Metal‐assisted etching is used in conjunction with block‐copolymer lithography to create ordered and densely‐packed arrays of high‐aspect‐ratio single‐crystal silicon nanowires with uniform crystallographic orientations. Nanowires with diameters and spacings down to 19 nm and 10 nm, respectively, are created as either continuous carpets or as carpets within trenches. Wires with aspect ratios up to 220 are fabricated, and capillary‐induced clustering of wires is eliminated through post‐etching critical point drying. The wires are single crystals with 〈100〉 axis directions. The distribution of wire diameters is narrow and closely follows the size distribution of the block copolymer, with a standard deviation of 3.12 nm for wires of mean diameters 22.06 nm. Wire arrays formed in carpets and in channels have hexagonal order with good fidelity to the block copolymer pattern. Fabrication of wires in topographic features demonstrates the ability to accurately control wire placement. Wire arrays made using this new process will have applications in the creation of arrays of photonic and sensing devices.

Self-assembly provides the ability to create well-controlled nanostructures with electronic or chemical functionality and enables the synthesis of a wide range of useful devices. Diblock copolymers self-assemble into periodic arrays of microdomains with feature sizes of typically 10-50 nm, and have been used to make a wide range of devices such as silicon capacitors and transistors, photonic crystals, and patterned magnetic media(1-3). However, the cylindrical or spherical microdomains in diblock copolymers generally form close-packed structures with hexagonal symmetry, limiting their device applications. Here we demonstrate self-assembly of square-symmetry patterns from a triblock terpolymer in which one organometallic block imparts high etch selectivity and etch resistance. Long-range order is imposed on the microdomain arrays by self-assembly on topographical substrates, and the orientation of both square lattices and in-plane cylinders is controlled by the substrate chemistry. Pattern transfer is demonstrated by making an array of square-packed 30 nm tall, 20 nm diameter silica pillars. Templated self-assembly of triblock terpolymers can generate nanostructures with geometries that are unattainable from diblock copolymers, significantly enhancing the capabilities of block copolymer lithography.

We demonstrated a versatile approach to obtain layered nanoparticle sheets with in-plane hexagonal order and 3-D ordered arrays of single nanoparticle chains in thin films upon blending nanoparticles with block copolymer (BCP)-based supramolecules. Basic understanding on the thermodynamic and kinetic aspects of the assembly process paved a path to manipulate these assemblies to meet demands in nanoparticle-based device fabrication and understand structure-property correlations.

Block copolymers can microphase-separate into periodic nanoscale structures with well-defined geometries and length scales, making them attractive materials for self-assembled nanolithography. [1][2][3][4] Ordered arrays of block copolymer spheres, cylinders, or lamellae have been used to pattern features in functional materials with sizes of $10-50 nm. The fabrication of a range of devices, such as silicon capacitors and transistors, discrete magnetic storage media, and photonic crystals, [5][6][7][8] have been demonstrated using block copolymer lithography.Previous work has mainly focused on diblock copolymers, with the study of triblock or multiblock copolymers being less actively pursued, largely due to the increased level of synthetic difficulty. However, these materials offer a wider range of geometries than the line and dot patterns available from diblock copolymers, making them potentially valuable for nanolithography applications. In particular, triblock terpolymers can form ring shaped features, which are useful in the fabrication of memories or sensors, [9][10][11] and quantum devices. [12][13][14] Ring-shaped structures have been formed previously from thin films of core/shell structured linear ABC triblock terpolymers, [15][16][17] in which the cylinders are oriented perpendicular to the film plane during the anneal process. However, this work, as well as work on thin film triblock terpolymers of other morphologies, [18] has focused on materials in which all three blocks consist of organic segments. This can limit the utility of these materials in nanoscale lithography because the etch selectivity between the blocks, and their etch resistance for subsequent pattern transfer steps, is typically low. It is therefore interesting to examine thin film triblock terpolymers in which one of the blocks contains inorganic components which impart high etch selectivity and etch resistance.Triblock copolymers containing inorganic blocks such as polyphosphazenes, [19,20] polysilanes [21,22] and polysulfides [23] have been prepared previously. However, these are symmetrical ABA type triblock copolymers, which phase separate on the nanoscale into morphologies comparable to diblock copolymers.There have been several studies on bulk ABC triblock terpolymers with an inorganic polydimethylsiloxane (PDMS) block, [24][25][26] such as polyisoprene-b-polystyrene-b-poly(dimethyl siloxane) [24,25] and poly(ethyleneoxide)-b-poly(dimethyl siloxane)-b-poly(methyl oxazoline). [26] Polyferrocenylsilane (PFS) is a metal-containing polymer with iron and silicon in the polymer backbone.[27] Synthesis of PFS with controlled molecular weights and narrow polydispersities is achieved by a living anionic mechanism. [28,29] PFS has also been incorporated into multiblock copolymers with a variety of organic and inorganic coblocks. [28][29][30][31][32][33][34] These block copolymers microphase-separate to give ordered arrays of iron and silicon containing nanostructures, which have already been used in lithographic applications. [35][36][37]...

