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A. Bittner, S. Klein, H. Seidel, U. Schmid:
"Reliability of Ag Thin Films Sputter Deposited on Silicon and Ceramic Based Substrates";
Vortrag: SPIE Europe: Microtechnologies for the New Millennium, Dresden, Deutschland; 04.05.2009 - 08.05.2009; in: "Proceedings of SPIE", Society of Photo-Optical Instrumentation Engineers (SPIE, 7362-7366 (2009), 7 S.

Silver (Ag) is regarded as advanced material for metallization purposes in microelectronic devices because of its high conductivity and its enhanced electromigration resistance. Besides the typical use of silicon based substrate materials for device fabrication, thin film metallization on ceramic and glass-ceramic LTCC (low temperature cofired ceramics) substrates gets more and more into focus as only thin film technology can provide the required lateral resolutions of
structures in the μm-range needed for high frequency application. Therefore, the reliability of Ag thin films is investigated under accelerated aging conditions, utilizing test structure which consist of 5 parallel lines stressed with a current density of 2.5⋅106 A/cm² at temperatures ranging from room-temperature up to 300°C. To detect the degradation via the temporal characteristics of the current signal a constant voltage is applied according to the overall resistance of the test structure. Knowing the mean time to failure (MTF) and activation energy at elevated temperatures lifetime
predictions can be made when extrapolating for room temperature scenarios. Applying this approach, the highest value of 6053 days is determined for Ag thin films on LTCC. When compared to Si/SiO2 and alumina substrates the poorer performance originates from the microstructure of the films. On polycrystalline aluminum oxide Ag thin films exhibit sharp discontinuities due to a pronounced graining originating from the substrate. This effect could limit the distance of electromigration tracks.

Silver, reliability, LTCC, electromigration

http://dx.doi.org/10.1117/12.821328