Anelasticity study on electromigration effect in Cu thin films

Electromigration (EM) tests on Cu thin film circuits below or near 373 K with the current density between 1 × 109 A/m2 and 8 × 109 A/m2 were carried out by means of the composite vibrating reed method. The resonant frequency (f) and the internal friction (Q−1) of the composite reed and the resistivity (R) of the thin film circuit were measured during isothermal EM tests for as deposited Cu/Ta films, Cu/Ta films annealed at 450 K and as deposited Ta/Cu/Ta films. An increase in f, a decrease in Q−1 and a decrease in R were commonly observed. The activation energies found for the EM process (EEM) range between 0.21 and 0.41 eV for the as deposited Cu/Ta films, between 0.21 and 0.59 eV for the annealed Cu/Ta films and around 0.3 eV for as deposited Ta/Cu/Ta films. It is suggested that a previously unrecognized mass transport process with low EEM operates in these Cu thin films.