US3702398A - Electron beam apparatus - Google Patents

Electron beam apparatus Download PDF

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Publication number
US3702398A
US3702398A US108408A US3702398DA US3702398A US 3702398 A US3702398 A US 3702398A US 108408 A US108408 A US 108408A US 3702398D A US3702398D A US 3702398DA US 3702398 A US3702398 A US 3702398A
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Prior art keywords
axis
point
lens
deflection
electron
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Expired - Lifetime
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US108408A
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English (en)
Inventor
Christopher Geoffrey Van Essen
Erland Maxwell Schulson
Richard Hugh Donaghay
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Cambridge Scientific Instruments Ltd
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Cambridge Scientific Instruments Ltd
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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
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/153—Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators
    • 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
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/147—Arrangements for directing or deflecting the discharge along a desired path
    • H01J37/1478—Beam tilting means, i.e. for stereoscopy or for beam channelling
    • 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
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams

Definitions

  • This invention relates to electron beam apparatus, primarily to the use of a modified form of scanning electron microscope, that is to say, an instrument in which a fine electron beam or probe is formed by lenses and caused to impinge on the surface of a specimen, the resulting secondary electrons, or back-scattered primary electrons, or the current from the specimen itself, being used to form an image on a recording device, such as the screen of a cathode ray tube, scanned in synchronism with the probe or specimen.
  • a recording device such as the screen of a cathode ray tube, scanned in synchronism with the probe or specimen.
  • the invention may also be applied to an instrument in which it is electromagnetic radiation (such as X-rays or light) generated by the impingement of the bean rather than the electrons that are detected and analysed.
  • a beam of electrons from an electron gun is forrned by a condenser lens system, usually comprising first and second electromagnetic lenses, and the resulting image of the source formed on the electron-optical axis, is de-magnified by a final, or objective, lens, again electromagnetic, of short focal length to form a reduced image on the surface of the specimen.
  • Scanning coils mounted within the back bore of the objective lens deflect the beam in two mutually perpendicular directions, both transverse to the axis of the beam.
  • Duncumb arranged two sets of scanning coils, axially spaced apart, for each scanning direction to deflect the beam away from the axis and then back towards it, so that the beam always passes through the relatively small final aperture.
  • the aim of the present invention is to provide an improved method of obtaining pseudo-Kikuchi patterns from small areas using electron beam apparatus of the general kind indicated in the opening paragrahhs above.
  • electron probe apparatus comprising means for forming a fine probe or beam of electrons that forms an image of a source substantially within a scanning coil system that is capable of deflecting the beam back and forth, and the resulting laterally scanned image is formed in the object plane of a lens that serves, not only for its usual purpose of focussing the image, but also for deflecting the beam back onto the optical axis at the surface of the specimen itself.
  • this lens forms part of the scanning system that causes the beam to rock angularly about its point of impact on the specimen.
  • the first deflection of the scanning system is obtained by the first set of coils alone and the second set of coils is removed, or at least switched off.
  • the aim is to derive information on the crystal structure at virtually a single point, i.e. at as small an area of the specimen as possible.
  • the unavoidable spherical aberration of the lens will result in variations of the point of impact with deflection, making the area covered larger than desirable. This can be offset by applying a correction signal, that varies in synchronism with the scanning signal.
  • the correction can be applied by rhythmically shifting, in synchronism with the scanning deflection, the apparent position along the electron-optical axis, of the image of the source that forms the object of the final lens.
  • the high inductance of an iron-cored electromagnetic lens severely limits the rate of change of such a correcting signal and consequently makes the overall scanning speed very slow; this seriously restricts the usefulness of the instrument. Therefore, we prefer to use for the final lens an air-cored so-called mini-lens or solenoid type lens. Or we may retain an iron-cored main final lens but apply the correction current to an auxiliary lens, preferably air-cored.
  • FIG. 1 shows diagrammatically the layout of an electron probe instrument
  • FIG. 2 is a ray diagram showing the orthodox scanning system for covering an area of a specimen surface
  • FIG. 3 is a similar ray diagram showing the previously proposed system for obtaining electron channelling (pseudo-Kikuchi) effects by the use of the existing double-deflection coil system;
  • FIG. 4 is a ray diagram showing the system according to the invention, employing a single set of scanning coils in conjunction with a lens used for deflection;
  • FIG. 5 is a diagram to illustrate the advantage of scanning by a spiral scan instead of a straightforward raster.
  • the secondary electrons or the back-scattered primary electrons emerging from the point of impact on the specimen surface are collected at D to produce a signal that is amplified and used to control the brightness of the spot of a cathode ray tube T, the beam of which is deflected in synchronism with the primary electron beam, by a common scanning generator B.
  • a two-dimensional image is built up on the screen of the tube T, showing the spatial distribution over the scanned area of the specimen surface, of some phenomenon which produces a variation in the backscatter, such as topography or electrical or magnetic state.
  • the two sets of deflection coils are contained in the back bore of the final lens, which is almost invariably electromagnetic.
  • the final lens has a small exit aperture AI, as illustrated in FIG. 2, which is a ray diagram showing the lower part of the column of the instrument of FIG. 1.
  • the aim is to vary in a cyclic manner the angle of impact of the beam on the specimen surface.
  • the effect in question is observable even when scanning an appreciable area of a specimen, provided the scanned area is a single crystal, it is much preferred to examine the effect at a single spot. This has been done by leaving the beam undeflected and by rocking the specimen about two orthogonal axes perpendicular to the electron-optical axis A and passing through the point of impact.
  • the information was again reproduced in the form of a two-dimensional image on the screen of the cathode ray tube T, with angular deflection of the primary beam in two directions represented in the image by linear displacement of the spot of the screen in two linear directions.
  • the resulting image displays a series of intersecting light and dark bands from which information can be obtained on the crystal structure at the point of impact.
  • the final lens L3 has its current adjusted so that it focusses the image from the plane of the coils D1 to form a reduced image at the specimen surface.
  • the plane of the deflecting coils D1 and the point of impact on the specimen surface are conjugate points with respect to the lens L3.
  • the lens L3 also acts as part of focussing deflection system. For, by its normal lens action, it refracts back towards the electronoptical axis A any ray that passes through it off the axis.
