Langmuir 2009, 25, 1911-1914
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Atomic Layer Deposition of Aluminum Oxide on Carboxylic Acid-Terminated Self-Assembled Monolayers Meng Li,† Min Dai,† and Yves J. Chabal*,†,‡ Department of Physics and Astronomy, Rutgers UniVersity, Piscataway, New Jersey 08854, and Materials Science and Engineering Department, UniVersity of Texas at Dallas, Richardson, Texas 75080 ReceiVed October 28, 2008. ReVised Manuscript ReceiVed December 9, 2008 In situ infrared absorption spectroscopy is used to monitor atomic layer deposition (ALD) of aluminum oxide (Al2O3) on carboxylic acid-terminated self-assembled monolayers (SAMs), Si(111)-(CH2)10-COOH (or COOH-SAMs), directly grafted on silicon (111) at ∼100 °C. The quality of resulting Al2O3 films is comparable to Al2O3 on SiO2. Both the SAM film and the Si/SAM interface remain chemically stable during growth and upon post annealing to 400 °C, suggesting that the tight packing of the alkyl chains and COOH-SAM head groups presents a diffusion barrier and promotes ordered nucleation for ALD.
1. Introduction Inorganic-organic interfaces are important for a variety of applications such as organic light-emitting diodes, microelectronic interconnectors, and polymers-based devices.1 Highly ordered and well-organized organic self-assembled monolayers (SAMs) are widely used as model systems to study the interaction and interface formation between organic films and functional inorganic substrates (e.g., metals, semiconductors, metal oxides). High quality inorganic-organic interfaces require careful control of deposition. Compared to other deposition techniques such as liquid phase, physical vapor, and chemical vapor deposition (CVD), atomic layer deposition (ALD)2 is the most attractive because of its precise nature of thickness control, range of materials that can be deposited, and conformal nature of the coating. ALD also features the speed and convenience of vacuum techniques, without problems associated with liquid phase deposition (lack of solubility, dissolution, capillary and particle precipitation effects). It is gentle enough and can be operated at temperatures that are compatible with organic materials. The deposition of inorganic thin films on metal/SAM stacks has been studied using different characterization methods, such as IR and X-ray photoelectron spectroscopy (XPS) for Al on Au/thiol-SAMs with different organic functional groups.3-5 For most device applications, the deposition of functional materials on semiconductor/SAM stacks needs to be investigated. Recently, Engstrom and co-workers6-8 studied the growth of * Corresponding author. E-mail:
[email protected]. † Rutgers University. ‡ University of Texas at Dallas. (1) Lebaron, P. C.; Wang, Z.; Pinnavaia, T. J. Applied Clay Science 1999, 15, 11–29. (2) Jones, A. C.; Aspinall, H. C.; Chalker, P. R.; Potter, R. J.; Kukli, K.; Rahtu, A.; Ritala, M.; Leskela, M. J. Mater. Chem. 2004, 14, 3101–3112. (3) Hooper, A.; Fisher, G. L.; Konstadinidis, K.; Jung, D.; Nguyen, H.; Opila, R.; Collins, R. W.; Winograd, N.; Allara, D. L. J. Am. Chem. Soc. 1999, 121, 8052–8064. (4) Fisher, G. L.; Hooper, A. E.; Opila, R. L.; Allara, D. L.; Winograd, N. J. Phys. Chem. B 2000, 104, 3267–3273. (5) Fisher, G. L.; Walker, A. V.; Hooper, A. E.; Tighe, T. B.; Bahnck, K. B.; Skriba, H. T.; Reinard, M. D.; Haynie, B. C.; Opila, R. L.; Winograd, N.; Allara, D. L. J. Am. Chem. Soc. 2002, 124, 5528–5541. (6) Killampalli, A. S.; Ma, P. F.; Engstrom, J. R. J. Am. Chem. Soc. 2005, 127, 6300–6310. (7) Dube, A.; Sharma, M.; Ma, P. F.; Engstrom, J. R. Appl. Phys. Lett. 2006, 89, 164108–164110. (8) Dube, A.; Sharma, M.; Ma, P. F.; Ercius, P. A.; Muller, D. A.; Engstrom, J. R. J. Phys. Chem. C 2007, 111, 11045–11058.
