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The ability to measure the relief parameters and absolute position accuracy of very fine relief structures in the nm-micron regime is of importance in modern micro-engineering. The wish list for metrology includes non-destructive testing, testing of large areas, and testing of large aspect ratio structures having sub-micron lateral dimensions. To address these requirements, the authors investigated the use of far-field diffraction metrology utilizing diffractive structures having enhanced sensitivity to fabrication errors in linewidth and each depth. Average fabrication errors of opaque and transparent structures in the order of a few nanometers can be determined. Furthermore, the authors have introduced scanning spot metrology of lithographic masks. Algorithms for extraction of edge locations from the detector signal are discussed. In contrast to the far-field diffraction metrology, this methods yields information about local errors.