Block Copolymer with an Extremely High Block-to-Block Interactionfor a Significant Reduction of Line-Edge Fluctuations in Self-Assembled PatternsJong Min Kim,†,‡ Yoon Hyung Hur,†,‡ Jae Won Jeong,‡ Tae Won Nam,‡ Jung Hye Lee,‡ Kiung Jeon,‡
YongJoo Kim,*,‡,§ and Yeon Sik Jung*,‡
‡Department of Materials Science and Engineering and §KI for Nano Century, Korea Advanced Institute of Science and Technology(KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea
*S Supporting Information
ABSTRACT: Directed self-assembly (DSA) of block copoly-mers (BCPs) with a high Flory−Huggins interactionparameter (χ) provides advantages of pattern size reductionbelow 10 nm and improved pattern quality. Despite theoreticalpredictions, however, the questions of whether BCPs with amuch higher χ than conventional high-χ BCPs can furtherimprove the line edge roughness (LER) and how to overcometheir 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 highercompared to that of poly(styrene-b-dimethylsiloxane) − a conventional high-χ BCP) and achieve a markedly low 3σ line edgeroughness 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 withan even larger χ could be beneficial for further improvement of self-assembled BCP pattern quality.
■ INTRODUCTION
The progress of semiconductor manufacturing technology thusfar has been mainly driven by the continuous advancement ofphotolithography.1,2 However, as the feature size of transistorscontinuously decreases with an increase in integration density,conventional photolithography faces serious difficulties in termsof resolution and cost due to the diffraction limit.3,4 Toovercome these challenges, several alternative lithographytechniques such as extreme ultraviolet lithography (EUVL),e-beam lithography (EBL), nanoimprint lithography (NIL),and directed self-assembly (DSA) have emerged.5−15 Amongthese, the DSA of block copolymers (BCPs) has attractedattention as a promising candidate for an alternative lithographyapproach because of its low cost, excellent resolution, andscalability.5−7,10,11,13−16
However, challenges such as minimization of defect densityand improvement of line edge roughness (LER) and line widthroughness (LWR) still should be addressed.17 According to theinternational technology roadmap for semiconductors (ITRS),the LER and LWR should be less than 8% of the criticaldimension (CD)17 because they directly influence the perform-ance of semiconductor devices.18,19 Previous theoretical studiesreported that these pattern quality parameters can besubstantially improved by using BCPs with a high Flory−Huggins interaction parameter (χ),20 which is the thermody-namic driving force for microphase separation and self-
assembly.21,22 LER and LWR of the patterns formed by DSAare indeed highly sensitive to the χ value of BCPs, because theinterfacial width (and also the sharpness of the interface)between two different domains is thermodynamically deter-mined by χ.23 We previously reported DSA pattern qualityimprovement using poly(styrene-b-dimethylsiloxane) (PS-b-PDMS)24−27 and poly(2vinylpyridine-b-dimethylsiloxane)(P2VP-b-PDMS).28 Also, other studies on self-assembledpattern formation based on high-χ BCPs such as poly-(styrene-b-ethylene oxide),13 polyhedral oligomeric silsesquiox-ane (POSS) con t a i n i n g BCPs , 2 9 , 3 0 a nd po l y -(trimethylsilylstryrene-b-D,L-lactide) (PTMSS-b-PLA) havebeen reported.31−35 Beside improved pattern quality usinghigh-χ BCPs, sequential infiltration synthesis (SIS) with low-χBCP such as PS-b-PMMA (polystyrene-b-poly(methyl meth-acrylate)) has been reported to be beneficial in terms ofreducing the LER by selectively hardening one block via atomiclayer deposition (ALD).36,37
However, the stringent requirement (LER and LWR < 8% ofline width) regarding DSA pattern quality has not been satisfiedby previous DSA processes with both high and low-χ BCPs.Patrone et al. reported that, based on calculations, in order to
Received: April 28, 2016Revised: July 22, 2016Published: July 25, 2016
