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Selective Ni-P Electroless Plating on Photopatterned Cationic Adsorption Films Influenced by Alkyl Chain Lengths of Polyelectrolyte Adsorbates and Additive Surfactants Masaru Nakagawa,*,† Nozomi Nawa,† and Tomokazu Iyoda†,‡ Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan, and CREST, JST, 4-1-8 Honmachi, Kawaguchi, Saitama 332-0012, Japan Received June 6, 2004. In Final Form: August 19, 2004 We demonstrated that the photopatterned single-layer adsorption film of poly(1-dodecyl-4-pyridinium bromide) on a silica surface was available for a template of nickel-phosphorus (Ni-P) electroless plating through sensitization with a SnCl2 aqueous solution and activation with a PdCl2 aqueous solution. Four kinds of poly(1-alkyl-4-vinylpyridinium halide)s bearing methyl, propyl, hexyl, and dodecyl groups were prepared. The cationic polymers were adsorbed by a negatively charged silica surface from their solutions, to form single-layer adsorption films exhibiting desorption-resistance toward deionized water and ethanol. The organic adsorption films could be decomposed completely by exposure to 172 nm deep-UV light. The formation and decomposition of the single-layer films were confirmed by deep-UV absorption spectral measurement and zeta-potential measurement. Ni-P electroless plating was carried out on the photopatterned adsorption films, using three types of SnOx colloidal materials without and with cationic or anionic surfactant as catalyst precursors in the sensitization step. In the case of the negatively charged SnOx colloids surrounded by anionic surfactant, Ni-deposition took place preferentially on the cationic adsorption films remaining in unexposed regions. The Ni-deposition was accelerated significantly on the cationic adsorption film bearing dodecyl groups. It was obvious by ICP-AES analyses that the hydrophobic long-chain dodecyl groups in the adsorption film could promote the adsorption of the negative SnOx colloids on the film surface, followed by much nucleus formation of zerovalent Pd catalysts useful for the electroless plating. The result of our experiment clearly showed that, in addition to electrostatic interaction, van der Waals interaction generating between the hydrophobic long-chain hydrocarbons of the adsorption film and the surfactant improved significantly the adsorption stability of the SnOx colloids, resulting in highly selective Ni-deposition in accord with the photopattern shape of the cationic single-layer adsorption film.
Introduction Photolithography using organic photoresist materials has been widely adopted to manufacture printed-wiring circuit boards with wiring widths from 10 µm to 1 mm in house electric appliances.1 The layer of the photoresist materials has a thickness of several tens of micrometers usually. The thick organic photoresist layer ends up as industrial waste in the manufacturing process. A novel method for manufacturing the printed-wiring circuit boards has been highly required to reduce the harmful industrial waste from a standpoint in green sustainable chemistry. There are two categories of subtractive and additive methods in electroless plating for preparing conductive metallic wires. The control of site-selective surface adsorption or chemical formation of colloidal palladium catalysts is a successful key to preparing such metal wires in the additive method. The use of selfassembled monolayers (SAMs) has attracted attention as a new additive method. The SAMs of a few nanometers in thickness will be capable of reducing obviously the organic industrial waste in comparison with the thick photoresist layer currently used. Calvert et al.2 and Dressick et al.3 have reported that the photopatterned SAMs derived from phenyltrichloro* Corresponding author. E-mail:
[email protected]. † Tokyo Institute of Technology. ‡ CREST, JST. (1) Landolt, D. J. Electrochem. Soc. 2002, 149, S9-S20. (2) Dulcey, C. S.; Georger, J. H., Jr.; Krauthamer, V.; Stenger, D. A.; Fare, T. L.; Calvert, J. M. Science 1991, 252, 551-554.
