Methods for the reconstruction of atomic force microscope data based on morphological image processing

At present, many researchers are working on different tasks to turn tactile scanning microscopy from a pure "Imaging tool" into a precision measuring instrument. Furthermore, the semiconductor industry requires larger and larger measuring ranges at a resolution below some nanometres. At the Ilmenau University of Technology, these new requirements were taken into account, and a novel measuring machine for nanometre resolution was developed in cooperation with the SIOS Mebetatechnik GmbH and the Zentrum fur Bild- und Signalverarbeitung e.V. This machine already possesses a measuring volume of 25 * 25 * 5 mm(3) (W * L * H), which is a million times more than that of conventional Atomic Force Microscopes. Furthermore, a resolution of 0.1 nm can be achieved. Due to the enormous resolution of the positioning units, a normal Atomic Force Microscope (AFM) is used for scanning the sample surface. If a metrological evaluation of the AFM data is to be carried out, the interactions between the sample and the tactile tip must be taken into account. If, on the other hand, only the geometrical effects of the scanning process are considered, they can be described by mathematical morphology. In other words, the scanning process is described by the dilatation of the sample surface with the tactile tip used. From this results the fact that the AFM measuring data can be improved by applying the mathematical reversal of dilatation (erosion), with the geometry of the tactile tip being exactly known. For this, however, the exact knowledge of the shape of the tactile tip is necessary In the technical literature, there are different approaches for determining the tip geometry, which were all investigated and assessed in detail. Here, the influence of disturbances, the so-called artifacts, on the reconstruction of the tactile tip has turned out to be particularly critical. It is shown how these disturbances can be minimized by applying suitable image processing algorithms, thus permitting the use of methods for the reconstruction of the AFM tips. In the second part of the paper, the physical interaction between the sample and the tip and its inclusion in the reconstruction process are dealt with. Some first concepts relating to this very complex field, as well as some first practical investigations are presented.