Article Cite This: Langmuir XXXX, XXX, XXX−XXX
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Formation of Micrometer Scale Metal Structures on Glass by Selective Electroless Plating on Photopatterned Titanium and Copper Containing Films Christopher E. J. Cordonier,*,†,‡ Kyohei Okabe,†,‡ Yoshio Horiuchi,† Akimasa Nakamura,§ Kaoru Ishikawa,§ Shozo Seino,‡ Shinsuke Takagi,‡ and Hideo Honma† †
Materials & Surface Engineering Research Institute, Kanto Gakuin University, 1162-2 Ogikubo, Odawara, Kanagawa 250-0042 Japan JCU Co., 2-4-3 Kurigi, Asao, Kawasaki, Kanagawa 215-0033 Japan § Tokyo Ohka Kogyo Co. Ltd., 1590 Tabata, Samukawa-machi, Koza-gun, Kanagawa 253-0114 Japan ‡
S Supporting Information *
ABSTRACT: A procedure for formation of catalytic SiO2 substrate adhesive layer patterns and selective electrochemical metal deposition on the catalyst images was investigated. A photoreactive solution containing a diazonaphthoquinone sulfonate ester and Ti and Cu complexes was developed to deposit Cu catalyst−TiO2 adhesive layer latent images on glass. Sub-micrometer/micrometer scale positive tone photoactive TiCu complex film patterns were formed using a conventional photolithography technique. The Cu ions in 40− 50 nm thick Ti and Cu oxide layers formed by pyrolysis of the TiCu complex films were reduced, residual Cu displaced with Pd then the porous Ti oxide structure filled and plated with Cu by selective electroless then electrolytic plating. Annealing the Cu plating filled TiO2 layers on glass resulted in formation of a smooth Ti3+/Cu1+ oxide interface that enabled formation of 20 μm thick Cu deposits on glass substrate with up to 1 kN/m adhesion strength. The adhesion strength was attributed to chemical bonding of Ti3+ and Cu1+ oxides to the glass and Ti4+ oxide to the Cu plating that was formed upon annealing the Cu filled TiO2 interlayer. Furthermore, a dip coating procedure was adapted that allowed copper film deposition on the entire surface of a 300 μm thick glass substrate with 50 μm in diameter holes enabling formation of electrically conductive through glass substrate interconnects.
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metal deposition on glass and ceramic substrates5−8 and glass/ ceramic-metal hermetic seals.9−11 Photopatterning of 2-nitrobenzyl 3,4-dihydroxybenzoate metal complex (NBOC-M) films by photoinduced ester cleavage resulting in carboxylic acid generation has been demonstrated. Selective alteration of irradiated film solubility in dilute alkaline solution enabled patterning of the complex films. The nitrobenzyl ester moiety bearing metal complexes could potentially be patterned with high resolution since a photoacid generating ligand is chelated to each metal atom.12 Conventionally, diazonaphthoquinone sulfonate ester (DNQ) compounds have been applied as photoacid generators in positive tone photoresists,13,14 where DNQ compounds function analogously to the 2-nitrobenzyl 3,4-dihydroxybenzoate compounds. However, despite optimization, the nitrobenzyl ester photoresponses have been low compared to DNQ based compositions, and atomic level resolution surpasses the resolution limits of industrial photolithography equipment.