silane and amino- and pyridyl-terminated alkoxysilanes are available as deposition templates in Ni and Cu electroless plating. Ni and Cu electroless deposition occurs selectively on the unexposed SAM surfaces patterned by exposure to 193 nm deep-UV light. The coordination bonds generating between surfaces of the SAM and Pd/Sn colloidal catalyst are utilized for the selective surface adsorption of the plating catalyst. Sugimura et al. have demonstrated that the octadecyltrimethoxysilane SAM patterned by irradiation with 172 nm deep-UV light is available as the single-layer preventive film against chemical formation of palladium nanoparticles on a bare silicon surface.4,5 The monolayer photolithography to control such metal depositions is underused in comparison with micro-contact printing6-9 and ink-jet printing10 in which plating catalysts (3) Dressick, W. J.; Calvert, J. M. Jpn. J. Appl. Phys. 1993, 32, 58295839. (4) Sugimura, H.; Hanji, T.; Takai, O.; Masuda, T.; Misawa, H. Electrochim. Acta 2001, 47, 103-107. (5) Sugimura, H.; Hayashi, K.; Saito, N.; Hong, L.; Takai, O.; Hozumi, A.; Nakagiri, N.; Okada, M. Trans. Mater. Res. Soc. Jpn. 2002, 27, 545-550. (6) Hidber, P. C.; Helbig, W.; Kim, E.; Whitesides, G. M. Langmuir 1996, 12, 1375-1380. (7) Hidber, P. C.; Nealey, P. F.; Helbig, W.; Whitesides, G. M. Langmuir 1996, 12, 5209-5215. (8) Geissler, M.; Kind, H.; Schmidt-Winkel, P.; Michel, B.; Delamarche, E. Langmuir 2003, 19, 6283-6296. (9) Kind, H.; Geissler, M.; Schmid, H.; Michel, B.; Kern, K.; Delamarche, E. Langmuir 2000, 16, 6367-6373. (10) Wang, T. C.; Chen, B.; Rubner, M. F.; Cohen, R. E. Langmuir 2001, 17, 6610-6615.
10.1021/la048606e CCC: $27.50 © 2004 American Chemical Society Published on Web 09/30/2004
Selective Electroless Plating on Adsorption Films
are transferred directly on organic and inorganic substrate surfaces. This situation probably arises from the following. First, photopatterned SAMs derived from organosilanes and organothiolates are formed on a specific surface. Consequently, the limitation of substrate choice often prevents us from utilizing the SAMs. SAMs available to various kinds of polymer substrates are more desirable for fabricating printing-wiring circuit boards for flexible flat liquid crystal displays and electroluminescent devices. Second, the photopatterned SAMs are prepared on a substrate surface through a liquid-phase adsorption method with ungreen organic solvents or a chemical vapor adsorption method11,12 with expensive vacuum equipments. Third, the molecules forming the patterned SAMs are more expensive than commonly used chemical reagents. To overcome these drawbacks, inexpensive organic ultrathin films derived from other than organosilanes and organothiolates should be developed, that are compatible with a wider variety of substrates and milder green solvents. We have recently reported a novel method for preparing the template to control the selective surface adsorption of colloidal poly(styrene) particles on silica and poly(ethylene terephthalate) (PET) surfaces.13 In the method, the cyclopentasilane derivative bearing plural pyridinium groups is used as a photodegradable multivalent cationic adsorbate. The cationic adsorbate adsorbed by negatively charged silica and PET surfaces is able to form the singlelayer adsorption film exhibiting desorption-resistance toward deionized water because of multipoint adsorption.14,15 UV-light irradiation causes fragmentation of the photoreactive cyclopentasilane skeleton in the adsorbate molecule. As a result, the UV-exposed adsorbate molecules are readily desorbed from the substrate surface by a simple rinse with deionized water because of a photochemical decrease in adsorption sites per molecule. In this way by photolithography, we can prepare the patterned template surface consisting of the cationic monolayer with a positive zeta-potential value and the bare substrate with a negative zeta-potential value. According to electrostatic attraction and repulsion, positively and negatively charged poly(styrene) spheres are adsorbed selectively on the chargepatterned template surface. The interfacial electronic phenomena motivate us to apply such a charge-patterned substrate surface to adsorption control of colloidal catalysts in nickel-phosphorus (Ni-P) electroless plating as illustrated in Figure 1. Ni-P deposition would take place on a negatively charged substrate surface in a UV-exposed region in the case of positively charged catalysts. In contrast, a positively charged ultrathin film surface in an unexposed region would be plated in the case of catalysts with negative charge. The purpose of this study is to prepare a deposition template for Ni-P electroless plating using four cationic polymer adsorbates of poly(1-alkyl-4-vinylpyridinium halide)s in a convenient and environment-friendly manner. The poly(1-alkyl-4-vinylpyridinium halide)s possessing side-chain alkyl groups, R, of a carbon number, Cn, were abbreviated as a generic name of QP4VP-Cn and are indicated in Figure 2. To begin, we studied the experimental conditions to obtain the single-layer adsorp(11) Tada, H.; Nagayama, H. Langmuir 1994, 10, 1472-1476. (12) Shimoda, T.; Miyashita, S.; Takai, O.; Sugimura, H. Jpn. Kokai Tokkyo Koho 2000, JP2000282240. (13) Nakagawa, M.; Nawa, N.; Seki, T.; Iyoda, T. Langmuir 2003, 19, 8769-8776. (14) Nakagawa, M.; Oh, S.-K.; Ichimura, K. Adv. Mater. 2000, 12, 403-407. (15) Ichimura, K.; Oh, S.-K.; Nakagawa, M. Science 2000, 288, 16241626.
