Threedimensional Tracking using Object Defocus - In Twodimensional Scanning Electron Microscope Images

This paper proposes a tracking algorithm for the extraction of threedimensional position data from SEM images. An algorithm based on active contours with region-based minimization is chosen as basis for twodimensional tracking. This algorithm is then augmented by the incorporation of defocus analysis to estimate the out-of-focus displacement of the object. To solve the ambiguity of the out-of-focus displacement, the astigmatism of the SEM images is used. The separate calculation of variances for the rows and columns of the image enables a successful direction estimation. With the information on the direction, the out-of-focus displacement and the working distance of the acquired image, the distance of the object to the electron gun can be calculated. In combination with the twodimensional part of the tracking, a full threedimensional coordinate set is generated. The approach is tested and evaluated using a positioning setup and the principal feasibility is shown.