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Size Effect on Crack Formation in Cu/Ta and Ta/Cu/Ta Thin Film Systems

Published online by Cambridge University Press:  15 March 2011

P. Gruber
Affiliation:
Universitét Stuttgart, Institut für Metallkunde, Stuttgart, Germany
J. Böhm
Affiliation:
Universitét Stuttgart, Institut für Metallkunde, Stuttgart, Germany
A. Wanner
Affiliation:
Universitét Karlsruhe, Institut für Werkstoffkunde I, Karlsruhe, Germany
L. Sauter
Affiliation:
Max-Planck-Institut für Metallforschung, Stuttgart, Germany
R. Spolenak
Affiliation:
Max-Planck-Institut für Metallforschung, Stuttgart, Germany
E. Arzt
Affiliation:
Universitét Stuttgart, Institut für Metallkunde, Stuttgart, Germany Max-Planck-Institut für Metallforschung, Stuttgart, Germany
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Abstract

Layered structures of Cu and Ta thin films on silicon are well established for many technological applications in microelectronics. Electronic circuits used for flexible displays or wearable electronics are becoming increasingly popular. For such applications, the Cu/Ta system must be transferred to flexible substrates, incorporating a design rule for several percent of total strain. We have investigated the deformation behaviour of different Cu/Ta and Ta/Cu/Ta thin film systems on a flexible polyimide substrate subjected to total strains of more than 5%. A novel synchrotron X-ray diffraction technique allowed us to characterize the evolution of mechanical stress in very thin metallic films during isothermal tensile tests. We found that samples with a Cu film thickness below 300 nm showed a sudden stress decrease at a total strain of about 2.5%. This stress drop was attributed to fracture of the entire film system, initiated by cracks in the Ta layers.

Type
Research Article
Copyright
Copyright © Materials Research Society 2004

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