Effects of Ag Addition on the Resistivity, Texture and Surface Morphology of Cu Metallization

Abstract

Doping Cu with some elements has been proved to be a promising method to improve the reliability of Cu interconnects. In this paper, Ag was chosen as the alloying element because of its low bulk resistivity and low solubility in Cu. Cu–Ag alloy film was prepared by layered evaporation and postdeposition annealing in vacuum. The resistivity of the films decreased with annealing temperature. After annealing at 400°C, most of the Ag atoms were segregated to the film surface because Cu–Ag system had a negative segregation energy. By comparing the texture evolution of pure Cu film and Cu–Ag films during annealing, it was found that Ag addition usually retarded the texture development of the alloy film. Vacuum annealing resulted in a rougher surface for the Cu–Ag films. The investigation of alloying effect on Cu agglomeration on TaN substrate suggested that Ag addition might impair the Cu wettability on TaN substrate. Possible methods for improving the surface morphology of Cu alloy were also proposed.

The effect of chromium dopant on the microstructure and mechanical properties of sputter-deposited copper films

“…First, contrary to the results in Ref. [4], some studies reveal that the additive of Ag or Sn impairs the thermal stability of Cu films due to the decrease of the melting temperature [13,14]. Besides, the reported resistivities of Cu alloy films vary from each another [15].…”

Facile Formation of Cu-Ag Film by Electrodeposition for the Oxidation-Resistive Metal Interconnect

“…When the annealing temperature was 350 • C, the main path for Ag diffusion was not through the Cu grains, but along the grain boundaries of Cu. 10 Therefore, the reduction of surface roughness was related to the Ag atoms when they filled up the grooves between the Cu grains during the annealing. In the AFM line profiling results (not shown here), the average depth between the grains after the annealing was reduced, even though it was increased in the case of pure Cu.…”

“…Especially, Cu films having a small amount of solute atoms show higher mechanical strength, and these types of films have a higher resistance against electromigration. 4,5,10,11 As the dimensions of semiconductor chips have been reduced to below 100 nm scale, improved reliability and higher performance of interconnection are needed. 12 Among various Cu-based bimetallic films, silver (Ag)-containing film showed the lowest resistivity of about 2.4 μ · cm which was comparable to pure Cu.…”

“…13 In addition to superior resistivity, Cu-Ag can enhance the electromigration resistance. It has been reported that Ag atoms were segregated not only at the grain boundaries but also at the surface of the film, 10 because the homogeneous mixture between Cu and Ag is barely formed. Since the major paths for electromigration of Cu are the free surface and the interfaces between Cu and the barrier layer, 14 segregated Ag atoms at the surface and the interface can act as a barrier to electromigration.…”

“…In general, Cu-Ag films have been prepared by electron beam evaporation, 10,20,21 electrodeposition in supercritical fluid, 11 and the deposition from the melted stage in the vacuum. 22 In terms of the application in the interconnection, low temperature and wet-process of Cu-Ag co-deposition is the most appropriate and controllable.…”