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Proceedings Paper

Effects of metal impuritites on the etch rate selectivity of (110)/(111) in (110) Si anisotropic etching
Author(s): Yoshiaki Hirata; Masahiro Tsugai; Koji Tanimoto; Teruo Usami; Yasuo Yamaguchi; Hiroshi Otani; Kunihiro Nakamura
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Paper Abstract

We have investigated the effects of metal impurities and thermal oxidation process on Si anisotropic KOH etching characteristics for fabricating microsensors and microactuators having precise deep narrow grooves or channels. The effect of metal impurities such as Al, Cr, Fe, Pb and Cu are evaluated using 30 wt percent KOH etchant at 60 degrees C. Al, Cr and Fe have no relation to the etching characteristics, however, Pb and Cu strongly affect the etching characteristics. The etching rate of Si decreases with increasing Pb and Cu concentration. The etch rate selectivity , which is an anisotropy ratio defined by the etch rate ratio of (110) and (111) plane, is not changed by Pb impurity, but extremely decreases with increasing Cu impurity. It dips form 150 to 80 when the Cu concentration is over 50ppb, and saturated over the concentration. With respect to the surface roughness within our evaluated metal impurities, Cu impurity also strongly affects the roughness of the etched surface. In addition to the effect of metal impurities, we have experienced the effect on the etching selectivity by the thermal oxidation process. The selectivity is decreased with repeating thermal oxidation process, and this tendency is more pronounced with higher oxygen concentration of evaluated Si wafers. As a result, controlling Cu impurity concentration and using a low oxygen concentration wafer are crucial considerations when fabricating sensors and actuators with narrow grooves or channels by Si anisotropic KOH etching.

Paper Details

Date Published: 30 August 1999
PDF: 8 pages
Proc. SPIE 3874, Micromachining and Microfabrication Process Technology V, (30 August 1999); doi: 10.1117/12.361231
Show Author Affiliations
Yoshiaki Hirata, Mitsubishi Electric Corp. (Japan)
Masahiro Tsugai, Mitsubishi Electric Corp. (Japan)
Koji Tanimoto, Mitsubishi Electric Corp. (Japan)
Teruo Usami, Mitsubishi Electric Corp. (Japan)
Yasuo Yamaguchi, Mitsubishi Electric Corp. (Japan)
Hiroshi Otani, Mitsubishi Electric Corp. (Japan)
Kunihiro Nakamura, Mitsubishi Electric Corp. (Japan)

Published in SPIE Proceedings Vol. 3874:
Micromachining and Microfabrication Process Technology V
James H. Smith; Jean Michel Karam, Editor(s)

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