The Journal of Scanning Microscopies
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SCANNING Vol. 19, 275–280 (1997)
© FAMS, Inc.
Received November 4, 1996
Accepted December 3, 1996
J.T.L. Thong and F. Li
Centre for IC Failure Analysis and Reliability, Faculty of Engineering, National University of Singapore, Singapore
Full-text (for Scanning subscribers)
The speed at which the focal properties of an iron-shrouded magnetic electron lens can be changed is fundamentally limited by Eddy currents in the magnetic material. The effects of such Eddy currents on the lens properties can be partially compensated by modifying the lens excitation to speed up the lens response. This work considers the application of excitation pre-emphasis techniques to scanning electron microscope lenses for small and large dynamic changes in excitation. Where transient material saturation effects come into play, attempts to further improve the lens response beyond that at the onset of saturation are futile. Under such circumstances, the use of a closed-loop feedback arrangement is proposed that can provide a degree of response improvement.
Key words: transient excitation of magnetic lens, Eddy currents
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