INTRODUCTION Functional metal and metal oxide films find diverse application in various amenities that enrich our lifestyle. Examples of functional materials are transparent conducting oxides, piezoelectric oxides, chemically catalytic metals and metal oxides, ferroelectric ceramics, photocatalytic materials, and materials used as electrochemical sensors. Devices may range from electronic, optical, medical, and not yet imagined applications. Development of patterned metal/metal oxide film formation techniques provides advantageous alternatives to device fabrication. Influence on the film material characteristics from the formation technique may allow for improved efficiency, densification, miniaturization, economic benefits, enhanced function, added function, or creation of not yet producible devices. Two examples have been the development of glass substrates for economic electronic device packaging (e.g., logic, memory, MEMS, sensor and RF devices)1,2 and development of economical fine mesh structured metal films as a transparent electrode material with improved conductivity compared to the commonly used tin doped indium oxide.3,4 In both examples, development of fabrication techniques has led to progress in the realization of their respective applications. Metal oxide layers have also served as adhesion layers for electrochemical © XXXX American Chemical Society
Received: September 22, 2017 Revised: November 18, 2017 Published: November 28, 2017 A
DOI: 10.1021/acs.langmuir.7b03329 Langmuir XXXX, XXX, XXX−XXX
Article
Langmuir Scheme 1. Outline of the Electroless Copper Pattern Formation Procedure
the glass substrate was not detected. This technique had enabled adhesion of copper plating almost directly on the glass substrate and is expected be compatible with the photopatterning technique. Had dip-coating been applied, this technique should also prove effective for plating on substrates with complex surfaces like through glass via holes (TGV) for formation of through substrate interconnects. Metallization of TGV substrates is one of the fundamental processes in development of glass substrate electronic device packaging.1,2 Furthermore, this plating method could be considered economic, as electroless copper plating could be accomplished without palladium.8 Therefore, photoreactive titanium and copper complex solutions were investigated for deposition of metallic patterns with high adhesion to glass surfaces. Solutions of titanium and copper complexes and DNQ ester were investigated as a means for photopatterning the catalytic TiO2 adhesive layer precursor with conventional photolithography apparatus according to the procedure outlined in Scheme 1 for direct metal pattern deposition. The photoreactive metal complex solutions were designed for photoinduced film solubility contrast using dilute aqueous alkaline solution as the developer. Photopatterned titanium oxide or copper oxide film formation from the respective NBOC-Ti12 or NBOC-Cu19 films has been demonstrated. To create an analogous system to the NBOC-M compounds, the combination of a 3,4-dihydroxybenzoate ester ligand and a DNQ ester was investigated. A DNQ ester of moderate solubility in coating solution solvents, low solubility in alkaline developer solution, high solubility in the developer solution after the 3indenecarboxylic acid generation by photoinduced Wolff rearrangement, and similar in structure to the 3,4-dihydroxybenzoate ester ligand was designed and synthesized. Photopatterning of films formed from optimized solutions, selective electroless copper plating, and plating adhesion were evaluated. For optimal selectivity, a nickel inclusive electroless copper bath containing tartrate as the complexing agent was investigated that is conducive to uniform deposition. To accommodate the lower reactivity toward catalytic Cu, exchange with Pd was performed. UV−vis analysis of component combinations was performed to verify the interactions between the constituents of the solutions used to form photoreactive metal complex films and the influences on the photoreaction. The plated metal− glass adhesion mechanism was considered based on Cu deposit/TiO2−Cu layer/glass substrate laminate characterization and analysis using scanning electron microscopy (SEM), STEM and X-ray photoelectron spectroscopy (XPS). An analogous NBOC-TiCu solution was also compared. In addition to development of a technique for direct submicrometer scale metal pattern deposition, an unprecedented level of copper plating adhesion to glass was realized, where smooth interfaces were maintained, and plated metal was not diffused into the glass surface. Since the prior reports, the mechanisms involved in the manifestation of the adhesion and functions of each thermal treatment in the process were clarified.8,15 The same level of copper film adhesion was
Among the investigated NBOC-M complexes, selective electroless plating on titanium oxide,15 niobium oxide,16 palladium and palladium composite films17 derived by pyrolysis of the respective patterned complex film has been accomplished. Patterned titanium oxide and niobium oxide films have been shown to selectively adsorb palladium catalyst, which initiated the autocatalytic deposition reaction resulting in direct formation of electroless plated metal patterns on a substrate surface. The titanium oxide or niobium oxide films had also been shown to function as an adhesion layer for the plated metal to the substrate. In another example, direct photopatterning of a 6-nitroveratryl 3,4-dihydroxybenzoate palladium complex film had enabled direct electroless plating on the substrate. For plating on glass, nickel inclusion in the photoreactive palladium complex film had been demonstrated to improve adhesion by formation of a nickel oxide anchor layer for the plated film as well as thermal formation of a ca. 10 nm deep nickel-glass intermetallic layer in the substrate surface had been observed.17 Among the direct pattern plating methods reported, adhesion has been evaluated by adhesive tape test or crosscut test and in most cases only on the thin (
