRANN investigated block copolymer-homopolymer ternary blends in trench structures that were etched into Si wafers. The block copolymers formed hexagonal arrays of perpendicularly oriented cylinders, the size of which were controlled by the addition of homopolymer. Of fundamental interest was the finding that for assemblies in which the dimensions of the blend and the substrate trench were incommensurate, the domain dimensions did not change uniformly in different lattice directions. As the domain size and spacing increased, the lattices swelled in the direction along the trench, while being constrained across the trench by the side walls. The scientists also found that the spacing of the cylinders across the trench feature was uniform, which is different from other structures, such as spheres, that form more tightly packed structures near the trench walls.
The dimensional control offered by the addition of homopolymer to the blend should be technologically significant by allowing the lattice shape to be tuned to a range of desired applications with just one set of materials. Additionally, manipulation of the anisotropic dimensional change in the lattice could be technologically useful by providing a degree of independent control of the lattice dimensions in the two orthogonal directions.
This work was published in the journal Nanotechnology.
About the author
The study was conducted through a collaboration between the research groups of professors Paul Nealey and Juan de Pablo at the University of Wisconsin-Madison, and Prof. Mick Morris at University College Cork, and CRANN. The Nealey research group continues to investigate block copolymer assembly on surfaces with an emphasis on unique surface modification techniques. The de Pablo group has an interest in macromolecule simulation related to block copolymer assembly. The Morris group is interested in nanoelectronic devices made from block copolymer templates and other techniques.