Abstract
A photo-crosslinked polystyrene (PS) thin film is investigated as a potential guiding sub-layer for polystyrene-block-poly (methyl methacrylate) block copolymer (BCP) cylindrical nanopattern formation via topographic directed self-assembly (DSA). When compared to a non-crosslinked PS brush sub-layer, the photo-crosslinked PS sub-layer provided longer correlation lengths of the BCP nanostructure, resulting in a highly uniform DSA nanopattern with a low number of BCP dislocation defects. Depending on the thickness of the sub-layer used, parallel or orthogonal orientations of DSA nanopattern arrays were obtained that covered the entire surface of patterned Si substrates, including both trench and mesa regions. The design of DSA sub-layers and guide patterns, such as hardening the sub-layer by photo-crosslinking, nano-structuring on mesas, the relation between trench/mesa width, and BCP equilibrium period, were explored with a view to developing defect-reduced DSA lithography technology.
Highlights
The self-assembly of block copolymers (BCPs) has, over the past decade, become a powerful technique for fabricating functional templates and scaffolds for advanced devices such as bit-patterned media [1], memory devices [2], nanowire-based transistors [3,4], arrays of quantum dots or metallic nanoparticles [5,6], and ultrafiltration membranes [7]
The process used to create the photo-crosslinked PS sub-layer films is depicted in Figure 1, wherein a PS-OH film is first spin coated onto an Si wafer, and thermally cured at 150 ̋ C under vacuum to chemically anchor the PS-OH polymer chains via dehydration
This report has demonstrated that a photo-crosslinked PS thin film can effectively function as a sub-layer to improve the uniformity of a directed self-assembly (DSA) nanopattern, which is made possible by a higher correlation length of the BCP nanostructuring layer
Summary
The self-assembly of block copolymers (BCPs) has, over the past decade, become a powerful technique for fabricating functional templates and scaffolds for advanced devices such as bit-patterned media [1], memory devices [2], nanowire-based transistors [3,4], arrays of quantum dots or metallic nanoparticles [5,6], and ultrafiltration membranes [7]. This has been made possible by the intrinsic ability of BCPs to form highly ordered polymeric structures with periodicities on a nanometer scale. Kim et al have demonstrated that a PS homopolymer brush, the thickness of which is dependent on the molecular weight of PS, is more useful for tuning the surfaces energy of substrates than the more widely-used grafting of poly
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