Synthesis of Polystyrene-block-poly(3-hydroxy-1-methacryloyloxyadamantane) (PS-b-PHAdMA) via RAFT Polymerization as Candidate Block Copolymers for Next Generation Lithography

The self-assembly of block copolymers (BCP) has appeared over the past two decades as a promising method for future patterning techniques for manufacture of integrated circuits and memory devices. However, generation of sub-20 nm feature sizes is challenging using conventional BCPs such as polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA). The realization of further miniaturization at scales of sub-10 nm in semiconductor devices depends on the design and development of new BCP materials. This study reports the synthesis of novel BCPs composed of polystyrene (PS) and polymers of 3-hydroxy-1-methacryloyloxyadamantane (HAdMA) by reversible addition-fragmentation chain-transfer (RAFT). The PHAdMA block has an elevated glass transition temperature (T_g) and is a bulky and sterically hindered segment. In this study we have demonstrated the synthetic conditions to achieve controlled polymer molecular weights and molecular weight dispersity. The physical properties, including solubility, thermal stability, film-forming capacity, self-assembly in solvent annealing and thermal annealing of polystyrene-block-poly(3-hydroxy-1-methacryloyloxyadamantane) (PS-b-PHAdMA) are reported in detail and indicate that this block copolymer is an excellent candidate for next-generation lithography materials. In particular, the analysis of the microphase morphologies in PS-b-PHAdMA thin films using atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) showed clear evidence of ordering of the BCPs into cylinders. This study significantly expands the ability of block copolymer lithography for producing patterns, an essential requirement for nanoscale device fabrication.