Two-dimensional Patterning by Using Block Copolymer Self-assembly
Toru Yamaguchi and Hiroshi Yamaguchi
Physical Science Laboratory
Block copolymer lithography has drawn considerable attention as a combined top-down/bottom-up nanopatterning method toward 16-nm-technology nodes and beyond. The most important challenge of its application to nanodevice fabrication is in achieving two-dimensional (2D) patterning by strictly controlling the alignment of the domain interface of the microphase-separated domains of a block copolymer. Here, we demonstrated that a flexibly designable 2D self-assembly of the symmetric poly(styrene-b-methylmethacrylate) (PS-b-PMMA) (Mn: 36 kg mol-1, lamellar period L0=28 nm) is achieved by graphoepitaxy using a hydrogen silsesquioxane (HSQ) resist pattern as the guide for alignment . The key to success is the combination of the neutralization of the bottom surface and the introduction of an intentionally designed 2D hydrophilic guiding pattern formed by top-down electron-beam lithography (EBL), which leads to vertical orientation and 2D alignment of lamellar domains, respectively [Fig. 1(a)].
For rectangular confinement, vertical lamellar domains with a thickness of 4La (La: average repeating period of the laterally aligned lamellar domains) and with a half-pitch of 16 nm can be forced to bend using right-angled guiding patterns [Fig. 1(b)]. It is noteworthy that these domain structures are formed in a pure block copolymer system, which can be achieved with high flexibility in the domain shape and period in graphoepitaxy of lamellar domains of diblock copolymers. For hexagonal confinement, we have successfully demonstrated that concentric cylindrical domains are formed [Fig. 1(c)]; these domains are characterized by high controllability of the number of layers of the PS or PMMA rings, which is achieved by varying the width of confinement between opposite sides. This precise control of the alignment of lamellar domains can be achieved by first taking full advantage of the bottom-up self-assembly of block copolymers and the top-down fabrication of the alignment guide by using high-precision EBL. We have also confirmed that these bent lamellae and concentric cylinders were successfully transferred to a semiconductor substrate with a 16-nm half-pitch resolution [Fig. 1(d)]. We are convinced that our method increases the applicability of block copolymer lithography to nanodevice fabrication, as the size scale is beyond the reach of the state-of-art top-down technology.
 T. Yamaguchi and H. Yamaguchi, Adv. Mater. 20 (2008) 1684.
Fig. 1. (a) Schematic diagram of the self-assembled structure in a hexagonal confinement. (b, c) Top-down
Scanning Electron Microscope (SEM) images of retained PS domains after the removal of the PMMA
domains in (b) rectangular and (c) hexagonal confinements. (d) Top-down SEM image of etched patterns.
All scale bars are 200 nm.
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