US3900734A - Scanning electron-beam instrument - Google Patents

Scanning electron-beam instrument Download PDF

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Publication number
US3900734A
US3900734A US462295A US46229574A US3900734A US 3900734 A US3900734 A US 3900734A US 462295 A US462295 A US 462295A US 46229574 A US46229574 A US 46229574A US 3900734 A US3900734 A US 3900734A
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United States
Prior art keywords
raster
final lens
scanning
signal
signals
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Expired - Lifetime
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US462295A
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English (en)
Inventor
David Kynaston
Peter Irving Tillett
Richard Stephen Paden
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Cambridge 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
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams

Definitions

  • FIG. 1 PRIOR ART C Y A W L r Rotation Lcos+Fsln Mi/ F
  • the raster Looked at in the Z direction (i.e. along the electron-optical axis) the raster has a certain orientation in relation to that axis at the region of the scanning coils, and in the straightforward case the X and Y directions, i.e. the line and frame deflections, coincide with the axes of the respective pairs of scanning coils, although there is known, and indeed we have used, deflection circuits which allow the X and Y directions to be rotated through any angle up to 360 about the Z-axis, while maintaining the orthogonal relationship between the line and frame vectors.
  • this raster will undergo rotation about the electron-optical axis before it reaches the specimen, by virtue of the action of the electromagnetic final lens.
  • the amount of rotation will depend on the excitation of the lens, which in its turn determines the focal length.
  • the rotation will depend on the spacing of the specimen along the axis from the exit pole piece of the lens, as this spacing determines the focal length to which the lens has to be adjusted.
  • the rotation of the scanned raster caused by this final lens effect is inconvenient as it upsets the alignment of the specimen stage movement (the specimen stage being normally movable in two orthogonal directions, i.e. along an X and a Y axis with the line and frame scanning vectors.
  • the line or the frame scan) of the raster coincides with this direction there is no great problem as the appropriate deflection signal can be multiplied by a correction signal dependent on the cosine of the angle of inclination.
  • the appropriate deflection signal can be multiplied by a correction signal dependent on the cosine of the angle of inclination.
  • this is only true for one value of the focal length of the final lens. At other values the raster is rotated more or less and so the distortion will produce a parallelogram or rhombus type of distortion of the raster.
  • the problem of distortion resulting from inclination of a specimen surface is overcome by introducing a correction for the final lens effect for this purpose which is independent of any provisions that may or may not be present for rotating the scanning raster at will under control of the operator.
  • This correction of the distortion is achieved by applying an appropriate attenuation factor electronically along the direction of steepest slope regardless of the orientation of the raster in relation to that direction (or by applying an amplifying factor in a direction across the slope) and at the same time making orientation of the raster automatically independent of the working distance.
  • FIG. 1 illustrates diagrammatically the scanning coils, final lens and specimen in a scanning electron beam instrument
  • FIG. 2 is a diagrammatic view looking along the Z- axis (the axis of the electron beam);
  • FIG. 3 shows diagrammatically a known correction circuit
  • FIG. 4 is a diagram that illustrates the distorting effect of tilting the plane of the specimen surface with respect to the Z-axis'
  • FIG. 5 shows a circuit in accordance with the present invention.
  • FIG. I shows only the final part of the beam-forming system of an electron probe instrument which may be for example a scanning electron microscope or a scanning X-ray micro-analyzer.
  • a beam B of electrons is brought to a final focus on a specimen S. the surface of which is to be examined, by a final electromagnetic lens shown diagrammatically in section at L.
  • the focal length of the final lens should be as short as possible but it has been exaggerated in FIG. I in the interests of clarity.
  • a scanning instrument the beam is caused to scan back and forth in a raster, usually like a television raster, that is to say in a number of lines making up a rectangular area, by means of line scanning and frame scanning coils FS and LS mounted in the back bore of the lens L.
  • line scanning and frame scanning coils FS and LS mounted in the back bore of the lens L.
  • the line scanning coils LS will deflect the beam in one direction perpendicular to the Z axis, which we will call the X axis, and the frame scanning coils will deflect the beam in a third direction, the Y axis, perpendicular to the other two.
  • the coils are supplied with sawtooth timebase signals, from line-scan and frame-scan timbase generators LT and FT.
  • the same generators also control the X and Y deflections of the beam of a cathode ray rube CR or equivalent recording device, the brightness of the beam being controlled by a detector D receiving secondary electrons, reflected electrons, or X-rays emanating from the point of impact of the electron beam B on the specimen surface, so that there appears on the screen of the cathode ray tube CR a rectangular image, corresponding to the scanned area of the specimen surface, of
