Electromigration transport mechanisms in Al thin-film conductors

Oates, A. S.

doi:10.1063/1.360925

Cited by 49 publications

(19 citation statements)

References 26 publications

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“…For the case of a bamboo-structured or single crystalline Al sample without passivation, since the surface is oxidized, electromigration is known to be dominated not by surface diffusion but by lattice diffusion (Heurle and Ames 1970; Oates and Barr 1994;Oates 1996). Concerning the electromigration in solders treated in the present paper, it can be similarly considered that lattice diffusion is dominant (Huynh et al 2001;Choi et al 2002).…”

Section: Afd For Lattice Diffusionmentioning

confidence: 82%

A simple method for testing the electromigration resistance of solders

et al. 2008

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Recently, the size of solder bump interconnects have been significantly reduced with the advent of highdensity packaging, and thus the evaluation of electromigration in solder bumps has become necessary. The present paper proposes a simple method to test the electromigration resistance of Pb-free solders. One of the key points of the present method is the fabrication of a simple solder sample that can produce sufficient current density to cause electromigration. Moreover, the actual local temperature of a small area subjected to electromigration in the sample was measured by a direct method. A right-angled diamondshaped hole was introduced in a thin film of solder using a focused-ion-beam system. A direct current was supplied to the film far from the hole, perpendicular to the diagonal of the hole. In this way, the current density was concentrated near to the corner of the hole, and the value of this was obtained through a theoretical analysis. It was noted that the steady temperature in the film along a line extending from the diagonal, remained constant, although the current density decreased gradually far from the corner. Therefore, the temperature at a position near the corner, where electromigration takes place, can easily be found by measuring the temperature far from the corner. The temperature was measured directly under current flow conditions by utilizing the chemical reagents with known melting points. Finally, by measuring the ratio of hillock volume to the time for the current supply as a measure of the atomic flux divergence due to electromigration, the corresponding resistances of some Pb-free solders to electromigration were evaluated.

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Section: Afd For Lattice Diffusionmentioning

confidence: 82%

A simple method for testing the electromigration resistance of solders

et al. 2008

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“…14 Suo 18 considered the motion and multiplication of dislocations under the influence of an electric current in a conductor line, and suggested that EM-driven dislocation multiplication could itself lead to dislocation densities high enough to affect EM degradation processes. Oates, 19 however, did not see any diffusivity effects that could be attributed to dislocations in his experimental study. Baker et al 13 through their experimental study of nanoindented Al lines (width = 1 lm, mean grain size = 1.1 lm) showed that the effect of a dislocation density of 10 16 /m 2 is comparable to diffusion through a grain boundary.…”

Section: Density Of Core Dislocations (Q Core ): Extent Of Plasticitymentioning

confidence: 98%

Electromigration-Induced Plasticity: Texture Correlation and Implications for Reliability Assessment

Budiman

Besser

Hau-Riege

et al. 2008

Journal of Elec Materi

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Plastic behavior has previously been observed in metallic interconnects undergoing high-current-density electromigration (EM) loading. In this study of Cu interconnects, using the synchrotron technique of white-beam x-ray microdiffraction, we have further found preliminary evidence of a texture correlation. In lines with strong (111) textures, the extent of plastic deformation is found to be relatively large compared with that of weaker textures. We suggest that this strong (111) texture may lead to an extra path of mass transport in addition to the dominant interface diffusion in Cu EM. When this extra mass transport begins to affect the overall transport process, the effective diffusivity, D eff , of the EM process is expected to deviate from that of interface diffusion only. This would have fundamental implications. We have some preliminary observations that this might be the case, and report its implications for EM lifetime assessment herein.

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“…Such a situation appears to occur in Al/SiO 2 conductors, where the measured v d is insensitive to the details of near-bamboo microstructure. 19 However, for Cu/low-k, it is not obvious that a similar situation occurs since diffusion in the single crystal region will occur along the Cu/cap layer interface. The activation energy difference for diffusion in the Cu single crystal compared to grain boundaries is, therefore, likely to be smaller than for Ai/SiO 2 , since in the latter single crystal transport appears to be controlled by lattice diffusion.…”

Section: Ta-based Linermentioning

confidence: 99%

Strategies to Ensure Electromigration Reliability of Cu/Low-k Interconnects at 10 nm

Oates

2014

ECS J. Solid State Sci. Technol.

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A key element for future silicon IC technology development is the containment of electromigration -induced failure of Cu / low-k interconnects. Continued progress in meeting electromigration reliability requirements for future technology nodes will require a multi-faceted approach to the problem: first the development of effective process solutions to limit the impact of technology scaling on electromigration life-time reduction; and second, the provision of models of failure that are representative of circuit operation to determine realistic current-limiting design rules. We will show that process solutions involve limiting the rate of transport along interfaces and grain boundaries in the damascene trench architecture using metal capping layers and Cu alloys. Most models of electromigration failure have been developed using DC stress conditions, while circuits predominantly operate with non-DC (pulsed DC or AC) signals. Understanding the relationship between failure under DC and non-DC conditions is a necessary aspect of realistic reliability characterization. In this paper we review: our recent studies that establish the relationship between Cu microstructure, metallic capping and dilute Cu alloy additions and thereby identify effective scenarios for mitigation with technology scaling; and experimental studies of electromigration failure under non-DC stress that explore the physical mechanisms involved. Electromigration failure of interconnects has been a long-standing concern for the development of highly reliable integrated circuits (IC). Despite intense efforts following the first observation of electromigration -related failure of Al circuit interconnects in 1966, 1 it has proven impossible to find a robust process solution by material modification for either Al or the more recently introduced Cu metal system. It remains an issue that can only be partially mitigated with process solutions, and ultimately it is controlled at the circuit level by the use of current limiting design rules. There is a prevalent concern that this method of control of the rate of electromigration failure will be detrimental to circuit performance. Therefore, during technology development, a balance must be found to ensure circuit performance is maintained without seriously impairing electromigration reliability. Achieving this balance requires a thorough fundamental understanding of the factors that determine the efficacy of process mitigation techniques. Moreover, current limiting design rules are extrapolated from accelerated test data using models of the failure mechanism, and the models must accurately reflect the physical mechanisms of failure.For the most advanced Si process technologies currently being manufactured with Cu and low-k dielectrics, electromigration failure times have decreased rapidly with technology progression, adding urgency to the problem of assuring electromigration reliability. Fig. 1 shows the reduction in failure time for both long conductor lengths and for shorter lengths; 2,3 for the latter, the Bl...

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Electromigration transport mechanisms in Al thin-film conductors

Cited by 49 publications

References 26 publications

A simple method for testing the electromigration resistance of solders

A simple method for testing the electromigration resistance of solders

Electromigration-Induced Plasticity: Texture Correlation and Implications for Reliability Assessment

Strategies to Ensure Electromigration Reliability of Cu/Low-k Interconnects at 10 nm

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