A high-resolution  in situ  scanning electron microscopic study was made of drift velocity test structures which were used to simulate a Cu-line/W-via structure. Electromigration comparison tests were carried out at 250 to 450C, using current densities of 5 x 105 to 2.1 x 106A/cm2. Under these conditions, the measured electromigration activation energy was 0.73eV. The measured critical length was of the order of 2.5 at a current density of 2.1 x 106A/cm2.

K.L.Lee, C.K.Hu, K.N.Tu: Journal of Applied Physics, 1995, 78[7], 4428-37