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LPCVD Silicon Dioxide Sacrificial Layer Etching for Surface Micromachining

Published online by Cambridge University Press:  15 February 2011

David J. Monk ,
David S. Soane  and
Roger T. Howe
David J. Monk
Affiliation:
Department of Chemical Engineering, University of California, Berkeley, California 94720. (510) 642-0958, FAX (510) 642-4778
David S. Soane
Affiliation:
Department of Chemical Engineering, University of California, Berkeley, California 94720. (510) 642-0958, FAX (510) 642-4778
Roger T. Howe
Affiliation:
Berkeley Sensor & Actuator Center, Department of Electrical Engineering & Computer Science, University of California, Berkeley, California 94720
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Abstract

The key step in producing a movable microstructure is the controllable sacrificial layer etching process. For the current study, a 1 μm silicon-rich silicon nitride structural layer was deposited on a 2 μm phosphosilicate glass (PSG) sacrificial layer that had been deposited on a single-crystal silicon wafer. Silicon nitride, unlike the more common polycrystalline silicon (poly-Si) structural material, is transparent and, therefore, allows the observation of an etch front in the underlying PSG sacrificial layer. The PSG is an amorphous silicon dioxide, with phosphorus added as a controlled impurity, that can be selectively etched in hydrofluoric acid. Several experiments have been performed with four HF concentrations using these test structures. Diffusion limited etching is observed at long etching times for each concentration. Additional experimental work has been done to determine appropriate kinetic expressions for the PSG/HF reactions.

The sacrificial layer etching process has been modeled as a chemical reaction/diffusion system. Constants for the kinetic expression have been found from independent experimental work. This Deal-Grove type model assumes isothermal conditions, constant density solution, onedimensional etching, and the equality of the diffusion and reaction fluxes. The model calculates the HF surface concentration and the length of PSG underetched as a function of time. It fits the data well but requires the use of an unphysical diffusion coefficient. An extension of the Deal-Grove model to nonfirst order kinetics allows for a reasonable estimate of the reactant/product mixture diffusivity in water to be used when fitting the model to experimental data.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 276: Symposia U/Y – Smart Materials Fabrication and Materials for Micro-Electro-Mechanical Systems , 1992 , 303
Copyright
Copyright © Materials Research Society 1992

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References

REFERENCES

1. Howe, R.T., J. Vac. Sci. Technol. 5&6, 1809 (1988).Google Scholar
2. Fan, L.-S., Tal, Y.-C., and Muller, R. S., IEEE Trans. Electron Devices 35, 724 (1988).Google Scholar
3. Tang, W., Sensors & Actuators A21–A23, 328 (1990).CrossRefGoogle Scholar
4. Schmidt, M. A., Howe, R. T., Senturia, S. D., and Haritonidis, J. H., IEEE Trans. Electron Devices 35, 750 (1988).Google Scholar
5. Kim, Y. W. and Allen, M. G. in 1991 International Conference on Solid-State Sensors and Actuators@ Transducers '91, (IEEE, San Francisco, CA, 1991), pp. 651.Google Scholar
6. Chang, R., Chemistry (Random House, New York, 1984).Google Scholar
7. Srinivasan, K. and Rechnitz, G. A., Anal. Chem. 40, 509 (1968).CrossRefGoogle Scholar
8. Judge, J. S., J. Electrochem. Soc. 118, 1772 (1971).CrossRefGoogle Scholar
9. Judge, J. S., in Proceedings of the Symposium on Etching for Pattern Definition, edited by Hughes, H. G. and Rand, M. J. (The Electrochemical Society, Princeton, New Jersey, 1976), pp. 19.Google Scholar
10. Mesmer, R. E. and Baes, C. F. Jr., Inorganic Chemistry 8, 618 (1969).CrossRefGoogle Scholar
11. Tenney, A. S. and Ghezzo, M., J. Electrochem. Soc. 120, 1091 (1973).CrossRefGoogle Scholar
12. Voros, K., (private communication).Google Scholar
13. Palmer, W. G., J. Chem. Soc. 1657 (1930).Google Scholar
14. Lund, K., Ph.D. Thesis, University of Michigan, 1974.Google Scholar
15. Lund, K., Fogler, H. S., McCune, C. C., and Ault, J. W., Chem. Eng. Sci. 20, 825 (1975).CrossRefGoogle Scholar
16. Fogler, H. S., Lund, K., and McCune, C. C., Chem. Eng. Sci. 30, 1325 (1975).Google Scholar
17. Born, H. K. H., Ph. D. Thesis, University of Texas, Austin, 1976.Google Scholar
18. Born, H. H. and Prigogine, M., J. Chim. Phys. 79, 538 (1979).Google Scholar
19. Kline, W. E., Ph. D. Thesis, University of Michigan, 1980.Google Scholar
20. Kline, W. E. and Fogler, H. S., Ind. Eng. Chem. Fundam. 20, 155 (1981).Google Scholar
21. O'Keefe, T. W. and Handy, R. M., Solid-State Electronics 11,261 (1968).Google Scholar
22. Deal, B. E. and Grove, A. S., J. Appl. Phys. 36, 3770 (1965).Google Scholar
23. Fogler, H. S., Elements of Chemical Reaction Engineering (Prentice-Hall, Englewood Cliffs, NJ, 1986).Google Scholar
24. Blumberg, A. A., J. Phys. Chem. 63, 1129 (1959).Google Scholar
25. Blumberg, A. A. and Stravrinou, S. C., J. Phys. Chem. 64, 1438 (1960).CrossRefGoogle Scholar
26. Monk, D. J., Soane, D. S. and Howe, R. T. in 1991 International Conference on Solid-State Sensors and Actuators@ Transducers '91, (IEEE, San Francisco, CA, 1991), pp. 647.Google Scholar
27. Reid, R. C., Prausnitz, J. M. and Poling, B. E., The Properties of Gases & Liquids (McGraw-Hill, New York, 1986).Google Scholar
28. Deckert, C. A., J. Electrochem. Soc. 125, 320 (1978).Google Scholar
29. Decked, C. A., J. Electrochem. Soc. 127, 2433 (1980).Google Scholar
30. Nisancioglu, K. and Newman, J., AIChE J 2, 797 (1973).CrossRefGoogle Scholar