Role of Penetrability into a Brush-Coated Surface in Directed Self-Assembly of Block Copolymers

Abstract

High density and high resolution line and space patterns on surfaces are obtained by directed selfassembly of lamella-forming block copolymers using wide-stripes chemical guiding patterns. When the width of the chemical pattern is larger than the half-pitch of the block copolymer, the interaction energy between each block copolymer domain and the surface is crucial to obtain the desired segregated film morphology. We investigate how the intermixing between block copolymers and polymer brush molecules at the surface influences the optimal surface and interface free energies to obtain a proper block copolymer alignment. We have found that computational models successfully predict the experimentally obtained guided patterns if the penetrability of the brush layer is taken into account instead of a hard, impenetrable surface. Experiments on directed self-assembly of lamella-forming PS-b-PMMA using chemical guiding patterns corroborate the models used in the simulations, where the values of the surface free energy between block copolymer and guiding and background stripes are accurately determined using an experimental method based on the characterization of contact angles in droplets formed after dewetting of homopolymer blends.to one of them, respectively. Therefore, a proper wetting balance of the polymer blocks to the substrate is needed to promote lamellae oriented perpendicular to the substrate. The most common way to control the orientation of the BCP micro-domains consists in using neutral surfaces to control the surface free energy, so that the difference in the surface interaction of the two blocks is small.. 9Thin films of vertical lamellae form patterns whose morphology is randomly oriented; the width of the lines being defined by the molecular weight of the BCP. Nevertheless, ordered arrays of lines with a predefined orientation and registered with respect to device boundaries are required for most of technological applications, not only for high volume manufacturing, but also as a general method to realize templates for anisotropic metal nanostructures 10 . This can be achieved by pre-structuring the substrate with guiding patterns of appropriate dimensions and shape. These guiding patterns are realized by grapho-or chemoepitaxy methods. In graphoepitaxy, [11][12][13] the guiding patterns are made of topographical features. Usually, the width of the trench becomes a limitation for achieving high density of integration. [14][15][16] Therefore, in order to avoid this limitation, chemical epitaxy methods have been intensively explored to produce highly dense patterns. 3,[17][18][19] Moreover, in chemical epitaxy there is a reduction of the edge roughness due to the self-healing of the BCP, which means that the irregularities of the guiding patterns are not transferred to the BCP pattern. 20 Chemical guiding patterns are fabricated by conventional topdown lithographic methods like optical, extreme ultraviolet (EUV) projection or electron beam lithography (EBL), in combination with a selective, local chemical...

Grain-Boundary-Induced Alignment of Block Copolymer Thin Films

“…The second case is the surface modification by an exposure to an electron beam, where we make use of the modification of the neutral brush layer due to interaction with charged particles. As explained by Evangelio et al [26], high electron beam exposure doses (e.g., 256 mC/cm 2 ) cause a change in the surface free energy of PS-r-PMMA and convert the nominally neutral brush layer into a brush layer that is preferentially wetted by PMMA. As explained before, this effect, in turn leads to horizontal self-assembly similar to the one observed after the removal of the neutral brush layer, but dispensing with the physical removal of material.…”

“…As the surface energy modification of a polymeric brush layer by direct e-beam exposure has been presented elsewhere [26], in this section we will focus on the surface energy modification induced by the m-AFM step.…”

“…The analysis of the wetting behavior of a homopolymer blend consisting of the components of the block copolymer can serve as a qualitative test for the surface energy in micrometric areas [26,42]. Here, we use this technique to qualitatively understand the surface energy by observing the behavior of a PS/PMMA blend in the modified and in the non-modified area.…”

“…Common ways to manipulate the surface free energy of a Polystyrene-random-polymethylmetacrylate (PS-r-PMMA) brush layer is to combine a lithography step with the exposure to UV light [23] or to oxygen plasma [24]. The critical dimension of the guiding pattern features has to correspond to (n − 0.5) times the block copolymer pitch [25,26] with n being a positive integer.…”

Self-assembly of block copolymers under non-isothermal annealing conditions as revealed by grazing-incidence small-angle X-ray scattering

“…Different structural nanodomains, such as lamellae, cylinders or spheres, can be obtained depending on the degree of interaction among the polymer chains, which is quantified by the Flory Huggins interaction parameter, , plus the number of monomers, N, and the volume fraction of each block, f. However, self-assembled nanopatterns usually present a random orientation and short order domains. To overcome this limitation, directed self-assembly (DSA) combines standard lithography techniques to create topo- (Gottlieb, Kazazis et al, 2018)] or chemical [chemo-epitaxy (Ferná ndez-Regú lez et al, 2014;Evangelio et al, 2019)] guiding patterns, so that a specific orientation and position of the BCP self-assembled structures can be obtained (Hu et al, 2014). DSA of BCPs is still considered by the semiconductor industry as a complementary approach to conventional photolithography and patterning towards improving parameters such as resolution, throughput or line edge roughness (IRDS, 2018).…”