meet the target LER goals, the χ of BCPs should be increasedsignificantly.20 However, for the adoption of new BCPs with anextremely high χ, systematic optimization of the self-assemblyconditions is indispensable. This is because the interdiffusivityof BCPs exponentially decreases as the χ value increases,38 andthus even conventional high-χ BCPs require a few to even tensof hours of thermal or solvent-vapor annealing time. A muchlarger χ than that (∼0.26 at RT) of PS-b-PDMS BCPs wouldeven prevent the assembly of BCP chains because of a largekinetic barrier.39
Previously, several solutions for boosting the kinetics of high-χ BCPs have been reported, such as microwave annealing,40,41
cold zone annealing42,43 and solvothermal annealing.26,44 Wesuggested warm solvent annealing (WSA) at a slightly elevatedtemperature (60 °C) for markedly more rapid self-assembly ofhigh-χ PS-b-PDMS within a few minutes compared to the caseof room temperature solvent annealing (RTSA).25 Recently, wealso reported in situ formation of sub-10 nm patterns usingwarm spin-casting (WSC) of the same BCP.45 However, aquestion remains as to whether a BCP with extremely high-χparameter can be assembled by the combination of a solventand a thermal activation strategy to demonstrate a considerablysmaller line roughness compared to conventional high-χ BCPpatterns.Here, as a demonstration of exceptionally high-χ DSA
process implementation, we report the synthesis and self-assembly of a poly(4vinylpyridine-b-dimethylsiloxane) (P4VP-b-PDMS) BCP, whose χ is estimated to be 7 times larger thanthat of PS-b-PDMS, a traditional high-χ BCP.10 We discuss howWSA treatment at 60 °C effectively facilitates the self-assemblykinetics of the P4VP-b-PDMS BCP, completing the assemblystep within a few minutes. As a result, an estimated LER of 0.98nm, which is approximately 6% of the line width, was achievedbased on grapho-epitaxy of the BCP. Another advantage of thisextremely high-χ DSA based on P4VP-b-PDMS BCP is that an
environmentally friendly and fast-evaporating ethanol can beused as a solvent for rapid self-assembly of the extremely high-χBCP. This pattern formation with a such high-χ BCP suggeststhat more opportunities based on the use of new self-assembling polymer systems with even larger interactionparameters can be exploited.
■ EXPERIMENTAL SECTIONBlock Copolymer (BCP) Self-Assembly. A P4VP-b-PDMS BCP
with a MW of 23 kg/mol (4VD23) and a hydroxyl-terminated P4VPwith MW of 19 kg/mol were synthesized by RAFT polymerization.PS-b-PDMS BCP with MW of 45 kg/mol (SD45) and a hydroxyl-terminated PDMS, PMMA, and PS homopolymer with a MW of 5 kg/mol, 30 kg/mol, and 22 kg/mol, respectively, were purchased fromPolymer Source Inc. (Canada). Isopropyl alcohol solutions of thehydroxyl-terminated P4VP homopolymer (1.5 wt %) and 4VD23 BCP(0.7−1 wt %) were prepared and used for the formation of BCP thinfilms. A hydroxyl-terminated PS homopolymer (1.5 wt %), SD45 BCP(0.8−1.2 wt %) dissolved in toluene and a heptane solution of thehydroxyl-terminated PDMS homopolymer (1.5 wt %) were used forthe formation of thin films. The Si trench templates for directed self-assembly (DSA) were fabricated using KrF photolithography followedby reactive ion etching. The hydroxyl-terminated PDMS, PS, andP4VP homopolymer solution were spin-coated on the Si substrate andthermal-annealed at 150 °C for 2 h. The brush-coated Si substrate wasthen washed with heptane, toluene, and isopropyl alcohol to removeunattached polymer chains. 4VD23 BCP was spin-coated and solvent-annealed with ethanol vapor in a temperature range of roomtemperature to 60 °C. SD45 BCP was spin-coated and solvent-annealed with toluene vapor in a temperature range of roomtemperature to 60 °C. After the self-assembly process, the sampleswere etched by CF4 plasma (50W, 20 s, 15 mTorr) to remove the topPDMS, followed by O2 plasma (60W, 30 s, 15 mTorr) to remove thePS or P4VP matrix to obtain well-defined SiOx line patterns.
