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Etch Selectivity of Novel Epitaxial Layers for Bulk Micromachining

Published online by Cambridge University Press:  10 February 2011

J. T. Borenstein ,
N. D. Gerrish ,
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
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

The present work demonstrates very high etch selectivity for a novel epitaxial layer in several standard bulk micromachining etchants. High selectivities have previously been achieved using high-concentration boron diffusions, resulting in a wide array of high performance micromechanical sensors. However, doping gradients, precipitates and dislocation arrays generated from the high boron concentrations can have deleterious effects on device performance. In this work, we report on the performance of a novel epitaxial structure composed of a silicon-germanium alloy device layer over a graded buffer layer. Chemical and microstructural analysis of the epitaxial layers reveal high purity and minimal defect densities. The selectivities of this layer and of boron-diffused layers are determined for a variety of etching conditions. High selectivity against low-doped silicon substrates is demonstrated in both ethylenediamine pyrocatechol and potassium hydroxide. Micromachined structures built using the SiGe epitaxial layer show smooth surfaces and precise build dimensions.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 546: Symposium AA – Materials Science of Microelectromechanical Systems (MEMS)… , 1998 , 69
Copyright
Copyright © Materials Research Society 1999

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