One of the great challenges in lithography today is to create reliable, reproducible patterns smaller than 30 nm.  At issue is the image perfection and ease of production, since electron beam lithography and X-ray lithography can already accomplish this.  Optical lithography is faced with the challenge of pattern formation with minimal edge defects, caused in many cases, by the local diffusion of photoactive compounds required for pattern formation.  Self-assembly in contrast uses the inherent ability of certain materials such as block copolymers (BCPs) to organize into structures below this 30 nm value.  However, challenges remain including the introduction of long-range order, densification and tailor-made shape formation, and development of the most suitable material.  To meet these requirements, we have focused our efforts on polyhedral oligomeric silsesquioxane (POSS)-containing BCPs.

POSS is an attractive organic-inorganic hybrid material because of its molecular cage structure, the flexible functionality based on the substituents on the silicon atoms, and the high etch resistance to oxygen plasma.  The POSS-containing BCPs, which consist of a hydrocarbon polymer such as polystyrene and polymethylmethacrylate (PMMA) and an organic-inorganic polymer tethered POSS in side chain, therefore, can be expected to form relatively smaller domains due to the strongly segregation property and to provide highly etch contrast in the resulting pattern.  These features may offer potential advantages in self-assembling lithography materials.  Here, we report the details of the living anionic polymerization of methacrylate-functionalized POSS and the synthesis of its block copolymers with PMMA (PMMA-b-PMAPOSS) resulting in spherical, cylindrical, and lamellar morphologies, and the characterization of the long-range ordered nanostructures on topographically and/or chemically patterned substrates formed by through directed self-assembly.  For instance, the resulting PMMA-b-PMAPOSS which self-assembles into hexagonally closed packed (hcp) array of dots with lattice spacing d=13nm was spin coated on the chemical template with doubled hcp lattice spacing d=26nm, and annealed under controlled CS₂ atmosphere.  By tuning the swell ratio of PMMA-b-PMAPOSS during annealing, an ordered array of dots with d=13nm, which corresponds to 3.3Tbit/in², was obtained by interpolating dots in between the chemical template pattern.  PMMA-b-PMAPOSS can potentially self-assemble into ordered domains with sub 10nm lattice spacing.  The results suggest further extending lithographical capability to very small dimensions for applications, including bit patterned media for next generation hard disk drives.