White light interferometry on large MEMS arrays

White light interferometers (WLI) are 3D measurement tools, which enable efficient topography measurements with nm resolution in a comparably large field of view. In the Fraunhofer Institute for Photonic Microsystems (IPMS) WLIs are used in the end test of MEMS micromirror arrays. Movability, calibration curves and natural frequencies are determined for each individual micromirror on million-mirror arrays. In industrial environments WLIs are operated highly automated twenty-four-seven. Obviously, regular readjustment is necessary for measurement results at highest possible resolution without any artifacts. However, WLI adjustment is time consuming, as numberless interferometer signals need simultaneous assessment. For micromirrors there may be an additional hurdle if deflection angles reach a couple of degrees. The consequence would be path length differences in the interferometer arms and field-dependent aberrations. Both may raise the measurement uncertainty considerably. We present recent advancements in the optical characterization of MEMS arrays, which were supported by tailored WLI adjustment techniques.