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Fatal Void Size Comparisons in Via-Below and Via-Above Cu Dual-Damascene Interconnects

Published online by Cambridge University Press:  17 March 2011

Z. -S. Choi
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
C. L. Gan
Affiliation:
Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore, 117576 School of Materials Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798
F. Wei
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
C. V. Thompson
Affiliation:
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore, 117576
J. H. Lee
Affiliation:
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
K. L. Pey
Affiliation:
Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore, 117576
W. K. Choi
Affiliation:
Singapore-MIT Alliance, 4 Engineering Drive 3, Singapore, 117576
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Abstract

The median-times-to-failure (t50's) for straight dual-damascene via-terminated copper interconnect structures, tested under the same conditions, depend on whether the vias connect down to underlaying leads (metal 2, M2, or via-below structures) or connect up to overlaying leads (metal 1, M1, or via-above structures). Experimental results for a variety of line lengths, widths, and numbers of vias show higher t50's for M2 structures than for analogous M1 structures. It has been shown that despite this asymmetry in lifetimes, the electromigration drift velocity is the same for these two types of structures, suggesting that fatal void volumes are different in these two cases. A numerical simulation tool based on the Korhonen model has been developed and used to simulate the conditions for void growth and correlate fatal void sizes with lifetimes. These simulations suggest that the average fatal void size for M2 structures is more than twice the size of that of M1 structures. This result supports an earlier suggestion that preferential nucleation at the Cu/Si3N4 interface in both M1 and M2 structures leads to different fatal void sizes, because larger voids are required to span the line thickness in M2 structures while smaller voids below the base of vias can cause failures in M1 structures. However, it is also found that the fatal void sizes corresponding to the shortest-times-to-failure (STTF's) are similar for M1 and M2, suggesting that the voids that lead to the shortest lifetimes occur at or in the vias in both cases, where a void need only span the via to cause failure. Correlation of lifetimes and critical void volumes provides a useful tool for distinguishing failure mechanisms.

Type
Research Article
Copyright
Copyright © Materials Research Society 2004

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