Area-Selective ALD of TiO2

Article pubs.acs.org/JPCC

Area-Selective ALD of TiO2 Nanolines with Electron-Beam Lithography Jie Huang,† Mingun Lee,†,‡ Antonio Lucero,† Lanxia Cheng,† and Jiyoung Kim*,† †

Department of Material Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States Dongjin Semichem Co. Ltd., 625-3, Yodang-ri, Yangam-myun, Hwasung-si, Kyungki-do 445-930, South Korea

‡

S Supporting Information *

ABSTRACT: We demonstrate a bottom-up approach to fabricate nanoline structures using self-assembled monolayer (SAM) modified substrates to selectively prevent nucleation during atomic layer deposition (ALD). Low-energy (≤5 kV) electron-beam lithography (EBL) was used to modify the hydrophobic functional groups (−CH3) of octadecyltrichlorosilane (OTS) SAM to hydrophilic species (e.g., −COOH), which allows chemisorption of the titanium isopropoxide (TTIP) and water to initiate titanium oxide (TiO2) nucleation. TiO2 thin films were selectively deposited on the OTS molecules which were properly functionalized or patterned. We systematically investigate the effects of e-beam dose and accelerating voltage on selective TiO2 deposition with nanoline patterns. The results indicate that the former parameter determines the resolution of individual line width, while the latter one is attributed to the minimum pitch dimension of dense line patterns achievable. Using the optimal e-beam parameters, i.e., accelerating voltages of 1−2 kV and a line dose of 10 nC/cm, TiO2 nanolines with a maximum resolution of 30 nm and a minimum pitch of 50 nm were achieved. This study offers a new approach to fabricate closepacked nanopatterns for IC devices without any challenging etching processes.

■

aforementioned lithography techniques.23 Electron-beam lithography (EBL) is another well-established lithography technique used particularly for nanopatterning. Compared to UV and soft lithography techniques, EBL offers higher resolution, more freedom of pattern design, and fewer problems with contamination from either the mold or the mask, which has physical contact with the resists.24 To date, isolated feature size down to sub-10 nm has been achieved by EBL using hydrogen silsesquioxane (HSQ) resist.25 Moreover, electron beams have been widely applied to modify functional groups of SAMs and construct 3-D nanostructures.26−34 However, limited research had been devoted to selective-ALD based on e-beam patterned SAMs. In this research, an octadecyltrichlorosilane (OTS) SAM served as a nucleation-inhibition layer to refrain chemisorption of ALD precursors. Low-energy electrons (≤5 kV), in contrast to conventional EBL (normally 10−30 kV), were applied to modify the functional groups of OTS SAM. We exposed selective areas on a nonpatterned blank OTS monolayer to ebeam irradiation, followed by titanium oxide (TiO2) deposition using ALD. We investigated the fundamental mechanism responsible for the area-selective deposition correlated to

INTRODUCTION Recently, extremely small feature patterning, such as gates, isolations and contacts, is required for the sub-10 nm technology node. However, these critical processing steps are facing limits due to complicated and expensive processes (e.g., double/multiple patterning). Selective deposition of sacrificial layer for double patterning (e.g., hard-mask layer for FIN or any other critical dimension) would be useful as a simple, cheap, and reliable process. Self-assembled monolayers (SAMs), an important subgroup of organic molecules spontaneously adsorbed on solid substrates, have not only been employed to control surface properties,1−5 such as wettability, adhesion, and lubrication, but also considered as ultrathin materials suitable for surface patterning with nanoscale dimensions.6−12 Depending on their terminal head groups, SAMs can either enhance or prevent chemical-reaction-based deposition due to their highly hydrophilic or hydrophobic nature. Area-selective deposition can be achieved by selectively alternating the functional groups of the SAMs, which determine nucleation and growth during the deposition process. Using SAMs patterned by UV light13 and soft lithography14−17 as a substrate, area-selective deposition has been shown using atomic layer deposition (ALD), which strongly depends on surface chemistry.18−22 To the best of our knowledge, the highest resolution of an area-selective deposition process achieved lateral dimensions as small as approximately 100 nm using both © 2014 American Chemical Society

Received: April 16, 2014 Revised: July 22, 2014 Published: September 9, 2014 23306

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312

The Journal of Physical Chemistry C

Article

Figure 1. Schematic of area-selective deposition: (a) SiO2/Si substrate was cleaned by UV/O3; (b) an OTS monolayer was self-assembled on the SiO2/Si substrate; (c) e-beam was applied to pattern the OTS SAM; (d) TiO2 thin film was selectively deposited on e-beam-irradiated area by ALD.

