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8 March 1996 Fabrication of microlenses by combining silicon technology, mechanical micromachining and plastic molding
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Silicon can be subjected to plasmaless isotropic etching in mixtures of elemental bromine and fluorine. BrF3 is generated in the etching process. This ensures a high etching rate on smooth surfaces. The addition of noble gases, e.g. xenon, allows extremely smooth surfaces to be etched. Thermally oxidized SiO2 layers are applied as the etching mask. Among other applications, this technique can be used to manufacture microlenses. As a consequence of the complete isotropy of the etching process, spherical depressions of 100 to 500 micrometers in diameter are produced in the silicon when small circular holes of 5 to 50 micrometers are underetched in the SiO2 mask. After removal of the SiO2 mask the silicon sample can be used as a mold insert for plastic molding. The molded microlenses have been checked dimensionally and verified optically. The microlenses are planned for technical use in a miniaturized endoscope. This requires further processing of the silicon sample. As no hemispherical recesses but calotte shells are needed, the silicon surface must be machine prior to molding. This is done by microgrinding with variable-grain diamond tools on CNC high- precision machines. To generate adjusting devices, stoppers, and holding structures, the ground silicon sample and a mechanically microstructured perforated plate are combined in a modular multi-level mold insert. The microlenses molded by hot embossing or injection molding are separated mechanically. They can then be integrated in the endoscope with a holding unit manufactured independently.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Uwe Koehler, Andreas E. Guber, W. Bier, Mathias Heckele, and Thomas Schaller "Fabrication of microlenses by combining silicon technology, mechanical micromachining and plastic molding", Proc. SPIE 2687, Miniaturized Systems with Micro-Optics and Micromechanics, (8 March 1996);

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