3D Calibration of a Scanning Force Microscope with Internal Laser Interferometers

Abstract

A commercial metrological scanning force microscope (SFM) has been modified to further improve its metrological performance and calibration. For this purpose, a three-dimensional (3D) measuring system consisting of three miniature laser interferometers has been incorporated into the SFM. Special attention is paid to the 3D nature of SFM measurements. 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 volume of the SFM. The effects can be significantly reduced by compensating for measured spatially dependent non-linearities, cross-talk and Abbe errors by modification of the SFM control software using regression functions. For characterizing the metrological performance, we have applied a model introduced in a three-coordinate measurement technique. Herewith, the spatially dependent performance is given by linear superposition of a set of one-dimensional functions. Further progress is achievable by logical reference to spatially distributed calibration points given by output signals of the laser interferometers. At the stage reached in the work at present, an expanded uncertainty U = 5 nm + 2 x 10 -4 . I (where I = distance) is estimated for the distance measured between two points within a measured volume. The SFM is used for topographical measurement of the thickness of coatings, evaluation of the topography of microstructures and determination of dimensional parameters arising from microhardness measurements.