Detection of current-induced vacancies in thin aluminum-copper lines using positrons

In situ depth-resolved positron annihilation spectroscopy (PAS) is used to show dynamic formation of vacancies in 1 μm×1 μm Al-0.5 wt% Cu lines under current flow. We show that the number of vacancies in these lines increases when a dc current (8×104 A/cm2) is applied. This increase in vacancy concentration is substantially greater than that due to thermal vacancy generation alone (4×1018 cm-3 versus 3×1017 cm-3). Isothermal measurements (with no current flow) yield a vacancy formation energy of 0.60±0.02 eV. These results show that PAS can be used to examine the initial stages of interconnect damage due to electromigration. © 1996 American Institute of Physics.