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Electromigration results are described for a dual damascene structure with copper metallization and a low-k dielectric material. The failure times follow a 3-parameter lognormal behavior, with a threshold failure time needed to represent the entire failure distribution. We found that the threshold failure time scales differently with current density from the median time to failure, which has significant implications for making reliability predictions. It is shown that the threshold failure time corresponds to damage (presumably voids) nucleation of the electromigration process. The observed current density dependency, along with scanning electron microscopy cross sections of stressed samples and Monte Carlo simulations of failure distributions, suggests that both void nucleation and void growth should be considered for accurate modeling of the electromigration lifetime. [ABSTRACT FROM AUTHOR]

The resistance of thick film (2 μm) Sn conductors deposited onto Ni/Cr underlays was found to decrease several percent during electromigration stressing. The application of dc was necessary to initiate the resistance decrease. Equivalent ac current (rms values equal) did not produce the effect and extensive aging at elevated temperature did not either, indicating that the effect is not purely thermally induced. It is suggested that the reduction in the electromigration induced chemical potential from reductions in resistivity associated with reorientation of the microstructure is responsible for the effect. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A relationship between the adhesion of a Cu conductor to its surrounding medium, the electromigration drift velocity, and lifetime in a conventional electromigration test has been demonstrated. Lifetime measurements demonstrate that the drift velocity and the activation energy for mass transport along an interface correlate with the measured adhesion energy of the interface as determined by a four-point bending test. The results indicate that a linear relationship is expected between the electromigration activation energy and the intrinsic work of adhesion, which is consistent with a simple model relating the two. The data indicate that interfacial cleanliness and bond character at the interface (i.e., metal/dielectric versus metal/metal bonding) have a significant impact on all measured parameters. [ABSTRACT FROM AUTHOR]

Considers a model which was constructed for electromigration failure. Method used in electromigration testing; Problems associated with electromigration testing; Modification of the standard median time to failure equation.

Presents a study which modeled electromigration failure as a nucleation and growth process, where void nucleation is due to the generation of nonequilibrium vacancy concentration from an electromigration induced mass flux divergence. Prediction on electromigration lifetimes; Description of the model; Effect of the tensile stress responsible for the void generation.

Presents information on a study which developed a statistical model of electromigration, incorporating the statistics of microstructure and concomittant variations in the activation energy for grain-boundary diffusion. Problem of scaling when applying the lognormal distribution to a line under stress; Model for electromigration induced failure; Derivation of element life distribution; Discussion on multilognormal as the fine line failure distribution.

Focuses on a study which determined the activation energy for electromigration failure in aluminum-copper conductor stripes covered with polyimide. Results; Discussion; Conclusions.

Proposes a model which accounts for electromigration induced void formation. Important concept in understanding electromigration damage; Implication of the model.

Discusses a study which numerically investigated the electromigration diffusion boundary value problem with the perfectly blocking diffusion barrier. Boundary conditions identified as physically meaningful; Use of a dimensionless parameter; Motive for a concerted effort to construct models in order to predict the reliability of electronic components which incorporate thin film metallic conductors.

When a high current density is applied to a conductor, it activates several driving forces for mass transport that can lead to device failure, the most prominent of which is electromigration. However, there are other driving forces operating as well that can counteract or add to the effects of electromigration. A major driving force is a stress gradient that is developed as a response to electromigration in the presence of a blocking boundary condition. When the electrical stress is interrupted by pulsing DC measurements at low frequency, relaxation of the stress is observed through longer lifetime. [ABSTRACT FROM AUTHOR]

Electromigration has been recognized as one of the most important wearout failure mechanisms in integrated circuits. As such, the problem of extrapolating test results for the purpose of reliability predictions is very important to the industry, and the topic has understandably received considerable attention in the professional literature. Over the years, however, there have been serious problems correlating experimental results with theoretical predictions. Recently this dilemma has become resolved through a better understanding of the failure process. This paper will review these developments and the process that has led us to where we are today. [ABSTRACT FROM AUTHOR]

Electromigration testing of an interconnect system comprised of copper metallization and a low-k dielectric material gives rise to bimodal lognormal statistics with early and late fails. When separated from one another, we observed failure modes characterized by a three-parameter lognormal distribution and the same threshold failure time. It is shown that the threshold failure time corresponds to damage (presumably voids) nucleation of the electromigration process. The dependence of the threshold failure time and the median time to failure on current density suggests that both void nucleation and void growth need to be considered for accurate modeling of the electromigration lifetime. [ABSTRACT FROM AUTHOR]

Under constant current electromigration, white tin exhibited a resistance drop of up to 10%. It has a body-centered-tetragonal structure, and the resistivity along the a and b axes is 35% smaller than along the c axis. Microstructure evolution under electromigration could be responsible for the resistance drop. Synchrotron radiation white beam x-ray microdiffraction was used to study this evolution. Grain-by-grain analysis was obtained from the diffracted Laue patterns about the changes of grain orientation before and after electromigration. We observed that high-resistance grains reorient with respect to the neighboring low-resistance grains, most likely by grain growth of the latter. A different mechanism of grain growth under electromigration from the normal grain growth is proposed and discussed. [ABSTRACT FROM AUTHOR]

Electromigration in thin-film polycides of Ta and W was studied. Extrusions formed after several weeks of powering at current densitites of 106 A/cm2 at a temperature of 400 °C. The extrusions were determined to be of aluminum, which had diffused from the wire bonds. [ABSTRACT FROM AUTHOR]

The problem of damage nucleation due to electromigration-induced copper depletion in an Al/Cu alloy is treated. The diffusion of aluminum in thin-film lines is sharply reduced by alloying with small amounts of copper. In this model, copper is depleted in a region at the cathode end of an Al/Cu alloy line. Assuming that the aluminum diffusion in this copper-deficient region is much faster than the diffusion of the copper, a quasisteady-state stress profile is established between the blocking boundary at the cathode and the copper front moving at the drift velocity. The time to reach a critical stress to initiate failure is shown to depend on the inverse of the square of the current density as observed experimentally. The model is appropriate for failure at contacts and vias, and at the end of long polycrystalline clusters in near-bamboo lines. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recent experimental results have indicated that the traditionally conceived role of copper in Al/Cu alloys in electromigration resistance may not be correct. A simple model is proposed based on Al/Cu intermetallic precipitates acting as local diffusion barriers limiting vacancy availability. [ABSTRACT FROM AUTHOR]

Comments on the effect of current crowding on vacancy diffusion and void formation in electromigration. Discussion on the concept of a driving force for vacancy diffusion; Difficulty in rationalizing the employment of electromigration effective valence; Elaboration on the presence of vacancies.