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Use of speckle interferometry for quality assurance in microfabrication

: Aswendt, P.; Höfling, R.; Neugebauer, Reimund

Rastogi, P.K.:
Trends in optical nondestructive testing and inspection
Amsterdam: Elsevier, 2000
ISBN: 0-08-043020-1
International Conference on Trends on Optical Nondestructive Testing <2000, Lugano>
Fraunhofer IWU ()
speckle interferometry; vibration deformation; non-destructive testing MEMS

The industrial manufacturing of microcomponents generates a new challenge for quality testing equipment in general. The non-contacting operation of optical metrology makes it attractive for a number of tasks in this field. Holographic Non-Destructive Testing (HNDT) is highly sophisticated for selected industrial applications and in particular, systems based upon speckle interferometry (ESPI) proved well suited for quality assurance purposes on the macroscopic level. The key for HNDT is the capability for detecting deformation, vibration, and strain with high sensitivity and for any point in the field of view by using an interferometric technique. This paper deals with possibilities and application limits of ESPI in the case of scaling down the object size below one millimeter. In a first part, both spatial resolution and displacement sensitivity of the technique are discussed. Theoretical considerations are shown together with experimental verification. Secondly, a micro speckle interferometer will be presented that has been built for the the use with different microscopes. Its capabilities are demonstrated by a practical application. The microcomponent under investigation is a bulk micromachined gyroscope, a demanding object with respect to its multilayer design. Developments aim at increasing the spatial resolution step by step and results obtained with different field of view will demonstrate the progress. Finally, the deformation behaviour of an X-shaped torsional spring with a width of 100 mu m could be characterized.