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A Block Copolymer with an Extremely High Block-to-Block Interaction for a Significant Reduction of Line-Edge Fluctuations in Self-Assembled Patterns Jong Min Kim, Yoon Hyung Hur, Jae Won Jeong, Tae Won Nam, Jung Hye Lee, Kiung Jeon, YongJoo Kim, and Yeon Sik Jung Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b01731 • Publication Date (Web): 25 Jul 2016 Downloaded from http://pubs.acs.org on July 25, 2016

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Chemistry of Materials

A Block Copolymer with an Extremely High Block-to-Block Interaction for a Significant Reduction of Line-Edge Fluctuations in SelfAssembled Patterns Jong Min Kim†,∥, Yoon Hyung Hur†,∥, Jae Won Jeong†, Tae Won Nam†, Jung Hye Lee†, Kiung Jeon†, YongJoo Kim*,†,‡, Yeon Sik Jung*,† †

Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ‡

KI for Nano Century, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea

poly(4vinylpyridine-b-dimethylsiloxane), Extremely high Flory-Huggins interaction parameter, Directed self-assembly, Warm solvent annealing, Pattern quality, Line edge roughness

ABSTRACT: Directed self-assembly (DSA) of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) provides advantages of pattern size reduction below 10 nm and improved pattern quality. Despite theoretical predictions, however, the questions of whether BCPs with a much higher χ than conventional high-χ BCPs can further improve the line edge roughness (LER) and how to overcome their extremely slow self-assembly kinetics remain unanswered. Here, we report the synthesis and assembly of poly(4vinylpyridine-b-dimethylsiloxane) BCP with an extremely high χ-parameter (estimated to be approximately 7 times higher compared to that of poly(styrene-b-dimethylsiloxane) – a conventional high-χ BCP) and achieve a markedly low 3σ line edge roughness of 0.98 nm, corresponding to 6% of its line width. Moreover, we demonstrate the successful application of an ethanol-based 60°C warm solvent annealing treatment to address the extremely slow assembly kinetics of the extremely high-χ BCP, considerably reducing the self-assembly time from several hours to a few minutes. This study suggests that the use of BCPs with an even larger χ could be beneficial for further improvement of self-assembled BCP pattern quality.

Introduction The progress of semiconductor manufacturing technology thus far has been mainly driven by the continuous advancement of photolithography.1, 2 However, as the feature size of transistors continuously decreases with an increase of integration density, conventional photolithography faces serious difficulties in terms of resolution and cost due to the diffraction limit.3, 4 In order to overcome these challenges, several alternative lithography techniques such as extreme ultraviolet lithography (EUVL), ebeam lithography (EBL), nanoimprint lithography (NIL), and directed self-assembly (DSA) have emerged.5-15 Among these, the DSA of block copolymers (BCPs) has attracted attention as a promising candidate for an alternative lithography approach due to its low cost, excellent resolution, and scalability.5-7, 10, 11, 13-16

However, challenges such as minimization of defect density and improvement of line edge roughness (LER) and line width roughness (LWR) still should be addressed.17 According to the international technology roadmap for semiconductors (ITRS), the LER and LWR should be less than 8% of the critical dimension (CD)17 because they directly influence the performance of semiconductor devices.18, 19 Previous theoretical studies reported that these pattern quality parameters can be substantially improved by using BCPs with a high Flory-Huggins interaction parameter (χ)20, which is the thermodynamic driving force for microphase separation and selfassembly.21, 22 LER and LWR of the patterns formed by DSA are indeed highly sensitive to the χ value of BCPs, because the interfacial width (and also the sharpness of the interface) between two different domains is thermodynamically determined by χ.23 We previously reported

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Figure 1. Preparation of P4VP-b-PDMS block copolymer via RAFT polymerization. (a) Synthesis route. (b) Characteristics of 1H NMR of the BCP. (c) Solubility parameters of P4VP and PDMS.