Figure 2. (a) AFM image of OTS monolayer after e-beam patterning and (b) FTIR differential absorption spectrum of OTS monolayer after e-beam irradiation. A pristine OTS monolayer spectrum was used as the reference.

cycle consisted of 0.1 s TTIP exposure, 30 s N2 purge, 0.1 s water exposure, and 30 s N2 purge. The growth rate of TiO2 was about 0.2 Å/cycle, as confirmed by simultaneous deposition on to a bare Si wafer. The purging time in this experiment was much longer than that of conventional ALD processes to ensure all physisorbed precursors were purged away. For materials characterization, Fourier transform infrared spectroscopy (FT-IR, Nicolet 4700) was executed over the 650−4000 cm−1 spectral region using a grazing angle attenuated total reflectance (ATR, Harrick Scientific) sample holder with a Ge ATR crystal. Absorption spectra were typically averaged over 1000 scans. Cross-sectional transmission electron microscopy (TEM) samples were prepared by the lift-out method using a focused ion beam (FIB, FEI Nova 2000) system equipped with a nanomanipulator and characterized using a field emission TEM (JEOL 2100). Surface morphological images were obtained using atomic force microscopy (AFM, Veeco Model 3100 Dimension V). Si cantilevers with a resonance frequency of 289−331 kHz and spring constant of 20−80 N/m were used to scan the pattern in ambient using tapping mode.

backscattered electrons. We also studied the highest achievable resolution of selectively deposited individual line patterns as a function of e-beam dose. Furthermore, we analyzed the contrast limitation of dense line patterns, dominated by the e-beam accelerating voltage, achieved with this approach.

■

EXPERIMENTAL METHODS Silicon wafers (Silicon Valley Microelectronics) with approximately 3 nm thermal oxide were used as substrates. The OTS (CH3(CH2)17SiCl3, purity 90+%, Aldrich Co. Ltd.) dissolved into toluene at a volume ratio of 1:200 was used as a dipping solution to deposit OTS SAM on the SiO2/Si substrate for 4 h at room temperature. Then the samples were rinsed in an ultrasonic tank for 5 min for each step with toluene, acetone, isopropyl alcohol (IPA), and deionized (DI) water to remove any physically adsorbed OTS molecules. A field emission scanning electron microscope (SEM, Zeiss Supra-40) equipped with a nanometer pattern generation system (NPGS 9.0) was used to generate e-beam patterns directly on OTS SAMs. The accelerating voltage and dosage were set up using the software. The beam current was measured using a Faraday cup. After patterning, all samples were rinsed with DI water and dried under a stream of N2 gas. TiO2 was deposited by ALD (Cambridge Nanotech) at the temperature of 150 °C. Titanium isopropoxide (TTIP, Ti(OCH(CH3)2)4, Sigma-Aldrich) and water (H2O) were used as precursors, evaporated at 75 and 20 °C, respectively. The flow rate of nitrogen (N2) carrier gas was 20 sccm. The

■

RESULTS AND DISCUSSION

The schematic of the area-selective deposition process includes four steps, as illustrated in Figure 1. For OTS deposition, the condensation reaction between −SiCl3 and surface hydroxyl groups (−OH) can form covalent bonds on the SiO 2 23307

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312

The Journal of Physical Chemistry C

Article

Figure 3. Idealized cartoon of chemical mechanism for selective ALD by TTIP and water on e-beam patterned OTS SAMs: (a) OTS deposition on the SiO2/Si substrate, (b) e-beam cleavage generating new functional groups, (c) oxidation of the new functional group into −COOH by H2O, (d) introducing TTIP to initiate the nucleation of TiO2, and (e) layer by layer growth of TiO2 on e-beam patterned region.

