APPLICATION OF TIME-RESOLVED SCANNING ELECTRON-MICROSCOPY TO THE ANALYSIS OF THE MOTION OF MICROMECHANICAL STRUCTURES

We applied a time-resolved scanning electron microscope to the analysi s of the movement of micromechanical structures. A detector signal mod ulation method is used in our experiment. The major advantage of this method is that no hardware modifications are required to a commerciall y available scanning electron microscope. The test devices are simple cantilever beams fabricated from silicon dioxide with and without an a luminum coating. These cantilever beams are electrostatically excited at resonance under several conditions. Both time-resolved images and p recise resonant frequency measurements of these microcantilever beams are obtained. We found that electrically floating silicon dioxide beam s without an aluminum coating can also be excited stably by an ac driv ing voltage at resonance under scanning electron microscopy observatio n. Accumulated charge on the cantilever beam caused by the electron be am irradiation is found to be positive and this charge results in a dr iving force between the cantilever beam and the driving electrode. A t ime-resolved scanning electron microscopy method is proved to be a use ful technique to determine the resonant frequencies and resonant mode shapes of micromechanical systems. (C) 1996 American Vacuum Society.