Performance of a combined chromatic confocal microscope with thin film interferometer

摘要

Chromatic confocal microscopy is a common way to interrogate topologies and is well understood. Thin film reflectometry (TFR), on the other hand, is a way to monitor film thicknesses. Semiconductor and optics producing industries, e.g., require information about topological, film thickness or optical constants. We developed a spectrometric measuring system which is capable of determining high precision thin film thickness and topographic information of a specimen at the same time. The spectral intensity distribution reflected by a transparent thin film differs from a spectroscopic confocal observation by a chromatic measurement head, since the spectral interference fringes appear in the spectra. The spectrometer-based system interrogates both confocal, as well as thin film signals employing an analytical model of the chromatic shift of the measuring head, film composition and a least-square estimator.Hence, the advantage of this combined measuring system is the concurrent determination of film thickness and distance to the measuring head. By scanning the surface of a specimen laterally, a both tomo- and topological image can be acquired. Spacial measurements at test objects were carried out to demonstrate this measurement principle and the results are discussed.