US3646344A - Scanning electron beam apparatus for viewing potential distribution on specimen surfaces - Google Patents
Scanning electron beam apparatus for viewing potential distribution on specimen surfaces Download PDFInfo
- Publication number
- US3646344A US3646344A US889762A US3646344DA US3646344A US 3646344 A US3646344 A US 3646344A US 889762 A US889762 A US 889762A US 3646344D A US3646344D A US 3646344DA US 3646344 A US3646344 A US 3646344A
- Authority
- US
- United States
- Prior art keywords
- grid
- specimen
- potential
- probe
- detector
- 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
Links
- 238000010894 electron beam technology Methods 0.000 title claims abstract description 14
- 239000000523 sample Substances 0.000 claims abstract description 27
- 239000007787 solid Substances 0.000 claims description 5
- 230000001360 synchronised effect Effects 0.000 claims description 3
- 238000005036 potential barrier Methods 0.000 abstract description 3
- 230000004888 barrier function Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- VZUGBLTVBZJZOE-KRWDZBQOSA-N n-[3-[(4s)-2-amino-1,4-dimethyl-6-oxo-5h-pyrimidin-4-yl]phenyl]-5-chloropyrimidine-2-carboxamide Chemical compound N1=C(N)N(C)C(=O)C[C@@]1(C)C1=CC=CC(NC(=O)C=2N=CC(Cl)=CN=2)=C1 VZUGBLTVBZJZOE-KRWDZBQOSA-N 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 238000005381 potential energy Methods 0.000 description 1
- 230000000979 retarding effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
Images
Classifications
-
- 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
- H01J37/266—Measurement of magnetic- or electric fields in the object; Lorentzmicroscopy
- H01J37/268—Measurement of magnetic- or electric fields in the object; Lorentzmicroscopy with scanning beams
-
- 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
-
- 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
- H01J2237/2448—Secondary particle detectors
-
- 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
Definitions
- ABSTRACT In electron beam apparatus, in which a finely focused probe is caused to impinge on the surface of a specimen and the resulting secondary electrons are collected and used to show potential distribution on the specimen surface the detector includes, between the collector and the specimen, a positive grid and a further grid, this further grid being of variable low or negative potential to form effectively a potential barrier of adjustable height to discriminate between electrons coming from regions of different potential.
- This invention relates to electron beam apparatus of the kind in which a beam of electrons, known as an electron probe, is caused to impinge on a specimen under examination and information about the voltage distribution at the specimen surface is obtained by using a detector to pick up electrons emanating from the specimen. Normally the beam will be focused to a fine spot and will be caused to scan the surface of the specimen and the signal is used to control the brightness of a cathode-ray tube display synchronized with the scanning of the beam, so that an image of the specimen surface is formed.
- a beam of electrons known as an electron probe
- Voltage contrast in the image may itself be of significance, for example where the specimen is a solid-state electronic component or a portion of an integrated circuit, or the voltage contrast may be indicative of some other physical phenomenon which it is desired to examine.
- the detector is normally placed on the same side of the specimen as the beam but to one side of the beam and is intended to pick up the secondary electrons emerging from the specimen.
- the detector normally subtends a relatively small solid angle at the specimen surface. As the beam scans over an area of uniform potential the mean number of secondary electrons picked up by the detector remains the same, but when a region of different potential is reached the absolute energy distribution of secondaries is upset and there is a change in the number of secondaries picked up, resulting in image contrast.
- difference dark may correspond to positive and light to negative or vice versa.
- a further difficulty is that the secondary electrons, as they move away from the point of impact and are attracted in curved paths and at relatively low velocities towards the detector may also be influenced by fields produced by potential gradients or potential differences in other parts of the specimen surface. Moreover the detector picks up not only true secondary electrons of low energy but also high-energy reflected primaries which are substantially unaffected by potential contrast. Finally it also picks up other low-energy secondary electrons generated in the surrounding casing and specimen mount by impingement of the reflected primaries, and these likewise are not affected by the potential contrast in the specimen, and so swamp still further the wanted signal. They may form as much as 30 percent of the low-energy electrons reaching the detector.
