The knife-edge technique in reflection mode is an alternative method for the characterization of in-plane motion and vibrations of microdevices. In this paper, we investigate this technique for sinusoidal vibration measurements of microresonators. First, we examine theoretically the effect of light reflection on the non moving substrate. It is shown that it has a significant effect on the sensitivity of the knife-edge technique to in-plane vibrations and that it introduces a slight sensitivity to out-of-plane vibrations. Then we demonstrate in-plane resonance measurements with a resolution in the nanometer range in the unfavourable case of a polysilicon resonator on a polysilicon coated substrate. Finally advantages, limitations and calibration issues of this technique are discussed.
Fringe pattern demodulation by the Fourier transform method associated with fringe extrapolation by the Gerchberg
algorithm was investigated in details for its application to fast profiling of surfaces with small patterns and/or cuttings.
For such surfaces, spectral leakage is a major concern as it corrupts data in a large part of the areas of interest if
extrapolation is not carried out. Simulated fringe patterns or real interferograms recorded on micromechanical devices by
interference microscopy were used for this evaluation. Different filter shapes in the Fourier space were tested for the
determination of valid areas in the interferogram, for the fringe extrapolation stage and for the final phase demodulation.
It is demonstrated that filters with a shape adapted to the modulation sidelobe in the Fourier space allow automated
measurements without user expertise while maintaining a high accuracy. Some practical rules for the choice of
extrapolation margins, fringe density, fringe extrapolation iteration number and other parameters are clarified to reach
accurate and fast automated measurements.
Microelectromechanical systems (MEMS) are based on the generation and/or detection of deformations, motion and vibrations of thin mechanical structures having lateral dimensions in the micrometer to millimeter range. A number of technological issues commonly appear during the development of MEMS fabrication processes such as non uniform etching or deposition, surface roughening, stiction and stress-induced deformations. Likewise, as mechanical properties of thin films are difficult to predict, and are very variable with process parameters. Consequently, experimental data on the (thermo)mechanical and dynamical behaviour of MEMS and on their reliability are often required. In this paper, after a short description of the basic principles and performances of interference microscopy techniques, we review the capabilities of full field interference microscopy techniques for these applications. They are illustrated by various examples taken during the development of MEMS fabrication and packaging processes, and by results of measurements as function of temperature or under vacuum.