| Stoykovich, et al. present results of incorporating directed self-assembly of BCPs for the fabrication of isolated features, and critical IC geometries. |
A review by Jeff Morse , PhD. National Nanomanufacturing Network
While self-assembly using block copolymers has demonstrated the ability to generate sub-100 nm features, patterns are typically limited to ordered arrays of cylindrical features. In the case of integrated circuit (IC) fabrication processes, a much more versatile patterning approach is needed in order to achieve the necessary geometries for circuit and device layout. Even with revolutionary changes to the IC layout and design rules, nanoelectronics still require an essential set of complex pattern geometries that may be required either in dense array form, or as isolated structures having ever decreasing critical dimensions. In contrast to ordered arrays of patterns, these geometries include lines, 90 degree bends, jogs, T-junctions, periodic arrays, and combinations thereof. A recent article by Stoykovich, et al. (ACS Nano 2007 1(3) 168-175) presented results of incorporating directed self-assembly of BCPs for the fabrication of isolated features, and critical IC geometries.
Specific geometries were achieved using a ternary block copolymer-homopolymer blend, which benefitted from the homopolymer redistribution within the lamellar domains to form nonregular geometries. Further preparation of local surface feaures using both low resolution and high resolution lithographic techniques combined with multiple exposures to chemically pattern the localized surface, enabled assembly of BCPs in complex, device-oriented structures. The article further details the process whereby the substrate is chemically modifed using a self assembled monolayer that is chemically grafted to the native oxide on the silicon substrate. Standard lithography (top down processes) can be used to pattern the surface providing regions of distinct chemistry and interfacial energy with respect to the two blocks of the copolymer. The researchers found that by varying the wetting properties of the chemically patterned surface and feature sizes, along with the composition of the copolymer-homopolymer blend, that both isolated and dense patterns and features could be achieved.
The suite of geometrical features could be achieved in both dense and isolated structures, with subsequent pattern transfer techniques, such as reactive ion etching and thin film deposition, conducted to form the actual pattern in the silicon substrate. While the processes developed established the means to generate IC like features using the directed assembly of BCPs, significant steps must be further developed to render this approach suitable for next generation IC manufacturing. Furthermore, new IC design rules must be established to exploit the patterns that are achievable using this approach, therefore specific devices and componenst may be realized earlier, such as memory or programmable gate array devices that can make use of the ordered array nature of directed self-assembly processes.