  • this lens is deflecting the beam back towards the axis to a degree dependent on its extent away from the axis, so as well as being brought to a focus at the specimen surface the beam is also caused always to impinge on a fixed spot on the specimen surface.
  • the deflection coils D1 cause the beam to scan back and forth, the beam rocks angularly about a fixed point of impact on the specimen surface. In a typical case the total angular scan in each case is 8 degrees, and the area of the region of impact is about microns (i.e.
  • the actual diameter of the beam at this point is only about one micron, but the scanning action, as well as the focussing action, of the lens L3 is subject to the spherical aberration of the lens, which means that the beam crosses the electronoptical axis at a point nearer the lens when the deflection is large than when it is small, so that the point of impact does in fact move during scanning.
  • the position of the specimen surface is therefore chosen at a point on the axis A where there is a circle of least confusion rather than the theoretical focus, and this circle is, as indicated, about 10 microns in diameter.
  • the coils D1 can cause the beam to scan the fixed point on the specimen surface in a solid angle by means of what we can call an angular raster, that is to say, by applying a rapid sawtooth time base voltage, analogous to the line scan in a television-type raster, to the deflection coils in one plane and a slower saw-tooth voltage, analogous to a television frame scan, to the coils in the other plane.
  • the image on the screen of the cathode ray tube T is in the form of a two-dimensional raster obtained exactly like a television raster from the same two saw-tooth voltages.
  • the minimum area scanned at the region of impact on the specimen surface can be reduced by correcting for the spherical aberration of the lens L3.
  • the method of moving the image I is by varying the current in the lens L2, or in lenses L1 and L2.
  • By appropriately manipulating the current in these three coils we are able to make the apparent origin of the primary scan, as viewed from the final lens L3, move along the axis as required, and this origin is always arranged to coincide with the position of the image I.
  • the second basic way of correcting for spherical aberration is by varying directly the current in the final lens L3 in step with the scanning, so as to vary its effective focal length in step with the radial distance from the axis A at which the electron beam passes through the lens.
  • the image I remains fixed and so the primary scan can be by the single set of coils D1, and the coils D2 and E can be omitted.
  • an iron-cored electromagnetic lens of the dimensions and power used for the lens L3 has a very substantial inductance and so it would be virtually impossible to vary the current in step with the line scan of a typical scanning raster, in which the total time taken for a frame may be of the order of a few seconds, and the time for a single line (or rather a single angular scan by the coils D1 in the line direction) may be only a hundredth of a second.
  • FIG. 5 an image in two-dimensional form (as it would be displayed on the screen of the cathode ray tube) comprising a series of straight lines making up a frame, as in a television-type raster.
  • the raster is square, although this is by no means essential.
  • this correcting signal As the correcting signal to be applied to the winding of the lens L3 depends only on this angular deflection, this correcting signal correspondingly only has to vary at frame frequency. Thus the correction can be applied with acceptable frame periods of the order of a few seconds, or less. It can be shown that, for a given maximum rate of change of the correcting signal, a given solid angle can be covered with a polar scan in half the time taken for only one line of a cartesian or raster-type scan.
  • the particular arrangement of the condenser lens system and apertures may be varied as desired, as well as the position of the primary scanning coils.
  • the aperture A2 may be above the lens L2, and there may be fewer or more than two lenses in the condenser lens system.
  • the only important thing is that an image is formed on the axis A at a point which, with respect to the final lens, is conjugate to the specimen surface, and a primary scanning system deflects the beam angularly away from the axis with this point as origin, the final lens itself forming the secondary scanning system that deflects the beam back onto the axis at the specimen surface.
  • an air-cored lens or so-called mini-lens is preferably used for the final lens as its self-inductance is very much lower than that of an orthodox iron-cored lens.
  • the main lens could be an orthodox iron-cored lens carrying a constant current and the correcting signal could be applied to an air-cored auxiliary lens.
  • the deflection rates may be arranged to obtain a constant velocity of the spot over the screen of the cathode ray tube, i.e. so that the angular velocity of scanning varies inversely with radial deflection.
  • the radial deflection passes straight through the zero point from one limit to the other and back again, as this avoids the need for a flyback, which is necessarily rapid.
  • the invention may be applied to an instrument specially built for the purpose, not by modifying an existing instrument.
  • the image should be formed from back-scattered electrons.
  • it could be formed from the specimen current or, where the specimen is of photo-luminescent material, the signal detected could be a light signal.
  • Electron probe apparatus comprising a source of electrons, beam forming means, said beam-forming means forming a beam from said electrons along an axis and forming an image of said source at a first point spaced along said axis from said source, first beamdeflection means, said deflection means being effective on said axis at said first point, means feeding a sawtooth deflection signal to said beam-deflecting means whereby to cause said beam to be deflected back and forth laterally from said axis in an angular manner centered on said first point, means defining an aperture around said axis at a second point on said axis further from said source than said first point, electron lens means disposed around said a erture,and serving to focus said beam to a spot at a t 1rd point on said axis,
  • said electron lens serving simultaneously to deflect said beam back towards said axis in dependence on the departure of said beam from said axis whereby said electron lens simultaneously forms second beam-deflection means causing said spot to remain substantially on said axis as said beam is scanned back and forth by said first beam-deflection means so that said beam effectively rocks angularly about said third point in step with said saw-tooth deflection signal, means for locating a specimen surface at said third point, detector means adapted to detect the response at said specimen surface to the impact of said beam, and display means connected to said detector means and said saw-tooth deflection signal feeding means to produce a visual display of the response of said detector means in accordance with the angular variation of the impact of the beam on said specimen surface.
  • Electron probe apparatus as set forth in claim 1 including means supplying a correcting signal to said electron lens, said correcting signal being variable in synchronism with said first beam-deflecting means and serving to correct the path of said beam for spherical aberration of said lens.
  • Electron probe apparatus as set forth in claim 2 wherein said first beam-deflecting means are such as to cause said beam to sweep out a conical path of slowly varying cone angle.
  • Electron probe apparatus as set forth in claim 3 wherein said display means are such as to produce a two-dimensional display by a spiral scan.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
US108408A 1970-01-21 1971-01-21 Electron beam apparatus Expired - Lifetime US3702398A (en)

