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Further Investigations of the Microstructural Mechanism of Electromigration Failure in Al-Cu Lines with Quasi-Bamboo Microstructures

Published online by Cambridge University Press:  15 February 2011

S. H. Kang ,
F. Y. Génin ,
C. Kim  and
J. W. Morris
S. H. Kang
Affiliation:
Center for Advanced Materials, Lawrence Berkeley National Laboratory and the Department of Materials Science and Engineering, University of California, Berkeley, CA 94720
F. Y. Génin
Affiliation:
Chemistry and Materials Science, Lawrence Livermore National Laboratory, Livermore, CA 94550
C. Kim
Affiliation:
Center for Advanced Materials, Lawrence Berkeley National Laboratory and the Department of Materials Science and Engineering, University of California, Berkeley, CA 94720
J. W. Morris
Affiliation:
Center for Advanced Materials, Lawrence Berkeley National Laboratory and the Department of Materials Science and Engineering, University of California, Berkeley, CA 94720
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Abstract

Thin-film Al-2Cu conducting lines with “quasi-bamboo” microstructures were investigated to understand the microstructural mechanism of electromigration failure. Both conventional test structures and electron-transparent lines fabricated on silicon nitride windows were utilized to identify the “weakest” polygranular segments. Even when the current density was reduced to 0.75 MA/cm2 and the segment length was on the order of a few microns, failure occurs at the upstream termination of the longest polygranular segment in the line, at a time that decreases exponentially with the segment length. There is no apparent “Blech length” in quasi-bamboo Al- Cu lines; the longest segments are the failure sites, and their lifetime decreases with segment length in a regular way, even when the longest segments are only a few microns in length. It follows (and is observed) that the time-to-failure distribution of a group of lines is fixed by the distribution of the longest polygranular segments within them. This distribution can be effectively controlled by post-pattern annealing, which can refine the quasi-bamboo structure so that the longest polygranular segments are short and the distribution of longest polygranular segment lengths is narrow. Consequently, post pattern annealing is a very effective method for improving reliability by increasing the time to first failure.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 428: Symposium L – Materials Reliability in Microelectronics VI , 1996 , 255
Copyright
Copyright © Materials Research Society 1996

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