Abstract
We present and discuss the capability of grain boundaries to induce order in block copolymer thin films between horizontally and vertically assembled block copolymer grains. The system we use as a proof of principle is a thermally annealed 23.4 nm full-pitch lamellar Polystyrene-block-polymethylmetacrylate (PS-b-PMMA) di-block copolymer. In this paper, grain-boundary-induced alignment is achieved by the mechanical removal of the neutral brush layer via atomic force microscopy (AFM). The concept is also confirmed by a mask-less e-beam direct writing process. An elongated grain of vertically aligned lamellae is trapped between two grains of horizontally aligned lamellae. This configuration leads to the formation of 90° twist grain boundaries. The features maintain their orientation on a characteristic length scale, which is described by the material’s correlation length ξ. As a result of an energy minimization process, the block copolymer domains in the vertically aligned grain orient perpendicularly to the grain boundary. The energy-minimizing feature is the grain boundary itself. The width of the manipulated area (e.g., the horizontally aligned grain) does not represent a critical process parameter.
Highlights
Block copolymers consist of two or more chemically different polymer chains covalently bonded together [1]
We present grain-boundary-induced alignment (GBIA) as an interesting complementary technique to direct the self-assembly of block copolymers, because it represents a versatile method to align the material on lengths up to its correlation length ξ
We have shown that the directed self-assembly of block copolymers by grain boundary induced alignment is possible either by the controlled removal of an intermediate polymeric brush layer or its local surface modification
Summary
Block copolymers consist of two or more chemically different polymer chains covalently bonded together [1]. Driven by the repulsive force between chemically different molecules, the chains self-assemble in periodic structures, with characteristic size between few nanometers and few tens of nanometers These periodic structures can be used as high resolution, bottom-up templates for nanofabrication processes, as for example bit patterned media for hard disk drives [2,3,4], finFETs [5], and contact holes [6]. The formation of a rich variety of defects leads to polycrystalline morphologies and represents limiting factor for the use of block copolymer self-assembly in many applications requiring a low defect density. As of this insufficiently low defect density is one of the main problems for the integration of block copolymer lithography in high volume manufacturing (HVM) processes [8]
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