Non-equilibrium supersaturation behavior in a Cu/Sn/Cu interconnect induced by room temperature electromigration

The non-equilibrium supersaturation behavior in a Cu/Sn/Cu interconnect induced by electromigration was investigated, for the first time, under room temperature. The sub-micron dimension solder interconnect was fabricated using a magnetron sputtering technique. The athermal electromigration force, rather than the Joule heating, induced a net Cu diffusion flux across the cathode Cu/Sn interface toward the Sn matrix (along the electron flow direction). The accumulation of Cu atoms formed meta-stable supersaturation of Cu in Sn. A local distorted lattice structures was formed as evidenced by spherical aberration corrected scanning transmission electron microscope. The Cu supersaturation behavior was governed by grain boundary diffusion in the polycrystalline Cu electrode and interstitial diffusion in the single crystal Sn matrix. The extent of supersaturation in the metal matrix is affected by electromigration period and geometrical (cathode/anode electrode) parameter.