Electrodeposition of Cu-Ag Alloy Thin Films Directly on W Diffusion Barrier By Controlling Complexing Agents and Organic Additives

Cu as an excellent electrical conductor has been used for interconnect in Si-based microelectronic devices. Recently Cu alloys instead of Cu have emerged as interconnect material for future microelectronic device fabrication because higher adhesion strength to foreign materials, larger resistance to electromigration, and improved electrical conductivity are required in very narrow interconnect lines. It is known that Cu-Ag alloy among Cu alloys has beneficial properties such as higher electrical conductivity, better formability, higher mechanical strength, and better resistance to electromigration than pure Cu.

In this research, we investigate the effect of electrodeposition parameters on the nucleation and growth of Cu-Ag alloy nano-nuclei and the formation of thin, smooth Cu-Ag alloy thin film. Cu-Ag alloys are electrodeposited directly on W diffusion barrier without employing a Cu seed layer. Area density, size, and morphology of Cu-Ag alloy nano-nuclei influence the microstructure, surface roughness, and thickness of Cu-Ag alloy thin film formed on the W diffusion barrier.

Sophisticated control of chemical equilibrium of electrolyte is carried out by managing the concentration and type of complexing agent and organic additives. Chelation behavior of Cu and Ag with complexing agent is also studied according to pH of electrolyte. Reduction rate and chemical composition of electrodeposited Cu-Ag alloy are controlled under diffusion-controlled deposition conditions.