- the main aim of the present invention is to provide a configuration of electrodes, including an electron detector, such that the sense of the change in collected current for a given change in specimensurface voltage is always the same, irrespective of the absolute value of either voltage, that is to say the collected current is a monotonic function of surface voltage.
- a further aim is to attempt to ensure that this configuration of electrodes can be made to give the same change in collected current for the same change in specimen surface voltage, whether the specimen surface voltage change be in space or in time, and wherever the electron probe might be situated or might move upon the specimen surface.
- a further aim is to provide that the collected electron current has as far as possible a linear relationship with the potential at the specimen surface.
- a further aim is to provide that the collected electron current is so far as possible independent of all influence other than the number of electrons emitted from the small area of specimen surface where the electron probe is instantaneously incident, and the voltage of that same point.
- the invention we propose to provide a detector subtending a substantial solid angle at the point of impact LII of the probe and to provide grids between the detector and the point of impact, the potential on at least one of the grids being such as to allow the passage only of the electrons of above a certain level of energy, the threshold energy," which may be set to any chosen value, and the potential on at least one other grid being at a substantial positive value to attract a high proportion of the available secondary electrons.
- the first grid encountered by the electrons that is at a substantial positive potential.
- the presence of this grid also produces a field that masks any disturbances of the field above the specimen induced by potential differences on the specimen surface in the neighborhood of the point of impact.
- the grids and the detector may be of part-spherical form, with their common center of curvature at the point of impact, or they could be planar (this is necessitated in many cases by the nature of the detector) or cylindrical, frustoconical, or of any other convenient form.
- FIG. I is a diagrammatic illustration of the apparatus according to the invention.
- FIG. 2 is a graph showing the energy distribution of secondary electrons
- FIG. 3 is a graph showing the relationship between collector current and potential difference.
- the probe-forming system is orthodox, comprising an electron gun G, an anode A, a first electron-optical lens LI and a final electron lens L2.
- the beam or probe of electrons formed by this system impinges on a specimen S and is caused to scan a small area of the specimen, for example a square measuring a fraction of a millimeter each way, by scanning coils C fed from a time base T which also controls the deflection plates of a cathode-ray tube CR.
- the brightness of the spot on the screen of the tube is controlled by the signal from a detector, indicated generally at D, so that there is reproduced on the screen an image of the scanned area of the specimen, the contrast in the image being determined by the change in signal at the detector D as the probe moves over the surface of the specimen.
- the detector is simply picking up the secondary electrons from the specimen and the contrast to be displayed is potential contrast at the specimen surface
- the known detectors suffer from the defects mentioned above.
- the changes that are to be detected are masked by backscattered highenergy primary electrons, by secondary electrons generated by impact of backscattered primary electrons on parts of the instrument around the specimen, and the by fact that the very potential contrast which one is seeking to detect produce fields above the surface of the specimen which themselves influence the paths of the low-energy secondary electrons and which thus mask unpredictably the contrast one is seeking to observe.
- the electron gun will be at a large negative potential, (for example -20 kv. and the specimen at earth potential, so that the electrons of the probe will have an energy (in the example quoted) of 20 kev. Any of these which are backscattered from the specimen will have energies of a similar order, i.e., of various values up to 20 kev. Consequently they will be fast and not easily deflected by small electric or magnetic fields.
- the true secondary electrons on the other hand have low energies of varying values, mostly under 5 electron volts, with a peak around about 2% electron volts. This is shown diagrammatically in FIG. 2.
- the grid G1 serves simply to attract the secondary electrons from the point of impact of the beam on the specimen surface towards the detector and has the additional function of producing an electrical field above the specimen surface that masks any field distortions caused in this region by the presence of potential differences in the specimen.
