US3783281A - Electron microscope - Google Patents
Electron microscope Download PDFInfo
- Publication number
- US3783281A US3783281A US00223382A US3783281DA US3783281A US 3783281 A US3783281 A US 3783281A US 00223382 A US00223382 A US 00223382A US 3783281D A US3783281D A US 3783281DA US 3783281 A US3783281 A US 3783281A
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- US
- United States
- Prior art keywords
- signal
- electron beam
- producing
- electrons
- reference signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/244—Detectors; Associated components or circuits therefor
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2443—Scintillation detectors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2445—Photon detectors for X-rays, light, e.g. photomultipliers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/24485—Energy spectrometers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2449—Detector devices with moving charges in electric or magnetic fields
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/245—Detection characterised by the variable being measured
- H01J2237/24507—Intensity, dose or other characteristics of particle beams or electromagnetic radiation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/245—Detection characterised by the variable being measured
- H01J2237/24571—Measurements of non-electric or non-magnetic variables
- H01J2237/24585—Other variables, e.g. energy, mass, velocity, time, temperature
Definitions
- ABSTRACT The application describes improved techniques for correcting an output detection signal from an electron microscope for aberrant variations in the electron beam produced by the microscope.
- the preferred embodiment comprise a a monitor assembly for producing a reference signal proportional to the magnitude of the electron beam and a correction circuit for varying the magnitude of the detection signal in response to variations in the reference signal.
- the monitor assembly may comprise a diverting assembly for diverting a portion of the electron beam from its normal path to produce a flow of diverted electrons and a transducer assembly for producing a signal proportional to the number of diverted electrons so that a reference signal is produced.
- the correction circuit may comprise logarithmic amplifiers, a subtraction circuit, and an anti logarithmic amplifier for producing a signal which corresponds to the ratio of the detection signal and the reference signal. This corrected signal may be used to drive a cathode ray tube display of the specimen.
- This invention relates to electron microscopes, and more particularly reates to the correction of variations in an output detection signal from the electron microscope due to variations in the electron beam.
- the reason for the current fluctuation is that the electron emission from the tip of the source of electrons is subject to periodic variations. These variations are generally caused by gas molecules that arrive at the tip and change local conditions to enhance or decrease the current over small regions of the total emission pattern. If one of these regions is on the axis of the microscope, the net effect is a substantial change in the intensity or current density of the electron beam which flows from the tip. The variations are particularly noticeable when a field emission tip is employed to increase the resolution of the microscope. 7
- correction of the detection signal is achieved by producing a signal corresponding to the ratio of the detection signal and the reference signal.
- the monitor assembly comprises apparatus: for diverting a portion of the electron beam from its normal path to produce a flow of diverted electrons and comprises a transducer for producing a signal proportional to the number of diverted electrons. This signal corresponds to the reference signal which is used by the correction means to correct the detection signal.
- FIG. 1 is a schematic drawing of a preferred form of the present invention as it is employed with an exemplary scanning electron microscope of the type described in U. S. Pat. No. 3,191,028 (Crewe June 22, 1965);
- FIG. 2 is a cross-sectional view of a preferred form of monitor means made according to the present invention as it is employed in the exemplary microscope shown in FIG. 1;
- FIG. 3 is an enlarged, fragmentary, cross-sectional, partially schematic view of the monitor means, together with additional apparatus shown in FIG. 2;
- FIG. 4 is a fragmentary top plan view taken along line 4-4 of FIG. 3.
- the electron beam is accelerated by electrodes 12 toward focusing magnets 14 that are controlled by a DC power supply 14a.
- the focusing magnets focus the electron beam into a spot a few angstroms (A) in diameter on the surface of a thin specimen 16.
- Deflection electrodes 18 and 20 are disposed between the specimen and the focusing magnets and are responsive to voltages from a sweep generator 22 of a cathode ray tube display device 28.
- the sweep generator and deflection electrodes cause the electron spot to sweep over the surface of specimen 16 in a predetermined pattern.
