[en] The uniformity of Cu growth on Pd nanocatalysts was controlled by using organic additives in the formation of electroless Cu seed layers. Polyethylene glycol (PEG, Mw. 8000) not only reduced the deposition rate but also improved the uniformity of Cu growth on each Pd nanocatalyst during the seed layer formation. The stronger suppression effect of PEG on Cu than on Pd reduced the difference in the deposition rate between the two surfaces, resulting in the uniform deposition. Meanwhile, bis(3-sulfopropyl) disulfide degraded the uniformity by strong and nonselective suppression. The sheet resistance measurement and atomic force microscopy imaging revealed that the uniform Cu growth by PEG was more advantageous for the formation of a thin and smooth Cu seed layer than the non-uniform growth. The uniform Cu growth also had a positive influence on the subsequent Cu electrodeposition: the 60-nm-thick electrodeposited Cu film on the Cu seed layer showed low resistivity (2.70 μΩ·cm), low surface roughness (6.98 nm), and good adhesion strength. - Highlights: • Uniform Cu growth on Pd was achieved in formation of electroless Cu seed layer. • PEG addition to electroless bath improved the uniformity of Cu growth on Pd. • A thin, smooth and continuous Cu seed layer was obtained with PEG. • Adhesion strength of the Cu seed layer was also improved with PEG. • The uniformity improvement positively affected subsequent Cu electrodeposition

[en] Additives having azole groups with different numbers of nitrogen atoms, such as indole, benzimidazole, indazole, benzotriazole (BTA), and 1H-benzotriazole-methanol (BTA-MeOH) were adopted to improve the mechanical hardness of electrodeposited Cu films. The effects of these additives on the film properties were elucidated in relation to their number of nitrogen atoms. Electrochemical current–potential behaviors showed that the additives containing three nitrogen atoms (BTA and BTA-MeOH) more effectively inhibited Cu electrodeposition. The inhibition strongly affected the film properties, resulting in reduced grain size and surface roughness, and increased resistivity and hardness. Cu films deposited with BTA or BTA-MeOH also exhibited 35% reduced grain size and 1.5-time higher hardness than Cu films deposited in electrolyte containing other BTA-derivatives having fewer nitrogen atoms. This notable grain refining effect of BTA and BTA-MeOH can be evaluated with respect to the strong interaction of their nitrogen atoms with the substrate and the copper ions, as well. - Highlights: • Additives of similar structure containing 1, 2, and 3 nitrogen atoms were used. • Additives with 3 nitrogen atoms more strongly inhibited Cu deposition than others. • Additives containing 3 nitrogen atoms efficiently affected film properties. • Additives having 3 nitrogen atoms remarkably improved film hardness

[en] Electrodeposition of Cu-based alloys has been researched for a variety of applications due to Cu-based alloys having superior properties compared to pure Cu, including higher chemical resistance, mechanical hardness, and electrocatalytic activity. Cu-Ag is the most electrically conductive among Cu-based alloys, and it has higher mechanical hardness and oxidation resistance compared to pure Cu. Cu-Ag co-deposition in cyanide-based electrolytes has been previously reported; however, the toxicity of cyanide limited its use. In this study, we introduce an ammonium hydroxide-based electrolyte for Cu-Ag electrodeposition and the properties of Cu-Ag films deposited in this electrolyte. Electrochemical measurements were performed to determine the potential range for co-electrodeposition of Cu and Ag, and the effect of nitrate reduction on the film deposition was examined. The effects of deposition potential and concentration of Ag ions in the electrolytes on the electrical resistivity and Ag contents of the films were investigated. The modulation of Ag ion concentration was found to be a more effective way to control Ag contents in the deposited films. Co-deposition of 4 at% Ag with Cu in the ammonium-hydroxide electrolyte markedly improved mechanical hardness and oxidation resistance compared to a pure Cu film without severe deterioration of electrical conductivity.

[en] Highlights: • The choline-based leveler having two quaternary ammoniums was synthesized. • The adsorption of this leveler with suppressor and accelerator was examined. • Galvanostatic Cu bottom-up filling was achieved with three-additive system. • The mechanism of gap-filling was elucidated based on the additive adsorption. - Abstract: Through Silicon Via (TSV) technology is essential to accomplish 3-dimensional packaging of electronics. Hence, more reliable and faster TSV filling by Cu electrodeposition is required. Our approach to improve Cu gap-filling in TSV is based on the development of new organic additives for feature filling. Here, we introduce our achievements from the synthesis of choline-based leveler to the feature filling using a synthesized leveler. The choline-based leveler, which includes two quaternary ammoniums at both ends of the molecule, is synthesized from glutaric acid. The characteristics of the choline-based additive are examined by the electrochemical analyses, and it is confirmed that the choline-based leveler shows a convection dependent adsorption behavior, which is essential for leveling. The interactions between the polymeric suppressor, accelerator, and the choline-based leveler are also investigated by changing the convection condition. Using the combination of suppressor, accelerator, and the choline-based leveler, the extreme bottom-up filling of Cu at trenches with dimensions similar to TSV are fulfilled. The mechanism of Cu gap-filling is demonstrated based on the results of electrochemical analyses and feature filling

[en] Highlights: • CuAg foils are electrodeposited using a combination of organic additives. • CuAg foils of 40 µm thickness comprising ~14 nm-sized grains are obtained. • As-deposited CuAg foil has high strength and conductivity, and moderate ductility. • Mild annealing at 100 °C increases the strength as well as the conductivity. • These improvements are due to stabilization of the grain boundary with annealing. -- Abstract: In this study, we fabricated nanocrystalline CuAg foils with a thickness of 40 µm using an electrodeposition method, and evaluated its structure and properties. Using an appropriate combination of organic additives and a continuous Ag⁺ supply system, compact and bright nanocrystalline CuAg foils were obtained. The as-deposited CuAg foil consisted of supersaturated CuAg crystals with a mean diameter of ~13 nm, and exhibited high ultimate tensile strength (993 MPa), high electrical conductivity (66.7% IACS), and moderate ductility. With mild annealing at 100 °C, both the strength and the conductivity were improved further (1043 MPa and 68% IACS, respectively), achieving properties comparable to those of the state-of-the-art deformed CuAg of greater thicknesses. Upon annealing at ~200 °C, Ag atoms that segregated at the grain boundary began to precipitate and grow, thereby destabilizing the Cu nanograins. This resulted in grain growth, decreased strength, and increased conductivity.