Figure 4. Cross-sectional TEM images demonstrating the selectivity of TiO2 deposition on e-beam-irradiated region of OTS monolayer.

surface.35,36 As a result, an OTS monolayer was deposited on top of the SiO2 surface. The thickness of this monolayer was approximately 2 nm, as measured by ellipsometry, which is close to the ideal thickness of one layer of OTS molecules.37 The OTS-covered surface was highly hydrophobic with a water contact angle of 105 ± 1° due to the exposed −CH3 functional groups, as expected.38 Electron-beam irradiation on an OTS SAM was exposed without any intentional line width using an accelerating voltage of 2 kV and dosage of 10 nC/cm. These parameters were obtained from careful investigation detailed below. Figure 2a shows AFM image of the OTS monolayer after e-beam patterning. It clearly illustrates that electrons involved into cleavage of the backbone of OTS molecules. To investigate a potential reaction mechanism of e-beam irradiation, a 5 × 5 mm square pattern on the OTS monolayer was exposed to the e-beam using an accelerating voltage of 2 kV and dosage of 10 nC/cm. Using a pristine OTS monolayer on a SiO2/Si substrate as a reference, the FTIR differential absorption spectrum of the OTS monolayer after e-beam exposure is shown in Figure 2b. Two distinct peaks are observed at approximately 2920 and 2850 cm−1 corresponding to the −CH2− stretching mode, signature peaks of the OTS alkyl chain, and the shoulder peak at approximately 2960 cm−1 corresponds to the −CH3 stretching mode. The fact that these peaks are negative indicates the loss of these vibrational modes due to cleavage of the C−C backbone of the monolayer during

irradiation. On the other hand, CC stretching was observed at approximately 1550 cm−1 after e-beam exposure. Also, two secondary peaks at approximately 1700 and 1400 cm−1 represent CO and C−O stretching of −COOH terminal groups, respectively.39−41 Therefore, a potential mechanism of selective deposition is shown in Figure 3. We believe that the electrons partially cleave the alkane chain, leaving −CHCH2 or −CH2• groups at the cleavage site (Figure 3b). During sample transfer from the EBL chamber to either the FTIR or ALD chamber, a portion of these new functional groups can react with water or oxygen in the atmosphere, forming carboxyl groups (−COOH). The modification of −CH3 functional group to −CC or −COOH under e-beam irradiation is also observed by XPS reported by other research groups.40,41 Any unreacted CC terminal groups can be fully oxidized by H2O during the first few cycles of the ALD process, resulting in a complete coverage of −COOH terminal groups within the e-beam-irradiated area (Figure 3c). The following TTIP precursor only reacts with hydrophilic (e.g., −OH or −COOH) but not hydrophobic (e.g., −CH3) functional groups to initiate the TiO2 growth (Figure 3d). As a result, thin film deposition occurred selectively on the e-beam exposed area. Cross-sectional TEM was applied to visualize the areaselective deposition. A rectangular pattern was defined by ebeam irradiation on an OTS monolayer, followed by TiO2 deposition for 1000 cycles using ALD. As shown in Figure 4, it 23308

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312

The Journal of Physical Chemistry C

Article

Figure 5. AFM images of individual TiO2 nanoline patterns via selective ALD. The patterns were generated by e-beam with an accelerating voltage of 2 kV and line doses of (a) 1, (b) 2, (c) 5, (d) 10, and (e) 20 nC/cm followed by TiO2 deposition using ALD.

