Block copolymers Well-Ordered Thin-Film Nanopore Arrays Formed Using a Block-Copolymer Template** Yeon Sik Jung and Caroline A. Ross* Following Moore’s law, the transistor density and hence the computing power of integrated circuits have scaled exponen- tially with time. [1] However, optical lithography technology, which has sustained Moore’s law over the last half century, is reaching a limit in pattern resolution. Unconventional lithography techniques are therefore required to enable the next generations of microelectronic device fabrication. The critical requirements are scalability, high throughput, low cost, and compatibility with existing fabrication techniques. During the past decade, films of self-assembled diblock copolymers (BCPs) have attracted significant attention for lithography applications because they can generate ordered microdomains with sizes below 30 nm by thermodynamically driven microphase separation [2–16] In this application, 2D arrays or monolayers of microdomains are desirable to facilitate pattern transfer. [4,7,13,14,17] Typically, self-assembled BCP microdomain arrays possess only short-range order, and thus to make technologically useful structures with long-range order and accurate registration, BCPs may be templated using features formed by another lithography techni- que. [4,5,9,10,13–15,17,18] The most common templates are chemical [5,15,19,20] or topographic [4,8,9,13,14,17] patterns defined by electron beam lithography or optical lithography. Chemical templates can regulate the orientation and position of BCP microdomains to high precision [5,15,19,20] in BCP films consisting of out-of-plane cylinders or lamellae, in which both blocks contact the chemically patterned substrate. Topographic patterns, with or without substrate surface functionalization, use spatial confinement to impose long-range ordering in BCPs of many morphologies including in-plane cylinders and spheres, [4,8,9,13,14,17] and can also form 3D assemblies, [21–24] including morphologies such as rings, spirals, disks, and hollow cylinders that are not found in bulk. [21–23,25,26] Of key importance is the ability to transfer patterns with good fidelity from block copolymers into a variety of materials, including metals that may be difficult to dry-etch. In this communication, we describe a simple route to fabricate thin films with well-ordered nanopores (antidot arrays) using self- assembled block-copolymer lithography and pattern transfer processes. Long-range ordering of a sphere-forming block copolymer is accomplished using a brush-coated 1D topo- graphic template and solvent annealing, and the spheres are used to make nanoporous patterns through a pattern reversal process. Examples of Ti, Pt, Ta, W, silica, and magnetic Co and Ni antidot arrays are presented. A second image reversal process was used to form Ni dot arrays. This general method may be used to make a diverse range of nanoatterned films that can be useful in applications including via formation in integrated circuits, filters, plasmonic and photonic bandgap structures, catalysts, templates, sensors, and solar cells. [27–35] The fabrication process for nanoporous metallic thin films is illustrated in Figure 1. A sphere-forming polystyrene-b- poly(dimethylsiloxane) (PS-PDMS) BCP was used to make nanoscale dot arrays. PS-PDMS (Figure 1a) has excellent microdomain ordering due to its large Flory–Huggins interaction parameter compared to other commonly used BCPs. It also has good etch selectivity between the two blocks due to the inorganic component (Si) in the PDMS. [13,14,26] An UV interference lithography system was employed to make 1.2-mm-period linear trenches with a depth of 40 nm (Figure 1b) that were then treated with a PDMS brush. A disordered 30-nm-thick PS-PDMS thin film was obtained by spin-coating a 1.5% toluene solution of the BCP onto the patterned substrate (Figure 1c), then the film was annealed in a toluene solvent vapor to obtain an equilibrium microdomain morphology (Figure 1d) consisting of a monolayer of close- packed PDMS spheres in a PS matrix sandwiched between thin PDMS brush layers at the film–substrate and film–air interfaces. [13,14,26] For simplicity, the thin PDMS layers are not shown in Figure 1d. Etching by CF 4 plasma followed by O 2 plasma removes the PS matrix and oxidizes the PDMS spheres (Figure 1e). A 55–70-nm-thick metal film was sputter- deposited on top of the PDMS (Figure 1f) and etched using CF 4 plasma. This slowly removes the metal, primarily by sputter-etching, until the oxidized PDMS is exposed, which is then etched quickly by forming volatile SiF x . [26] Thus, the final morphology is a reverse image of the original PDMS dot patterns (Figure 1g). The detailed patterning mechanism will be discussed below. Figure 2a–c shows scanning electron microscopy (SEM) images of self-assembled PDMS spheres in the trenches after removing the PS. The average diameter of the structures is 17.9  1.1 nm, and the average center-to-center distance is 35.0  1.5 nm. Each 960-nm-wide trench templates 32 rows of hexagonally ordered dots, and Figure 2d shows the fast Fourier transform of the image. The height of the dots is around 10– communications [  ] Prof. C. A. Ross, Y. S. Jung Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, MA 02139 (USA) E-mail: caross@mit.edu [  ] The support of the Semiconductor Research Corporation is grate- fully acknowledged. DOI: 10.1002/smll.200900053 1654 ß 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim small 2009, 5, No. 14, 1654–1659