3D CALIBRATION OF A SCANNING FORCE MICROSCOPE WITH INTERNAL LASER INTERFEROMETERS

A commercial metrological scanning force microscope (SFM) has been mod ified to further improve its metrological performance and calibration. For this purpose, a three-dimensional (3D) measuring system consistin g of three miniature laser interferometers has been incorporated into the SFM. Special attention is paid to the 3D nature of SFM measurement s. The metrological characteristics are spatially dependent. The goal therefore is to calibrate the scales of the movement axes, as well as cross-talk and Abbe errors, with respect to the entire measurement vol ume of the SFM. The effects can be significantly reduced by compensati ng for measured spatially dependent non-linearities, cross-talk and Ab be errors by modification of the SFM control software using regression functions. For characterizing the metrological performance, we have a pplied a model introduced in a three-coordinate measurement technique. Herewith, the spatially dependent performance is given by linear supe rposition of a set of one-dimensional functions. Further progress is a chievable by logical reference to spatially distributed calibration po ints given by output signals of the laser interferometers. At the stag e reached in the work at present, an expanded uncertainty U = 5 nm + 2 x 10(-4) . l (where I = distance) is estimated for the distance measu red between two points within a measured volume. The SFM is used for t opographical measurement of the thickness of coatings, evaluation of t he topography of microstructures and determination of dimensional para meters arising from microhardness measurements. (C) 1997 by John Wiley & Sons, Ltd.