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Scanning Electron Microscope with Apparatus for Controlling Contrast

IP.com Disclosure Number: IPCOM000084296D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

DeStafeno, JJ: AUTHOR [+3]

Abstract

In a conventional scanning electron microscope, a primary electron beam is directed to the specimen and secondary electrons, represented by a line 2, are emitted by the specimen. A grid 3 at a potential of 250 volts directs these secondary electrons to a scintillator that operates at a high voltage to produce a light output, represented by a line 4, that is converted to a normal electrical video signal by a photomultiplier. A problem occurs in this conventional system if the specimen has a wide range of contrast. The apparatus can be adjusted for appropriate contrast of the bright elements or the dark elements, but not both.

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Scanning Electron Microscope with Apparatus for Controlling Contrast

In a conventional scanning electron microscope, a primary electron beam is directed to the specimen and secondary electrons, represented by a line 2, are emitted by the specimen. A grid 3 at a potential of 250 volts directs these secondary electrons to a scintillator that operates at a high voltage to produce a light output, represented by a line 4, that is converted to a normal electrical video signal by a photomultiplier. A problem occurs in this conventional system if the specimen has a wide range of contrast. The apparatus can be adjusted for appropriate contrast of the bright elements or the dark elements, but not both.

In the apparatus of the drawing the conventional apparatus is designated Channel A, and a separate channel designated Channel B provides a signal that modifies the video signal for contrast control. A metal cup 5 that is represented schematically has an inside radius of about 15 millimeters and a hole of about 8 millimeters diameter that the primary beam passes through. Secondary electrons that strike the cup are applied to an amplifier 6.

This apparatus supplies a sufficient current to be detected in amplifier 6 and to prevent cup 5 from acquiring sufficient charge to repel the secondary electrons. The signal at the output of amplifier 6 is inverted with respect to the normal video signal (or vice versa), and the two signals are combined in a mixer to produce a video signal...