Confocal optoelectronic holography microscope for materials and structural characterization of MEMS
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Confocal optoelectronic holography microscope for materials and structural characterization of MEMS Cosme Furlong, Adam M. Siegel, and Ryszard J. Pryputniewicz NEST – NanoEngineering, Science, and Technology CHSLT – Center for Holographic Studies and Laser micro-mechaTronics Mechanical Engineering Department Worcester Polytechnic Institute Worcester, MA 01609, U.S.A. ABSTRACT In this paper, we describe confocal optoelectronic holography microscopy (COEHM) technique specifically being developed for characterizing the shape of MEMS and microelectronics. This is particularly important because shape is directly related to the functionality, performance, and integrity of the microstructures of interest. A specific feature of COEHM is that it allows characterization of high aspect ratio MEMS and microelectronics. Representative applications demonstrating the capabilities of COEHM are presented. It is shown that measurement resolution is highly dependent on the numerical aperture (NA) of the optical components comprising COEHM and on the quality of image digitization. By utilizing optical components characterized by a magnification factor of 50x and a NA of 0.45, measurement resolution of 25 nm is achieved. The resolution is increased to 8 nm when utilizing optical components characterized by a magnification factor of 100x and a NA of 0.73. INTRODUCTION Typical processes utilized for manufacturing of MEMS and microelectronics include, but are not limited to, bulk micromanufacturing, surface micromachining, and LIGA [1-3]. In general, these processes consist of adding material to substrates, i.e., Si wafers, in the form of thin films, or removing sections of material from substrates. Such additions and/or removals of material produce three-dimensional (3D) geometrical features and shape of MEMS and microelectronics. For certain applications, accurate nondestructive and noninvasive characterization of their 3D shape is necessary. This is particularly important because shape is directly related to the functionality, performance, and integrity of components [4-6]. Characterization of surface shape, therefore, can be applied to such areas as quality control, process simulation, rapid prototyping, and reverse engineering. In this paper, confocal optoelectronic holography microscopy (COEHM) technique being developed for characterizing MEMS and microelectronics is described. It is shown that micrometer spatial resolution and nanometer measurement accuracy can be achieved. SCANNING CONFOCAL MICROSCOPY Figure 1 depicts major components of a scanning confocal optoelectronic holography microscope (COEHM) being specifically developed to characterize MEMS and microelectronic components and packages, especially those with a high geometric aspect ratio [7].
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Figure 1. Scanning confocal optoelectronic holography microscope (COEHM) system with the capabilities to measure shape of components characterized by a high geometric aspect ratio.
According to Figure 1, the illumi
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