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.

Contents
1 Introduction
2 Micro-phase separations of block copolymers (BCPs)
3 Directed self-assembly (DSA) of BCPs in thin films
3.1 Preparation of pre-templates
3.2 Control of template surface properties on self-assembly
3.3 DSA methods: grapho-epitaxy and chemcal-epitaxy
3.4 Other factors affecting the DSA morphology
3.5 Characterization and evaluation methods
4 Conclusion