Chemical Patterns for Directed Self-Assembly of Lamellae-Forming Block Copolymers with Density Multiplication of Features

Abstract

Lamellae-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films, with bulk period L 0, were directed to assemble on lithographically nanopatterned surfaces. The chemical pattern was comprised of “guiding” stripes of cross-linked polystyrene (X-PS) or poly(methyl methacrylate) (X-PMMA) mats, with width W, and interspatial “background” regions of a random copolymer brush of styrene and methyl methacrylate (P(S-r-MMA)). The fraction of styrene (f) in the brush was varied to control the chemistry of the background regions. The period of the pattern was L s. After assembly, the density of the features (domains) in the block copolymer film was an integer multiple (n) of the density of features of the chemical pattern, where n = L s/L 0. The quality of the assembled PS-b-PMMA films into patterns of dense lines as a function of n, W/L 0, and f was analyzed with top-down scanning electron microscopy. The most effective background chemistry for directed assembly with density multiplication corresponded to a brush chemistry (f) that minimized the interfacial energy between the background regions and the composition of the film overlying the background regions. The three-dimensional structure of the domains within the film was investigated using cross-sectional SEM and Monte Carlo simulations of a coarse-grained model and was found most closely to resemble perpendicularly oriented lamellae when W/L 0 ∼ 0.5–0.6. Directed self-assembly with density multiplication (n = 4) and W/L 0 = 1 or 1.5 yields pattern of high quality, parallel linear structures on the top surface of the assembled films, but complex, three-dimensional structures within the film.

Kinetics of directed self-assembly of block copolymers on chemically patterned substrates

“…In our simulation study we have illustrated the dependence on incompatibility and strength of the surface interactions. In agreement with experiments and previous simulations that focused on the equilibrium properties [14,15], we observe that sparse guiding patterns of A-attractive lines with a background that is weakly attractive to the other species, B, are preferable to neutral backgrounds. Our simulations indicate that such a weak background preference results in a more symmetric structure at the end of the initial pattern-directed spinodal self-assembly (i.e.…”

“…The equilibrium properties of copolymers on sparse guiding patterns have been carefully investigated by Detcheverry et al [14] and Ramirez-Hernandez and co-workers [15]. Efficiently equilibrating the structures by a sophisticated variety of Monte-Carlo moves -single-bead displacements, reptation, whole-chain translation, and swapping of the two blocks -they observed that a weakly B-attractive background increases the stability of defect-free standing lamellae in comparison to alternate structures, and this finding has been corroborated by experiments [14,15]. Two-dimensional density profiles for the same system as in Fig.…”

“…The stripe structure of the block copolymer mitigates the line-edge roughness [11,12] or small imperfections of the guiding pattern. Alternatively the periodicity of the L/S guiding pattern can be a small multiple of the bulk lamellar structure of the copolymer ("density multiplication" [13,14,15]). In this case the copolymer structure will "fill-in" the missing lines and multiply the density of the L/S guiding pattern fabricating a pattern with periodicity of a few tens of nanometers.…”

Polarity-switching Top Coats for Silicon-containing Block Copolymer Orientation Control

“…Annealing strategies that mitigate preferential top interface interactions have been developed that utilize solvent vapor, which both plasticizes the BCP to induce self-assembly and creates nonpreferential top interface interactions. 4 We view traditional thermal annealing as a highly preferable process because it is both compatible with technology widely utilized in industry today 5,6 and accesses thermodynamically minimum energy states. Control of the top interface is thus crucial to translate current thermal annealing processes to Si-BCPs.…”

Enabling complex nanoscale pattern customization using directed self-assembly

“…The directed self-assembly (DSA) of BCP thin films using chemical [3][4][5][6][7][8] or topographical [9][10][11][12][13][14][15][16] templates to impose long-range order and registration on the BCP domains has garnered increased interest in recent years as a means to enhance lithographic resolution by multiplying the feature density [5][6][7][8][13][14][15] and rectifying pattern non-uniformity or imperfections 5,6,17,18 of lithographically defined templates. Selective removal or alteration of one block then creates a mask that may be combined with other manufacturing techniques to fabricate devices such as patterned magnetic recording media 19 , silicon nanowire transistors 20 or FinFETs 21 .…”