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Directed self-assembly (DSA) of block copolymers (BCPs) is one approach to the pattern density multiplication required to achieve high-volume manufacturing of the next-generation memory and storage devices. One important application for DSA is in manufacturing of nanoimprint templates for the next-generation bit patterned media. A hybrid chemo-/grapho-epitaxy DSA process has been developed that produced 5 nm line-and-space DSA patterns on a chromium hard mask surface. The guide lines for this process were produced by imprint lithography. The process requires a polar guide stripe, which is the trim-etched imprint resist, and a near neutral substrate, which is the etched chromium. This requires selective grafting of near neutral polymer brushes to the etched chromium and not to the etched imprint guidelines. This selectivity is one critical requirement for the process [1]. Orientation and alignment of line-and-space patterns that traverse through the entire BCP film were successfully employed to pattern the chromium hard mask. We have investigated the reactivity of etched chromium surfaces with various polymer brush chemistries and found that the choice of the end-functional groups, monomer structures, and grafting temperature all play significant roles in selective functionalization. The etched chromium surface was found to be more reactive with various polymer brushes than etched silicon under mild brush grafting conditions. Hence, lower grafting temperatures could be exploited for achieving selectivity of polymer brush to the etched chromium while not reacting with the etched imprint guidelines. Thus, several polymer brushes that form a thin layer of brush on etched chromium were found to modify the surface energy of the etched chromium without significant interaction with the etched imprint resist. Successful pattern transfer of 5 nm line-and-space patterns was achieved. 1. Lane, A. P., et al. ACS Nano (2017), 11 (8), 7656–7665.
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