DSA pattern quality improvement using poly(styrene-bdimethylsiloxane) (PS-b-PDMS)24-27 and poly(2vinylpyridine-b-dimethylsiloxane) (P2VP-bPDMS)28. Also, other studies on self-assembled pattern formation based on high-χ BCPs such as poly(styrene-bethylene oxide),13 polyhedral oligomeric silsesquioxane 30 (POSS) containing BCPs29, , and poly(trimethylsilylstryrene-b-D,L-lactide) (PTMSS-b-PLA) have been reported.31-35 Beside improved pattern quality using high-χ BCPs, sequential infiltration synthesis (SIS) with low-χ BCP such as PS-b-PMMA (polystyrene-bpoly(methyl methacrylate)) has been reported to be beneficial in terms of reducing the LER by selectively hardening one block via atomic layer deposition (ALD).36, 37 However, the stringent requirement (LER and LWR < 8% of line width) regarding DSA pattern quality has not been satisfied by previous DSA processes with both high and low-χ BCPs. Patrone et al. reported that, based on calculations, in order to meet the target LER goals, the χ of BCPs should be increased significantly.20 However, for the adoption of new BCPs with an extremely high χ, systematic optimization of the self-assembly conditions is indispensable. This is because the interdiffusivity of BCPs exponentially decreases as the χ value increases,38 and thus even conventional high-χ BCPs require a few to even tens of hours of thermal or solvent-vapor annealing time. A much larger χ than that (~0.26 at RT) of PS-b-PDMS

BCPs would even prevent the assembly of BCP chains due to a large kinetic barrier.39 Previously, several solutions for boosting the kinetics of high-χ BCPs have been reported, such as microwave annealing40, 41, cold zone annealing42, 43 and solvothermal annealing.26, 44 We suggested warm solvent annealing (WSA) at a slightly elevated temperature (60°C) for markedly more rapid self-assembly of high-χ PS-b-PDMS within a few minutes compared to the case of room temperature solvent annealing (RTSA).25 Recently, we also reported in situ formation of sub-10 nm patterns using warm spin-casting (WSC) of the same BCP.45 However, a question remains as to whether a BCP with extremely high-χ parameter can be assembled by the combination of a solvent and a thermal activation strategy to demonstrate a considerably smaller line roughness compared to conventional high-χ BCP patterns. Here, as a demonstration of exceptionally high-χ DSA process implementation, we report the synthesis and selfassembly of a poly(4vinylpyridine-b-dimethylsiloxane) (P4VP-b-PDMS) BCP, whose χ is estimated to be 7 times larger than that of PS-b-PDMS, a traditional high-χ BCP.10 We discuss how WSA treatment at 60°C effectively facilitates the self-assembly kinetics of the P4VP-b-PDMS BCP, completing the assembly step within a few minutes. As a result, an estimated LER of 0.98 nm, which is approximately 6% of the line width, was achieved based on grapho-epitaxy of the BCP. Another advantage of this

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Chemistry of Materials (1.5 wt%) were used for the formation of thin films. The Si trench templates for directed self-assembly (DSA) were fabricated using KrF photolithography followed by reactive ion etching. The hydroxyl-terminated PDMS, PS, and P4VP homopolymer solution were spin-coated on the Si substrate and thermal-annealed at 150 oC for 2 hours. The brush-coated Si substrate was then washed with heptane, toluene, and isopropyl alcohol to remove unattached polymer chains. 4VD23 BCP was spin-coated and solventannealed with ethanol vapor in a temperature range of room temperature to 60°C. SD45 BCP was spin-coated and solvent-annealed with toluene vapor in a temperature range of room temperature to 60°C. After the selfassembly process, the samples were etched by CF4 plasma (50W, 20 s, 15 mtorr) to remove the top PDMS, followed by O2 plasma (60W, 30 s, 15 mtorr) to remove the PS or P4VP matrix to obtain well-defined SiOx line patterns. Characterization The thickness of the BCP films was measured by a UV thickness measurement tool (F20-UV, Filmetrics, F20UV). The self-assembled morphologies were characterized by field emission scanning electron microscopy (FE-SEM: Hitachi S-4800) with an acceleration voltage of 15 kV and a working distance of 4.0 mm. For quantitative analyses of the critical dimension (CD), pitch, line width roughness (LWR), and line edge roughness (LER) based on SEM images, commercial image analysis software (SuMMIT) was used. (See more details in the Supporting Information regarding the examples of quantitative data processing.)

