A method for copper deposition on glass and ceramics was investigated by direct plating on 20-30 nm thick copper inclusive titanium oxide films formed on the substrate surface. The copper inclusive titanium oxide film functioned as an adhesion layer and as a catalyst for autocatalytic copper deposition. Copper inclusive titanium oxide films were formed by pyrolysis of solution deposited 1-hydroxy phenyl ketone titanium-copper complex films. After deposition of electroless copper seed layers, 15-20 μm thick electrolytic copper films were formed, where upon thermal treatment up to 0.5 kN/m adhesion strength was attained on borosilicate glass. This process enabled electroless copper plating without the use of palladium as a catalyst on non-roughened smooth glass or ceramic substrate surfaces. The copper-titanium oxide adhesion layers were characterized and cross-sectional transmission electron microscopy illustrated the adhesion mechanism and catalyst structure. Despite poor thermal conductivity, due to properties such as transparency, smooth surface, chemical and thermal stability, coefficient of thermal resistance, dielectric constant, electrical insulation and physical strength, glass has gained attention an electronic substrate material.1-3 Two examples are in 2.5 D/3 D electronic device and RF module packaging. [4][5][6][7] In addition to these properties, abundance and availability in a wide range of shape and size make glass an attractive economic substitute for silicon in interposers. [4][5][6][7] Development of through substrate interconnect via hole formation technology for glass has progressed however, metallization technology relies on vacuum deposition, the silver mirror reaction or surface roughening followed by electroless plating for conductive seed layer formation. [8][9][10][11] Using sputtered Cu, Ti/Cu or Cr base layers, relatively high adhesion strength has been attained.12-14 However, dry processes have productivity limiting disadvantages such as size restriction, need for expensive equipment and high running cost. Therefore, economic wet methods have been studied as an alternative. In direct electroless plating methods, adhesion between the glass and the plated films has been accomplished by etching the glass surface with hydrofluoric acid, but with the sacrifice of its original transparency and smoothness. [15][16] Furthermore, employment of expensive palladium catalyst also introduces the need for a palladium removal procedure in order to prevent migration and short circuits that lead to poor device reliability. [17][18][19] Solution processed adhesion layers for direct electroless plating on glass have been demonstrated where a few tens of nanometer thick Pd-NiO, 20 Pd grafted TiO 2 , 21 or Pd-SnO 2 22 films served as catalytic anchor layers. Based on those results, the method outlined in Figure 1 for direct electroless copper plating on the substrate was investigated, where the catalytic anchor layer consisting of copper and titanium oxides was formed by pyrolysis of a metal complex film ...

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A procedure for formation of catalytic SiO 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-TiO 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 TiO layers on glass resulted in formation of a smooth Ti/Cu 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 Ti and Cu oxides to the glass and Ti oxide to the Cu plating that was formed upon annealing the Cu filled TiO 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.

Introduction  Glass has characteristics such as transparency, smooth surface, chemical and thermal stability, coefficient of thermal resistance similar to silicon, high dielectric constant, electrical insulation and physical strength, deaming it an attractive substrate material for electronic devices. Examples of application are 2.5D/3D electronic device and RF module packaging. Glass can be metallized electroless plating however, problems remain, the most predominant being inadequate adhesion between glass and plated films. Using a catalytic Ti-Cu oxide adhesive layer formed on the glass, adhesion strength of 0.5 kN/m has been obtained1 ) In this study, circuit formation by semi-additive process that’s often used in the formation of fine circuit and the influence of the Ti-Cu oxide layer on post-treatment steps was investigated. Experimental 　Schott Co., Ltd. Tempax 50 mm × 50mm × t 0.7 mm was used as the test substrate. Circuit formation by the semi-additive process is shown in figure 1. After the circuit formation, the removal of the Ti-Cu oxide layer was accomplished by immersion in an aqueous sodium hydroxide 100 g/dm3, trisodium citrate 5 g/dm3 solution at 80 ℃ for 10 min. Electroless NiP plating was performed as a post-process to evaluate the effectiveness of the Ti-Cu oxide layer removal method. Results and Discussion  Circuits of L / S = 50/50~200/200 µm and t=10 µm dimension were formed using the semi-additive process where adhesion after circuit formation was maintained. After the circuit formation, average roughness (Ra) was observed by atomic force microscopy (AFM) and elemental analysis was performed by X-ray photoelectron spectroscopy (XPS). The Ra was 6.4 nm and 14.9 %Ti was detacted prior to removal and when performing electroless NiP plating as the post-treatment, abnormal deposition occurs between the wiring patterns. On the other hand, after performing Ti-Cu oxide layer removal treatment, the Ra was 0.5 nm and 0.3%Ti detected. Abnormal deposition of electroless nickel does not occur, therefore it was possible to deposit the electroless plating selectively on the copper circuit. Conclusions 　L / S = 50/50 ~ 200/200 um circuits formed on a smooth glass substrate was possible.The adhesion layer of Ti-Cu oxide can be removed by an alkaline solution. By performing the Ti-Cu oxide layer removal process, abnormal deposition of electroless nickel plating in a post-treatment step can be prevented.   Acknowledgments  This work was funded in part by the “MEXT-supported Program for the Strategic Research Foundation at Private Universities” and the “Tokyo Ohka Foundation for the promotion of Science and Technology.”   References  1)K. Okabe, T. Kagami, Y. Horiuchi, O. Takai, H. Honma, and C. E. J. Cordonier, “Copper Plating on Glass Using a Solution Processed Copper-Titanium Oxide Catalytic Adhesion Layer”, Journal of The Electrochemical Society, Vol.163, No.6, p. D201-D205, (2016) Figure 1

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