- the grid G1 may be at a positive potential of 500 volts but the actual voltage will depend on the distance from the specimen; it is desirable that the potential gradient should be not less than 5,000 volts per meter. This would give a value of 25 volts where the grid is 5 millimeters from the specimen surface.
- the gradient is at least volts per meter.
- the potential on G1 should be at least 25 volts to have a worthwhile effect.
- the heart of the invention lies in the control grid G2, which forms a potential barrier of variable height to discriminate between secondary electrons emanating from regions of the specimen surface of different potential.
- the grid G2 like the grids G1 and G3 can be in the form of a mesh of wires and its effective potential is not that on the wires themselves but that of the field in the gaps between the wires, which is largely determined by the potential on the wires but is also influenced to some extent by potentials of surrounding electrodes. if this effective potential is zero, secondary electrons coming from a point on the specimen surface which is at zero potential will get through the grid G2 as they will have a potential energy of about 2% electron volts or more.
- Electrons coming from a region of the specimen surface which is at, say, 5 volts will get through it easily as they will have the added energy of 5 electron volts derived from their acceleration in the field from 5 volts up to zero. Electrons coming from a region at +5 volts, on the other hand, are retarded and only those which started with an intrinsic energy of greater then 5 electron volts will get through the grid. As will be seen from FIG. 2, this will only be a small proportion. Thus the signal picked up by the detector will vary as the probe scans over a region of the specimen surface that varies in potential, those portions which are more negative producing a larger signal in the detector than those which are more positive.
- the detector is thus able to discriminate between regions of the specimen surface of different potential and a potential contrast image is formed on the screen of the cathode-ray tube CR.
- a potential contrast image is formed on the screen of the cathode-ray tube CR.
- the grid G2 forms a barrier B as indicated in FIG. 2, all those electrons which lie to the right of the barrier being able to pass through it.
- the barrier will normally be set approximately to the peak of the curve, or to the point of the curve of steepest slope, or the point of inflexion, to the right of the peak, or somewhere between these two points.
- Linearity of response is also desirable, i.e., a uniform change in signal at the detector for a uniform change in potential at the specimen surface, and this is best achieved by working at the point of inflexion.
- FIG. 3 shows approximately how the collector current [c varies with the value of the difference between the effective potential Vg on the grid G2 and the potential Vs on the specimen surface. Effectively this represents the integral of the curve of FIG. 2, but with the zero of the horizontal axis shifted by approximately 5 volts to allow for the fact that the potential difference in question has to be up to 5 volts negative to overcome the intrinsic energy of the secondary electrons. it is desirable to work over the nearly linear part of the curve around 2% volts.
- a scintillator is preferably used to pick up the electrons. as it has a very low-noise factor. its potential is unimportant to the above reasoning and is of any typical value used for scintillators for example 10 kv.
- the grid G3 has the function of a suppressor grid to avoid the signal being upset by secondary emission from the collector itself, resulting from impact of high-energy backscattered primary electrons. For convenience we connect this third grid to the first grid G1, so that it has the same potential of 500 volts in the present example.
- the potential on the control grid G2 may vary the potential on the control grid G2 cyclically in a sinusoidal .or other manner about its mean value.
- the absolute value of sensitivity varies to some extent with the potential on the control grid, i.e., away the straight part of the curve of FIG. 3, the cyclic variation does itself introduce some distortion and so its amplitude should be not more than necessary.
- the grids and the scintillator are arranged in line on an axis which is normal to the surface of the specimen, and the electron probe is brought in at an angle to clear them but it would be possible for the probe to be normal to the surface, the detector then being to one side.
- the grids need not be flat but could, for example be part-spherical or even cylindrical, surrounding the normal to the specimen, and in that case the collector may be other than a scintillator, since a scintillator is generally necessarily flat.
- this window W defining the area of scintillator exposed.
- the purpose of this window is to increase the proportion, in the collected electron current, of electrons emitted with small energies (and thus contributing to the voltage contrast) to the proportion of electrons emitted with high energies.