Figure 2. In situ BCP film measurement during warm solvent annealing (WSA) and room temperature solvent annealing (RTSA). (Top) Swelling dynamics of P4VP-bPDMS for RTSA and WSA with ecofriendly ethanol solvent. (Bottom) A schematic diagram of the warm solvent annealing system is also shown.

extremely high-χ DSA based on P4VP-b-PDMS BCP is that an environmentally-friendly and fast-evaporating ethanol can be used as a solvent for rapid self-assembly of the extremely high-χ BCP. This pattern formation with a such high-χ BCP suggests that more opportunities based on the use of new self-assembling polymer systems with even larger interaction parameters can be exploited. Experimental section Block copolymer (BCP) self-assembly A P4VP-b-PDMS BCP with a MW of 23 kg/mol (4VD23) and a hydroxyl-terminated P4VP with MW of 19 kg/mol were synthesized by RAFT polymerization. PS-b-PDMS BCP with MW of 45 kg/mol (SD45) and a hydroxylterminated PDMS, PMMA, and PS homopolymer with a MW of 5 kg/mol, 30 kg/mol, and 22 kg/mol, respectively, were purchased from Polymer Source Inc. (Canada). Isopropyl alcohol solutions of the hydroxyl-terminated P4VP homopolymer (1.5 wt%) and 4VD23 BCP (0.7~1 wt%) were prepared and used for the formation of BCP thin films. A hydroxyl-terminated PS homopolymer (1.5 wt %), SD45 BCP (0.8~1.2 wt %) dissolved in toluene and a heptane solution of the hydroxyl-terminated PDMS homopolymer

Results and Discussion We synthesized poly(4vinylpyridine)-bpoly(dimethylsiloxane) (P4VP-b-PDMS, molecular weight (MW) = 23 kg/mol, 4VD23) via reversible addition fragmentation chain transfer (RAFT) polymerization. As shown in Figure 1a, a PDMS-RAFT macro chain transfer agent was first synthesized by following a previously reported N,N'-dicyclohexylcarbodiimide (DCC) coupling.46, 47 Hydroxyl terminated PDMS, 2-{[(butylsulfanyl)carbonothioyl]sulfanyl}propanoic acid (RAFT chain transfer agent),48 4-dimethylaminopyridine (DMAP), and DCC in methylene chloride were reacted for 48 h at room temperature. Subsequently, the mixture was washed with methanol and water for removal of unreacted chemicals, and drying under reduced pressure yielded a yellowish oil. The fidelity of the PDMS-RAFT macro chain transfer agent was confirmed by a 1H nuclear magnetic resonance (NMR) analysis, which is depicted in Figure S1. 4VD was then synthesized via RAFT polymerization. A distilled 4VP monomer, PDMS-RAFT macro-chain transfer agent, and 2,2’-azobisisobutyronitrile (AIBN) were placed in a three-neck flask. The mixture was dissolved in toluene, and RAFT polymerization was then carried out at 83°C. After polymerization, the addition of excess hexane produced precipitated products, which were investigated by 1 H NMR (see Figure 1b) and Fourier-transform infrared spectroscopy (FTIR) analyses. The results showed that 4VD BCP was successfully synthesized without noticeable side reactions. The molecular weight (MW) of 4VD was



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Figure 3. Solvent-annealed morphologies of P4VP-b-PDMS BCP depending on solvent vapor annealing temperature. Self-assembled patterns generated with trench templates with a width of (a), (d) 1 µm, (b), (e) 350 nm, and (c), (f) 120 nm via room-temperature solvent annealing (RTSA, a - c) and warm solvent annealing (WSA, d - f). The BCPs treated with WSA showed much faster self-assembly kinetics.

estimated by 1H NMR and the analysis data are summarized in Table S1 (run 1 - 4). To explore the correlation between the high χ value of a BCP and the self-assembled pattern quality, we synthesized a 4VD BCP with an MW of 23 kg/mol (4VD23, minority volume fraction = 44.4 %) for WSA. Compared to PS-b-PDMS (χ ~ 0.26 at 300 K), which is a well-known high-χ BCP, the χ value of P4VP-b-PDMS is predicted to be much larger because of the greater hydrophilicity of the P4VP block compared to PS. However, estimation of χ for P4VP-b-PDMS using neutron scattering or X-ray scattering is hindered by the high order-todisorder transition (ODT) temperature.49, 50 Thus, the solubility parameter difference was alternatively used to estimate χ. The solubility parameters of PS and PDMS have consistently been reported to be approximately 18.5 MPa1/2 and 15.5 Mpa1/2, respectively.51 However, the reported solubility parameter values of P4VP ranged from 22.0 MPa1/2 to 25.0 MPa1/2 with an average value of 23.0 MPa1/2.52-55 The solvent vapor swelling method could be a more reliable method to calculate the solubility parameter of a polymer.56 Nevertheless, we alternatively used the contact angle measurement method due to its simplicity. By using the contact angle measurement, as shown in Figure S2, we also estimated the solubility parameter of

