Well‐Ordered Thin‐Film Nanopore Arrays Formed Using a Block‐Copolymer Template

Abstract

Following Moore's law, the transistor density and hence the computing power of integrated circuits have scaled exponentially 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][3][4][5][6][7][8][9][10][11][12][13][14][15][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 technique. [4,5,9,10,[13][14][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][22][23][24] including morphologies such as rings, spirals, disks, and hollow cylinders that are not found in bulk. [21][22][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 topographic 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]...

Preparation and Characterization of Ordered Nanostructured Cobalt Films via Lyotropic Liquid Crystal Templated Electrodeposition Method

“…Also, the generation of ordered arrays of nanoscale holes in various metallic thin films by using a mask made from a 35-nm-period, 18-nmsphere-diameter spherical morphology block copolymer film and a CF 4 plasma etching process that sputter-etches the metal films were demonstrated. 19 It was concluded that in this work and in the work established in literature, the advantages of the liquid crystal template method are the unchanged topology of the phase throughout the progress of the reaction and the calcinations process and the ability to fabricate thin films with high surface area via electrodepostion. 20 The present work describes the fabrication of nanostructured mesoporous cobalt films (H 1 -eCo) by the electrodeposition of cobalt from the aqueous domain of the hexagonal liquid crystal phase of p84.…”

Strategies for Inorganic Incorporation using Neat Block Copolymer Thin Films for Etch Mask Function and Nanotechnological Application

“…[ 88 ] Another work detailed a similarly impressive level of control in generating nanopore arrays via a sphere forming PS-b -PDMS template and radio frequency sputtering of metals for magnetic study ( Figure 5 b-i). [ 89 ] Adv. Mater Top-down SEM image of g) a porous host PS template and h) Pt/Ti nanodots, as shown schematically in (i).…”

“…In contrast, excellent work has been shown by Ross and co-workers using PS-b -PDMS templates and radio frequency sputtering of a variety of metals coupled with plasma etching. [86][87][88][89] PSb -PDMS is a BCP of major focus in the BCP nanopatterning community due to its high χ (χ ≈ 0.26) enabling small feature sizes and the PDMS block is a silicon containing backbone producing etch contrast when oxidized. After developing well-oriented oxidized PDMS linespace features following selective etching, radio frequency sputtering of Ti, W, Pt, Co, Ni, Ta, Au, and Al along with selective dry etching of the sputtered metal led to resulting metal wires with sub-10 nm feature size.…”

Enhancing the Potential of Block Copolymer Lithography with Polymer Self-Consistent Field Theory Simulations

“…[12][13][14][15] Our prior work also showed that oxidized PDMS patterns obtained from the BCP can be used as a robust etch mask to pattern soft polymeric films such as a conducting polymer using an oxygen etch 15 and for patterning metal films into dot, ring, line, and antidot arrays. 16,17 (Figures S1 and S2 in the Supporting Information show another example of pattern transfer into a polymer resin.) In this Letter, we demonstrate transfer of high-quality linear patterns into a variety of metals, Ti, W, Pt, Co, Ni, Ta, Au, and Al, to make nanowires of widths down to 9 nm that can be used as interconnect lines or memory device components, and we describe their magnetic and electrical properties.…”

“…Terminating the etch process at that point results in a reverse-contrast image in the W film with a thickness equal to that of the BCP pattern. The etch rates of metallic films range from 2.3 to 25 nm/ min compared to 140 nm/min for the oxidized PDMS, 17 and thus once the buried PDMS patterns are exposed to the 450 W CF 4 plasma, they are etched away in 6 s. The electrical resistance of the metallic films was monitored during the plasma etching process in order to estimate the remaining thickness and to prevent overetching. Figure 3a demonstrates a range of metallic nanowire patterns with a pattern density of 2.94 × 10 5 cm -1 made using 45.5 kg/mol PS-PDMS.…”