- a momentum analyzing spectrometer 24 is mounted after the specimen 16 and is adjusted to separate electrons transmitted through the-specimen 16 into discrete energy levels thereof.
- a scintillation detector 26 comprising detectors 26a-26e is coupled to a photomultiplier 27 comprising photomultiplier tubes 27a-27c.
- scintillation detector 26 and photomultiplier 27 comprise detection apparatus for producing a detection signal corresponding to the flow of electrons from specimen 16.
- spectrometer 24 may be arranged so that electrons of all energy levels are received by detector 26a.
- each of the detectors 26a-26e may be connected to photomultiplier tube 270, so that the signal produced thereby corresponds to the electrons transmitted at all energy levels. Additional features of the exemplary electron microscope may be understood with reference to US Pat. No. 3,l9l,028 wherein like numbers refer to like parts of FIGS. 1 and 2.
- a preferred form of the present invention intended for use in connection with the above-described exemplary scanning electron microscope basically comprises a monitor assembly 29 and a correction circuit 31. More specifically, monitor assembly 29 comprises a diverting assembly 170 and a transducer assembly 182.
- diverting assembly 170 comprises an enclosed metal box 172 having an upper surface 174 that defines an aperture 176 having a 200 micron diameter. As shown in FIG. 2, the monitor assembly is located between elements 80 and 82 of the electron microscope described therein. Box 172 also has a lower surface 178 that defines an aperture 180 having a 100 micron diameter. As shown in FIG. 3, apertures 176 and 180 are concentric and have a center line located approximately in the middle of electron beam 11.
- Transducer assembly 182 comprises a metal coil 184 that surrounds the electron beam between upper and lower surfaces 174, 178.
- the transducer assembly also comprises a scintillator 186, a light pipe 188, and a photomultiplier 190 schematically arranged as showm.
- Those skilled in the art will appreciate that electrons striking the scintillator are converted to light which is transmitted to photomultiplier 190 by light pipe 188.
- Photomultiplier 190 produces a reference signal proportional to the magnitude of electron beam 11, which is transmitted over a conductor 191.
- metal coil 184 is an important element. Absent such a device, the electric field from the voltage on the remaining portions of the transducer assembly would deflect and produce serious astigmatism in the electron beam. If possible, the metal coil should be biased at ground potential. However, if it is necessary to place a voltage on the coil, great care should be taken to shield any insulators from the electron beam.
- correction circuit 31 comprises a ratio circuit for producing a corrected signal corresponding to the ratio of the detection signal and the reference signal.
- This ratio circuit comprises logarithmic amplifiers 194 and 196, a subtraction circuit 198, and an antilogarithmic amplifier 200 connected as shown by conductors 195, 197, 199 and 201.
- amplifier 200 produces a corrected signal corresponding to the ratio of the detection signal and the reference signal.
- the corrected signal is conducted over a conductor 202 to provide a video information signal by which a micrograph display may be produced on cathode ray tube 28.
- Elements 194, 196, 198 and 200 are well-known to those skilled in the electronic arts, and may be made and used by such individuals based on the present disclosure.
- Electron beam 11 passes through aperture 176 into diverting assembly 170. Since aperture is smaller than aperture 176, a portion of the electron beam strikes the surface 178 in the area around aperture 180. The electrons which strike this area are diverted from their normal path to produce a flow of diverted electrons 11a. Some of these electrons strike scintillator 186 and are converted to light rays in a well-known manner. The light rays are then conducted along light pipe 188 and are converted to a corresponding reference signal by photomultiplier 190. The reference signal is transmitted over conductor 191. As previously mentioned, the reference signal is proportional to the magnitude of the diverted electrons which are, in turn, proportional to the magnitude of the electron beam 11.
- Electron beam 11 is then focused onto specimen 16 by focusing magnets 14 and is scanned over the surface of the specimen by deflection electrodes 18, 20.
- the resulting flow of electrons from specimen 16 is detected by detection apparatus 25 in order to form a detection signal on conductor 197.