P4VP. The obtained value (23.4 MPa1/2) is close to the average of the reported values mentioned above. Thus, using the calculated solubility parameter of P4VP and the general relation that the χ value is square-proportional to the difference of solubility parameters between two blocks, the χ of P4VP-b-PDMS is predicted to be about 7 times higher than that of PS-b-PDMS with a reported value of 0.26 at RT.57 As mentioned above, the slow assembly kinetics of highχ BCPs is associated with the exponential decrease of the interdiffusivity of polymer chains with the increase of χ.38 Thus, the extremely high block-to-block interaction of P4VP-b-PDMS inevitably causes a large kinetic barrier for polymer chain rearrangement and results in extremely slow pattern formation kinetics. Therefore, application of effective activation strategies for BCP chain diffusion would be critical. Figures 2 schematically illustrates the WSA chamber system equipped with an in situ optical thickness monitoring device,25 which provided timedependent swelling ratio (SR; solvent-swollen thickness divided by initial thickness) curves measured for the 4VD23 BCP at RT (23oC) and at an elevated temperature of 60oC. According to Figure 2, RTSA and WSA provided slightly different swelling dynamics. The faster solvent evaporation in the case of WSA led to faster saturation of


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Figure 4. Comparison of self-assembled P4VP-b-PDMS BCPs obtained with various brush surfaces. P4VP-b-PDMS line patterns generated with (a) PDMS (MW = 5 kg/mol), (b) P4VP (MW = 19 kg/mol) brushes, and (c) bare native oxide surface. (d) Contact angle measurement data of the brush surfaces. (e) 3σ LER and LWR of the line patterns on different brush surfaces. (Examples of statistical data analysis are shown in Figures S3 and S4 in the Supporting Information.)

SR of the BCP films. In general, the self-assembly kinetics for solvent-annealed BCP thin films highly depends on their SR, and a saturated SR of ~1.6 led to the formation of well-ordered cylindrical nanopatterns from the 4VD23 BCP for both RTSA and WSA treatment. After BCPs are swelled and self-assembled, we opened the upper lid of the chamber for both WSA and RTSA to evaporate the solvent rapidly to retain the morphology of the BCPs at the equilibrated swollen state, because slow solvent removal provides enough time for the BCPs to reorganize. Figure 3 depicts the self-assembled cylindrical morphologies of 4VD23 BCP obtained with RTSA and WSA (60oC), respectively. Before the assembly process, template substrates for graphoepitaxy-type DSA implementation were precoated with a thin PDMS brush to boost the selfassembly kinetics.10 The effect of the brush material on the pattern quality will be discussed in a later part of this paper. To investigate the assembly kinetics, ethanol was used to swell the BCP. Ethanol was expected to be highly selective for the P4VP block because of the much smaller difference of the Hildebrand solubility parameter (26.2 MPa1/2),51 compared to the difference between the Hildebrand solubility parameters of ethanol and PDMS. Although thermal treatment at 150 oC for 15 hours on the 4VD23 BCP produced lamellar structures aligned parallel to the substrate (Fig S5), both RTSA and WSA treatments using ethanol (a P4VP-selective solvent) induced the for-

mation of PDMS cylinder patterns due to the significant augmentation of the effective volume fraction of P4VP compared to the dry state. We compared the effectiveness of RTSA and WSA in terms of pattern formation throughput. To obtain wellordered patterns by RTSA, as shown in Figures 3a – 3c, the required self-assembly time was at least several hours (15 hours, 9 hours and 8 hours for 1 μm, 350 nm and 120 nm-wide trench substrates, respectively), which is imposed by the high χ of the P4VP-b-PDMS BCP. In contrast, the self-assembly time remarkably decreased compared to RTSA due to the thermal activation effect. The self-assembled pattern formation was complete within 10 min, 5 min, and 3 min for 1 μm, 350 nm, and 120 nm-wide trench patterns, respectively. From these results, we confirmed that the issue of extremely slow self-assembly kinetics of the P4VP-b-PDMS BCP can be resolved by the application of WSA. Furthermore, we evaluated the edge roughness of self-assembled patterns obtained with WSA and RTSA by using a power spectral density (PSD) analysis, as presented in Figure S6. Because edge roughness is composed of a broad band of spatial frequencies, a PSD analysis can provide more detailed information of the roughness as a function of frequency. From the PSD data depicted in Figure S6, WSA and RTSA presented similar values throughout the analyzed frequency range, which



