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Proceedings Paper

Characterization of MEMS structures by microscopic digital holography
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Paper Abstract

We propose the use of digital holography (DH) as a metrological tool for inspection and characterization of MEMS structures. We show that DH can be efficiently employed to assess the fabrication process of micro structures as well as to test their behavior in operative conditions. DH allows reconstructing both the amplitude and phase of microscopic objects and, compared to traditional microscopy, it provides quantitative phase determination. We demonstrate that DH allows determination of full field deformation maps that can be compared with analytical and/or numerical models of the deformed microstructure. Application of DH on structures with several different geometries and shapes, like cantilever beams, bridges and membranes is reported and result will be discussed. Dimensions of the inspected microstructures ranging from 1 to 50μm. Examples of application are presented were DH allows determination with high accuracy out of plane deformations due to the residual stress introduced by the fabrication process. An optical set-up for recording digital holograms based on a Mach-Zehnder interferometer was adopted and a laser source which wavelength is λ=532nm was employed. The light reflected by the object under investigation was made to interfere with a plane wave front. Holograms were recorded by a CCD array with 1024 x 1280 square pixels with 6.7 μm size. A mirror mounted on a piezo-actuator was inserted along the reference arm of the interferometric in order to introduce controlled phase steps and to employ phase shifting technique. This technique allows suppressing both the zeroth-order and the conjugate wave-front in the numerical holographic reconstruction process. A method for compensating numerically curvature of the wave front and introduced by the microscopic objective lens is proposed and discussed.

Paper Details

Date Published: 25 March 2003
PDF: 8 pages
Proc. SPIE 4945, MEMS/MOEMS: Advances in Photonic Communications, Sensing, Metrology, Packaging and Assembly, (25 March 2003); doi: 10.1117/12.471989
Show Author Affiliations
Giuseppe Coppola, IMM/CNR (Italy)
Sergio De Nicola, Istituto di Cibernetica/CNR (Italy)
Pietro Ferraro, IMM/CNR (Italy)
Andrea Finizio, Istituto di Cibernetica/CNR (Italy)
Simonetta Grilli, Istituto Nazionale di Ottica Applicata (Italy)
Mario Iodice, IMM/CNR (Italy)
Carlo Magro, STMicroelectronics srl (Italy)
Giovanni Pierattini, Istituto di Cibernetica/CNR (Italy)


Published in SPIE Proceedings Vol. 4945:
MEMS/MOEMS: Advances in Photonic Communications, Sensing, Metrology, Packaging and Assembly

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