Langmuir, Vol. 20, No. 22, 2004 9845
Figure 1. Schematic illustrations of methods for patterning electroless plating involving (a) the photodegradation of a cationic single-layer adsorption film on a negative silica surface, the site-selective adsorption of catalysts with (b) positive charge and (c) negative charge, and (d) the electroless plating.
Figure 2. Chemical structures of poly(1-alkyl-4-vinylpyridinium halide)s used as cationic polymer adsorbates in this study. QP4VP-Cn is the generic name of the polymer adsorbates, Cn is the alkyl chain length, R is the alkyl group, and X is the halide anion. QP4VP-C1, R ) -CH3, X ) I; QP4VP-C3, R ) -C3H7, X ) Br; QP4VP-C6, R ) -C6H13, X ) Br; QP4VP-C12, R ) -C12H25, X ) Br.
tion film of QP4VP-Cn on a silica plate surface. The formation of the adsorption films and the decomposition by exposure to 172 nm deep-UV light were investigated by zeta-potential and contact angle measurements and UV-visible and deep-UV absorption spectral measurements. During studies on Ni-P electroless deposition on photopatterned QP4VP-Cn films with alkyl groups of different lengths, we obtained some results that led to difficulty in explaining the surface adsorption of SnOx colloidal catalyst precursors based on electrostatic interaction. It was suggested that in addition to the electrostatic interaction, the van der Waals interaction between the hydrophobic long-chain hydrocarbons of the polymer adsorbates and surfactants surrounding the SnOx colloids played a significant role in determining the location selectivity of the Ni-P electroless deposition. Experimental Section Materials. Poly(4-vinylpyridine) (Mw ) 7.0 × 104, Mn ) 3.1 × 104, Mw/Mn ) 2.3) was purchased from Sigma-Aldrich. The synthesis and characterization of poly(1-alkyl-4-vinylpyridinium halide)s, abbreviated as QP4VP-Cn, possessing alkyl groups of a different carbon number (Cn) were described in the Supporting Information. In this Article, QP4VP-C1, QP4VP-C3, QP4VP-C6,
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and QP4VP-C12 represent poly(1-methyl-4-vinylpyridinium iodide), poly(1-propyl-4-vinylpyridinium bromide), poly(1-hexyl4-vinylpyridinium bromide), and poly(1-dodecyl-4-pyridinium bromide), respectively. Deionized water of 18 MΩ cm after purification with a Millipore Mili-Q system was used. Other agents were of reagent grade and were purchased from Kanto Kagaku in Japan. A fused silica substrate (Nippon Rika Glass Co., Ltd.) and a synthetic silica substrate of high quality grade (Asahi Glass Co., Ltd.) were used for UV-visible and deep-UV absorption spectral measurement and zeta-potential measurement. Fabrication and Photopatterning of Single-Layer Adsorption Films. A silica substrate was cleaned by irradiation with 172 nm deep-UV light emitting from a Xe excimer lamp (UER20-172A, Ushio, Inc.) under a reduced pressure of 1000 Pa for 5 min. The cleaned silica substrate was immersed in a 1.0 × 10-2 mol dm-3 solution of QP4VP-Cn at 20 ( 5 °C for 1 h, rinsed with a pure solvent, and dried with N2 gas, to give a silica substrate modified with an adsorption film of QP4VP-Cn. Deionized water was used as a solvent for QP4VP-C1 and QP4VPC3, and ethanol was used as a solvent for QP4VP-C6 and QP4VPC12. A copper photomask with 100 µm holes (200A, Okenshoji Co., Ltd.) was placed on the silica substrate adsorbing QP4VPCn. The silica substrate was irradiated with 172 nm deep-UV light for 5 min through the photomask and rinsed with deionized water thoroughly. Nickel-Phosphorus Electroless Plating. Catalyzation of a photopatterned adsorption film on a silica plate