Characterization. The thickness of the BCP films was measuredby a UV thickness measurement tool (F20−UV, Filmetrics, F20−UV).The self-assembled morphologies were characterized by field emissionscanning electron microscopy (FE-SEM: Hitachi S-4800) with an
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.
acceleration voltage of 15 kV and a working distance of 4.0 mm. Forquantitative analyses of the critical dimension (CD), pitch, line widthroughness (LWR), and line edge roughness (LER) based on SEMimages, commercial image analysis software (SuMMIT) was used (seemore details in the Supporting Information regarding the examples ofquantitative data processing.)
■ RESULTS AND DISCUSSION
We synthesized poly(4vinylpyridine)-b-poly(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 byfollowing a previously reported N,N′-dicyclohexylcarbodiimide(DCC) coupling.46,47 Hydroxyl terminated PDMS, 2-{[(bu-tylsulfanyl)-carbonothioyl]sulfanyl}propanoic acid (RAFTchain transfer agent),48 4-dimethylaminopyridine (DMAP),and DCC in methylene chloride were reacted for 48 h at roomtemperature. Subsequently, the mixture was washed withmethanol and water for removal of unreacted chemicals, anddrying under reduced pressure yielded a yellowish oil. Thefidelity of the PDMS-RAFT macro chain transfer agent wasconfirmed by a 1H nuclear magnetic resonance (NMR)analysis, which is depicted in Figure S1. 4VD was thensynthesized via RAFT polymerization. A distilled 4VPmonomer, PDMS-RAFT macro-chain transfer agent, and 2,2′-azobis(isobutyronitrile) (AIBN) were placed in a three-neckflask. The mixture was dissolved in toluene, and RAFTpolymerization was then carried out at 83 °C. Afterpolymerization, the addition of excess hexane producedprecipitated products, which were investigated by 1H NMR(see Figure 1b) and Fourier-transform infrared spectroscopy(FTIR) analyses. The results showed that 4VD BCP wassuccessfully synthesized without noticeable side reactions. Themolecular weight (MW) of 4VD was estimated by 1H NMRand the analysis data are summarized in Table S1 (run 1−4).To explore the correlation between the high χ value of a BCPand the self-assembled pattern quality, we synthesized a 4VDBCP with an MW of 23 kg/mol (4VD23, minority volumefraction = 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 ispredicted to be much larger because of the greater hydro-philicity of the P4VP block compared to PS. However,estimation of χ for P4VP-b-PDMS using neutron scatteringor X-ray scattering is hindered by the high order-to-disordertransition (ODT) temperature.49,50 Thus, the solubilityparameter difference was alternatively used to estimate χ. Thesolubility parameters of PS and PDMS have consistently beenreported to be approximately 18.5 MPa1/2 and 15.5 MPa1/2,respectively.51 However, the reported solubility parametervalues of P4VP ranged from 22.0 MPa1/2 to 25.0 MPa1/2 withan average value of 23.0 MPa1/2.52−55 The solvent vaporswelling method could be a more reliable method to calculatethe solubility parameter of a polymer.56 Nevertheless, wealternatively used the contact angle measurement method dueto its simplicity. By using the contact angle measurement, asshown in Figure S2, we also estimated the solubility parameterof P4VP. The obtained value (23.4 MPa1/2) is close to theaverage of the reported values mentioned above. Thus, usingthe calculated solubility parameter of P4VP and the generalrelation that the χ value is square-proportional to the differenceof 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 high-χBCPs is associated with the exponential decrease in theinterdiffusivity of polymer chains with the increase in χ.38 Thus,the extremely high block-to-block interaction of P4VP-b-PDMSinevitably causes a large kinetic barrier for polymer chainrearrangement and results in extremely slow pattern formationkinetics. Therefore, application of effective activation strategiesfor BCP chain diffusion would be critical. Figures 2 schemati-