- the positive first grid G1 will tend to pull in towards the normal to the specimen the preferred low-energy secondaries, more than it does high-energy electrons.
- the high-kinetic energy of these preferred electrons at the first grid G1 means they are less bent by the retarding field between the grids G1 and G2 than they would be without the additional kinetic energy given by the first grid.
- the positive third grid G3 will again pull in towards the specimen normal those electrons penetrating the grid G2 with a low energy.
- an electron emitted with high energy will be much less deflected from its course by the various grid potentials.
- the window W allows through to the collector only those electrons which are close to the normal to the specimen. Hence the net effect is that electrons from a larger solid angle of emission are collected for low-emission energies than for high-emission energies.
- the detector arrangement in accordance with the invention may be used in conjunction with AC sorting methods, or in conjunction with the stroboscopic scanning methods disclosed in our copending U.S. Pat. application Ser. No. 813,176 filed on Apr. 3, 1969.
- Electron beam apparatus comprising electron gun means for forming a high-energy probe of electrons having an energy of the order of thousands of electron volts, lens means focusing said probe, a specimen having a surface thereof in the path of said probe for impact thereon of said probe, a detector adapted to receive secondary electrons emerging from said specimen surface as a consequence of the impact thereon of said probe said detector subtending a restricted solid angle at said specimen surface, image display means connected to said detector to receive signals therefrom generated by said secondary electrons, deflection means acting on said probe to deflect said probe laterally, said image display means being synchronized with said deflection means such as to produce an image of a region of said specimen surface in terms of said secondary electrons, a first grid between said specimen surface and said detector, said first grid being at a substantial positive electric potential with respect to said specimen; such as to create a voltage gradient between said first grid and specimen surface which is not less than 5,000 volts per meter, and said potential being not less than 25 volts, a second grid between said first
- Electron beam apparatus as set forth in claim 1 including a third grid between said second grid and said collector.
Abstract
In electron beam apparatus, in which a finely focused probe is caused to impinge on the surface of a specimen and the resulting secondary electrons are collected and used to show potential distribution on the specimen surface the detector includes, between the collector and the specimen, a positive grid and a further grid, this further grid being of variable low or negative potential to form effectively a potential barrier of adjustable height to discriminate between electrons coming from regions of different potential.
Description
United States Plows et al.
atent [54] SCANNING ELECTRON BEAM APPARATUS FOR VIEWING POTENTIAL DISTRIBUTION ON SPECIMEN SURFACES [72] Inventors: Graham Plows, 80, Brent Court,
Stevenage, Hertfordshire; William Charles Nixon, 2, Causewayside, Fen Causeway, Cambridge, both of England 22 Filed: Dec.3l,l969
211 Appl.No.: 889,762
[30] Foreign Application Priority Data June 2, 1969 Great Britain ..300/69 [52] US. Cl. ..250/49.5 A, 250/495 PE, 250/49.5 AE [51] Int. Cl. ..H0lj 37/28 [58] Field of Search ..250/49.5 A, 49.5 PE, 49.5 AE
[56] References Cited UNITED STATES PATENTS 3,461,306 8/1969 Stout et al. ..250/49.5 PE
[ Feb. 29, 1972 OTHER PUBLlCATlONS Electronics; Vol. 37, N0. 16; May, l964;pp. ll9.
Tharp et al; Journal of Applied Physics; Vol. 38, No. 8; July, 1967; PP- 3320- 3330.
Lander et aL; Review of Scientific Instr; Vol. 33, No. 7; July 1962, 782, 783.
Primary Examiner-Anthony L. Birch A ttorneyScrivener Parker Scrivener and Clarke [5 7] ABSTRACT In electron beam apparatus, in which a finely focused probe is caused to impinge on the surface of a specimen and the resulting secondary electrons are collected and used to show potential distribution on the specimen surface the detector includes, between the collector and the specimen, a positive grid and a further grid, this further grid being of variable low or negative potential to form effectively a potential barrier of adjustable height to discriminate between electrons coming from regions of different potential.
