High‐Fidelity, Sub‐5 nm Patterns from High‐χ Block Copolymer Films with Vapor‐Deposited Ultrathin, Cross‐Linked Surface‐Modification Layers

Abstract

Despite their capability, sub‐10 nm periodic nano‐patterns formed by strongly segregating block copolymer (BCP) thin films cannot be easily oriented perpendicular to the substrate due to the huge surface energy differences of the constituent blocks. To produce perpendicular nano‐patterns, the interfacial energies of both the substrate and free interfaces should be controlled precisely to induce non‐preferential wetting. Unfortunately, high‐performance surface modification layers are challenging to design, and different kinds of surface modification methods must be devised respectively for each neutral layer and top coat. Furthermore, conventional approaches, largely based on spin‐coating processes, are highly prone to defect formation and may readily cause dewetting at sub‐10 nm thickness. To date, these obstacles have hampered the development of high‐fidelity, sub‐5 nm BCP patterns. Herein, an all‐vapor phase deposition approach initiated chemical vapor deposition is demonstrated to form 9‐nm‐thick, uniform neutral bottom layer and top coat with exquisite control of composition and thickness. These layers are employed in BCP films to produce perpendicular cylinders with a diameter of ≈4 nm that propagate throughout a BCP thickness of up to ≈60 nm, corresponding to five natural domain spacings of the BCP. Such a robust approach will serve as an advancement for the reliable generation of sub‐10 nm nano‐patterns.

Bicyclic Topology Transforms Self-Assembled Nanostructures in Block Copolymer Thin Films

“…[16][17][18][19][20] Such a prediction could be achieved by synthetically optimizing the chemistry, volume fraction fi, χ, and N values of the block chains of l-BCP, and optimizing the processes of nanostructure formation, which include thermal and solvent annealing and substrate surface modification. [1][2][3][4][5][6][7][8][9][10][21][22][23][24][25][26][27][28][29][30][31] The domain feature of BCP could be further reduced by changing its molecular topology from linear to cyclic, wherein cyclic BCPs (c-BCPs) were reported to reveal 5-16% smaller domains in the bulk state [32][33][34][35][36] and 33% smaller domains in the thin film state. 37 Overall, these domain spacing reductions are less than those (3037%) predicted theoretically.…”

“…In terms of determining suitable application for l -BCPs, the spacing (i.e., size) of the phase-separated domains has been deemed to be the most crucial factor. More specifically, the mean field theory predicts that smaller domain features in the phase-separated nanostructure of a symmetric l -BCP, which are based on fully flexible block chains, can be formed by a lower degree of polymerization ( N ) and a higher interaction parameter (χ) of the block chains; however, the following condition must be satisfied: χN > 10.5. − Such a prediction could be achieved by synthetically optimizing the chemistry, volume fraction f i , χ, and N values of the block chains of l -BCP, and optimizing the processes of nanostructure formation, which include thermal and solvent annealing and substrate surface modification. − ,− The domain feature of BCP could be further reduced by changing its molecular topology from linear to cyclic, wherein cyclic BCPs ( c -BCPs) were reported to reveal 5–16% smaller domains in the bulk state − and 33% smaller domains in the thin film state . Overall, these domain spacing reductions are less than those (30–37%) predicted theoretically. − In the search for other effective approaches that substantially downsize BCP domains, strategies involving other variations such as bicyclic or tricyclic topologies have not been investigated experimentally or theoretically as of yet.…”

Recent advances in block copolymer self‐assembly: From the lowest to the highest

“…51 However, to obtain a perpendicular orientation of other high-χ BCPs with significantly different surface energies between the blocks, a top surface needs to be also neutralized. Over the years, various methods have been developed to induce perpendicular orientation of high-χ BCPs from the top surface, such as polarity-switching top-coat implementation, 52 initiated chemical vapor deposition (iCVD), 53,54 and using polymer additives. 26,49 Son et al developed a universal neutralization method for realizing the perpendicular orientation of various BCPs including high-χ BCPs, through the filter plasma method.…”

From macromonomers to bottlebrush copolymers with sequence control: synthesis, properties, and applications

“…16 For high χ BCPs, both the top surface and bottom substrate generally need to be neutralized, and thus various top coating approaches have been proposed. 207,277–284 Using surface-active additives such as polymer-coated Au nanoparticles and star polymers, it has been shown that these additives are accumulated at interfaces to act as neutral layers, leading to the vertically oriented BCP microdomains. 281–283 These authors have further extended this concept and designed random-BBCP additives containing A- r -B random copolymer sidechains to control the orientation of A- b -B BCP microdomains, as depicted in Fig.…”