Enhancement of image contrast by fluorescence in microtechnology

New developments in production technology increasingly focus on hybrid microsystems. Especially for systems with movable components, the process step of assembly is mandatory. In general, the accuracy of positioning of the parts has to be better than 1 mu m. This makes specialized and automated production equipment necessary, which can lead to a conflict with the aim of flexibility of the range of products. Design for manufacturing is a well known remedy. Assembly aids are common practice today. These features of the workpieces bear no functionality for the end product but considerably ease certain process steps. By standardization of assembly aids generalized production equipment free from product-specific features could be developed. In our contribution, we demonstrate the photogrammetric determination of the positions of workpieces without reference to their exterior shape, using circular fiducial marks of 150 mu m in diameter. The surface properties of the workpieces, however, still have an influence on image formation. As an example, the marks may be hidden by local specular reflections. A solution to this problem is to add an exclusive optical property to the fiducial marks to get an image with high contrast against the surface of the workpiece. In biology and medicine samples are stained with fluorescing dyes to enhance the contrast in optical microscopy. In fluorochromes, light of a characteristic wavelength is emitted after the absorption of light with a shorter wavelength. In our experiments we added a fluorochrome to a common photoresist and coated the surface of the workpiece with a thin layer thereof. Using photolithography as a patterning technique we generated fiducial marks with structures down to 25 mu m. These marks can be identified by their characteristic emission wavelength under short-wavelength illumination. Only the fiducial marks remain visible in the images and processing these images is straightforward. The generation of fluorescing patterns by photolithography opens new possibilities for testing and process control in many fields of microtechnology.