  • contrast is representative of the variations in the nature or topography of the specimen surface over that area.
  • the specimen S is usually mounted on a specimen stage (not show) that is movable along two mutually orthogonal axes in a plane parallel to the specimen sur face so as to allow different regions of the surface to be brought under the beam.
  • these axes should coincide with the directions of the X and Y axes at the specimen surface.
  • the orientations of the X and Y axes at the specimen surface are not the same as those of the coils FS and LS because the focus sing action of the final lens L causes the electrons to move in a spiral-helical path that effectively rotates the whole raster about the Z axis between the coils and the specimen surface, If the working distance, i.c.
  • the distance of the specimen surface from the final lens is fixed, and therefore the excitation of the lens is constant, it is possible to allow for this by correctly orientating the scanning coils FS and LS in relation to the specimen stage movements when initially setting up the instrument.
  • FIG. 2 shows a raster C and a raster C rotated counterclockwise with respect to the raster C through an angle 4) about the Z axis.
  • the coordinates of any point P with reference to one set of axes X, Y can be represented in the other set of coordinates (xfly'), where Therefore it is known to mix the signals (of magnitude L and F) from the two timebase generators LT and Fl to produce new signals L' and F where F F cos d; L sin (b and a suitable known circuit is shown diagrammatically in FIG. 3.
  • the value of the angle d may be manually controlled, allowing the operator to rotate the raster as much as he likes, so that the line scan is in any direction he selects. This allows him to orientate the raster with the specimen stage movements (or with any other feature) without moving the positions of the scanning coils themselves.
  • FIG. 5 shows a circuit according to the invention which corrects this electronically by introducing a correction that remains true regardless of the orientation of the raster in relation to the line of steepest slope and regardless of changes in the working distance.
  • the line and frame signals L and F from the saw-tooth timebase generators LT and FF are fed unchanged to the deflection circuits of the cathode ray tube CR as before.
  • the signals are first mixed, in the manner described above, with each other and with signals of variable magnitude sin 0 and cos 6 to produce derived signals L and F where:
  • F' Fcos0Lsin6 This is done in a manner that need not be described in detail as the necessary circuits elements are readily commercially available and comprise analogue multipliers Ml-M4 to form the factors L cos 6, F sin 6 and so on, and sum and difference amplifiers S and DI respectively to combine the factors appropriately.
  • operational amplifiers such as those sold by Texas Instruments under the description 702 may be used.
  • the value of 6 is under the control of the operator and can be made adjustable throughout the range from 0 to 360.
  • Each of the input resistors of value R/cos d), and R/sin d) of the two summing amplifiers is not a single resistor but one of a number of resistors of different values, corresponding to different values of the angle (it, and selected by a multi-way switch ganged to a switch that selects different values of the excitation current of the final lens L.
  • the values are arranged so that for any value of the excitation current the correction introduced by the summing amplifiers SA] and 8A2, i.e. the
  • the angular position of the raster is therefore independent of the working distance.
  • the specimen stage has its X and Y movements aligned with the line and,
  • the angle 8 can be altered as much as one likes, i.e. the raster can be rotated with complete freedom, without affecting orthogonality of the raster, and so the image on the screen of the cathode ray tube CR (which has remained rectangular throughout anyway) remains a true and undistorted image of the scanned region on the specimen surface. This is unaffected by changes in the working distance.
  • trapezium distortion is also introduced by the tilting of the specimen but this can also be corrected, if desired, by other means, which are not shown and do not form directly part of the present invention. and which are based on automatically attenuating the across-the-slope component of the signal by an amount which varies with the magnitude of the down-the-slope component.
  • a scanning electron beam instrument comprising means for forming a fine probe of electrons along an axis, a variable-focus electromagnetic final lens acting on said probe, line and frame time base generators capable of generating line and frame scanning signals.
  • line and frame scanning coils disposed to act on said probe ahead of said final lens whereby to cause the formation of a raster on a specimen placed at the focus of said final lens, variable control means controlling the focal length of said final lens, signal mixing means connected to said frame and time base generators and operative to mix said signals and feed derived line and frame scanning signals to said line and frame scanning coils respectively, said derived signals being such as to rotate said raster about said axis as compared with a raster produced by said first-mentioned signals, an interconnection between said signal-mixing means and said variable control means such as to vary the rotation of said raster by said signal-mixing means in opposition to rotation of said raster introduced by said final lens, whereby the orientation of said raster at the focus is independent of the focal length of

