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Proceedings Paper

Modeling of stress-induced curvature in surface-micromachined devices
Author(s): William D. Cowan; Victor M. Bright; Alex A. Elvin; David A. Koester
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Paper Abstract

This paper compares measured to modeled stress-induced curvature of simple piston micromirrors. Two similar flexure-beam micromirror designs were fabricate using the 11th DARPA-supported multi-user MEMS processes (MUMPs) run. The test devices vary only in the MUMPs layers used for fabrication. In one case the mirror plate is the 1.5 micrometers thick Poly2 layer. The other mirror design employs stacked Poly1 and Poly2 layers for a total thickness of 3.5 micrometers . Both mirror structures are covered with the standard MUMPs metallization of approximately 200 angstrom of chromium and 0.5 micrometers of gold. Curvature of these devices was measured to within +/- 5 nm with a computer controlled microscope laser interferometer system. As intended, the increased thickness of the stacked polysilicon layers reduces the mirror curvature by a factor of 4. The two micromirror designs were modeled using IntelliCAD, a commercial CAD system for MEMS. The basis of analysis was the finite element method. Simulated results using MUMPs 11 film parameters showed qualitative agreement with measured data, but obvious quantitative differences. Subsequent remeasurement of the metal stress and use of the new value significantly improved model agreement with the measured data. The paper explores the effect of several film parameters on the modeled structures. Implications for MEMS film metrology, and test structures are considered.

Paper Details

Date Published: 2 September 1997
PDF: 12 pages
Proc. SPIE 3225, Microlithography and Metrology in Micromachining III, (2 September 1997); doi: 10.1117/12.284554
Show Author Affiliations
William D. Cowan, Air Force Institute of Technology (United States)
Victor M. Bright, Air Force Institute of Technology (United States)
Alex A. Elvin, IntelliSense Corp. (United States)
David A. Koester, MCNC (United States)

Published in SPIE Proceedings Vol. 3225:
Microlithography and Metrology in Micromachining III
Craig R. Friedrich; Akira Umeda, Editor(s)

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