Directly Patternable Block Copolymer Systems

Gopalan and coworkers have also taken steps towards the use of chemical amplification in block copolymers. They have synthesized a block copolymer containing a photoacid generator 

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The microphase separation of block copolymers in a constrained situation has attracted interest both from experiments and theories. There are several important characters to make this system favorable in fabricating nanoscale features. Firstly, the constrained situation helps confine the dimension of microphase separation into microscale or nanoscale, so the materials formed in such a system spontaneously possess microstructures. Secondly, the constrained situation can suppress the fluctuation of phase separation and help create an ordered pattern at large scale. Thirdly, the surface of the constrained situation can be deliberately modified to direct the microphase separation of block copolymers with attention to make nonbulk structures. 

The addition of homopolymers further enhances the tolerance of mismatching and allows chemical epitaxy of stractures more complex than the typical bulk phases of block copolymers. Stoykovich et al. introduced a ternary blend to further extend their surface-directed method. Such a blend system enables the block copolymer lamellae to conform to substrate stripe arrays with sharp bends. In the imblended block copolymer S3 tem, a high strain builds up in the polymer film at sharp comers of the chemical pattern because the comer-to-comer distance is much larger than the natural periodicity of the block copolymer. Successful replication of arrays of tilt boundaries with 45° and 90° angles was observed as a result of the redistribution of the homopolymer. (The polymer blend includes 20% PMMA homopolymer, 20% PS homopolymer, and 60% symmetric PS-b-PMMA.) Homopolymers are depleted above commensurate regions and concentrated above the distorted regions of the pattern to reduce the strain from incommensurability. 

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