clearly illustrates that TiO2 was uniformly deposited on the ebeam-irradiated area with an ideal thickness of approximately 20 nm, whereas the e-beam unexposed area was TiO2 free. The planar dimensions of selectively deposited TiO2 nanoline patterns are expected to highly depend on the practical electron distribution and eventually the number of OTS molecules modified by incident and scattered electrons. To confirm the resolution achievable with selective ALD, single-pass individual line patterning was performed by e-beam on OTS SAMs. Figure 5 shows all AFM images were taken after the e-beam patterning and ALD process, where TTIP/ H2O was deposited for 150 cycles (approximately 3 nm) After the ALD process, at low e-beam doses, such as 1−2 nC/cm, no sharp lines were observed in the AFM images, as shown in Figure 5a,b. Since the incident and scattered electrons may incompletely react with the OTS functional group (−CH3), growth of a TiO2 layer would be retarded until all unreacted methyl functional groups are covered. With increasing e-beam doses, the selectively deposited TiO2 line became distinct and continuous, as shown in Figure 5c−e. As the dose of incident electrons increased to 10 nC/cm, most OTS terminal groups in the e-beam exposed area were converted from hydrophobic (−CH3) to hydrophilic (−COOH) species, which allowed layer-by-layer growth of ALD films. These TiO2 lines are approximately 1.5 nm in height. Considering that the cleaved alkane chain length of the OTS monolayer (Figure 2a) and TiO2 thin film thickness are approximately 1.5 and 3.0 nm, respectively, the measured step height is quite reasonable. Once the e-beam dose reached 20 nC/cm, the TiO2 line width broadened to approximately 30 nm, showing a height similar to that of the 10 nC/cm case. The results of both line width and step height versus e-beamline dose are summarized into plots, as shown in Figure 6, indicating 10 nC/cm is the optimal ebeam dose to get the smallest line width with ideal TiO2 thickness, with estimated e-beam patterning efficiency of 2%;42 i.e., approximately 50 electrons are involved in modifying one OTS molecule. The effect of electrons on SAMs depends not only on their dose but also on their energy.43 Similar to conventional EBL, owing to proximity effect,44−46 backscattered electrons (BEs) normally cause partial exposure of adjacent SAM-covered areas.

Figure 6. Line width/step height as a function of e-beam line dose with accelerating voltage of 2 kV.

A Monte Carlo simulation (Cascade V242) is used to understand backscattering phenomena of incident electrons to an OTS-covered SiO2/Si substrate (details shown in the Supporting Information). As a result, it is challenging to achieve high contrast for dense patterns. To address this issue, it is necessary to minimize electron scattering by optimizing the ebeam accelerating voltage. Thus, parallel line patterns with pitches of 50, 100, and 150 nm were designed. The acceleration voltages were tested from 1 to 5 kV. Voltages below 1 kV would cause alignment difficulties for the e-beam writer used in this study. An e-beam line dose of 10 nC/cm, which was the optimal dosage for individual line patterns aforementioned, was applied to write single-pass dense lines with a variety of pitches. AFM images of selectively deposited dense line patterns are shown in Figure 7. For an accelerating voltage of 1 kV, the ebeam-irradiated area was mostly covered by TiO2. The unexposed hydrophobic OTS monolayer did not chemically react with TTIP or water. Nanolines with pitches of 50 nm or larger can be isolated. However, possibly due to the electron scattering caused energy loss, some OTS was left unmodified by electrons, limiting the number of ALD nucleation sites. Therefore, island-type growth is expected, resulting in discontinuities in the TiO2 lines, as shown in Figure 7a. As the voltage increased to 2 kV, a small amount of TiO2 deposition was observed between the lines at a pitch size of 23309

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312

The Journal of Physical Chemistry C

Article

Figure 7. AFM images of dense TiO2 line patterns via selective ALD. The patterns were generated by e-beam with accelerating voltages of (a) 1, (b) 2, and (c) 5 kV and a line dose of 10 nC/cm followed by TiO2 deposition using ALD. Pitch dimension is 50 nm (10 parallel lines in the center), 100 nm (5 parallel lines on both side of 50 nm ones), and 150 nm (5 parallel line on both side of 100 nm ones) from center to both sides.