titanium nitride (TiN) on a Si/SiO2/SAM stack using ALD, for a variety of organic functional groups for the SAM. Selective ALD growth on organic layers has also been thoroughly investigated by Bent and co-workers with the aim to develop better photoresists.9-11 In previous studies, the focus has been on examining the interface between the organic SAM and the inorganic film, with little attention paid to the interface between the SAM and the substrate, despite its importance for most of the device performance using a semiconductor/SAM/inorganic film stack. Furthermore, the nature of that first interface can also affect the quality of the growth of the inorganic film on top of the SAM.11 In the present study, we study the ALD of Al2O3, on COOHterminated SAMs with in situ IR spectroscopy, using trimethylaluminum (TMA) and water, giving particular attention to the SAM/Si and SAM/Al2O3 interfaces. The molecule CH2d CH(CH2)8-COOH, used to graft the COOH/SAM directly on Si via hydrosilylation of its alkene end group,12,13 involves the hydroxyl group from the carboxylic acid end group (-COOH) that is expected to react readily with TMA.14-16 ALD growth of Al2O3 using TMA/H2O has been extensively studied on silica,14 H-terminated Si (H/Si),17,18 alumina19 and polymer20 surfaces. Quantitative comparisons can therefore be made between H/Si and COOH/SAM/Si, thus providing insight as to the stability of (9) Chen, R.; Kim, H.; McIntyre, P. C.; Porter, D. W.; Bent, S. F. Appl. Phys. Lett. 2005, 86, 191910. (10) Chen, R.; Kim, H.; McIntyre, P. C.; Bent, S. F. Chem. Mater. 2005, 17, 536–544. (11) Chen, R.; Kim, H.; McIntyre, P. C.; Bent, S. F. Appl. Phys. Lett. 2004, 84, 4017–4019. (12) Linford, M. R.; Fenter, P.; Eisenberger, P. M.; Chidsey, C. E. D. J. Am. Chem. Soc. 1995, 117, 3145–3155. (13) Faucheux, A.; Gouget-Laemmel, A. C.; de Villeneuve, C. H.; Boukherroub, R.; Ozanam, F.; Allongue, P.; Chazalviel, J. N. Langmuir 2006, 22, 153–162. (14) Yates, D. J. C.; Dembinski, G. W.; Kroll, W. R.; Elliott, J. J. J. Phys. Chem. 1969, 73, 911–921. (15) Wade, L. G. J. Organic Chemistry, 3rd ed.; Prentice-Hall, Inc.: New York, 1995; p 943-944. (16) Lee, B. H.; Lee, K. H.; Im, S.; Sung, M. M. Org. Electron. 2008, 9, 1146–1153. (17) Frank, M. M.; Chabal, Y. J.; Green, M. L.; Delabie, A.; Brijs, B.; Wilk, G. D.; Ho, M. Y.; da Rosa, E. B. O.; Baumvol, I. J. R.; Stedile, F. C. Appl. Phys. Lett. 2003, 83, 740–742. (18) Frank, M. M.; Chabal, Y. J.; Wilk, G. D. Appl. Phys. Lett. 2003, 82, 4758–4760. (19) Dillon, A. C.; Ott, A. W.; Way, J. D.; George, S. M. Surf. Sci. 1995, 322, 230–242. (20) Wilson, C. A.; Grubbs, R. K.; George, S. M. Chem. Mater. 2005, 17, 5625–5634.
10.1021/la803581k CCC: $40.75 2009 American Chemical Society Published on Web 01/13/2009
1912 Langmuir, Vol. 25, No. 4, 2009
Letters
a mixed Si-C/Si-H interface. Also, the reactivity of TMA with COOH-SAM can be quantitatively compared to studies of ALD TMA/H2O on SiO2 and H/Si.18
2. Materials and Methods H/Si(111) samples are prepared by hydrofluoric acid (HF) etching followed by NH4F immersion and rinsing with deionized (DI) water.21 Carboxylic acid-terminated SAMs are prepared by immersion of H/Si into neat 1-undecylenic acid, CH2dCH(CH2)8-COOH, predeoxygenated for at least 1 h at 50 °C and then cooled to room temperature. The hydrosilylation is performed at 120 °C for 2 h under N2 purging. Excess reagent is removed after reaction, and the sample is rinsed sequentially with tetrahydrofuran (THF), dichloromethane, hot 10% acetic acid, and DI water, and then dried in N2 gas. After introduction into a home-built ALD reactor connected to a Fourier transform infrared (FTIR) spectrometer (Nicolet Nexus 670 with external MCT-B detector),18,22 the Si(111)-(CH2)10-COOH sample is preannealed at 120 °C in dry N2 gas (300 sccm flow), purified in a Centorr model 2A N2 purifier (