- photomultiplier 27a to which log amplifier 196 is connected, normally produces a signal proportional to the flow of electrons 'at a particular energy level.
- photomultiplier 27a may be modified to produce a signal proportional to the flow of electrons at all energy levels.
- each of the detectors 26a-26e and photomultipliers 27a-27e may be connected with a correction circuit, such as circuit 31, and a cathode ray tube to individually display the electrons transmitted at various energy levels.
- the detection signal on conductor 197 is conducted to logarithmic amplifier 194 that produces a first signal on conductor 199 corresponding to the logarithm of the detection signal.
- the reference signal is conducted to logarithmic amplifier 194 that produces a second signal on conductor corresponding to the logarithm .of the reference signal.
- the first and second signals are then conducted to subtraction circuit 198 that produces a remainder signal on conductor 20] corresponding to the difference between the first and second signals.
- the remainder signal is then conducted to an antilogarithmic amplifier 200 which produces a corrected signal on conductor 202 corresponding to the antilogarithm of the remain.- der signal.
- the corrected signal corresponds to the ratio of the .detection and reference signals.
- the corrected signal is then used as a video information signal by which a micrograph display may be produced on cathode ray tube 28.
- an electron microscope comprising an electron source for producing an electron beam and comprising detection means for producing a detection signal corresponding to the flow of electrons from a specimen placed in the electron beam, improved apparatus for limiting variations in the detection signal due to variations in the electron beam comprising:
- monitor means for producing a reference signal having a magnitude determined by the magnitude of the electron beam, said monitor means comprising means for isolating an electric field produced by the monitor means from the electron beam;
- correction means for producing a corrected signal corresponding to the ratio of the detection signal and the reference signal, whereby the corrected signal is free from changes in signal magnitude due to variations in the electron beam.
- correction means comprises:
- a first logarithmic amplifier for producing a first signal corresponding to the logarithm of the detection signal
- a second logarithmic amplifier for producing a sec- 6 0nd signal corresponding to "the logarithm of the reference signal
- a subtraction circuit for subtracting the second signal from the first signal to produce a remainder signal' an antilogarithmic amplifier for producing a corrected signal which corresponds to the antilogarithm of the remainder signal;
- monitor means comprises:
- a second metal surface that defines a second aperture smaller than the first aperture through which a portion of the electron beam may pass, whereby a por tion of the electrons in the electron beam are diverted by the area of the second metal surface surrounding the second aperture;
- a scintillator for receiving diverted electrons and for converting the diverted electrons to light
- a photomultiplier responsive to the light transmitted by the light pipe.
Abstract
Description
Claims (4)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US22338272A | 1972-02-03 | 1972-02-03 |
Publications (1)
Publication Number | Publication Date |
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US3783281A true US3783281A (en) | 1974-01-01 |
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ID=22836273
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US00223382A Expired - Lifetime US3783281A (en) | 1972-02-03 | 1972-02-03 | Electron microscope |
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US (1) | US3783281A (en) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3916191A (en) * | 1974-03-01 | 1975-10-28 | Minnesota Mining & Mfg | Imaging apparatus and method for use with ion scattering spectrometer |