cally illustrates the WSA chamber system equipped with an insitu optical thickness monitoring device,25 which providedtime-dependent swelling ratio (SR; solvent-swollen thicknessdivided by initial thickness) curves measured for the 4VD23BCP at RT (23 °C) and at an elevated temperature of 60 °C.According to Figure 2, RTSA and WSA provided slightlydifferent swelling dynamics. The faster solvent evaporation inthe case of WSA led to faster saturation of SR of the BCP films.In general, the self-assembly kinetics for solvent-annealed BCPthin films highly depends on their SR, and a saturated SR of∼1.6 led to the formation of well-ordered cylindrical nano-patterns from the 4VD23 BCP for both RTSA and WSAtreatment. After BCPs are swelled and self-assembled, weopened the upper lid of the chamber for both WSA and RTSAto evaporate the solvent rapidly to retain the morphology of the
Figure 2. In situ BCP film measurement during warm solventannealing (WSA) and room temperature solvent annealing (RTSA).(Top) Swelling dynamics of P4VP-b-PDMS for RTSA and WSA withecofriendly ethanol solvent. (Bottom) Schematic diagram of the warmsolvent annealing system is also shown.
BCPs at the equilibrated swollen state, because slow solventremoval provides enough time for the BCPs to reorganize.Figure 3 depicts the self-assembled cylindrical morphologies
of 4VD23 BCP obtained with RTSA and WSA (60 °C),respectively. Before the assembly process, template substratesfor graphoepitaxy-type DSA implementation were precoatedwith a thin PDMS brush to boost the self-assembly kinetics.10
The effect of the brush material on the pattern quality will bediscussed in a later part of this paper. To investigate theassembly kinetics, we used ethanol to swell the BCP. Ethanolwas expected to be highly selective for the P4VP block becauseof the much smaller difference of the Hildebrand solubilityparameter (26.2 MPa1/2),51 compared to the differencebetween the Hildebrand solubility parameters of ethanol andPDMS. Although thermal treatment at 150 °C for 15 h on the4VD23 BCP produced lamellar structures aligned parallel to thesubstrate (Figure S5), both RTSA and WSA treatments usingethanol (a P4VP-selective solvent) induced the formation ofPDMS cylinder patterns due to the significant augmentation ofthe effective volume fraction of P4VP compared to the drystate.We compared the effectiveness of RTSA and WSA in terms
of pattern formation throughput. To obtain well-orderedpatterns by RTSA, as shown in Figures 3a−c, the requiredself-assembly time was at least several hours (15, 9, and 8 h for1 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 activationeffect. The self-assembled pattern formation was completewithin 10, 5, and 3 min for 1 μm, 350 nm, and 120 nm widetrench patterns, respectively. From these results, we confirmedthat the issue of extremely slow self-assembly kinetics of theP4VP-b-PDMS BCP can be resolved by the application ofWSA. Furthermore, we evaluated the edge roughness of self-assembled patterns obtained with WSA and RTSA by using apower spectral density (PSD) analysis, as presented in FigureS6. Because edge roughness is composed of a broad band ofspatial frequencies, a PSD analysis can provide more detailedinformation on the roughness as a function of frequency. Fromthe PSD data depicted in Figure S6, WSA and RTSA presentedsimilar values throughout the analyzed frequency range, whichindicates that the rapid self-assembly of WSA does notcompromise the DSA pattern quality.We also investigated the effect of brush treatment on the self-
assembly behavior of the P4VP-b-PDMS BCP. Figure 4a−cdepicts the pattern formation results of 4VD23 BCP ondifferent brush surfaces (PDMS brush, P4VP brush, and baresubstrates, respectively). As quantitatively compared in Figure4e, the lowest line roughness values were obtained with thePDMS brush, achieving an estimated LER of 1.15 nm, whichcorresponds to approximately 6.8% of the line width. For eachdata point, 10 areas were randomly selected for the statisticalLER and LWR evaluations. To be more concrete, we dividedthe sample into 10 areas and then we captured SEM images ofeach area. In this manner, the images obtained from the whole
Figure 3. Solvent-annealed morphologies of P4VP-b-PDMS BCP depending on solvent vapor annealing temperature. Self-assembled patternsgenerated with trench templates with a width of (a, d) 1 μm, (b, e) 350 nm, and (c, f) 120 nm via (a−c) room-temperature solvent annealing(RTSA) and (d−f) warm solvent annealing (WSA). The BCPs treated with WSA showed much faster self-assembly kinetics.