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Figure 5. Comparison of pattern quality having a similar pitch between PS-b-PDMS and P4VP-b-PDMS. SEM images of (a) PS-b-PDMS (45 kg/mol) and (b) P4VP-b-PDMS (23 kg/mol) patterns in 350-nm-wide trench template. High-magnification SEM images and quantitative analysis results are also shown. (LER = line edge roughness, LWR = line width roughness)

indicates that the rapid self-assembly of WSA does not compromise the DSA pattern quality. We also investigated the effect of brush treatment on the self-assembly behavior of the P4VP-b-PDMS BCP. Figures 4a – 4c depict the pattern formation results of 4VD23 BCP on different brush surfaces (PDMS brush, P4VP brush, and bare substrates, respectively). As quantitatively compared in Figure 4d, the lowest line roughness values were obtained with the PDMS brush, achieving an estimated LER of 1.15 nm, which corresponds to approximately 6.8 % of the line width. For each data point, 10 areas were randomly selected for the statistical LER and LWR evaluations. To be more concrete, the sample was divided into 10 areas and then we captured SEM images of each area. In this manner, the images obtained from the whole sample were used to calculate the average roughness values. Furthermore, we also investigated the 3-sigma roughness values of self-assembled patterns depending on the line length to determine the minimum line length for accurate roughness characterization, as shown in Figure S7. Given

that the evaluated 3-sigma roughness values saturate for the line length over ~ 80 nm, we used a sufficiently larger pattern length of 120 nm for the image analysis and calculation of the LER and LWR values. However, when a P4VP brush or a bare Si trench was used, the line roughness values significantly increased. We also tested the use of other brushes such as PMMA and PS for the self-assembly of 4VD23, as shown in Figure S8. Comparing the various brushes, the PDMS-brush-treated substrate provided the best pattern quality. Understanding these considerably different pattern qualities as a function of brush treatment requires more systematic consideration of the degree of interaction between the BCP and the bottom surface. In the case of the P4VP brush, the P4VP block will segregate on the P4VP brush, whereas the PDMS brush would be in contact with the PDMS block. This different configuration of selfassembled BCP chains depending on the substrate surface would differentiate the degree of interaction between BCP and substrate. One question here is whether the PDMS-


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Figure 6. Power spectral density (PSD) functions. (a) Line width roughness and (b) line edge roughness of PS-bPDMS and P4VP-b-PDMS, respectively.

PDMS interaction is weaker than the P4VP-P4VP interaction as the experimental results indicate, because an easier rearrangement of polymer chains through the diffusion of polymer chains along the surface would help the BCP chains escape from a kinetically trapped state. This can be estimated by the cohesive energy densities of PDMS and P4VP. Because the Hildebrand solubility parameter is the square root of the cohesive energy density and the solubility parameter of PDMS is 15.5 MPa1/2, which is smaller than that (23.0 MPa1/2) of P4VP, a much weaker interaction between PDMS brush and BCP is expected. This may explain the better pattern quality in the case of the PDMS brush. The markedly different self-assembly results depending on the brush are also supported by a previous study where it was reported that a polymer surface diffusion coefficient can vary by ~ 100 times by altering the hydrophilicity of the surface.58 Figure 4e compares the water contact angle measurement results for the different surfaces at ambient relatively humidity (RH = 35%). As expected, PDMS shows a higher water contact angle (95.38o) than those of P4VP (67.23o) and bare Si (49.51o). The bare Si substrate was cleaned by acetone and methanol solvent before the measurement. This suggests that the PDMS brush would significantly reduce the kinetic energy barrier for self-assembly. Furthermore, we also carried out a power spectral density analysis of the roughness depending on the brush type, and the results are presented in Figure S9. The PSD analysis results depending on the brush type confirmed that the PDMS

