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Anticoincidence Technique to Suppress Noise in Scanning Electron Microscopes

IP.com Disclosure Number: IPCOM000040814D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Jenkins, KA: AUTHOR

Abstract

A technique is described for suppressing unwanted noise signals from rescattering of backscattered electrons. In many cases of electron microscopy, only the secondary emission electrons are of interest. The detector is usually placed so that backscattered electrons, due to their directional nature, do not strike the scintillator. Some backscattered electrons will, however, strike a nearby surface and rescatter, or create secondary electrons (commonly called Type III electrons). If they reach the detector, these electrons become an unwanted part of the signal.

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Anticoincidence Technique to Suppress Noise in Scanning Electron Microscopes

A technique is described for suppressing unwanted noise signals from rescattering of backscattered electrons. In many cases of electron microscopy, only the secondary emission electrons are of interest. The detector is usually placed so that backscattered electrons, due to their directional nature, do not strike the scintillator. Some backscattered electrons will, however, strike a nearby surface and rescatter, or create secondary electrons (commonly called Type III electrons). If they reach the detector, these electrons become an unwanted part of the signal.

Use of the anticoincidence technique described herein can suppress this noise. An electron detector is placed near the surface which causes problems as shown in the figure. This detector will respond to backscattered electrons striking it. Thus, the offending surface is blocked by an active detector. The signal from this backscatter detector can be used in either of two ways. If the primary beam intensity is high, the signals from the secondary and backscattered detectors are separately integrated, and then subtracted by an analog mixing circuit. If the primary beam intensity is very low, individual electrons can be detected and turned into digital pulse trains. Here the backscatter pulse can be used to veto secondary pulses with a digital anticoincidence gate. Low intensity primary beams are likely to occur in low voltage (1 pe < 6...