Electromigration multistress pattern technique for copper drift velocity and Black’s parameters extraction

Package electromigration tests were performed on dual damascene copper interconnects issued from the 90, 65 and 45 nm-node technologies. By varying the stress conditions during the steady state regime of the resistance increase, we study drift velocity evolution as a function of the current density j. Thus we show some large deviation of the Black´s law, which assumes a linear dependence of the lifetime with j. Finally we have determined the Black´s exponent n in a broad range of current density j (2.5-50 mA/mum²). For 250 mum long lines, a n=1 is obtained between 10 and 20 mA/mum², it increases up to 2 for j=2.5 mA/mum².