Study of conductance fluctuations (1/f~α noise) in metal film during electromigration stressing

摘要

We have studied the conductance fluctuation in metal film which is under electromigration stressing. The apparatus used by us allows measurement of noise with an ac 5-probe technique with a superimposed dc stressing current (typically 2MA/cm~2). This allows measurement of noise in the film at different stages of the electromigration process till the film is damaged completely. We study both the spectral power S_V(f) and also the probability density function (PDF) from the time series. The electromigration stressing was done to elevated temperature on Al and Cu metal lines grown by RF magnetron sputtering. Principal motivation of the investigation is to study low frequency defect relaxations in the metal film due to electromigration that give rise to conductance fluctuations with a spectral power S_V(f) ∝ 1/f~α. S_V(f)) (both magnitude as well as the spectral power quantified through α ) shows changes continuously and some times non-monotonically during the electromigration process and it is large just before the damage of the film. Itwas also observed that the PDF width increases significantly during the course of the em stressing and it changes from a Gaussian to a non Gaussian PDF.