Block Copolymer Lithography toward 16-nm-technology Nodes


Toru Yamaguchi and Hiroshi Yamaguchi
Physical Science Laboratory

 Block copolymer lithography (BCL) has attracted considerable attention as a combined top-down/bottom-up approach to nanopatterning. It involves the use of microphase-separated nanometer-sized domains of block copolymers as lithography templates. In recent times, the significance of BCL in the field of lithography is particularly increased due to the fact that top-down lithography will soon be reaching its limit in the 22-nm regime, necessitating the development of innovative technologies. BCL has great potential for exceeding the resolution limit of the state-of-art top-down lithography because its resolution is determined solely by the molecular size of the block copolymer. The most important challenge in BCL is the achievement of a strict control on the alignment of various microphase-separated domains. Among these domains, vertical lamellar domains composed of alternating stacked layers of two dissimilar polymer chain blocks A and B (Fig. 1) have critical advantages as lithography templates for nanodevice fabrication on account of their line shape, high aspect ratio, and wide flexibility in pattern configuration. However, the difficulty encountered in the formation of vertical lamellae was that the lamellar interface should be aligned in two directions, perpendicular to the substrate surface and parallel to the lithographically created features.
 Here, we report our novel method of aligning lamellar domains by means of graphoepitaxy using a resist pattern as an alignment guide [1]. Graphoepitaxy is a technique that uses the surface topography of the substrate to direct the epitaxial growth of the block copolymer film. The key to its success is the combination of the neutralization of a bottom surface and the introduction of a hydrophilic guiding pattern; this makes it possible to independently control the surface affinity of the substrate surface and the sidewall surface of the guiding pattern, which leads to the vertical orientation and lateral alignment of lamellar domains, respectively (Fig. 1). We have successfully demonstrated that the lateral alignment of the lamellar structure of a symmetric poly(styrene-b-methyl methacrylate) is achieved in confined spaces of about 3La (La: laterally aligned lamellar period, La 〜 32 nm) between hydrogen silsesquioxane (HSQ) resist patterns on a neutral surface (Fig. 2). It is important to consider that a lamellar structure with a period shorter than the pitch of the guide pattern could be formed by this method. We believe that the combination of the artificial layout of the guide patterns and the best polymer materials could lead to a new type of high-resolution lithographic technology in the 16-nm (1/2 La) regime.

[1] T. Yamaguchi and H. Yamaguchi, J. Photopolym. Sci. Technol. 19 (2006) 385.

Fig. 1. Lateral alignment of lamellar domains.
Fig. 2. AFM phase image of aligned domains.

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