Layer-by-layer Stacking Method for 3-D Nano Structure Fabrication Using Block Copolymer Self Assembly
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Layer-by-layer Stacking Method for 3-D Nano Structure Fabrication Using Block Copolymer Self Assembly Shin’ichi Warisawa1, Ryosuke Kanameda1, Reo Kometani1 and Sunao Ishihara1 Department of Mechanical Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan
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ABSTRACT In this paper, we present layer-by-layer stacking method to fabricate self-assembled structures of block copolymers (BCP) toward the out-of-plane direction. Layer-by-layer stacking is realized by transferring a BCP film on one substrate to another. Specifically, a water-soluble polymer film is coated on the former substrate, which is placed and fixed in contact with a target substrate. Consequently, the BCP film is released from the substrate and transferred to the target substrate when immersed in de-ionized water. In our experiment, PS-b-PMMA is used to form and transfer self-assembled structures, and polyvinyl alcohol is used as a water-soluble polymer. We prepared two kinds of target substrates; one has horizontal cylindrical structures by BCP self assembly, and the other has groove structures by EB lithography. In the case of BCP patterned substrate, BCP film with vertical cylindrical structures is transferred onto the line structures of BCP. In the case of EB lithography patterned substrate, BCP film with vertical cylindrical structures is transferred in a doubly suspended condition. Furthermore, vertical and horizontal cylindrical structures are also observed to align along the grooves. INTRODUCTION Recent block copolymer self-assembly research has demonstrated the potential to form aligned line patterns [1], periodical sphere structures [2], and directed line and sphere patterns using chemical and physical templates at the nanoscale. However, many of these have been examined mainly on two-dimensional flat substrates [3, 4]. On the contrary, BCP thin films with microdomains oriented normal to a substrate have paid much attention, and thus many methods such as shear force flow [5, 6], electric field [7], solvent evaporation [8] and so on are employed to obtain ordered thicker or larger film effectively. Since most of these apply a unidirectional field to the entire film, obtained structures have an orientation in the applied field direction, and then fabricated structures are limited. In this research, we offer the possibility of extending selfassembled structures in the out-of-plane direction based on a layer-by-layer stacking method using thin film transfer. LAYER-BY-LAYER STACKING METHOD Figure 1 shows a layer-by-layer stacking method that we propose. Layer-by-layer stacking is realized by transferring a BCP film of one substrate (source substrate) onto another (target substrate). The source substrate is coated by a water-soluble polymer, and then coated by a block copolymer. The source substrate may be either flat or topographically patterned. The target substrate is prepared in advance with its surface patterned by self-assembled block
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copolymer or topographically patterned by lithogr
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