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GB282970 1970-01-21
GB3205970 1970-07-02

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JP (1) JPS5425391B1 (enrdf_load_stackoverflow)
DE (1) DE2102616A1 (enrdf_load_stackoverflow)
FR (1) FR2075739A5 (enrdf_load_stackoverflow)
GB (1) GB1284061A (enrdf_load_stackoverflow)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3801784A (en) * 1972-04-14 1974-04-02 Research Corp Scanning electron microscope operating in area scan and angle scan modes
US3801792A (en) * 1973-05-23 1974-04-02 Bell Telephone Labor Inc Electron beam apparatus
EP0013738A1 (en) * 1979-01-18 1980-08-06 International Business Machines Corporation Method and apparatus for producing a high brightness electron beam
FR2605739A1 (fr) * 1986-10-27 1988-04-29 Atomika Tech Physik Gmbh Procede de balayage en spirale par un faisceau de particules
US4780216A (en) * 1986-11-19 1988-10-25 Olin Corporation Calcium hypochlorite sanitizing compositions
DE3924605A1 (de) * 1988-07-25 1990-02-01 Hitachi Ltd Rasterelektronenmikroskop
US4990779A (en) * 1989-06-06 1991-02-05 Nippon Steel Corporation Method and apparatus for evaluating strains in crystals
US20020125444A1 (en) * 2001-01-17 2002-09-12 Nikon Corporation Illumination-beam scanning configurations and methods for charged-particle-beam microlithography
US20040051542A1 (en) * 2002-07-04 2004-03-18 University Of Bristol Of Senate House Scanning probe microscope
US20040232321A1 (en) * 2001-02-06 2004-11-25 University Of Bristol Of Senate House Scanning near-field optical microscope
US6930308B1 (en) * 2002-07-11 2005-08-16 Kla-Tencor Technologies Corporation SEM profile and surface reconstruction using multiple data sets
US20100327179A1 (en) * 2009-06-26 2010-12-30 Carl Zeiss Nts Gmbh Charged particle beam column and method of operating same
US20110108736A1 (en) * 2009-11-09 2011-05-12 Carl Zeiss Nts Gmbh SACP Method and Particle Optical System for Performing the Method
WO2018122015A1 (en) * 2016-12-30 2018-07-05 Imec Vzw Characterization of regions with different crystallinity in materials

