Spatially Resolved Characterization of Electromigration-Induced Plastic Deformation in al (0.5WT% CU) Interconnect
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SPATIALLY RESOLVED CHARACTERIZATION OF ELECTROMIGRATION-INDUCED PLASTIC DEFORMATION IN AL (0.5WT% CU) INTERCONNECT R.I. Barabash and G.E. Ice Metals & Ceramics Divisions, Oak Ridge National Laboratory, Oak Ridge TN 37831 N. Tamura and J.R. Patel Advanced Light Source, 1 Cyclotron Road, Berkeley CA 94720 B.C. Valek and J. C. Bravman Dept. Materials Science & Engineering, Stanford University, Stanford CA 94305 R. Spolenak Max-Planck-Institut für Metallforschung, Heisenbergstrasse 3, D-7056 Stuttgart, Germany ABSTRACT Electromigration during accelerated testing can induce early stage plastic deformation in Al interconnect lines as recently revealed by the white beam scanning X-ray microdiffraction. In the present paper, we provide a first quantitative analysis of the dislocation structure generated in individual micron-sized Al grains during an in-situ electromigration experiment. Laue reflections from individual interconnect grains show pronounced streaking after electric current flow. We demonstrate that the evolution of the dislocation structure during electromigration is highly inhomogeneous and results in the formation of unpaired randomly distributed dislocations as well as geometrically necessary dislocation boundaries. Approximately half of all unpaired dislocations are grouped within the walls. The misorientation created by each boundary and density of unpaired individual dislocations is determined. INTRODUCTION During service, the tiny Al or Cu metallic interconnect lines which connect discrete components in modern integrated circuits, experience extremely high current densities on the order of 1 MA/cm2. The so-called electron “wind” force is sufficient to “physically” displace the constitutive atoms in the interconnect lines. This phenomenon, called electromigration, depletes material at the cathode end of the interconnect line and causes accumulation near the anode end1. Ultimately electromigration leads to failure by open(void formation) or short- (cracking of the passivation layer and material extrusion) circuit (Fig.1). Electromigration-induced failure in metal interconnect constitutes a major reliability problem in the semiconductor industry2. Open circuit failure is caused by voids. Short circuit failure is caused by the formation of hillocks and/or whiskers that crack the passivation and build a conducting path to a neighboring line. While the general mechanism of electromigration is understood3, the effect of the atomic flow on the local metallic line microstructure is largely unknown. Recently, experimental techniques capable of probing grain orientation and stress with a spatial resolution compatible with the dimensions of the lines have emerged4-12. White beam X-ray microdiffraction 4-8 is
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particularly well suited to the in-situ study of electromigration. The technique was used to probe microstructure in interconnects4,13-16 and recently unambiguously unveiled the plastic nature of the deformation induced by mass transport during electromigration in Al(Cu) lines17 even before m
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