Process engineering and failure analysis of MEMS and MOEMS require static and dynamical characterization of both their in-plane and out of plane response to an excitation. A remarkable characteristic of Digital Holography Microscopes (DHM) is the extremely short acquisition time required to grab the whole information necessary to provide 3D optical topography of the sample: a unique frame grab, without any vertical or lateral scan provides the information over the full field of view. First, it ensures DHM measurements to be insensitive to vibrations. Second, it opens the door to fast dynamical characterization of micro-systems. For periodic movement analysis, DHM can operate in stroboscopic mode with standard cameras. It enables precise characterization up to excitation frequencies of 100 kHz with recovery cycle of 10% simply by triggering properly the camera. Pulsed sources can be used for investigation of higher excitation frequencies. For non periodic movement analysis fast acquisition cameras and postponed treatment are used. DHM are therefore unique and very efficient tool for dynamical characterization of in-plane and out-of-plane response. In this paper we show the basics of the technology and illustrate process engineering and failure analysis using DHM with an example of in and out of plane characterization of movements of a variable capacitor using the stroboscopic mode of acquisition.
Digital Holographic Microscopes (DHM) enables recording the whole information necessary to provide real time nanometric vertical displacement measurements with a single image acquisition. The use of fast acquisition camera or stroboscopic acquisition mode makes these new systems ideal tools for investigating the topography and dynamical behavior of MEMS and MOEMS. This is illustrated by the investigation of resonant frequencies of a dual axis micromirror. This enables the definition of the linear, non-linear, and modal resonance zones of its dynamical response.
With the recent technological advances, there is an increasing need for measurement systems providing interferometer resolution for inspection of large quantities of individual samples in manufacturing environments.. Such applications require high measurement rates, robustness, ease of use, and non-contact systems.We show here that Digital Holographic Microscopy (DHM), a new method that implements digitally the principle of holography, is particularly well suited for such industrial applications. With the present computers power and the developments of digital cameras, holograms can be numerically interpreted within a tenth of second to provide simultaneously: the phase information, which reveals object surface with vertical resolution at the nanometer scale along the optical axis, and intensity images, as obtained by conventional optical microscope.The strength of DHM lies in particular on the use of the so-called off-axis configuration, which enables to capture the whole information by a single image acquisition, i.e. typically during a few ten of microseconds. These extremely short acquisition times make DHM systems insensitive to vibrations. These instruments can operate without vibration insulation means, making them a cost effective solution not only for R&D, but also especially for an implementation on production lines.Numerous application examples are presented in this paper such as shape and surface characterization of high aspect ratio micro-optics, surface nanostructures, and surface roughness.
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