The mechanism of copper deposition by direct plating on a nonconductive substrate has been investigated. Studies using electron spectroscopic chemical analysis show that the immersion of a sodium sulfide solution does lead to the formation of palladium sulfide. Sulfide acts as a bridging ligand; it can increase the speed of direct plating dramatically. Compounds with similar bridging property were later found to show the same promotion effect in the direct plating process. These compounds include thiourea, sodium thiocyanate, potassium iodide, and sodium cyanide. It was also found that the addition of these compounds could cause a shift of the rest potential. In addition, copper was found to partially dissolve if the current was interrupted. These phenomena can all be explained by the proposed mechanism.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-15 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35 Downloaded on 2015-03-15 to IP
Poly͑N-vinyl-2-pyrrollidone͒ ͑PVP͒ has been widely used as a stabilizer to synthesize various kinds of nanoparticles. However, the effect of PVP and its role in the formation process of Ag/Pd nanoparticles are not well understood. In our PVP-protected Ag/Pd nanoparticles system, Ag + ions have higher priority to be reduced in the formation process of Ag/Pd nanoparticles. The presence of PVP hinders both Pd 2+ and Ag + ions. However, the steric obstacle effect of PVP is more pronounced for Pd 2+ ions and thus Pd 2+ ions are more difficult to diffuse through the polymeric barrier in the particle growth stage. Accordingly, Pd 2+ ions deposit onto the preformed nuclei later than Ag + ions rendering the palladium-rich surface structure of Ag/Pd nanoparticles. Moreover, the steric barrier of PVP is less effective with increasing molecular weight, possibly owing to the decreasing molecular numbers. The feasibility of Ag/Pd nanoparticles as activators for electroless copper deposition was also carried out. The crystalline structure of electroless Cu film was not affected by the manner of activation. Furthermore, the Ag/Pd ͑3/7͒ nanoparticles had the shortest induction period and thus exhibited the highest activity, which demonstrated their potential to be novel activators for electroless deposition.
Poly(N-vinyl-2-pyrrolidone) ͑PVP͒ stabilized Ag/Pd nanoparticles have been successfully synthesized at various molar ratios. The transmission electron microscopy images show the diameters of Ag/Pd nanoparticles decrease with increasing Pd molar ratios. Data from UV-vis absorption spectroscopy, X-ray diffraction and energy-dispersive X-ray analysis ͑EDX͒ all confirm the formation of a bimetallic structure. Additionally, the EDX shows that the average composition of the bimetallic nanoparticle is approximately equal to the feeding solution while the X-ray photoelectron spectroscopy reveals the surface is palladium-rich, which implies an inhomogeneous alloy structure. The Ag/Pd ͑3/7͒ nanoparticles have the highest deposited amount of copper owing to its larger surface area even though their specific activity is less than palladium nanoparticles. Furthermore, the effect of the molecular weight of the protective agent was also studied. Higher molecular weight will result in a greater thickness of the protective layer and therefore decrease the specific activity (PVP-8000 Ag/Pd (3/7) Ͼ PVP-29000 Ag/Pd(3/7) Ͼ PVP-58000 Ag/Pd(3/7)). A preliminary test has demonstrated that copper can be successfully deposited and filled in 0.25 m pattern wafer. Accordingly, the Ag/Pd nanparticles show promising application as a novel activator for electroless copper deposition.Nanoparticles possess unique physical and chemical properties different from bulk material due to the drastic reduction of particle size. In addition, the alloy structure usually exhibits a tailored structure and high activity. 1 They have many potential applications as magnetic materials, 2 surface plasma band energies, 3 and catalytic properties. 4 Therefore, we applied the alloy nanoparticles to investigate the catalytic property of the electroless copper deposition.Electroless copper deposition has been widely employed in processes like plating-through-hole ͑PTH͒ in the printed circuit board ͑PCBs͒ industry and copper interconnection for electronic devices. 5 Electroless metal deposition in theory should cover all chemical processes for metal deposition except the conventional electrodeposition. In practice, it refers to only the process of autocatalytic electroless deposition that involves metal reduction by a chemical reducing agent on a catalytic surface.The electroless copper deposition process comprises a series of procedures, and the most critical one is the activation step. In the activation step, the colloidal activator will adsorb onto the insulating substrate and initiate the subsequent electroless copper plating. The most widely used activator is Pd/Sn colloid. 6 This colloid is stabilized by a layer of Sn͑II͒ and its counterions. However, the stabilizing layer of Sn͑II͒, which prevented the nanoparticles from agglomeration, is easily oxidized by oxygen dissolved in the solution rendering precipitation of the activator colloid. 7 The instability of the Sn/Pd colloid causes a cost problem in industry. Accordingly, it is necessary to replace the Sn͑II͒...
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