Block-copolymer lithography refers to the use of the selfassembling domain structure in thin films of block copolymers to template dense patterns into materials at the scale of 5±50 nm. Applications of this technology include the fabrication of quantum dots, [1,2] photonic crystals, [3,4] nanowires, [5,6] magnetic-storage media, [7] silicon capacitors, [8] and flash memory devices. [9,10] The major challenges facing block-copolymer lithography and its potential impact with respect to the fabrication of nanometer-scale devices is the emulation of the following essential attributes of current photolithographic materials and processes: 1) nearly perfect patterning over very large areas, and 2) registration of the pattern with features of the underlying substrate. Some of the strategies that are pursued in order to increase the length scale over which the domains in block-copolymer films are desirably oriented and ordered include graphoepitaxy, [11±13] in-plane electric fields, [14] directional solidification, [15] solvent evaporation, [16] and chemical surface patterns.[17] Recently we demonstrated that perpendicularly oriented lamellar domains in blockcopolymer films could be induced to assemble such that the ordering of domains was perfect over arbitrarily large areas and each domain was registered with the underlying substrate.[17] Imaging layers were patterned with advanced lithography in order to produce stripes of different chemical functionality. Adjacent stripes exhibited neutral wetting and preferential wetting towards the blocks of the copolymer, and if the period of the stripes, L s , closely matched the bulk lamellar period of the block copolymer, L o , then the domain structure in the film self-assembled in an epitaxial manner with respect to the chemically nanopatterned substrate. Here we demonstrate the process latitude of epitaxial block-copolymer lithography, that is, the range of dimensions of features (or periodicity of structures) that can be patterned with perfection using the same composition and molecular weight block copolymer, is significantly improved by increasing the contrast in interfacial energy or wetting behavior between adjacent chemically patterned regions onto which the polymer films self-assemble. The impact of incommensurate periods, L s and L o , on domain ordering, and the types of defects that occur due to incommensurability have been investigated both experimentally [18±20] and theoretically. [21±27] In epitaxial assembly of lamellar structures onto neutral/preferential wetting striped surfaces consisting of self-assembled monolayers, perfect epitaxial assembly occurred only if L s was within a few percent of L o .[17] If L s = 45 nm and L o = 48 nm, pairs of dislocation defects were observed in the compressed lamellae, and if L s was greater than 52.5 nm and L o was 48 nm, herring-bone defects, tilted domains, and domains unregistered with the surface pattern were observed. Rockford et al. [18] investigated the structure of 30 nm thick films of block copolymers of differe...
A new method for the patterning of ionic layer-by-layer assembled films with micron-sized features is presented. Self-assembled monolayers (SAMs) were used as templates to direct the deposition of sulfonated polystyrene (SPS) and poly(diallyldimethylammonium chloride) (PDAC) multilayers onto a surface. Both polyelectrolytes were assembled electrostatically from dilute solutions (10 and 20 mM on a repeat unit basis) with varying amounts of sodium chloride. The ionic content was varied from 0 to 4 M NaCl. The optimal conditions for templating were found at moderate salt contents. At high salt contents (≥1 M NaCl) the templating behavior of the chemically patterned SAM surface completely reversed due to electrostatic screening and dehydration of an oligo(ethylene glycol)surface, indicating that ionic strength can be used to dramatically alter polyion deposition behavior on the functionalized surface.
We used local thermal analysis and ellipsometry to measure the glass transition temperatures (T g ) of supported thin films of poly͑4-hydroxystyrene͒ ͑PHS͒ and hydroxy terminated polystyrene ͑PS-OH͒. The films were spuncast from solution onto silicon oxide substrates and annealed under vacuum at elevated temperatures to graft the polymer to the substrate. Grafting was verified and characterized in terms of the thickness of and the advancing contact angle of water on the residual layer after solvent extraction. For PHS, each segment of the polymer chain was capable of grafting to the substrate. The thickness of the residual layer increased with increasing annealing temperature. For this polymer the critical thickness below which the T g of the film deviated from the bulk value was nearly 200 nm after annealing at the highest temperature ͑190°C͒; the T g of films 100 nm thick or less were elevated by more than 50°C above the bulk value. For PS-OH films the polymer was only capable of grafting at one chain end, forming a brush layer at the substrate interface. The critical thicknesses for PS-OH films and the T g elevations were substantially higher than for ungrafted PS films, but were not as large as for PHS. The film thickness dependence of T g for PHS and PS-OH were well described as piecewise linear, consistent with a ''dual-mechanism'' model.
Hyperbranched polymers were prepared from a variety of mono‐ and difunctional monomers and used in the development of novel UV‐imprint lithography (UV‐IL) resists. The unique physical and chemical properties of these hyperbranched materials significantly increase the range of molecular systems that could be imprinted. Traditional challenges, such as the use of monomers that have low boiling points or the use of insoluble/highly crystalline momomers, are overcome by the preparation of hyperbranched polymers that incorporate these repeat units. In addition, the low viscosity of the hyperbranched macromolecules and the large number of reactive chain ends overcome many difficulties that are traditionally associated with the use of polymeric materials as imprint resists. Hyperbranched polymers containing up to 12 mol % pendant vinyl groups, needed for secondary crosslinking during imprinting, were prepared with a wide range of repeat unit structures and successfully imprinted with features from tens of microns to ∼ 100 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6238–6254, 2008
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