Effect of impurities and microstructure of Cu electroplated film on reliability of Cu interconnects using CuAl alloy seed

In order to improve reliability of Cu interconnects, Cu–Al alloy seed have been applied. In this paper, the effects of impurities in electroplated Cu (ECP–Cu) film on Cu interconnects have been investigated in detail. It is revealed that high concentration of impurities in ECP–Cu films suppresses the diffusion of Al into ECP–Cu films and confines Al in Cu–Al seed layer. This effect improves via electro-migration (EM) reliability. On the other hand, an ECP–Cu film with high concentration of impurities leads to increase line resistance, due to its small grain size and the existence of impurities in grains. Hence, the control of the impurities in ECP–Cu film is a key issue for the integration of Cu interconnects.

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► The control of the impurities in Cu films is a key issue for Cu interconnects.
► High impurities in electroplated Cu films suppress Al diffusion from CuAl seed.
► This effect improves electro-migration reliability with narrow via.