A range of proposed devices relies on the electronic, optical or magnetic properties of one-dimensional (1D) chains of nanoparticles. Here, well-controlled 1D arrays have been formed by templating a spherical-morphology block copolymer within a narrow groove. Significantly, the domains are distorted into ellipses with aspect ratio and major axis orientation controlled by the groove width. This technique gives unprecedented control over the period, particle size, aspect ratio, and orientation of nanoparticles in 1D arrays, making it valuable for creating self-assembled masks for the fabrication of novel devices.

The self-assembly of a spherical-morphology block copolymer into V-shaped grooves has been investigated. Although spherical morphology block copolymers typically form a bcc sphere array in bulk, the V groove promotes the formation of a well-ordered fcc close-packed sphere array with the (111) planes of the array parallel to the groove walls. The sphere size in the block copolymer adjusts depending on the commensurability between the periodicity of the block copolymer and the film thickness within the V groove. The top surface of the close-packed array, parallel to the substrate, shows a square symmetry, unlike the hexagonal symmetry seen in monolayers of spherical domains, which may provide a useful geometry for block copolymer lithography.

A systematic study of metal‐catalyzed etching of (100), (110), and (111) silicon substrates using gold catalysts with three varying geometrical characteristics: isolated nanoparticles, metal meshes with small hole spacings, and metal meshes with large hole spacings is carried out. It is shown that for both isolated metal catalyst nanoparticles and meshes with small hole spacings, etching proceeds in the crystallographically preferred <100> direction. However, the etching is confined to the single direction normal to the substrate surface when a catalyst meshes with large hole spacings is used. We have also demonstrated that the metal catalyzed etching method when used with metal mesh with large hole spacings can be extended to create arrays of polycrystalline and amorphous vertically aligned silicon nanowire by confining the etching to proceed in the normal direction to the substrate surface. The ability to pattern wires from polycrystalline and amorphous silicon thin films opens the possibility of making silicon nanowire array‐based devices on a much wider range of substrates.

Articles you may be interested inBlock copolymer self assembly for design and vapor-phase synthesis of nanostructured antireflective surfaces J. Vac. Sci. Technol. B 32, 06FE02 (2014); 10.1116/1.4896335Directed self-assembly of ternary blends of block copolymer and homopolymers on chemical patterns J. Vac. Sci. Technol. B 31, 06F301 (2013); 10.1116/1.4818882 Curing process of silsesquioxane in self-organized diblock copolymer template Block copolymers can self-assemble to generate patterns with nanoscale periodicity, which may be useful in lithographic applications. Block copolymers in which one block is organic and the other contains Si are appealing for self-assembled lithography because of the high etch contrast between the blocks, the high etch resistance of the Si-containing block, and the high Flory-Huggins interaction parameter, which is expected to minimize line edge roughness. The locations and long range order of the microdomains can be controlled using shallow topographical features. Pattern generation from poly͑styrene͒-poly͑ferrocenyldimethylsilane͒ and poly͑styrene͒-poly͑dimethyl-siloxane͒ block copolymers, and the subsequent pattern transfer into metal, oxide, and polymer films, is described.