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Current Dependence of Reversible Electromigration Induced Resistance Changes in Short Al Lines and Interpretation of Irreversible Effects

Published online by Cambridge University Press:  15 February 2011

A. H. Verbruggen ,
M. J. C. Van Den Homberg ,
A. J. Kalkman ,
J. R. Kraayeveld ,
A. W.-J. Willemsen  and
S. Radelaar
A. H. Verbruggen
Affiliation:
Delft Institute of Microelectronics and Submicron Technology, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
M. J. C. Van Den Homberg
Affiliation:
Delft Institute of Microelectronics and Submicron Technology, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
A. J. Kalkman
Affiliation:
Delft Institute of Microelectronics and Submicron Technology, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
J. R. Kraayeveld
Affiliation:
Delft Institute of Microelectronics and Submicron Technology, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
A. W.-J. Willemsen
Affiliation:
Delft Institute of Microelectronics and Submicron Technology, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
S. Radelaar
Affiliation:
Delft Institute of Microelectronics and Submicron Technology, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
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Abstract

Changes in the electrical resistance induced by electromigration in short (< 20 μm) Al lines show a rather well-defined behavior. For current densities j below a critical value jc the resistance change saturates with time and the resistance fully recovers when the current is switched off. Above the critical current density the induced resistance changes do not saturate and vary approximately linearly with time. In this case the resistance changes recover only partially after removal of the current. We report (i) measurements of the current dependence of the magnitude of the reversible resistance changes and (ii) the results of atomic force microscopy (AFM) inspection of the lines after stressing with current densities above jc. The resistance measurements were made with a high-resolution AC bridge technique. The samples were pure, unpassivated Al lines with a film thickness of 100 nm and a line width of 2 gm. The results show a linear dependence between the magnitude of the reversible changes and the current density. The linear dependence is predicted by two models. The first is based on a description of the vacancy flux and the second on a description of the build-up of mechanical stress during an electromigration experiment. To study the origin of the irreversible effects, samples were stressed at current densities above jc, and the induced irreversible changes in the resistance were recorded. Both negative and positive changes of the resistance were observed. After six hours the experiment was stopped and the lines were inspected by atomic force microscopy. It was always possible to observe a void, a hillock or a hillock/void pair that was created during the passage of the DC current. Moreover, lines with decreasing resistance during stress always showed a hillock and lines with an increased resistance always showed a void.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 428: Symposium L – Materials Reliability in Microelectronics VI , 1996 , 121
Copyright
Copyright © Materials Research Society 1996

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References

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