The small lateral dimension of structures often is a problem for the measuring techniques, because the optical resolution of the methods is usually not sufficient to resolve them. For example, Trenches can have widths of less than 1 μm.
The WLI FL is an optical 3D surface sensor based on white light interferometry. It is characterized by fast, area topography measurements with excellent height resolution in the sub-nanometer range. This makes the sensor in extended phase mode (EPSI) ideal for roughness measurements on flat surfaces. Topography measurements are performed with high resolution in vertical scan mode (VSI). Typical measurement tasks are investigations of components such as micro mirrors, lenses, MEMS, micro fluidic systems and micro electronics. With the help of a special algorithm, the WLI FL enables the determination of the depth of etching structures with widths down to 0.7 μm. In this case the aspect ratio can be up to 3:1. This opens up dimensions that have not yet been reached in this way. With this method, all currently used variants of TSVs can be measured.
In white light interferometry, a camera is used to capture interference images resulting from the superposition of the light from the measurement object with the light reflected from a reference mirror. For a topography measurement, the z-position of the lens is adjusted in small steps and an interference image is recorded at each position. The result is a stack of images from which the height data is calculated. By using a white-light source with a short coherence length, surfaces can be captured with the very good height resolution known from interferometric measurement methods.
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