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Silicon Germanium Epitaxy: A New Material for MEMS

Published online by Cambridge University Press:  17 March 2011

J.T. Borenstein ,
N.D. Gerrish ,
R. White ,
M.T. Currie  and
E.A. Fitzgerald
J.T. Borenstein
Affiliation:
Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139
N.D. Gerrish
Affiliation:
Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139
R. White
Affiliation:
Charles Stark Draper Laboratory, 555 Technology Square, Cambridge, MA 02139
M.T. Currie
Affiliation:
Department of Materials Science & Engineering, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139
E.A. Fitzgerald
Affiliation:
Department of Materials Science & Engineering, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139
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Abstract

A wide array of materials have been investigated as candidate fabrication templates for precision microelectromechanical structures, including boron-diffused silicon, boron-doped epitaxial silicon, polysilicon, silicon-on-insulator, and wafer-thick bulk structures. Here we present the latest fabrication results for epitaxial silicon-germanium alloys, a new class of materials which possess excellent crystalline structure, are compatible with non-toxic etchants in bulk micromachining, and are capable of on-chip integration with electronics. For MEMS applications, silicon-germanium alloy layers are grown using a graded buffer approach, resulting in very high quality micromachined structures. Very low defect densities are obtained through the use of these relaxed buffers. Original etch-stop studies determined that Ge doping provided a very weak selectivity in anisotropic etchants such as KOH and EDP. However, by extending the range of Ge concentration to over 20%, we have found extremely high etch selectivities in a variety of etchants. Unlike boron-doped layers, SiGe exhibits etch stop characteristics in the non-toxic, process compatible solution TMAH. The combination of independence from boron doping concentration and etchant compatibility make SiGe a material which is ideal for integration with on-chip electronics.

In this work we present the latest fabrication data on comb-drive resonators built using SiGe epitaxial layers. Process compatibility issues related to wafer curvature, surface finish and reactive-ion-etching chemistries are addressed. An unexpected result of the fabrication process, curvature of released structures, is resolved by annealing wafers after the SiGe deposition. Changes in Young's modulus arising from the high atomic fraction of Ge in the device can be determined by simple beam analysis based on observed resonant frequencies. Overall, build precision for these devices is excellent. We conclude by addressing the remaining challenges for wide-scale implementation of silicon-germanium epitaxial MEMS.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 657: Symposia EE – Materials Science of Microelectromechanical Systems (MEMS) Devices III , 2000 , EE7.4
Copyright
Copyright © Materials Research Society 2001

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References

REFERENCES

1. Kourepenis, A., Borenstein, J., Connelly, J., Elliott, R., Ward, P. and Weinberg, M. in IEEE Position, Location and Navigation Symposium, (IEEE, Palm Springs CA, 1998), pp. 1–8.Google Scholar
2. Fitzgerald, E. A., Wu, K. C., Currie, M., Gerrish, N., Bruce, D., and Borenstein, J. T. in Microelectromechanical Structures for Materials Research, edited by Brown, S., Gilbert, J., Gückel, H., Howe, R., Johnston, G., Krulevitch, P. and Muhlstein, C., (Mater. Res. Soc. Proc. 518, Pittsburgh, PA, 1998) pp. 233–238.Google Scholar
3. Borenstein, J. T., Gerrish, N. D., Currie, M. T. and Fitzgerald, E. A., in Materials Science of Microelectromechanical Systems (MEMS) Devices, edited by Heuer, A.H. and Jacobs, S.J., (Mater. Res. Soc. Proc. 546, Pittsburgh, PA, 1999) pp. 69–74.Google Scholar
4. Wu, K.C., Shay, P.A., Borenstein, J.T. and Fitzgerald, E.A. in Materials for Mechanical and Optical Microsystems, edited by Reed, M.L., Elwenspoek, M., Johansson, S., Obermeier, E., Fujita, H. and Uenishi, Y., (Mater. Res. Soc. Proc. 444, Pittsburgh, PA, 1997) pp. 197–202.Google Scholar
5. Seidel, H., Csepregi, L., Heuberger, A. and Baumgärtel, H., J. Electrochem. Soc., 137 3626 (1990.)Google Scholar
6. Cho, S.T., in Micromachining and Microfabrication Process Technology, edited by Markus, K.W., (SPIE Press, Vol. 2639, Bellingham, WA, 1995) pp. 10–17.Google Scholar
7. Ayon, A.A., Chen, K.-S., Lohner, K.A., Spearing, S.M., Sawin, H.H. and Schmidt, M.A. in Materials Science of Microelectromechanical Systems (MEMS) Devices, edited by Heuer, A.H. and Jacobs, S.J., (Mater. Res. Soc. Proc. 546, Pittsburgh, PA, 1999) pp. 51–62.Google Scholar
8. Borenstein, J. T., Greiff, P., Sohn, J.B. and Weinberg, M.S. in Micromachining and Microfabrication Process Technology II, edited by Pang, S.W. and Chang, S.-C., (SPIE Press, Vol. 2879, Bellingham, WA, 1996) pp. 116–125.Google Scholar
9. Bernstein, J., Cho, S., King, A.T., Kourepenis, A., Maciel, P. and Weinberg, M. in Proc. of the IEEE MEMS Workshop, edited by Pisano, A. and Lang, J., (IEEE, 1993) pp. 143–148.Google Scholar
10. Young, W.C.C. and Roark, R.J., Roark's Formulas for Stress and Strain, 6th ed., (McGraw-Hill, New York, 1990.)Google Scholar
11. Senturia, S.D., this proceedings.Google Scholar
12. Vegard, L., Z. Phys., 5 17 (1921.)Google Scholar
13. Wortman, J.J. and Evans, R.A., J. Appl. Phys. 36 153 (1965.)Google Scholar
14. Borenstein, J. T., Gerrish, N. D., Currie, M. T. and , Fitzgerald in Proc. of 12th Intl. Workshop on MEMS, edited by Gabriel, K. and Najafi, K., (IEEE, Orlando, FL, 1999), pp. 205–210.Google Scholar