was carried out through two steps of sensitization and activation. In the sensitization step, three kinds of sensitization solutions A-C were used: the sensitization solution A containing no surfactant, the sensitization solution B containing 1.31 mmol dm-3 cetyltrimethylammonium chloride (CTAC) as cationic surfactant, and the sensitization solution C containing 17.3 mmol dm-3 sodium dodecyl sulfate (SDS) as anionic surfactant. SnCl2 (0.50 g) and 1 mol dm-3 HCl (0.2 mL) were dissolved in deionized water (100 mL). The aqueous solution was kept standing for 5 days to form SnOx colloids from SnCl2. The colloidal solution was used as the sensitization solution A. To the solution A was added the cationic surfactant CTAC or the anionic surfactant SDS to prepare the sensitization solution B or C. These sensitization solutions were used after ultrasonic agitation for 10 min, and the diameter and zeta-potential value of the colloidal materials in the solutions were monitored with an electrophoretic light scattering spectrometer prior to use. PdCl2 (0.030 g) and concentrated HCl (0.1 mL) were dissolved in deionized water (300 mL) to give an activation solution of pH 3.0, which was used in the activation step. First, a photopatterned adsorption film of QP4VP-Cn on a silica substrate was dipped in one of the sensitization solutions A-C for 3 min and washed with deionized water thoroughly. Subsequently, the silica substrate was dipped in the activation solution for 3 min and washed with deionized water. Finally, the silica plate was immersed in the nickel-phosphorus electroless plating bath containing Ni(H2PO2)2 (0.15 g dm-3), H3BO3 (0.12 g dm-3), CH3COOH (0.025 g dm-3), and (NH4)2SO4 (0.013 g dm-3) whose pH value adjusted to 5.5 by adding a dilute NaOH aqueous solution. After the plating, the silica substrate was rinsed with deionized water and dried by N2 gas blowing, to prepare a Niplated silica substrate. Physical Measurement. UV-visible absorption spectra were taken on a weak absorption spectrophotometer (MAC-1, JASCO). Deep-UV absorption spectra were taken on an absorption spectrophotometer (KV-201, Bunkoh-Keiki Co., Ltd. in Japan). Atomic force microscope images in a tapping mode were taken on an atomic force microscope (SPM-9500 J2, Shimadzu Co., Ltd.). Sessile contact angles were measured using a contact angle meter (CA-X, Kyowa Interface Science Co., Ltd.). Zeta-potential values of colloidal materials formed from SnCl2 and surfacemodified silica substrates were measured at 25 ( 1 °C with an electrophoretic light scattering spectrophotometer (ELS-8000, Otsuka Electronics Co., Ltd.). pH values in the zeta-potential measurement were recorded on a pH meter (B-212, Horiba, Ltd.). The detailed procedures of the zeta-potential measurements were described in our previous report.13 Optical microscope images were observed with an Olympus BX60 microscope and captured
Nakagawa et al. by an Olympus DP70 CCD camera. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was carried out using a Shimadzu ICPS-8100. Twenty silica substrates after treatment with the sensitization solution and the activation solution were immersed in nitrohydrochloric acid to dissolve heavy metal species. The amounts of adsorbed elements Sn and Pd were determined by ICP-AES and expressed in mol cm-2 unit. Oxidation states of adsorbed Pd species were characterized by X-ray photoelectron spectroscopy (XPS; ESCA3400, Shimadzu) using Mg Ka radiation. Binding energy scales were referenced to 285.0 eV, as was determined by the location of a maximum peak on the C(1s) spectra of the hydrocarbon.
