Directed Self-Assembly of Block Copolymers

Block Copolymers (BCPs) have been investigated widely in recent years due to their ability of self assembly in nanoscale and periodical patterns with feature sizes below 10 nm in thin films. Making use of the advantages of self-assembly of block copolymers in thin films, directed self-assembly (DSA) of block copolymers combines the "bottom to top" self-assembly of block copolymers in films and the "up to down" optical lithography or e-beam lithography technologies to prepare guide templates. Morphology diversity of nanostructures such as layer, columnar and holes can be obtained by molecular design of block copolymers. The pattern-wise introduction of chemical heterogeneity on the substrate surface allows the energetic of the polymer surface interaction to be controlled in a spatially localized way that directs the alignment of block copolymer domains in films. Two main methods of self-assembly considered so far have been the grapho-epitaxy (topographic guiding patterns), which is based on creating pre-pattern on the surface of the template by lithography, and the chemical-epitaxy (chemical guiding patterns), which is based on the surface chemical modification of the template to direct the self-assembly process for instance by grafting a neutral layer material. Consequently, with higher resolution, denser and better ordered nano-patterns can be fabricated by tailoring, surface modification and size-control on micro phase and DSA is becoming one of the most promising advanced lithography technologies.