Effect of Sn grain orientation on Ni substrate dissolution and intermetallic compounds precipitation in Cu/Sn/Ni interconnect undergoing electromigration

Abstract

The solid Sn exists in the β-type possesses a body-centered tetragonal (BCT) structure. The diffusion coefficient of Ni atoms along the c-axis of Sn grains is about 3×104 times faster than the a-axis at 150 °C. Ni atoms show different EM characteristics in relation with β-Sn crystallographic orientation in solder interconnect. The effects of Sn orientation on the dissolution of Ni substrate and intermetallic compounds (IMCs) precipitation during electromigration were investigated in the present work. When the c-axis of Sn grain was parallel to the electron flow direction, extensive Ni dissolution and massive (Ni,Cu) 3 Sn 4 IMC precipitation would occur due to the large diffusion flux of Ni atoms. When the c-axis of Sn grain was roughly perpendicular to the electron flow direction, the diffusion of Ni atoms was strongly retarded, resulting in little dissolution of Ni substrate and the precipitation of (Cu,Ni) 6 Sn 5 IMC in anode.