It is important to develop lithographic materials and techniques for future devises of which size scale becomes ever smaller. However, conventional lithographic processes become increasingly more difficult and expensive, especially at a minimum feature size of less than 22 nm. Thus, it is crucial to develop innovative routes to circumvent both cost and manufacturing issues. In recent years, BCP lithography has emerged as an attractive alternative to drive down the feature size. BCPs can spontaneously self-assemble into dense, periodic array of nanostructures such as spheres, cylinders, and lamellae with feature sizes less than 50 nm.
 
The ideal BCP for nanolithography applications exhibits (1) one highly etch-resistant block, (2) high repulsive interaction, and (3) thermal stability at ambient temperature. In order to satisfy these criteria, we are focusing on designing and fabricating POSS-containing BCPs. The high density of silicon in the POSS provides extremely high etch contrast between the constituent organic block when treated in an oxygen plasma, which is advantageous for high-aspect-ratio pattern transfer into underlying materials. Also POSS shows high repulsive interaction between constituent organic polymer, which is important to smallest attainable self-assembled structure. Compared to other silicon-containing polymer such as silicones, POSS-containing polymers are extremely thermally robust, which is crucial property for uniformly cast onto the substrate and keep the ideal morphology at ambient temperature.
 
We have succeed living anionic polymerization of a series of POSS-sustituted methacrylates (PMAPOSSs) and block copolymererization with organic polymers such as polystyrene (PS) and poly(methyl methacrylate) (PMMA). Obtained POSS-containing BCPs have shown extremely long-range-ordered structure, of which size is down to 10 nm. We have also demonstrated directed self-assembly (DSA) of POSS-containing BCPs on chemically patterned templates to arbitrary align the self-assembled structure. A combination of density multiplication system and thermal annealing gave perfectly aligned hexagonally arranged spheres over an area of around 6Tera-dots/inch2. This result would change the future lithographic processes as introduced on .
 
Our next challenge for these POSS-based BCPs is to reduce the POSS-cotaining polymer/organic polymer interface roughness in order to reduce the line-edge roughness (LER) of the nanopattern. Currently we are investigating the interface structure using synchrotron X-ray scattering analyses to understand correlation between molecular structure and interface structure. We are now refining the molecular structure based on the fundamental understanding of POSS-containing BCPs.
 

 

 
In addition to BCP lithography, we are attempting "molecular" lithography by utilizing POSS-based liquid crystalline molecules. Self-assembled structure formed by BCPs usually have a size range between 10~50 nm while the one formed by liquid crystalline molecules have a size of sub-10nm. Also single molecular weight of the liquid crystalline molecules would be advantageous for long-range ordering of the self-assembled structure.
 
Currently we are in collaboration with companies to develop double-decker-shaped silsesquioxane (DDSQ) molecules, and POSS molecules with long alkyl chains. Obtained molecules showed extremely high resolution pattern derived from silicone-containing part and alkyl chain part. Our next challenge is applying these molecules to directed-self-assembly in order to perfectly ordering on the substrate such as silicon wafer.