Molecular Tailoring of Poly(styrene-b-methyl methacrylate) Block Copolymer Toward Perpendicularly Oriented Nanodomains with Sub-10 nm Features

Abstract

We demonstrate a novel approach for fabricating vertically orientated, sub-10 nm, block copolymer (BCP) nanodomains on a substrate via molecular tailoring of poly(styrene-bmethyl methacrylate) (PS-b-PMMA) BCP, one of the most widely used BCPs for nanopatterning. The idea is to incorporate a short middle block of self-attracting poly(methacrylic acid) (PMAA) between the PS and PMMA blocks, where the PMAA middle block promotes phase separation between PS and PMMA, while maintaining the domain orientation perpendicular to the substrate. The designed PS-b-PMAA-b-PMMA triblock copolymers, which were synthesized via well-controlled anionic polymerization, exhibited order−disorder transition temperatures higher than that of pristine PS-b-PMMA BCPs, indicating the promotion of phase separation by the middle PMAA block. For PS-b-PMAA-b-PMMA BCPs with total molecular weights of 21 and 18 kg/mol, the domain spacing corresponds to 19.3 and 16.7 nm, respectively, allowing us to fabricate sub-10 nm nanodomain structures. More importantly, it was demonstrated that the PMAA middle block, which has a higher surface energy than PS and PMMA, does not significantly alter lateral concentration fluctuations, which are responsible for phase-separation in the lateral direction. This enabled the vertical orientation of microdomains with sub-10 nm feature size on a PS-r-PMMA neutral surface without an additional neutral top layer. We anticipate that this approach provides an important platform for next-generation lithography and nanopatterning applications that require sub-10 nm features over large areas with simple process and reduced cost.

Microphase segregation and selective chain scission of poly(2‐methyl‐2‐oxazoline)‐block‐polystyrene

“…BCPs with highly disparate segments are termed “high χ” polymers . The field of high χ BCPs exhibiting sub‐10 nm feature sizes is a rich and active field of research …”

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

“…It is worth noting that PMAA has been reported to undergo intra‐ and inter‐molecular cross‐linking via cyclodehydration reaction at above 190 °C . However, as shown in our previous work, this side reaction can be significantly suppressed sterically in the presence of much larger blocks. Similarly, in this work there is no noticeable effect of cross‐linking on the self‐assembled morphology of PS‐ b ‐PMAA in bulk (Figure S1, Supporting Information) and the microdomain orientation in thin film was dependent on the interfacial conditions, suggesting that the timescale for self‐assembly is shorter than that for any meaningful cross‐linking.…”

“…Cylinder‐forming polystyrene‐block‐poly(methacrylic acid) (PS‐ b ‐PMAA; M n = 6.7 kg mol −1 Đ = 1.19, and 63 vol% of PS block; see Schemes S1 and S2, and Figure S1, Supporting Information, for detailed information) was used in this study. In our previous work, we demonstrated that the presence of a very short PMAA block placed between the blocks of PS‐ b ‐PMMA significantly enhances phase separation between PS and PMAA blocks through the high interaction parameter (χ = −0.141 + 205.9/ T where T is the temperature in Kelvin). The domain spacing L 0 of the PS‐ b ‐PMAA BCP was L 0 = 11.7 nm, as analyzed by small angle X‐ray scattering (Figure S1, Supporting Information).…”

Microphase separation of highly amphiphilic, low N polymers by photoinduced copper-mediated polymerization, achieving sub-2 nm domains at half-pitch

“…The thermodynamic driving force of BCP self-assembly ( phase separation) is directly related to a balance between the incompatibility of blocks (the Flory-Huggins interaction parameter, chi, χ) and the total degree of polymerization of the polymer (N), therefore, reaching the limits of ultrasmall domain spacings requires high χ-low N BCPs. 5 One of the most widely studied block copolymers for microphase separation in the bulk (solid state) is polystyreneb-poly(methyl methacrylate), [6][7][8][9] although the smallest achievable lamellar domain spacing is limited to 17.5 nm full-pitch, as a result of relatively low χ. 10 Self-consistent mean-field theory (SCFT) predicts that the order-disorder transition (ODT) of a perfectly symmetrical diblock copolymer occurs when χN > 10.…”