Journal of Microscopy, Vol. 237, Pt 3 2010, pp. 325–328 doi: 10.1111/j.1365-2818.2009.03252.x Received 19 September 2008; accepted 31 March 2009 Identification of electron beam vibration sources by separation of magnetic distortion from electric distortion on scanning electron microscope imaging M. PLUSKA ∗, †, A. CZERWINSKI ∗ , J. RATAJCZAK ∗ , J. K  ATCKI ∗ , L. OSKWAREK † & R. RAK † ∗ Institute of Electron Technology, al. Lotnik´ ow 32/46, 00-668 Warsaw, Poland †Institute of Theory of Electrical Engineering, Measurement and Information Systems, Faculty of Electrical Engineering Warsaw University of Technology, ul. Koszykowa 75, 00-661 Warsaw, Poland Key words. Electromagnetic interference, image distortions, scanning electron microscopy. Summary Different types of distortions in scanning electron microscopy require different methods of their elimination, and therefore influence of these types on particular elements of the SEM system should be known. The proposed method allows for separation of the direct influence of the magnetic field on the electron beam in the SEM chamber from its influence in the SEM column and from the distortions generated in the SEM scanning block. For this purpose, a series of distorted images is registered for several working distances (between the final aperture of the electron column and the specimen) and for several energies of the electrons. Magnitudes of the distortions are measured on these images. For each applied electron energy, the dependence of the results versus the working distance is approximated with the second-order polynomial function. The analysis of the polynomial coefficients allows for the separation of the above-mentioned kinds of distortions. The presented method enables a selection of the most efficient solution to the distortions reduction. It utilizes the SEM itself and does not need any additional equipment. Introduction Image distortions in a scanning electron microscope (SEM) are caused by the direct influence of the external magnetic field on the electron beam and/or by electric distortions of signals in circuits responsible for the electron beam deflection, i.e. for the scanning (Vladar, 2003). The latter can occur due Correspondence to: Mariusz Pluska, Institute of Electron Technology, al. Lotnik´ ow 32/46, 00-668 Warsaw, Poland. Tel: +48 22 548 7764; fax: +48 22 8470631; e-mail: mpluska@ite.waw.pl to the induction of distortions within electric circuits and/or interference of electric distortions produced by power supplies. Generally, the distribution of a distorting magnetic field in the column of an SEM is different from that in its chamber, because their geometry and shielding efficiency differ. Thus, a unique distortion of the electron beam path in the SEM column and chamber occurs. A method for measurement of the magnetic field inside the SEM chamber that allows for separation of the direct field influence on the electron beam in the chamber from the other influences was previously described and applied (Pluska et al., 2008). After subtraction of the determined image deformations caused by the magnetic field in the SEM chamber, the remaining deformations originate from the distortions generated in the SEM column. The method presented in this paper enables a separation of the direct magnetic field influence on the electron beam in the SEM column from the distortions of signals in the scanning block of the SEM, which consists of scan generators, amplifiers and scanning coils. This separation is important for the efficient reduction of the distortions because each type of distortions has its own elimination procedure (Peng et al., 2004; Pluska et al., 2006). The presented separation method is based on the analysis of SEM images and does not require any additional equipment. Materials and methods The SEM electron-beam deflection at each moment is determined by the magnitude of the currents in the scanning coils, the level of external magnetic field penetrating the column and the chamber of the SEM, magnitudes of distortion signals in the SEM scanning block, the energy of the electrons C  2009 Institute of Electron Technology, Poland Journal compilation C  2009 The Royal Microscopical Society