50 nm, where OTS was partially modified due to the proximity effect, as shown in Figure 7b. Since the BEs may incompletely react with the OTS functional group (−CH3), TiO2 was deposited after a certain incubation time during the ALD process even though the e-beam did not directly irradiate those regions of the SAM. At a higher voltage, i.e. 5 kV, the proximity effect dominates the OTS difunctionalization for dense line patterns with 50 nm pitch. The range of BEs is highly overlapping, resulting in heavy exposure of the OTS molecules located between the lines of direct e-beam exposure and eventually allowing chemisorption of TTIP precursors. As a result, TiO2 was deposited in a “belt” structure rather than in 10 parallel lines. However, lines with 100 nm or larger pitch size are still isolated from each other, as shown in Figure 7c. To investigate the proximity effect on selective deposited pattern, the term “contrast” should be introduced. The conventional definition of pattern contrast, K, is as follows:47 K=

Zmax − Zmin Zmax + Zmin

Figure 8. Pattern contrast as a function of e-beam voltage and pitch dimension (dashed lines for guiding the eyes).

approaches Kmax ≈ 1 when line−line spacing is over 100 nm. Conversely, the contrast approaches infinitely to Kmin ≈ 0 as the pitch size drops below 50 nm since the proximity effect becomes dominant factor resulting in heavy overexposure of SAMs, and with identical pitch size, the contrast normally increases as the voltage decreases, whereas voltages below 1 kV cause alignment difficulties. Even if local heating generated by e-beam irradiation, or corresponding secondary electrons and X-ray would participate in cleavage of SAMs, these data confirm our assumption that the proximity effect of BEs dominates broadening of dense nanoline patterns for selective ALD.

(1)

In experimental data, i.e. AFM tomography profiles, Zmax and Zmin are defined as the maximum and minimum values in terms of height, and the lowest point in AFM line profile is defined as yaxis = 0. Using eq 1, the contrast as a function of e-beam voltage and pitch dimension for dense TiO2 line patterns was calculated, as plotted in Figure 8. (For simplicity, we assume that all contrast values approach 0 when the pitch dimension is smaller than 3 nm, because practically it is difficult to reduce the beam diameter within 3 nm or less, especially for low accelerating voltages such as 1−2 kV, and all contrast values approach 1 when the pitch dimension is larger than 1 μm.) Two clear trends are observed: with constant voltage, the contrast increases as the pitch size increases and eventually

■

CONCLUSION In this study, we have demonstrated a bottom-up approach to fabricate TiO2 nanolines using EBL combined with ALD. Area selectivity is based on the OTS SAM selectively engineered by electron-beam irradiation. 2-D OTS patterns have been successfully transferred into TiO2 nanostructures using this 23310

