Electromigration-induced abrupt changes in electrical resistance associated with void dynamics in aluminum interconnections

Abstract

Electromigration-induced failure mechanisms were investigated by means of extremely sensitive resistance change measurements and simultaneous observations using scanning electron microscopy. Abrupt changes in resistance ( ACRs), classified into three types: downward steps, upward steps, and oscillations, were found to occur frequently during the dc current stressing test. It was conspicuously observed that there was a rapid void annihilation associated with an abrupt increase in resistance, and a rapid void formation with a decrease in resistance. ACRs are considered to be caused by a rapid change in the number of excess vacancies concomitant with void annihilations or formations. The thermodynamical analysis on the stability of a void strongly suggests that the change of a local stress from tensile to compressive causes a rapid annihilation of voids, and the opposite one causes a rapid formation. Temperature dependence of the intensity of ACRs exhibited an activation energy of 0.43 eV, which implied that grain boundary electromigration was the driving force of ACRs.

Hopf bifurcation, bistability, and onset of current-induced surface wave propagation on void surfaces in metallic thin films

“…In Ref. [25], it was described in detail that the computed electrical resistance evolution of the film containing the morphologically evolving void, qualitatively consistent with experimental observations obtained in accelerated electromigration testing [26], resembles closely the evolution of y max (t). For consistency, we use the evolution of y max (t) to construct a proper morphological norm for our bifurcation analysis.…”

“…4a shows a representative case of electrical resistance evolution, R(t), when the asymptotic state has been reached in a metallic thin film that contains one morphologically evolving void under electromigration conditions, expressed by the parameter values m = 1, A = 10, C = 90, K = 0.6, and / = 90°, that lead to propagation of stable surface waves on the void. Our theoretical prediction for R(t) shown in connect lines during electromigration testing [26]. The major quantitative difference in comparing our simulation results (such as those in Ref.…”

“…[18]. Furthermore, the evolution of the metallic film's electrical resistance, R(t), is calculated through Ohm's law using the computed electrostatic potential difference at the ends of the film at each time instant, t, under constant current conditions; this computed electrical resistance evolution, R(t), can be compared with experimentally measured ones during electromigration testing experiments [26].…”

“…Moreover, we have shown that stable surface waves can propagate on void surfaces in films with high and low symmetry of surface diffusional anisotropy on the film plane driven by a stronger than critical electric field [23,24]. Such void dynamical responses affect directly the evolution of the electrical resistance of a metallic thin film, such as in an interconnect line [25]; such electrical resistance evolution can be accurately measured experimentally [26]. In spite of the recent theoretical progress on current-driven oscillatory dynamical responses on void surfaces, the onset of oscillatory dynamics is still not well understood and systematic investigations for providing the conditions to stabilize oscillatory responses observed on void surfaces have not been carried out; in addition to contributing to our fundamental understanding of surface electromigration-induced dynamics, such studies may also have useful applications to improving interconnect reliability in microelectronics.…”

Electromechanically driven chaotic dynamics of voids in metallic thin films

“…These comparisons include electromigration-driven void surface morphological evolution, 8,15 void morphological instabilities resulting in the formation of stress-induced cracks emanating from electromigration-induced slits, 10,15 and electrical resistance evolution in metallic interconnect lines, 19 including quantitative agreement of our modeling predictions 22 with the only experimental measurement that has been reported of a stable time-periodic state in the evolution of electrical resistance. 31 To the best of our knowledge, controlled experiments of electromigration-driven void evolution in metallic thin films under the simultaneous action of mechanical stress have not been reported to date. Nevertheless, we hope that our study will motivate systematic protocols of such controlled experiments that will confirm our modeling predictions.…”