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Statistical Analysis of Electromigration Lifetimes and Void Evolution for Cu Interconnects

Published online by Cambridge University Press:  17 March 2011

M. Hauschildt ,
M. Gall ,
S. Thrasher ,
P. Justison ,
L. Michaelson ,
R. Hernandez ,
H. Kawasaki  and
P. S. Ho
M. Hauschildt
Affiliation:
The University of Texas at Austin, PRC/MER, Mail Code R8650, Austin, TX 78712
M. Gall
Affiliation:
Freescale Semiconductor, MD K10, 3501 Ed Bluestein Blvd, Austin, TX 78721
S. Thrasher
Affiliation:
Freescale Semiconductor, MD K10, 3501 Ed Bluestein Blvd, Austin, TX 78721
P. Justison
Affiliation:
Freescale Semiconductor, MD K10, 3501 Ed Bluestein Blvd, Austin, TX 78721
L. Michaelson
Affiliation:
Freescale Semiconductor, MD K10, 3501 Ed Bluestein Blvd, Austin, TX 78721
R. Hernandez
Affiliation:
Freescale Semiconductor, MD K10, 3501 Ed Bluestein Blvd, Austin, TX 78721
H. Kawasaki
Affiliation:
Freescale Semiconductor, MD K10, 3501 Ed Bluestein Blvd, Austin, TX 78721
P. S. Ho
Affiliation:
The University of Texas at Austin, PRC/MER, Mail Code R8650, Austin, TX 78712
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Abstract

Electromigration (EM) failure statistics and the origin of the lognormal deviation (σ) for Cu interconnects have been investigated by analyzing the lifetime statistics and void size distributions at various stages during EM testing. Experiments were performed on 0.18 μm wide Cu interconnects with tests terminated after specific amounts of resistance increases, or after a specified test time. Void size distributions of resistance-based, as well as time-based EM tests were obtained using focused ion beam (FIB) microscopy. The lifetime and void size distributions were found to follow lognormal distribution functions. The σ values of EM lifetime and time-based void size distributions decrease with higher percentages of resistance increase, reaching an asymptotic value of σ ∼ 0.14. In contrast, σ values of resistance-based void size distributions are significantly smaller and do not show an obvious dependence on time. The statistics of resistance-based void size distributions can mainly be accounted for by geometrical variations of the void shape, while the statistics of time-based void size distributions requires consideration of kinetic aspects of the EM process. The σ values of EM lifetime distributions at long times can be simulated based on measured void size distributions, taking into account geometrical and experimental factors of EM. In contrast, for short times the statistics of initial void formation and the kinetics of interfacial mass transport have to be considered.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 812: Symposium F – Materials, Technology and Reliability for Advanced Interconnects and Low-k Dielectrics-2004 , 2004 , F7.7
Copyright
Copyright © Materials Research Society 2004

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