sample were used to calculate the average roughness values.Furthermore, we also investigated the 3-sigma roughness valuesof self-assembled patterns depending on the line length todetermine the minimum line length for accurate roughnesscharacterization, as shown in Figure S7. Given that theevaluated 3-sigma roughness values saturate for the line lengthover ∼80 nm, we used a sufficiently larger pattern length of 120nm for the image analysis and calculation of the LER and LWRvalues. However, when a P4VP brush or a bare Si trench wasused, the line roughness values significantly increased. We alsotested the use of other brushes such as PMMA and PS for theself-assembly of 4VD23, as shown in Figure S8. Comparing thevarious brushes, the PDMS-brush-treated substrate providedthe best pattern quality.Understanding these considerably different pattern qualities
as a function of brush treatment requires more systematicconsideration of the degree of interaction between the BCP andthe bottom surface. In the case of the P4VP brush, the P4VPblock will segregate on the P4VP brush, whereas the PDMSbrush would be in contact with the PDMS block. This differentconfiguration of self-assembled BCP chains depending on thesubstrate surface would differentiate the degree of interactionbetween BCP and substrate. One question here is whether thePDMS-PDMS interaction is weaker than the P4VP-P4VPinteraction as the experimental results indicate, because aneasier rearrangement of polymer chains through the diffusion ofpolymer chains along the surface would help the BCP chainsescape from a kinetically trapped state. This can be estimatedby the cohesive energy densities of PDMS and P4VP. Because
the Hildebrand solubility parameter is the square root of thecohesive energy density and the solubility parameter of PDMSis 15.5 MPa1/2, which is smaller than that (23.0 MPa1/2) ofP4VP, a much weaker interaction between PDMS brush andBCP is expected. This may explain the better pattern quality inthe case of the PDMS brush. The markedly different self-assembly results depending on the brush are also supported bya previous study where it was reported that a polymer surfacediffusion coefficient can vary by ∼100 times by altering thehydrophilicity of the surface.58 Figure 4d compares the watercontact angle measurement results for the different surfaces atambient relatively humidity (RH = 35%). As expected, PDMSshows a higher water contact angle (95.38°) than those ofP4VP (67.23°) and bare Si (49.51°). The bare Si substrate wascleaned by acetone and methanol solvent before the measure-ment. This suggests that the PDMS brush would significantlyreduce the kinetic energy barrier for self-assembly. Further-more, we also carried out a power spectral density analysis ofthe roughness depending on the brush type, and the results arepresented in Figure S9. The PSD analysis results depending onthe brush type confirmed that the PDMS brush showed a muchlower intensity compared to other brushes over the entirefrequency 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 MWof 45 kg/mol (minority volume fraction =33.7%) with a similarpitch size of 34 nm. Because the χ value of 4VD23 is estimatedto be several times higher than that of SD45, PS-b-PDMS (45
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 thebrush surfaces. (e) 3σ LER and LWR of the line patterns on different brush surfaces (examples of statistical data analysis are shown in Figures S3 andS4).
