Electric current effects upon the Sn/Cu and Sn/Ni interfacial reactions

Electromigration-induced failures in integrated circuits have been intensively studied recently; however, electromigration effects upon interfacial reactions have not been addressed. These electromigration effects in the Sn/Cu and Sn/Ni systems were investigated in this study by analyzing their reaction couples annealed at 200 degrees C with and without the passage of electric current. The intermetallics formed were epsilon-(Cu3Sn) and eta-(Cu6Sn5) phases in the Sn/Cu couples and Ni3Sn4 phase in the Sn/Ni couples. The same intermetallics were formed in the two types of couples with and without the passage of electric current. The thickness of the reaction layers was about the same in the two types of couples of the Sn/Cu system. In the Sn/Ni system, the growth of the intermetallic compound was enhanced when the flow direction of electrons and that of diffusion of Sn were the same. But the effect became inhibiting if the directions of these two were opposite. Theoretical calculation indicated that in the Sn/Ni system, the electromigration effect was significant and was 28% of the chemical potential effect for the Sn element flux when the Ni3Sn4 layer was 10 mu m thick. For the Sn and Cu fluxes in the Sn/Cu reaction couples, similar calculations showed that the electromigration effects were only 2 and 4% of the chemical potential effects, respectively. These calculated results were in good agreement with the experimental observations that in the Sn/Cu system the electric current effects were insignificant upon the interfacial reactions.