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
US462295A 1973-04-19 1974-04-18 Scanning electron-beam instrument Expired - Lifetime US3900734A (en)

Applications Claiming Priority (1)

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GB1914273A GB1441824A (en) 1973-04-19 1973-04-19 Scanning electronbeam instrument

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US3900734A true US3900734A (en) 1975-08-19

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US (1) US3900734A (enrdf_load_stackoverflow)
JP (1) JPS5031770A (enrdf_load_stackoverflow)
DE (1) DE2418279C2 (enrdf_load_stackoverflow)
GB (1) GB1441824A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4057722A (en) * 1975-09-25 1977-11-08 Siemens Aktiengesellschaft Method and apparatus for the generation of distortion-free images with electron microscope
FR2493041A1 (fr) * 1980-10-24 1982-04-30 Jeol Ltd Dispositif de balayage a faisceau de particules chargees
US4379231A (en) * 1979-03-14 1983-04-05 Hitachi, Ltd. Electron microscope

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5721830B2 (enrdf_load_stackoverflow) * 1973-06-04 1982-05-10
JPS50158273A (enrdf_load_stackoverflow) * 1974-06-10 1975-12-22
JPS5294768A (en) * 1976-02-04 1977-08-09 Jeol Ltd Electronic microscope
JPS587024B2 (ja) * 1976-06-23 1983-02-08 日本電子株式会社 電子顕微鏡等の像表示装置
JPS5875748A (ja) * 1981-10-30 1983-05-07 Shimadzu Corp 走査型分析装置の像回転補正装置
JPS58165968U (ja) * 1982-04-30 1983-11-05 株式会社島津製作所 電子線走査型分析装置
JPS6161357A (ja) * 1984-08-31 1986-03-29 Jeol Ltd 電子線装置の走査回転装置
JPS61135457U (enrdf_load_stackoverflow) * 1985-02-14 1986-08-23
EP0314947A1 (de) * 1987-11-03 1989-05-10 Siemens Aktiengesellschaft Schaltung zur vergrösserungsunabhängigen Bildverschiebung in einem Korpuskularstrahlgerät
JPH0748366B2 (ja) * 1988-07-29 1995-05-24 日本電子株式会社 集束イオンビーム注入装置

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3746855A (en) * 1970-10-28 1973-07-17 Ass Elect Ind Electron microscopes
US3753034A (en) * 1969-10-10 1973-08-14 Texas Instruments Inc Electron beam apparatus

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3753034A (en) * 1969-10-10 1973-08-14 Texas Instruments Inc Electron beam apparatus
US3746855A (en) * 1970-10-28 1973-07-17 Ass Elect Ind Electron microscopes

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4057722A (en) * 1975-09-25 1977-11-08 Siemens Aktiengesellschaft Method and apparatus for the generation of distortion-free images with electron microscope
US4379231A (en) * 1979-03-14 1983-04-05 Hitachi, Ltd. Electron microscope
FR2493041A1 (fr) * 1980-10-24 1982-04-30 Jeol Ltd Dispositif de balayage a faisceau de particules chargees
US4439681A (en) * 1980-10-24 1984-03-27 Jeol Ltd. Charged particle beam scanning device

Also Published As

Publication number Publication date
GB1441824A (en) 1976-07-07
DE2418279A1 (de) 1974-11-07
DE2418279C2 (de) 1983-12-08
JPS5031770A (enrdf_load_stackoverflow) 1975-03-28

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Effective date: 19830621