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312

The Journal of Physical Chemistry C

Article

(7) Ryan, D.; Parviz, B. A.; Linder, V.; Semetey, V.; Sia, S. K.; Su, J.; Mrksich, M.; Whitesides, G. M. Patterning Multiple Aligned SelfAssembled Monolayers Using Light. Langmuir 2004, 20, 9080−9088. (8) Chen, M.; Dulcey, C. S.; Chrisey, L. A.; Dressick, W. J. Deep-UV Photochemistry and Patterning of (Aminoethylaminomethyl)phenethylsiloxane Self-Assembled Monolayers. Adv. Funct. Mater. 2006, 16, 774−783. (9) Critchley, K.; Zhang, L.; Fukushima, H.; Ishida, M.; Shimoda, T.; Bushby, R. J.; Evans, S. D. Soft-UV Photolithography Using SelfAssembled Monolayers. J. Phys. Chem. B 2006, 10, 17167−17174. (10) Chen, S.; Chen, G. Nanoseeding via Dual Surface Modification of Alkyl Monolayer for Site-Controlled Electroless Metallization. Langmuir 2011, 27, 12143−12148. (11) Love, J. C.; Estroff, L. A.; Kriebel, J. K.; Nuzzo, R. G.; Whitesides, G. M. Self-Assembled Monolayers of Thiolates on Metals as a Form of Nanotechnology. Chem. Rev. 2005, 105, 1103−1169. (12) Turchanin, A.; Golzhauser, A. Carbon Nanomembranes from Self-Assembled Monolayers: Functional Surfaces without Bulk. Prog. Surf. Sci. 2012, 87, 108−162. (13) Shi, Z.; Walker, A. V. Synthesis of Nickel Nanowires via Electroless Nanowire Deposition on Micropatterned Substrates. Langmuir 2011, 27, 11292−11295. (14) Jeong, D.; Park, J.; Park, N.; Shin, H.; Lee, J.; Sung, M.; Kim, J. Fabrication of Cu/ZrO2/Si Structure Capacitors by a Novel Selective Deposition Technique on Patterned Self-Assembled Monolayers (SAMS). AVS Top. Conf. At. Layer Deposition 2003, 225−226. (15) Park, M. H.; Jang, Y. J.; Sung-Suh, H. M.; Sung, M. M. Selective Atomic Layer Deposition of Titanium Oxide on Patterned SelfAssembled Monolayers Formed by Microcontact Printing. Langmuir 2004, 20, 2257−2260. (16) Jiang, X.; Bent, S. F. Area-Selective ALD with Soft Lithographic Methods: Using Self-Assembled Monolayers to Direct Film Deposition. J. Phys. Chem. C 2009, 113, 17613−17625. (17) Farm, E.; Lindroos, S.; Ritala, M.; Leskela, M. Microcontact Printed RuOx Film as an Activation Layer for Selective-Area Atomic Layer Deposition of Ruthenium. Chem. Mater. 2012, 24, 275−278. (18) Hausmann, D.; Becker, J.; Wang, S.; Gordon, R. G. Rapid Vapor Deposition of Highly Conformal Silica Nanolaminates. Science 2002, 298, 402−406. (19) Bouman, M.; Zaera, F. The Surface Chemistry of Atomic Layer Deposition (ALD) Processes for Metal Nitride and Metal Oxide Film Growth. ECS Trans. 2010, 33, 291−305. (20) Parsons, G. N.; George, S. M.; Knez, M. Progress and Future Directions for Atomic Layer Deposition and ALD-Based Chemistry. MRS Bull. 2011, 36, 865−871. (21) Sivasubramani, P.; Park, T. J.; Coss, B. E.; Lucero, A.; Huang, J.; Brennan, B.; Cao, Y.; Jena, D.; Xing, H.; Wallace, R. M.; Kim, J. In-Situ X-ray Photoelectron Spectroscopy of Trimethyl Aluminum and Water Half-Cycle Treatments on HF-treated and O3-Oxidized GaN Substrates. Phys. Status Solidi RRL 2012, 6, 22−24. (22) Kim, J.; Kim, T. W. Initial Surface Reactions of Atomic Layer Deposition. JOM 2009, 61, 17−22. (23) George, A.; Knez, M.; Hlawacek, G.; Hagedoorn, D.; Verputten, H. H. J.; van Gastel, R.; ten Elshof, J. E. Nanoscale Patterning of Organosilane Molecular Thin Films from the Gas Phase and Its Applications: Fabrication of Multifunctional Surfaces and Large Area Molecular Templates for Site-Selective Material Deposition. Langmuir 2012, 28, 3045−3052. (24) Dickey, M.; Stewart, M.; Willson, G.; Palard, M.; Bakir, M. S. NNIN Nanotechnology Open Textbook, Chapter 5.3: Advanced Lithography: Electron-beam Lithography, 2007. (25) Manfrinato, V. R.; Zhang, L.; Su, D.; Duan, H.; Hobbs, R. G.; Stach, E. A.; Berggren, K. K. Resolution Limits of Electron-Beam Lithography toward the Atomic Scale. Nano Lett. 2013, 13, 1555− 1558. (26) Golzhauser, A.; Eck, W.; Geyer, W.; Stadler, V.; Weimann, T.; Hinze, P.; Grunze, M. Chemical Nanolithography with Electron Beams. Adv. Mater. 2001, 13, 803−806.

method. The e-beam dosage was the dominant factor in determining the resolution of individual line widths, while the accelerating voltage determined the minimum pitch dimension we could achieve. As a result, TiO2 lines with 30 nm resolution and 50 nm pitch have been selectively deposited by ALD following EBL on the OTS SAM using accelerating voltages of 1−2 kV with a line dose of 10 nC/cm. For dosages below 10 nC/cm, incomplete modification of OTS functional groups was yield, resulting in inhibition of TiO2 nucleation, whereas for dosages above 10 nC/cm, nanoline broadening was observed. On the other hand, for accelerating voltages above 2 kV, the proximity effect caused overexposure of the unpatterned OTS SAM regions, resulting in lower contrast in the area-selective deposition. However, for voltages below 1 kV, there were difficulties of e-beam alignment. This research offers a new approach to fabricate close-packed nanopatterns for IC devices without using any etching processes.