brush showed a much lower intensity compared to other brushes over the entire frequency range. As demonstrated in Figure 5, using the same PDMS brush, we also compared the pattern quality between the P4VP-b-PDMS (4VD23) and PS-b-PDMS (SD45) BCPs with an MW of 45 kg/mol (minority volume fraction = 33.7%) with a similar pitch size of 34 nm. Because the χ value of 4VD23 is estimated to be several times higher than that of SD45, PS-b-PDMS (45 kg/mol) with a higher MW was used to match the pitch size with 4VD23 because the microdomain periodicity is proportional to χ1/6N2/3. 4VD23 and SD45 BCPs were spin-coated onto the PDMS-brush-treated substrates with 350-nm-wide guide templates. The solubility parameter of PS (18.5 MPa1/2) limits the choice of non-toxic solvent for solvent vapor annealing. Although it is possible to use propylene glycol monomethyl ether acetate (PGMEA), a benign solvent allowed in semiconductor manufacturing lines, because of its extremely low vapor pressure, longer treatment time would be required. In contrast, as mentioned above, the hydrophilic P4VP block in the 4VD23 BCP allows the use of ethanol with a relatively higher vapor pressure for rapid swelling of the BCP. To compare the pattern quality of 4VD23 and SD45, we applied the WSA process to promote the self-assembly of high-χ BCPs within 5 min. From self-assembled patterns, the estimated LER (0.98 nm) and LWR (1.91 nm) of the patterns obtained from the 4VD23 BCP were 59.3 % and 50.9 % lower, respectively, than those of SD45 with a similar pitch size (~34 nm), as shown in Figure 5 (more data regarding comparison of line edge and width deviation between 4VD23 and SD45 BCPs are available in Figures S10 and S11 in the Supporting Information.). It should be also noted that a small LER < 1 nm was obtained despite the relatively high polydispersity index (PDI = 1.20 – 1.31) of our BCPs, as shown in Table S1 in the Supporting Information, which is due to the nature of RAFT polymerization. We expect reduction of PDI using other synthesis methods such as living anionic polymerization may further improve the pattern quality of the BCPs. It should be also noted that the LER of 0.98 nm is also lower that the values (1.8 – 2.0 nm) for poly(2vinylpyridine-bdimethylsiloxane)(P2VP-b-PDMS) with a relatively higher χ than PS-b-PDMS, which was reported in our previous study.28 This result suggests that the P4VP-b-PDMS BCP has a even higher χ than P2VP-b-PDMS. For a quantitative evaluation of the roughness of the patterns, we also carried out a PSD analysis. Figure 6 shows the LER and LWR PSD curves for 4VD23 and SD45 with a similar pitch size, indicating that the PSD values of 4VD23 are lower than those of SD45 over the entire frequency range. These results show that the pattern quality of DSA patterns can be significantly improved by further increasing the FloryHuggins interaction parameter of BCPs. Conclusion In summary, we designed and synthesized P4VP-bPDMS as an extremely high-χ BCP via RAFT polymerization and successfully produced self-assembled patterns



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with improved pattern quality compared to conventional high-χ BCPs. Based on the analysis data, the χ parameter of P4VP-b-PDMS was estimated to be approximately 7 times higher than that of PS-b-PDMS. The sharp interface between the two blocks provided an unusually small LER (0.98 nm) of the P4VP-b-PDMS BCP, corresponding to < 6% of the pattern width. By demonstrating that the wellordered patterns can be obtained within a few minutes (< 3 min in 120-nm-wide trench templates) of WSA treatment time, we also confirmed that eco-friendly ethanolbased warm solvent annealing at 60°C is highly effective for promoting rapid self-assembly of the P4VP-b-PDMS BCP with intrinsic slow kinetics. Our results suggest that there is significant room for improving the DSA pattern quality without compromising the pattern formation throughput by adopting BCPs with an even higher FloryHuggins interaction parameter. Moreover, such high-χ BCPs may enable the formation of ultrahigh-density patterns in the sub-5 nm regime.

ASSOCIATED CONTENT Supporting Information Related experimental data are shown in Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Authors * E-mail : [email protected], * E-mail : [email protected].

Author Contributions ∥

These authors contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (10048504) and KSRC(Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device.

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