Fabrication of Cu-Ag Film By Electrodeposition in Ammonia-Based Electrolyte
Authors: Jeon Youngkeun , Kim Myung Jun , Choe Seunghoe , Kim Hoe Chul , Kim Jae Jeong 
Published: February 2020

Copper (Cu) has been utilized as a conductor transferring electrical signal in various electronic devices due to its excellent electrical conductivity. However, Cu is mechanically weak material and vulnerable to corrosion and oxidation. The formation of Cu-based bimetallic material such as Cu-Ag, Cu-Ti, Cu-Sn, Cu-Mg could be a potential way to obtain both high mechanical strength and resistance against the oxidation.[1,2] However, the electrical resistivity of Cu-based bimetallic material is higher than that of pure Cu because of addition of the secondary metal, which is a drawback of Cu-based bimetallic material. It was reported that silver (Ag) among various secondary materials can particularly minimize this drawback of the increase in the resistivity and Cu-Ag can improve mechanical strength and chemical resistance, compared to pure Cu.[2-4] Therefore, it is expected that Cu-Ag could realize high speed conductor with superior mechanical strength and oxidation resistance.
Cu-Ag film can be simply fabricated by electro-deposition. The characteristics of electrodeposition are strongly determined by the electrolyte, therefore, finding the appropriate electrolyte for Cu-Ag electrodeposition is the most important to obtain uniform and superior Cu-Ag thin films. Among various electrolytes, ammonia-based electrolyte can be the most appropriate electrolyte because the ammonia can easily form the complex with Cu and Ag ions, which enables the electrolyte to have high stability. Also, it is much environmental-friendly as compared to the cyanide-based electrolyte.
We introduced ammonia-based electrolyte for electrodeposition of Cu-Ag to obtain Cu-Ag films having superior mechanical property and oxidation resistance as well as good electrical property. Electrochemical behavior of copper and silver ions in ammonia-based electrolyte was investigated by electrochemical analysis. The potential where Cu and Ag are simultaneously deposited was determined on the basis of the result of electrochemical analysis. the Optimum deposition potential was selected in terms of electrical resistivity of Cu-Ag films. The atomic concentration of Ag in Cu-Ag films was successfully controlled by varying the concentration of Ag source in the electrolyte. The increase in Ag content led to the increment in electrical resistivity. But after annealing, the electrical resistivity of Cu-Ag films was decreased. Also as the atomic concentration of Ag in Cu-Ag films increased, Cu-Ag films had better oxidation resistance and hardness. In this research, we obtained the Cu-Ag film with enhanced hardness and resistance against oxidation and comparable electrical resistivity after annealing, as compared to those of pure Cu film.
References
[1] K. Maki, Y. Ito, H. Matsunaga, H. Mori, Scripta Mater., 68, 777 (2013).
[2] M. J. Kim, H. J. Lee, S. H. Yong, O. J. Kwon, S. K. Kim, J. J. Kim, J. Electrochem. Soc., 159, D253 (2012).
[3] M. J. Kim, K. J. Park, T. Lim, O. J. Kwon, J. J. Kim, J. Electrochem. Soc., 160, D3126 (2013).
[4] S. Strehle, J.W. Bartha, K. Wetzig, Thin solid films, 517, 3320 (2009).