■

ASSOCIATED CONTENT

S Supporting Information *

Experimental details and results and discussion. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (J.K.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors appreciate suggestions and guidance regarding EBL, both theoretical and experimental, from Profs. W. Hu and B. Gnade and Dr. K. Triveti at The University of Texas at Dallas. This project was supported by the IT R&D program of MKE/KEIT [10030694, Nanoscale selective multilayer deposition technology with ALD and SAM], Leading Foreign Research Institute Recruitment Program through National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP)2013K14A3055679, and KMU InFUSION program.

■

REFERENCES

(1) Ulman, A. Formation and Structure of Self-Assembled Monolayers. Chem. Rev. 1996, 96, 1533−1554. (2) Malinsky, M. D.; Kelly, K. L.; Schatz, G. C.; van Duyne, R. P. Chain Length Dependence and Sensing Capabilities of the Localized Surface Plasmon Resonance of Silver Nanoparticles Chemically Modified with Alkanethiol Self-Assembled Monolayers. J. Am. Chem. Soc. 2001, 123, 1471−1482. (3) Calhoun, M. F.; Sanchez, J.; Olaya, D.; Gershenson, M. E.; Podzorov, V. Electron Functionalization of the Surface of Organic Semiconductors with Self-Assembled Monolayers. Nat. Mater. 2008, 7, 84−89. (4) Vilan, A.; Yaffe, O.; Biller, A.; Salomon, A.; Kahn, A.; Cahen, D. Molecules on Si: Electronics with Chemistry. Adv. Mater. 2010, 22, 140−159. (5) Huang, J.; Lee, M.; Lucero, A.; Kim, J. Organic-Inorganic Hybrid Nano-Laminates Fabricated by Ozone-Assisted Molecular-Atomic Layer Deposition. Chem. Vap. Deposition 2013, 19, 142−148. (6) Xia, Y.; Rogers, J. A.; Paul, K. E.; Whitesides, G. M. Unconventional Methods for Fabricating and Patterning Nanostructures. Chem. Rev. 1999, 99, 1823−1848. 23311

