Patterning and characterization of strain in sSOI materials

Strained silicon layers are patterned for fundamental analysis by electron beam lithography in combination with dry etching (cryo-etching (RIE) at -110°C using a SF6/O2 chemistry). Different patterns down to 50 nm feature size are prepared. Examples are shown in Fig. 1.


Fig. 1: SEM images of patterned strained silicon layers. The bare indicates 1µm.

There is a large number of methods to measure the strain in thin layers but only a few are applied to strained silicon. For characterization of strain in non-patterned layers X-ray diffraction methods and UV- Raman spectroscopy are generally used. Especially UV- Raman spectroscopy is the method of choice because it is a non-destructive method, easy to handle, allows fast measurements, and can be applied in CMOS process lines. Because the penetration depth of the laser light mostly used for excitation (λ = 325nm) is about 10 nm in silicon, UV Raman spectroscopy is applicable also for very thin strained silicon layers required for fully depleted device fabrication. The application of the conventional UV-Raman technique, however, is limited to patterned device layers. Fig. 2 shows a TEM cross-sectional image of the patterned strained silicon layer of a sSOI substrate. The blue area in the image corresponds to the diameter of the laser beam (about 800 nm) which is larger than an individual structure. Therefore the strong Si-Si vibration mode of the silicon base wafer appears and the Si-Si vibration mode of the thin strained silicon structures cannot clearly be identified anymore.


Fig. 2: TEM cross-sectional image of a patterned strained silicon layer of a sSOI substrate. The blue area indicates the diameter of the laser beam using a “conventional” UV µRaman setup.

1.Moutanabbir, M. Reiche, W. Erfurth, R. Scholz, and U. Gösele, Strain relaxation in nanostructured ultra thin SOI, 2008 IEEE International SOI Conference Proceedings , p 71-72 IEEE, Piscataway, USA (2008)

2.Moutanabbir, M. Reiche, W. Erfurth, N. Zakharov, R. Scholz, F. Naumann, M. Petzold, and U. Gösele, Proc. EUROSOI, Göteborg (2009)

3.N. Hayazawa, M. Motohashi, Y. Saito, and S. Kawata, Appl. Phys. Lett. 86, 263114 (2005).

4.L. Zhu, J. Atesang, P. Dudek, M. Hecker, J. Rinderknecht, Y. Ritz, H. Geisler, U. Herr, R. Geer, and E. Zschech, Materials Science – Poland 25, 19 (2007).

5.P. Zhang, A.A. Istratov, E.R. Weber, C. Kisielowski, H. He, C. Nelson, and J.C.H. Spence, Appl. Phys. Lett. 89, 161907 (2006).

6.M. Hytch, F. Houdellier, F. Hüe, and E. Snoeck, Nature 453, 1085 (2008).



back  |  print  |  to top