Characterization of Two Electromigration Failure Modes In Submicron Vlsi

Atakov, E.M.; Clement, J. J.; Miner, B.

doi:10.1557/proc-309-133

Cited by 18 publications

(3 citation statements)

References 12 publications

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“…For wider strips, the bamboo structure develops more slowly; beyond the critical width, it is never reached. This is consistent with experimental observations showing the bamboo structure for narrow lines but not for wide lines after post-patterning annealing [6].…”

Section: Introductionsupporting

confidence: 93%

The Effect of Variability Among Grain Boundary Energies on Grain Growth in Thin Film Strips

et al. 1994

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Grain growth in thin-film strips is important to interconnect reliability because grain boundary structures strongly effect the rate and mechanism of electromigration-induced failure. Previous simulations of this process have indicated that the transformation to the fully bamboo structure proceeds at a rate which decreases exponentially with time, and which is inversely proportional to the square of the strip width. We have also reported that grain boundary pinning due to surface grooving implies that there exists a maximum strip width to thickness ratio beyond which the transformation to the bamboo structure does not proceed to completion. In this work we have extended our simulation of grain growth in thin films and thin film strips to consider the effects of variations in grain boundary energy. Boundary energy is taken to depend on the misorientation between the two neighboring grain and the resulting variations in grain boundary energy mean that dihedral angles at triple junctions deviate from 1200. The proportionality between boundary velocities and local curvatures, and the critical curvature for boundary pinning due to surface grooving also both depend on boundary energy. In the case of thin-film strips, the effect of boundary energy variability is to impede the transformation to the bamboo structure, and reduce the width above which the complete bamboo structure is never reached. Those boundaries which do remain upon stagnation tend to be of low energy (low misorientation angle) and are therefore probably of low diffusivity, so that their impact on reliability is probably reduced. INTRODUCTIONGrain growth in thin film strips has recently become an important concern for reliability because of the reduced width of aluminum interconnect lines and the associated increase in electric current densities. The resistance to electromigration-induced damage is largely determined by the grain boundary microstructure present. In previous work [1-3] we simulated the evolution of the grain structure in thin film strips using the approximation that all boundaries had identical mobilities and energies. The first condition considered was the case in which there is no boundary pinning due to surface grooving. If the initial grain size is sufficiently small compared to the line width there may be a period of normal grain growth. As grain growth proceeds, a few grains will eventually span the width of the line, creating bamboo segments separated by non-bamboo segments or polycrystalline clusters. The grain structure evolution proceeds by the shrinkage of the polycrystalline segments. At any given time the distribution of cluster lengths is approximately exponential. Each cluster shrinks in length at a rate which is approximately constant, and this behavior results in an exponential decay of the fraction of the line which is not bamboo. The time required for a line to become completely bamboo is determined by the length of the longest cluster. It is therefore a statistically variable quantity which depends on line length. Furt...

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Section: Introductionsupporting

confidence: 93%

The Effect of Variability Among Grain Boundary Energies on Grain Growth in Thin Film Strips

et al. 1994

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“…The extra j dependence arises here since N1 = np M and N2 = n(M + 1)qp M depend exponentially on L B (through M) and thus also exponentially on 1/j . The trend shown is much more in keeping with the data of Atakov et al [31]. However, the assumption of lognormality for type-1 and type-2 failure must be properly assessed [29].…”

Section: Analysis Of Early Failuressupporting

confidence: 82%

An analysis of the weakest-link model for early electromigration failure

Dwyer¹

2004

J. Phys. D: Appl. Phys.

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The application of the weakest-link or failure-unit model to electromigration failure is discussed in relation to a simple model that should describe the early failures in fine-line, as-patterned aluminium reasonably well. The earliest failures are expected to be due to the presence of at least one polygranular cluster longer than some critical (Blech) length, while the next earliest are assumed to arise from linked shorter clusters. Using a simple model of the microstructure, the probability density function for the number of each of these types of failure-unit is determined as a function of the linewidth. For this simple model the overall failure distribution may be calculated essentially exactly using the Theory of Runs; consequently we can compare these exact results with some common approximations. It is demonstrated through Jensen's inequality that a common approximate method is in fact a rigorous upper bound for the failure distribution. The model exhibits the expected increase in median-time-to-failure and deviation-in-time-to-failure values with decreasing linewidth when forcing a lognormal distribution. Although this would suggest an eventual decrease in reliability with scale reduction, the exact results show that this is not the case.

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“…Clusters that were too small to support stress levels high enough to cause damage at low current density, can as the current density is increased. Therefore, the 1/j 2 relationship no longer exists and a higher exponent would be measured [30].…”

Section: Effect Of Microstructurementioning

confidence: 99%

Electromigration in thin film conductors

Lloyd¹

1997

Semicond. Sci. Technol.

110

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The state of the art in understanding of electromigration induced failure is outlined in the following review. An overview of the basic principles responsible for electromigration in conductors is followed by an explanation of what the consequences of electron flow directed mass transport are in circuit wiring with an emphasis on the recent appreciation of the role of mechanical stress and where it comes from. The effects of thermal stress, microstructure and precipitation are discussed within this context. Finally, suggestions for further work are made.

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Characterization of Two Electromigration Failure Modes In Submicron Vlsi

Abstract: Grain-bondary erosion-type voids and transgranular slit-like voids are found to be two competing electromigration failure modes in VLSI interconnects. The effects of interconnect linewidth, microstructure, process variables and stress conditions on the two failure modes were studied.

Cited by 18 publications

References 12 publications

The Effect of Variability Among Grain Boundary Energies on Grain Growth in Thin Film Strips

The Effect of Variability Among Grain Boundary Energies on Grain Growth in Thin Film Strips

An analysis of the weakest-link model for early electromigration failure

Electromigration in thin film conductors

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