The electromigration drift velocity and the reliability of dual-damascene copper interconnect trees

Cu has replaced Al as the interconnect metal of choice for high performance Si-based integrated circuits. Its electromigration behavior must be quantified and an experimental basis for a circuit-level reliability assessment is needed. Experiments on straight two-terminal via-to-via Cu dual-damascene segments with different line lengths, both with via-above and via-below geometries, have been carried out. By contrasting the failure characteristics of via-above and via-below structures, the Cu/Si3N4 interface has been identified as the site for void nucleation and the most dominant diffusion path. Consequently, an asymmetry in lifetime exists between via-above and via-below interconnect lines. It has also been found that at short line lengths, true Blech immortality occurs only for very short lines, at best, due to the ease of void nucleation. Immortality due to void growth saturation is also limited, because, in the absence of the conducting refractory-metal current-shunting overlayers characteristic of Al technology, very small voids at vias can cause failures. We find that at long lengths a sub-population of Cu lines is immortal. We propose that this is a result of non-blocking liners at the base of the vias associated with the high stresses developed at the ends of the lines. In order to quantify the fundamental Cu electromigration kinetics which precedes all failure modes, electromigration drift velocity measurements were carried out using fully processed interconnect structures. It was observed that in a significant fraction of the test population, the resistance of the lines increased steadily over time prior to failure.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Wei, Frank L. (Frank Lili), 1977-

Advisor dc:contributor.advisor

• Carl V. Thompson.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30124

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30124