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Determination of dimensional parameters in MEMS components by vibration analyses

: Kurth, S.; Mehner, J.; Shaporin, A.V.; Michael, S.; Ebert, M.; Gessner, T.

Society for Experimental Mechanics -SEM-, Bethel:
Modal Analysis Conference 2007, IMAC-XXV. Vol.3 : A Conference & Exposition on Structural Dynamics; February 19 - 22, 2007, Orlando, Florida.
Modal Analysis Conference (IMAC) <25, 2007, Orlando>
Fraunhofer ENAS ()
Fraunhofer IZM ()

Measuring of geometry and mechanical stress are among the main concerns of MEMS testing because monitoring of this parameters in the fabrication line offers the possibility to respond to drift of fabrication parameters and to select chips which are out of the specification before the relatively expensive packaging procedure. This contribution deals with a method for fast determination of geometry and mechanical stress in membranes, beams or other spring-mass-configurations which is suitable for integration into the fabrication line. A finite element modal analysis of the device with variation of the interesting parameters is conducted and the eigenfrequencies are expanded to a multi-variable polynomial of the interesting parameters for one time at the beginning of the procedure. Using a wafer probe station the following on-line test of each MEMS-chip is based on measurement of eigenfrequencies of by electrostatic mechanical excitation and optical vibration detection. The measurements are done at wafer level and without mechanical contact between instrumentation and the devices under test. Applying an algorithm using method of least square fit, geometry and mechanical stress are determined very time effective. Algorithms, instrumentation and implementation in the fabrication line will be discussed in the contribution on several examples.