1 - Erich Schmid Institute

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A A Direct Method of Determining Complex Depth Profiles of Residual Stresses
A.7 Comparison of the ILR Method With Other Techniques
A large number of techniques, such as the wafer curvature method, 1–3 microcantilever
techniques14–17 and methods that are based on optical interferometry18, 19 have been
developed to determine average stresses or simple stress gradients in thin films. Most
methods use the original Stoney’s equation or modifications to determine the residual
stresses.
Besides the developed ILR method, the only existing technique that permits the determination
of complex depth profiles of residual stresses on a nanoscale is the grazing incidence
X-ray scattering (GIXS) method. 5 Although the GIXS method is non-destructive,
the advantages of the ILR method are the lateral resolution of a few micrometers, the
straight-forward calculation procedure and the possibility of investigating stress profiles
in amorphous thin films.
The method developed by Kang et al., 20 which detects the stress-induced relaxation
of the film in the vicinity of a FIB-fabricated slot, allows the investigation of residual
stresses in amorphous as well as crystalline thin films. Theoretically, this technique can
be used to determine depth profiles of residual stresses, but this capability has yet to be
demonstrated.
Similar methods, although on the micrometer or millimeter scale, respectively, are the
hole drilling strain-gage and the incremental hole drilling method. 21, 22
A.8 Conclusion
The FIB-based ILR method is a useful tool for determining residual stress profiles in nearsurface
regions on a nanoscale. The calculation and experimental procedure developed
can be used for arbitrary combinations of crystalline or amorphous layered materials. To
ensure linear elastic behavior of the material(s), the thickness of the cantilever should be
adapted to the actual materials and the estimated mean stresses. The influence of ion
damage due to FIB fabrication and the plastic relaxation in the presented Ni/Si system
was evaluated. This evaluation showed that the stress profile in the thin Ni film was not
significantly affected.
A.9 Acknowledgements
The authors thank the Austrian Science Foundation FWF for supporting this work and
G. Dehm, F.D. Fischer, T. Antretter, D. Kiener, W. Ecker and K.J. Martinschitz for
helpful discussions.
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