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Precise three dimensional (3D) profile measurements of vertical sidewalls of concave micro-structures are impossible by conventional profiling techniques. This paper introduces a simple technique which can obtain 3D sidewall geometry by means of laser fluorescent confocal microscopy and an intensity gradient algorithm. The measurement principle is: when a concave micro-structure is filled up with fluorescent solution, the position where the maximum intensity variation lays represents the profile of the micro-structure in the fluorescent 3D volume image. The physical essence behind this measurement principle is analyzed in this paper in detail. The strengths and limitations of this technique are studied by experiments or by illustrations. The factors that are able to improve the measurement accuracy are discussed. This technique has demonstrated the capability for measuring of 3D geometry of various concave features, such as vertical, buried and other micro channels with sub-mum (RMS) measurement accuracy and repeatability.

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Current trends in miniaturization of microelectromechanical systems (MEMS) require the use of smaller and smaller components. Development of these microcomponents, e.g. microbeams in an accelerometer and membranes in a microphone, requires state-of-the-art test and measurement methodologies to inspect the deformation of the microcomponents for further understanding of their mechanical properties. In this paper we describe a system developed for testing deformation of a microbeam in an accelerometer under point-force load and a membrane in a microphone under applied voltage. The technique is based on optical interferometry. A collimated monochromatic beam is directed into an air wedge consisting of an optical reference plate and the microcomponent under test. The resulting interference fringe patterns from the air wedge are captured by a CCD camera mounted on a long working-distance microscope and subsequently stored in a computer. The fringe patterns that are related to deformations of the test object are analysed by a simple algorithm for recording both integral and fractional fringes. From the fringe pattern, deformation of the microbeam and membrane in the sub-micrometre range are obtained. The proposed method is potentially applicable to the in situ inspection of microcomponents in MEMS.