Effects of mechanical properties on the reliability of Cu/low-k metallization systems

Cu and low-dielectric-constant (k) metallization schemes are critical for improved performance of integrated circuits. However, low elastic moduli, a characteristic of the low-k materials, lead to significant reliability degradation in Cu-interconnects. A thorough understanding of the effects of mechanical properties on electromigration induced failures is required for accurate reliability assessments. During electromigration inside Cu-interconnects, a change in atomic concentration correlates with a change in stress through the effective bulk modulus of the materials system, B, which decreases as the moduli of low-k materials used as inter-level dielectrics (ILDs) decrease. This property is at the core of discussions on electromigration-induced failures by all mechanisms. B is computed using finite element modeling analyses, using experimentally determined mechanical properties of the individual constituents. Characterization techniques include nanoindentation, cantilever deflection, and pressurized membrane deflection for elastic properties measurements, and chevron-notched double-cantilever pull structures for adhesion measurements. The dominant diffusion path in Cu-interconnects is the interface between Cu and the capping layer, which is currently a Si3N4-based film. We performed experiments on Cu-interconnect segments to investigate the kinetics of electromigration. A steady resistance increase over time prior to open-circuit failure, a result of void growth, correlates with the electromigration drift velocity. Diffusive measurements made in this fashion are more fundamental than lifetime measurements alone, and correlate with the combined effects of the electron wind and the back stress forces during electromigration induced void growth.

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

2007

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/1721.1/42026

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/42026