Boundary-Directed Epitaxy of Block Copolymers

Historically, there have been two strategies—graphoepitaxy and chemoepitaxy—for directing the self-assembly of block copolymers (BCPs) into useful nanoscale patterns. We have recently discovered a third paradigm—termed “boundary-directed epitaxy”—in which templates consisting only of planar, low-resolution features are used to drive the formation of more complex BCP patterns with enhanced feature resolution. The templates are comprised of spatial boundaries separating regions on a surface with different composition, formed at the edges of isolated stripes on a background substrate. Vertical BCP lamellae are pinned by chemical contrast at each stripe/substrate boundary, align parallel to the boundaries, selectively form on the stripes (whereas horizontal lamellae form on the background substrate), and register to wide and incommensurate stripes to multiply the feature density. Isolated BCP line arrays with half-pitch of 6.4 nm are demonstrated on stripes wider than 80 nm. Boundary-directed epitaxy circumvents the need for topographic structures used in graphoepitaxy or ultra-narrow guiding features used in chemoepitaxy to direct assembly of sub-10 nm BCP features, and provides an attractive path towards nanofabrication beyond the resolution of conventional lithography.