Thermomechanical Stresses in Copper Films at Elevated Temperature

Author(s)
Martin Lederer, Javad Zarbakhsh, Rui Huang, Thomas Detzel, Brigitte Weiss
Abstract

Thermomechanical stresses in metallic films are a root cause for material fatigue which limits the lifetime of electronic devices. Since the yield stress of metals is temperature dependent, plastic deformations during thermal cycling are increased at elevated temperature. This effect reduces the reliability of electronic parts. In order to investigate this problem, a 20 mm thick copper film was deposited on a silicon wafer. After annealing at 4008C, the sample was exposed to thermal cycles in the temperature range between room temperature and 6008C. The different values for the coefficient of thermal expansion of copper and silicon lead to a curvature of the sample. The wafer curvature was measured by a multilaser beam method. On the basis of the experimental results, a new theoretical model was developed that describes the stress evolution in the film during thermal cycling. In this investigation, the relation between wafer curvature and film stress is calculated by analogy to a model by Freund which is an improvement to the well-known Stoney formula. In addition to the elastic response, the new model considers plasticity of the copper film as well as temperature dependence of creep. It is demonstrated that the model can describe the experiment well and thus thermomechanical stress in copper films.

Organisation(s)
Physics of Nanostructured Materials
External organisation(s)
Kompetenzzentrum Automobil- und Industrie-Elektronik GmbH (KAI), Infineon Technologies Austria AG
Journal
Journal of Microelectronics and Electronic Packaging
Volume
7
Pages
99-104
No. of pages
6
ISSN
1551-4897
Publication date
2010
Peer reviewed
Yes
Austrian Fields of Science 2012
1030 Physics, Astronomy
Portal url
https://ucris.univie.ac.at/portal/en/publications/thermomechanical-stresses-in-copper-films-at-elevated-temperature(15ed8e7e-3876-44b5-951c-2ab31bc1469a).html