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Origins of Residual Stress in Mo and Ta Films: the Role of Impurities, Microstructural Evolution, and Phase Transformations

Published online by Cambridge University Press:  15 February 2011

L. J. Parfitt ,
O. P. Karpenko ,
Z. U. Rek ,
S. M. Yalisove  and
J. C. Bilello
L. J. Parfitt
Affiliation:
The Materials Science and Engineering Department, The University of Michigan, Ann Arbor, MI 48109–2136
O. P. Karpenko
Affiliation:
The Materials Science and Engineering Department, The University of Michigan, Ann Arbor, MI 48109–2136
Z. U. Rek
Affiliation:
Stanford Synchrotron Radiation Laboratory, Stanford, CA 94025
S. M. Yalisove
Affiliation:
The Materials Science and Engineering Department, The University of Michigan, Ann Arbor, MI 48109–2136
J. C. Bilello
Affiliation:
The Materials Science and Engineering Department, The University of Michigan, Ann Arbor, MI 48109–2136
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Abstract

Both the sign and magnitude of residual stress can vary with the thickness of sputter deposited films. The origins of this behavior are not well understood. In this work, we consider the correlation between the residual stress behavior and the depth dependence of impurities in thin (2.5 nm - 150 nm) sputtered Mo and Ta films. We also consider the effects of phase transformations and microstructural changes on the stress behavior. Films were deposited onto Si substrates with native oxide. The residual stress observed in the Mo films varied from highly compressive at 2.5 nm film thickness to ∼ 0 ˜ 10 nm thickness. Ta films also exhibited a high compressive stress, which relaxed from highly compressive to tensile between 10 nm and 50 nm film thickness. Impurities in the films may originate from the sputtering targets, the background gases, and the substrate surfaces. Auger Electron Spectroscopy (AES) results showed the presence of O and C contamination near the film/Si interface; these impurities contributed to the compressive stresses in the thinner films. As anticipated, both Mo and Ta films exhibited grain growth as a function of film thickness, which may have contributed to the relaxation in the compressive stress. The Mo films were entirely bcc. The Ta films showed a transformation from the amorphous phase to the β crystalline phase between 2.5 nm and 20 nm film thickness, which contributed to the relaxation in stress observed in that thickness regime.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 436: Symposium CC – Thin Films Stresses and Mechanical Properties VI , 1996 , 505
Copyright
Copyright © Materials Research Society 1997

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