Low coherent Linnik interferometer optimized for use in Nano Measuring Machines
The precise acquisition of three-dimensional geometrical data in micro- and nanotechnology is crucial for advanced fabrication processes. Scanning white-light interferometry (SWLI) achieves nanometer resolution in the axial direction, but the lateral resolution is far more critical. The requirements for an areal measuring optical sensor in a Nano Measuring Machine are very high. The resolution in every dimension and the working distance have to be as high as possible. In contrast to a Mirau interferometer a Linnik interferometer does not need any components in front of the objective lens. This benefit permits both, a long working distance and a high lateral resolution. In the EC-funded project “NanoCMM” we developed a Linnik interferometer providing a working distance of more than 5 mm and a lateral resolution of 0.3 μm. With this interferometer we measured the full modulation depth and the rectangular shape of a pitch standard close to the Rayleigh resolution limit.