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Proceedings Paper

Electromigration in VLSI metallization
Author(s): Thomas Kwok
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Paper Abstract

There are increasing reliability concerns of electromigration-induced and thermal stress-induced failures in submicron interconnects carrying the projected high current density and in multilevel interconnection with W studs. Electromigration characteristics of Al and Al-Cu submicron lines, two level Al-Cu lines with W studs, Al fine lines under pulsed current stressing at high frequencies, and Al and Al-Cu fine lines under temperature cycling have been systematically studied. Lifetime is affected by grain size, grain morphology and bend structure in submicron metal lines. The lifetime of W stud chains is less than a half of that of Al-Cu flat lines. The discontinuity of Cu supply at Al-Cu/W interfaces account for most of the reduction in the electromigration resistance of W stud chains. Under pulsed current stressing at frequencies 50-200 MHz, our data indicate no threshold frequency for drastic change in lifetime. However, lifetime increases with duty cycle as tso cc r- Z.', which is a remarkable improvement over an av¬ erage current density model. Lifetime also depends explicitly on both current on-time and current off period. The extra thermal stress induced by temperature cycling shortens the lifetime of both Al and Al-Cu fine lines by more than an order of magnitude. Our results also show that the addition of Cu in Al fine lines improves the resistance to thermal stress-induced failures, probably by the suppression of grain boundary sliding and migration.

Paper Details

Date Published: 1 December 1991
PDF: 12 pages
Proc. SPIE 1596, Metallization: Performance and Reliability Issues for VLSI and ULSI, (1 December 1991); doi: 10.1117/12.51012
Show Author Affiliations
Thomas Kwok, IBM/Thomas J. Watson Research Ctr. (United States)

Published in SPIE Proceedings Vol. 1596:
Metallization: Performance and Reliability Issues for VLSI and ULSI
Gennady Sh. Gildenblat; Gary P. Schwartz, Editor(s)

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