kg/mol) with a higher MW was used to match the pitch sizewith 4VD23 because the microdomain periodicity is propor-tional to χ1/6N2/3. 4VD23 and SD45 BCPs were spin-coatedonto the PDMS-brush-treated substrates with 350 nm-wideguide templates. The solubility parameter of PS (18.5 MPa1/2)limits the choice of nontoxic solvent for solvent vaporannealing. Although it is possible to use propylene glycolmonomethyl ether acetate (PGMEA), a benign solvent allowedin semiconductor manufacturing lines, because of its extremelylow vapor pressure, longer treatment time would be required.In contrast, as mentioned above, the hydrophilic P4VP block inthe 4VD23 BCP allows the use of ethanol with a relativelyhigher 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, theestimated LER (0.98 nm) and LWR (1.91 nm) of the patternsobtained from the 4VD23 BCP were 59.3% and 50.9% lower,respectively, than those of SD45 with a similar pitch size (∼34nm), as shown in Figure 5 (more data regarding comparison ofline edge and width deviation between 4VD23 and SD45 BCPsare available in Figures S10 and S11). It should be also noted
that a small LER < 1 nm was obtained despite the relativelyhigh polydispersity index (PDI = 1.20−1.31) of our BCPs, asshown in Table S1, which is due to the nature of RAFTpolymerization. We expect reduction of PDI using othersynthesis methods such as living anionic polymerization mayfurther improve the pattern quality of the BCPs. It should bealso noted that the LER of 0.98 nm is also lower that the values(1.8−2.0 nm) for poly(2vinylpyridine-b-dimethylsiloxane)-(P2VP-b-PDMS) with a relatively higher χ than PS-b-PDMS,which was reported in our previous study.28 This result suggeststhat the P4VP-b-PDMS BCP has a even higher χ than P2VP-b-PDMS. For a quantitative evaluation of the roughness of thepatterns, we also carried out a PSD analysis. Figure 6 shows theLER and LWR PSD curves for 4VD23 and SD45 with a similarpitch size, indicating that the PSD values of 4VD23 are lowerthan those of SD45 over the entire frequency range. Theseresults show that the pattern quality of DSA patterns can besignificantly improved by further increasing the Flory−Hugginsinteraction parameter of BCPs.
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 analysisresults are also shown. (LER = line edge roughness, LWR = line width roughness).
■ CONCLUSIONIn summary, we designed and synthesized P4VP-b-PDMS as anextremely high-χ BCP via RAFT polymerization andsuccessfully produced self-assembled patterns with improvedpattern quality compared to conventional high-χ BCPs. Basedon the analysis data, the χ parameter of P4VP-b-PDMS wasestimated to be approximately 7 times higher than that of PS-b-PDMS. The sharp interface between the two blocks providedan unusually small LER (0.98 nm) of the P4VP-b-PDMS BCP,corresponding to <6% of the pattern width. By demonstratingthat the well-ordered patterns can be obtained within a fewminutes (<3 min in 120 nm-wide trench templates) of WSAtreatment time, we also confirmed that eco-friendly ethanol-based warm solvent annealing at 60 °C is highly effective forpromoting rapid self-assembly of the P4VP-b-PDMS BCP withintrinsic slow kinetics. Our results suggest that there issignificant room for improving the DSA pattern quality withoutcompromising the pattern formation throughput by adoptingBCPs with an even higher Flory−Huggins interactionparameter. Moreover, such high-χ BCPs may enable theformation of ultrahigh-density patterns in the sub-5 nm regime.
■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.chemma-ter.6b01731.
Author Contributions†J.M.K. and Y.H.H. contributed equally to this work.
NotesThe authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This research was supported by the MOTIE(Ministry of Trade,Industry & Energy (10048504) and KSRC (Korea Semi-conductor Research Consortium) support program for thedevelopment of the future semiconductor device. This workwas also supported by Open Innovation Lab Project fromNational Nanofab Center (NNFC).
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Figure 6. Power spectral density (PSD) functions. (a) Line widthroughness and (b) line edge roughness of PS-b-PDMS and P4VP-b-PDMS, respectively.
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