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The effects of passivation layer and film thickness on the mechanical behavior of freestanding electroplated Cu thin films with constant microstructure

Published online by Cambridge University Press:  01 February 2011

Yong Xiang ,
Joost J. Vlassak ,
Maria T. Perez-Prado ,
Ting Y. Tsui  and
Andrew J. McKerrow
Yong Xiang
Affiliation:
Division of Engineering and Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138
Joost J. Vlassak
Affiliation:
Division of Engineering and Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138
Maria T. Perez-Prado
Affiliation:
Department of Physical Metallurgy, Centro Nacional de Investigaciones Metalurgicas, CSIC Avda.Gregorio del Amo, 8, 28040 Madrid, Spain
Ting Y. Tsui
Affiliation:
Texas Instruments Inc., MS 3736, 13560 N. Central Expressway, Dallas, TX 75243
Andrew J. McKerrow
Affiliation:
Texas Instruments Inc., MS 3736, 13560 N. Central Expressway, Dallas, TX 75243
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Abstract

The goal of this paper is to investigate the effects of film thickness and the presence of a passivation layer on the mechanical behavior of electroplated Cu thin films. In order to study the effect of passivating layers, freestanding Cu membranes were prepared using standard silicon micromachining techniques. Some of these Cu membranes were passivated by sputter depositing thin Ti films with thicknesses ranging from 20 nm to 50 nm on both sides of the membrane. The effect of film thickness was evaluated by preparing freestanding films with varying thickness but constant microstructure. To that effect, coatings of a given thickness were first vacuum annealed at elevated temperature to stabilize the microstructure. The annealed films were subsequently thinned to various thicknesses by means of chemical mechanical planarization (CMP) and freestanding membranes were prepared both with and without Ti passivation. The stress-strain curves of the freestanding Cu films were evaluated using the bulge test technique. The residual stress and elastic modulus of the film are not affected significantly by the passivation layer. The elastic modulus does not change with film thickness if the microstructure keeps constant. The yield stress increases if the film is passivated. For passivated films, yield stress is proportional to the inverse of the film thickness, which is consistent with the formation of a boundary layer of high dislocation density near the interfaces.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 795: Symposium U – Thin Films - Stresses and Mechanical Properties X , 2003 , U11.37
Copyright
Copyright © Materials Research Society 2004

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References

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