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Mechanical properties of porous and fully dense low-κ dielectric thin films measured by means of nanoindentation and the plane-strain bulge test technique

Published online by Cambridge University Press:  01 February 2006

Y. Xiang ,
X. Chen ,
T.Y. Tsui ,
J-I. Jang  and
J.J. Vlassak
Y. Xiang
Affiliation:
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138
X. Chen
Affiliation:
Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, New York 10027
T.Y. Tsui
Affiliation:
Texas Instruments Inc., Dallas, Texas 75243
J-I. Jang
Affiliation:
Department of Materials Science and Engineering, Hanyang University, Seoul 133-791, South Korea
J.J. Vlassak*
Affiliation:
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138
*
a)Address all correspondence to this author. e-mail: vlassak@esag.deas.harvard.edu
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Abstract

We report on the results of a comparative study in which the mechanical response of both fully dense and porous low-κ dielectric thin films was evaluated using two different techniques: nanoindentation and the plane-strain bulge test. Stiffness values measured by nanoindentation are systematically higher than those obtained using the bulge test technique. The difference between the measurements is caused by the Si substrate, which adds significantly to the contact stiffness in the indentation measurements. Depending on the properties of the coatings, the effect can be as large as 20%, even if the indentation depth is less than 5% of the film thickness. After correction of the nanoindentation results for the substrate effect using existing models, good agreement is achieved between both techniques. The results further show that densification of porous material under the indenter does not affect stiffness measurements significantly. By contrast, nanoindentation hardness values of porous thin films are affected by both substrate and densification effects. It is possible to eliminate the effect of densification and to extract the yield stress of the film using a model for the indentation of porous materials proposed by the authors. After correcting for substrate and densification effects, the nanoindentation results are in close agreement with the bulge test measurements. The results of this comparative study validate the numerical models proposed by Chen and Vlassak for the substrate effect and by Chen et al. for the densification effect.

Keywords

Mechanical propertiesNanoindentationThin film
Type
Articles
Information
Journal of Materials Research , Volume 21 , Issue 2 , February 2006 , pp. 386 - 395
Copyright
Copyright © Materials Research Society 2006

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