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Mechanical Properties of Boron Doped Si and Si/SiO 2 Membranes

Published online by Cambridge University Press:  01 February 2011

Gabe Kuhn
Affiliation:
School of Mechanical and Materials Engineering Washington State University, Pullman, WA 99164-2920.
Todd Myers
Affiliation:
School of Mechanical and Materials Engineering Washington State University, Pullman, WA 99164-2920.
Susmita Bose
Affiliation:
School of Mechanical and Materials Engineering Washington State University, Pullman, WA 99164-2920.
Amit Bandyopadhyay
Affiliation:
School of Mechanical and Materials Engineering Washington State University, Pullman, WA 99164-2920.
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Abstract

In our research, PZT film actuated micro-machined Si substrates are being developed for numerous applications in which membranes are actuated primarily in flexural mode. Silicon wafers, 3-inches in diameter, underwent boron doping in order to act as an etch stop. Approximately 200-nm of SiO2 was grown on the boron-doped side of the wafers. Photolithography and backside etching using EDP resulted in 2-μm thick membranes. Using reactive ion etching (RIE), beam structures resulted from the membranes. Nano-mechanical testing of the beams indicated that there were substantial residual tensile stresses in these structures. Initial calculations reveal a tensile stress of 57.7 MPa in the Si/SiO2 beams. The residual tensile stress subsequently caused the overall beam stiffness to be two orders of magnitude higher than it would be without stress. After stripping the oxide with a buffered oxide etchant (BOE), a residual stress of 26.5 MPa was measured, which is presumably caused from the remaining boron concentration. The aim of this paper is to understand influences of boron doping and processing variables on residual stresses.

Type
Research Article
Copyright
Copyright © Materials Research Society 2002

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