Results and Discussion Fabrication of QP4VP-Cn Single-Layer Adsorption Films on a Silica Surface. Cationic polymers are adsorbed by negatively charged solid surfaces in a solution, to form an irreversible adsorption layer on the solid surface.16 From zeta-potential17,18 and surface forces19 measurements and IR-visible sum frequency spectroscopy20 and atomic force microscopy,21 it is verified that an adsorption manner of the charged polymers is varied with adsorbate concentration, pH, and ionic strength in a solution.14 For example, a pH value of the solutions influences the adsorption manner of polymers, because the charge density of a solid adsorbent surface is changed.18 In this study, we noticed four poly(1-alkyl-4-vinylpyridinium halide)s, QP4VP-Cn, as cationic polymer adsorbates. The reasons arise from the following. The QP4VPCn polymers are inexpensive and soluble in environmentfriendly water/alcohol media. The length of the side-chain alkyl group is readily tunable by the quaternization reactions of poly(4-vinylpyridine) with the corresponding alkyl halides, when the QP4VP-Cn adsorbates were compared to photodegradable cationic adsorbates we studied previously.13,22 In addition, to our knowledge, there is no systematic study on the effect of the side-chain length on interfacial electronic phenomena. The single-layer adsorption films of QP4VP-Cn have been never utilized as deposition templates in electroless plating. There are several reports on the adsorption behaviors and manners of partially quaternized poly(4-vinylpyridine)s affected by quaternization degrees.23-26 First, we investigated how to prepare reproducibly a single-layer adsorption film of poly(1-dodecyl-4-vinylpyridinium bromide), QP4VP-C12, on a silica plate by using contact angle, zeta-potential, and UV-visible spectral measurements. Various types of adsorption films were prepared from QP4VP-C12 by immersing once a cleaned silica plate in ethanol solutions with a different QP4VP-C12 concentration of 10-4-10-1 mol dm-3 at 20 ( 2 °C for 1 h, followed by multiple rinses with pure ethanol. Part a of Figure 3 shows the sessile contact angle (16) von Klitzing, R.; Tieke, B. Adv. Polym. Sci. 2004, 165, 177-210. (17) Schwarz, S.; Eichhorn, K.-J.; Wischerhoff, E.; Laschewsky, A. Colloids Surf., A 1999, 159, 491-501. (18) McNamee, C. E.; Matsumoto, M.; Hartley, P. G.; Mulvaney, P.; Tsujii, Y.; Nakahara, M. Langmuir 2001, 17, 6220-6227. (19) Kurihara, K.; Kunitake, T.; Higashi, N.; Niwa, M. Langmuir 1992, 8, 2087-2089. (20) Kim, J.; Kim, G.; Cremer, P. S. J. Am. Chem. Soc. 2002, 124, 8751-8756. (21) Rojas, O. J.; Ernstsson, M.; Neuman, R. D.; Claesson, P. M. Langmuir 2002, 18, 1604-1612. (22) Nakagawa, M.; Ichimura, K. Jpn. Kokai Tokkyo Koho 2003, JP2003133696. (23) Sukhishvili, S. A.; Granick, S. J. Chem. Phys. 1998, 109, 68616868. (24) Sukhishvili, S. A.; Dhinojwala, A.; Granick, S. Langmuir 1999, 15, 8474-8482. (25) Schmitz, K. S. Macromolecules 2000, 33, 2284-2285. (26) Ruths, M.; Sukhishvili, S. A.; Granick, S. J. Phys. Chem. B 2001, 105, 6202-6210.
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Langmuir, Vol. 20, No. 22, 2004 9847 Table 1. Contact Angles for Water and Zeta-Potential Values in a 10 mmol dm-3 NaCl Aqueous Solution at pH 7.0 Observed for Single-Layer Adsorption Films of QP4VP-Cn
probed substrate
adsorption film of QP4VP-Cn 1 3 6 12
bare silica plate
contact angle for 19 ( 3 23 ( 1 45 ( 2 75 ( 3
