Precise Control over Molecular Dimensions of Block‐Copolymer Domains Using the Interfacial Energy of Chemically Nanopatterned Substrates

Abstract

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...

Thin films of complexed block copolymers

“…[54][55][56][57] Incommensurate patterns result in novel complex nanostructures, 58 whereas patterns with a multiple of the periodicity recently proved to be able to multiply the density of a pattern (Fig. 5).…”

Perpendicular Block Copolymer Microdomains in High Aspect Ratio Templates

“…35 This led to a surface that was considerably less attractive to PDMS than the brush-coated sidewall was. A process flow showing the fabrication method is described in the supplementary material.Interfacial interactions have a very important influence on the final equilibrium morphology of BCP self-assembly, 36,37 and form the basis of templating strategies. 16,38 In a high aspect-ratio template we consider three pairs of interfacial energies with respect to a lamellar-forming A-B diblock copolymer: γ Top , γ Bot , γ Side , where γ is the interfacial energy and "Top", "Bot", and "Side" refer to the top (i.e.…”

Lithography for enabling advances in integrated circuits and devices

“…When the surface-modified substrate is coated with a thin block copolymer film and thermally annealed, preferential wetting drives each block to migrate towards chemically compatible surface regions, so as to minimize the free energy of the system. If the contrast in the surface pattern is strong, then significant mismatch in the periods L s and L o can be tolerated before increased defectivity is observed [84]. With strong polymer-surface interactions, the block copolymer domains can be directed into many of the essential features required for manufacturing integrated circuits with regular fabric architectures, including dense and isolated bends, jogs, spots, line terminations and T-junctions [83,85].…”