The relationship between resistance changes and void volume changes in passivated aluminum interconnects

We performed electromigration tests on 11 passivated Al lines at 212°C and 3 MA/cm² inside a high voltage scanning electron microscope (HVSEM). Our automated experimental apparatus saved an image of the entire test structure every six minutes while it continuously measured and recorded the resistance of each line. We determined the void volume as a function of time using digital image processing. While it is straightforward to determine resistance changes knowing the changes in the void geometry, it remains to be seen whether one can perform the reverse calculation. From our data, the amount of information that can be extracted solely from the resistance versus time curves appears limited. The nucleation time of the first void can usually be found, but it is not possible to detect the nucleation of subsequent voids. The resistance change depends much more critically on void shape than void size, making an estimation of the void volume from the resistance impossible