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


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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. © 2006 Materials Research Society.
Original languageEnglish
Pages (from-to)386-395
Number of pages10
JournalJournal of Materials Research
Issue number2
Early online date1 Feb 2006
Publication statusPublished - Feb 2006
Externally publishedYes

Bibliographical note

This work was supported primarily by the Materials Research Science and Engineering Center of the National Science Foundation under NSF Award No. DMR-0213805 and by the Semiconductor Research Corporation (Task ID 1292.010). X.C. acknowledges support from NSF Award No. CMS-04077432. The authors would like to thank George Pharr for use of the nanoin-denter.


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