ELECTROMIGRATION DRIFT AND THRESHOLD IN CU THIN-FILM INTERCONNECTS

The electromigration-induced ionic drift velocity and critical length- current density product, (jl(c)) of Cu thin film conductors, were meas ured using the Blech-Kinsbron edge-displacement technique, Unencapsula ted Cu edge-displacement segments on TiN conductors were stressed in v acuum at a modest current density of 6 x 10(5) A/cm(2) in the temperat ure range of 175-275 degrees C. Drift velocity was observed to be betw een 1-1/2 to 3 orders-of-magnitude lower than that previously measured for unencapsulated Al in this temperature range, We measured an activ ation energy for EM-induced drift of 1.25 +/- 0.08 eV which correspond s to grain boundary diffusion in Cu, Critical lengths were measured an d the jl(c) threshold was estimated to range between 900-1600 A/cm, We calculated a Cu grain boundary Z value of -0.7, to our knowledge, th is study is the first to measure Z for electromigration in Cu thin fi lm conductors.