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL7204859A (enrdf_load_stackoverflow) * 1972-04-12 1973-10-16
JPS5788659A (en) * 1980-11-21 1982-06-02 Jeol Ltd Electron ray device

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2886727A (en) * 1955-12-12 1959-05-12 Vickers Electrical Co Ltd Electron optical apparatus
US3453485A (en) * 1966-03-15 1969-07-01 Siemens Ag Deflector system for corpuscular-beam apparatus
US3549883A (en) * 1968-10-07 1970-12-22 Gen Electric Scanning electron microscope wherein an image is formed as a function of specimen current
US3585382A (en) * 1968-05-28 1971-06-15 Jeol Ltd Stereo-scanning electron microscope

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2886727A (en) * 1955-12-12 1959-05-12 Vickers Electrical Co Ltd Electron optical apparatus
US3453485A (en) * 1966-03-15 1969-07-01 Siemens Ag Deflector system for corpuscular-beam apparatus
US3585382A (en) * 1968-05-28 1971-06-15 Jeol Ltd Stereo-scanning electron microscope
US3549883A (en) * 1968-10-07 1970-12-22 Gen Electric Scanning electron microscope wherein an image is formed as a function of specimen current

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3801784A (en) * 1972-04-14 1974-04-02 Research Corp Scanning electron microscope operating in area scan and angle scan modes
US3801792A (en) * 1973-05-23 1974-04-02 Bell Telephone Labor Inc Electron beam apparatus
EP0013738A1 (en) * 1979-01-18 1980-08-06 International Business Machines Corporation Method and apparatus for producing a high brightness electron beam
FR2605739A1 (fr) * 1986-10-27 1988-04-29 Atomika Tech Physik Gmbh Procede de balayage en spirale par un faisceau de particules
US4780216A (en) * 1986-11-19 1988-10-25 Olin Corporation Calcium hypochlorite sanitizing compositions
DE3924605A1 (de) * 1988-07-25 1990-02-01 Hitachi Ltd Rasterelektronenmikroskop
US4990779A (en) * 1989-06-06 1991-02-05 Nippon Steel Corporation Method and apparatus for evaluating strains in crystals
US20020125444A1 (en) * 2001-01-17 2002-09-12 Nikon Corporation Illumination-beam scanning configurations and methods for charged-particle-beam microlithography
US7498564B2 (en) * 2001-02-06 2009-03-03 University Of Bristol Of Senate House Resonant scanning near-field optical microscope
US20040232321A1 (en) * 2001-02-06 2004-11-25 University Of Bristol Of Senate House Scanning near-field optical microscope
US7473887B2 (en) 2002-07-04 2009-01-06 University Of Bristol Of Senate House Resonant scanning probe microscope
US20040051542A1 (en) * 2002-07-04 2004-03-18 University Of Bristol Of Senate House Scanning probe microscope
US6930308B1 (en) * 2002-07-11 2005-08-16 Kla-Tencor Technologies Corporation SEM profile and surface reconstruction using multiple data sets
US20100327179A1 (en) * 2009-06-26 2010-12-30 Carl Zeiss Nts Gmbh Charged particle beam column and method of operating same
US8129693B2 (en) 2009-06-26 2012-03-06 Carl Zeiss Nts Gmbh Charged particle beam column and method of operating same
US8558190B2 (en) 2009-06-26 2013-10-15 Carl Zeiss Microscopy Gmbh Charged particle beam column and method of operating same
US20110108736A1 (en) * 2009-11-09 2011-05-12 Carl Zeiss Nts Gmbh SACP Method and Particle Optical System for Performing the Method
US9093246B2 (en) 2009-11-09 2015-07-28 Carl Zeiss Microscopy Gmbh SACP method and particle optical system for performing the method
WO2018122015A1 (en) * 2016-12-30 2018-07-05 Imec Vzw Characterization of regions with different crystallinity in materials

Also Published As

Publication number Publication date
DE2102616A1 (de) 1971-07-29
FR2075739A5 (enrdf_load_stackoverflow) 1971-10-08
GB1284061A (en) 1972-08-02
JPS5425391B1 (enrdf_load_stackoverflow) 1979-08-28

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