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Brittle-to-ductile transition in ultrathin Ta/Cu film systems

Published online by Cambridge University Press:  31 January 2011

Patric A. Gruber ,
Eduard Arzt  and
Ralph Spolenak
Patric A. Gruber*
Affiliation:
Universität Stuttgart, Institute of Physical Metallurgy, D-70569 Stuttgart, Germany
Eduard Arzt
Affiliation:
INM Leibniz Institute for New Materials, D-66123 Saarbrücken, Germany
Ralph Spolenak*
Affiliation:
Laboratory for Nanometallurgy, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland
*
a) Present address: Universität Karlsruhe, Institut für Zuverlässigkeit von Bauteilen und Systemen, D-76131 Karlsruhe, Germany.
b) Address all correspondence to this author. e-mail: ralph.spolenak@mat.ethz.ch
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Abstract

Current semiconductor technology demands the use of compliant substrates for flexible integrated circuits. However, the maximum total strain of such devices is often limited by the extensibility of the metallic components. Although cracking in thin films is extensively studied theoretically, little experimental work has been carried out thus far. Here, we present a systematic study of the cracking behavior of 34- to 506-nm-thick Cu films on polyamide with 3.5-to 19-nm-thick Ta interlayers. The film systems have been investigated by a synchrotron-based tensile testing technique and in situ tensile tests in a scanning electron microscope. By relating the energy release during cracking obtained from the stress-strain curves to the crack area, the fracture toughness of the Cu films can be obtained. It increases with Cu film thickness and decreases with increasing Ta film thickness. Films thinner than 70 nm exhibit brittle fracture, indicating an increasing inherent brittleness of the Cu films.

Keywords

CuFractureThin film
Type
Articles
Information
Journal of Materials Research , Volume 24 , Issue 6 , June 2009 , pp. 1906 - 1918
Copyright
Copyright © Materials Research Society 2009

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