Electromigration threshold length effect in dual damascene copper-oxide interconnects

Electromigration threshold lengths have been previously observed in aluminium interconnects and more recently in copper interconnects. It was found that shorter interconnects are less susceptible to electromigration failures than longer ones. Blech (1976) proposed that the threshold length was due to the electromigration induced mechanical stress gradient that generates a back flow opposite to the electromigration flux. As a consequence a threshold product j.L_th can be considered which provides immortal interconnect length L and benefits circuit design. In this study we report a set of experiments which provide a value of 3000 A/cm at 250°C for electromigration threshold length in copper-oxide interconnects.