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312

The Journal of Physical Chemistry C

Article

(27) La, Y.; Kim, H. J.; Maeng, I. S.; Jung, Y. J.; Park, J. W.; Kang, T.; Kim, K.; Ihm, K.; Kim, B. Differential Reactivity of Nitro-Substituted Monolayers to Electron Beam and X-ray Irradiation. Langmuir 2002, 18, 301−303. (28) Jung, Y. J.; La, Y.; Kim, H. J.; Kang, T.; Ihm, K.; Kim, K.; Kim, B.; Park, J. W. Pattern Formation through Selective Chemical Transformation of Imine Group of Self-Assembled Monolayer by Low-Energy Electron Beam. Langmuir 2003, 19, 4512−4518. (29) Mendes, P. M.; Jacke, S.; Critchley, K.; Plaza, J.; Chen, Y.; Nikitin, K.; Palmer, R. E.; Preece, J. A.; Evans, S. D.; Fitzmaurice, D. Gold Nanoparticle Patterning of Silicon Wafers Using Chemical eBeam Lithography. Langmuir 2004, 20, 3766−3768. (30) Sarveswaran, K.; Hu, W.; Huber, P. W.; Bernstein, G. H.; Lieberman, M. Deposition of DNA Rafts on Cationic SAMs on Silicon [100]. Langmuir 2006, 22, 11279−11283. (31) Rundqvist, J.; Hoh, J. H.; Haviland, D. B. Directed Immobilization of Protein-Coated Nanospheres to Nanometer-Scale Patterns Fabricated by Electron Beam Lithography of Poly(ethylene glycol) Self-Assembled Monolayers. Langmuir 2006, 22, 5100−5107. (32) Gadegaard, N.; Chen, X.; Rutten, F. J. M.; Alexander, M. R. High-Energy Electron Beam Lithography of Octadecylphosphonic Acid Monolayers on Aluminum. Langmuir 2008, 24, 2057−2063. (33) Ballav, N.; Schilp, S.; Zharnikov, M. Electron-Beam Chemical Lithography with Aliphatic Self-Assembled Monolayers. Angew. Chem., Int. Ed. 2008, 47, 1421−1424. (34) Khan, M. N.; Tjong, V.; Chilkoti, A.; Zharnikov, M. Fabrication of ssDNA/Oligo(ethylene glycol) Monolayers and Complex Nanostructures by an Irradiation-Promoted Exchange Reaction. Angew. Chem., Int. Ed. 2012, 51, 10303−10306. (35) Harada, Y.; Girolami, G. S.; Nuzzo, R. G. Growth Kinetics and Morphology of Self-Assembled Monolayers Formed by Contact Printing 7-Octenyltrichlorosilane and Octadecyltrichlorosilane on Si(100) Wafers. Langmuir 2004, 20, 10878−10888. (36) Foisner, J.; Glaser, A.; Leitner, T.; Hoffmann, H.; Friedbacher, G. Effects of Surface Hydrophobization on the Growth of SelfAssembled Monolayers on Silicon. Langmuir 2004, 20, 2701−2706. (37) Richter, A. G.; Durbin, M. K.; Yu, C. J.; Dutta, P. In-Situ TimeResolved X-ray Reflectivity Study of Self-Assembly from Solution. Langmuir 1998, 14, 5980−5983. (38) Song, Y.; Nair, R. P.; Zou, M.; Wang, Y. Superhydrophobic Surfaces Produced by Applying a Self-Assembled Monolayer to Silicon Micro/Nano-Textured Surfaces. Nano Res. 2009, 2, 143−150. (39) Seitz, O.; Fernandes, P. G.; Mahmud, G. A.; Wen, H. C.; Stiegler, H. J.; Chapman, R. A.; Vogel, E. M.; Chabal, Y. J. One-Step Selective Chemistry for Silicon-on-Insulator Sensor Geometries. Langmuir 2011, 27, 7337−7340. (40) Zharnikov, M.; Grunze, M. Modification of Thiol-Derived SAMs by Electron and X-ray Irradiation. J. Vac. Sci. Technol., B 2002, 20, 1793−1807. (41) Seshadri, K.; Froyd, K.; Parikh, A. N.; Allara, D. L.; Lercel, M. J.; Craighead, H. G. Electron-Beam-Induced Damage in Self-Assembled Monolayers. J. Phys. Chem. 1996, 100, 15900−15909. (42) Huang, J.; Lee, M.; Kim, J. Selective Atomic Layer Deposition with Electron-Beam Patterned Self-Assembled Monolayers. J. Vac. Sci. Technol., A 2012, 30 (1), 128. (43) Meyerbroker, N.; Zharnikov, M. Modification of NitrileTerminated Biphenylthiol Self-Assembled Monolayers by Electron Irradiation and Related Applications. Langmuir 2012, 28, 9583−9592. (44) Chang, T. H. P. Proximity Effect in Electron-Beam Lithography. J. Vac. Sci. Technol. 1975, 12, 1271−1275. (45) McCord, M. A.; Newman, T. H. Low Voltage, High Resolution Studies of Electron Beam Resist Exposure and Proximity Effect. J. Vac. Sci. Technol., B 1992, 10 (6), 3083−3087. (46) Dobisz, E. A.; Marrian, C. R. K.; Salvino, R. E.; Ancona, M. A.; Perkins, F. K.; Turner, N. H. Reduction and Elimination of Proximity Effects. J. Vac. Sci. Technol., B 1993, 11 (6), 2733−2740. (47) Plummer, J. D.; Deal, M. D.; Griffin, P. D. Silicon VLSI Technology: Fundamentals, Practice and Modeling, 1st ed.; Prentice Hall: Upper Saddle River, NJ, 2000. 23312

dx.doi.org/10.1021/jp5037662 | J. Phys. Chem. C 2014, 118, 23306−23312