US3944829A (en) * | 1973-03-27 | 1976-03-16 | Nihon Denshi Kabushiki Kaisha | Method and apparatus for processing a video signal from a scanning electron microscope |
DE3412715A1 (en) * | 1983-04-04 | 1984-10-11 | Hitachi, Ltd., Tokio/Tokyo | ELECTRON MICROSCOPE |
US4990778A (en) * | 1988-09-30 | 1991-02-05 | Jeol Ltd. | Scanning electron microscope |
US6211525B1 (en) * | 1996-07-01 | 2001-04-03 | Ke Developments Limited | Detector devices |
EP2006881A3 (en) * | 2007-06-18 | 2010-01-06 | FEI Company | In-chamber electron detector |
US20180233322A1 (en) * | 2017-02-16 | 2018-08-16 | Fei Company | Emission noise correction of a charged particle source |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
SU156251A1 (en) * | ||||
US3191028A (en) * | 1963-04-22 | 1965-06-22 | Albert V Crewe | Scanning electron microscope |
US3351755A (en) * | 1964-09-25 | 1967-11-07 | Applied Res Lab Inc | Method of and apparatus for spectroscopic analysis having compensating means for uncontrollable variables |
-
1972
- 1972-02-03 US US00223382A patent/US3783281A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
SU156251A1 (en) * | ||||
US3191028A (en) * | 1963-04-22 | 1965-06-22 | Albert V Crewe | Scanning electron microscope |
US3351755A (en) * | 1964-09-25 | 1967-11-07 | Applied Res Lab Inc | Method of and apparatus for spectroscopic analysis having compensating means for uncontrollable variables |
Non-Patent Citations (1)
Title |
---|
Techniques for Electron Microscopy, by D. Kay, published by Blackwell Scientific Publications, Oxford, 1961, page 8. * |
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3944829A (en) * | 1973-03-27 | 1976-03-16 | Nihon Denshi Kabushiki Kaisha | Method and apparatus for processing a video signal from a scanning electron microscope |
US3916191A (en) * | 1974-03-01 | 1975-10-28 | Minnesota Mining & Mfg | Imaging apparatus and method for use with ion scattering spectrometer |
DE3412715A1 (en) * | 1983-04-04 | 1984-10-11 | Hitachi, Ltd., Tokio/Tokyo | ELECTRON MICROSCOPE |
GB2139455A (en) * | 1983-04-04 | 1984-11-07 | Hitachi Ltd | Scanning electron microscope (s e m) |
US4588891A (en) * | 1983-04-04 | 1986-05-13 | Hitachi, Ltd. | Scanning type electron microscope |
US4990778A (en) * | 1988-09-30 | 1991-02-05 | Jeol Ltd. | Scanning electron microscope |
US6211525B1 (en) * | 1996-07-01 | 2001-04-03 | Ke Developments Limited | Detector devices |
EP2006881A3 (en) * | 2007-06-18 | 2010-01-06 | FEI Company | In-chamber electron detector |
US8164059B2 (en) | 2007-06-18 | 2012-04-24 | Fei Company | In-chamber electron detector |
US20180233322A1 (en) * | 2017-02-16 | 2018-08-16 | Fei Company | Emission noise correction of a charged particle source |
EP3364442A1 (en) | 2017-02-16 | 2018-08-22 | FEI Company | Emission noise correction of a charged particle source |
CN108447758A (en) * | 2017-02-16 | 2018-08-24 | Fei公司 | The displacement noise of charged particle source corrects |
US10453647B2 (en) * | 2017-02-16 | 2019-10-22 | Fei Company | Emission noise correction of a charged particle source |
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AS | Assignment |
Owner name: MNC CREDIT CORP., 502 WASHINGTON AVE., STE. 700, T Free format text: SECURITY INTEREST;ASSIGNOR:ETEC, A CORP. OF NV;REEL/FRAME:005262/0967 Effective date: 19900223 |
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Owner name: ETEC, A CORP. OF NV, NEVADA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:PERKIN-ELMER CORPORATION, THE;REEL/FRAME:005366/0501 Effective date: 19900315 |
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Owner name: ETEC SYSTEMS, INC., A CORP. OF NV Free format text: CHANGE OF NAME;ASSIGNOR:ETEC, A CORP. OF NV;REEL/FRAME:005475/0559 Effective date: 19900814 |
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Owner name: CONNECTICUT NATIONAL BANK, THE Free format text: SECURITY INTEREST;ASSIGNOR:ETEC SYSTEMS, INC.;REEL/FRAME:005949/0850 Effective date: 19911115 |
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Owner name: ETEC, A CORP. OF NEVADA, CALIFORNIA Free format text: RELEASED BY SECURED PARTY;ASSIGNOR:MNC CREDIT CORP., A MD CORP.;REEL/FRAME:006014/0078 Effective date: 19911220 |