6 Claims, 3 Drawing Figures SCANNING ELECTRON BEAM APPARATUS FOR VIEWING POTENTIAL DISTRIBUTION ON SPECIMEN SURFACES This invention relates to electron beam apparatus of the kind in which a beam of electrons, known as an electron probe, is caused to impinge on a specimen under examination and information about the voltage distribution at the specimen surface is obtained by using a detector to pick up electrons emanating from the specimen. Normally the beam will be focused to a fine spot and will be caused to scan the surface of the specimen and the signal is used to control the brightness of a cathode-ray tube display synchronized with the scanning of the beam, so that an image of the specimen surface is formed.
Voltage contrast in the image may itself be of significance, for example where the specimen is a solid-state electronic component or a portion of an integrated circuit, or the voltage contrast may be indicative of some other physical phenomenon which it is desired to examine.
The detector is normally placed on the same side of the specimen as the beam but to one side of the beam and is intended to pick up the secondary electrons emerging from the specimen. The detector normally subtends a relatively small solid angle at the specimen surface. As the beam scans over an area of uniform potential the mean number of secondary electrons picked up by the detector remains the same, but when a region of different potential is reached the absolute energy distribution of secondaries is upset and there is a change in the number of secondaries picked up, resulting in image contrast.
However, such an arrangement is not predictable. For a given voltage, difference dark may correspond to positive and light to negative or vice versa.
Further, it is not normally possible to arrange that, for a given electron probe current, the collected current changes by a certain amount for a given change in specimen surface voltage. Hence, the magnitude and sign of the specimen surface voltage difference cannot be deduced from the change in collected current.
A further difficulty is that the secondary electrons, as they move away from the point of impact and are attracted in curved paths and at relatively low velocities towards the detector may also be influenced by fields produced by potential gradients or potential differences in other parts of the specimen surface. Moreover the detector picks up not only true secondary electrons of low energy but also high-energy reflected primaries which are substantially unaffected by potential contrast. Finally it also picks up other low-energy secondary electrons generated in the surrounding casing and specimen mount by impingement of the reflected primaries, and these likewise are not affected by the potential contrast in the specimen, and so swamp still further the wanted signal. They may form as much as 30 percent of the low-energy electrons reaching the detector.
The main aim of the present invention is to provide a configuration of electrodes, including an electron detector, such that the sense of the change in collected current for a given change in specimensurface voltage is always the same, irrespective of the absolute value of either voltage, that is to say the collected current is a monotonic function of surface voltage. A further aim is to attempt to ensure that this configuration of electrodes can be made to give the same change in collected current for the same change in specimen surface voltage, whether the specimen surface voltage change be in space or in time, and wherever the electron probe might be situated or might move upon the specimen surface. A further aim is to provide that the collected electron current has as far as possible a linear relationship with the potential at the specimen surface. A further aim is to provide that the collected electron current is so far as possible independent of all influence other than the number of electrons emitted from the small area of specimen surface where the electron probe is instantaneously incident, and the voltage of that same point.
According to the invention we propose to provide a detector subtending a substantial solid angle at the point of impact LII of the probe and to provide grids between the detector and the point of impact, the potential on at least one of the grids being such as to allow the passage only of the electrons of above a certain level of energy, the threshold energy," which may be set to any chosen value, and the potential on at least one other grid being at a substantial positive value to attract a high proportion of the available secondary electrons.
Preferably it is the first grid encountered by the electrons that is at a substantial positive potential. The presence of this grid also produces a field that masks any disturbances of the field above the specimen induced by potential differences on the specimen surface in the neighborhood of the point of impact. The grids and the detector may be of part-spherical form, with their common center of curvature at the point of impact, or they could be planar (this is necessitated in many cases by the nature of the detector) or cylindrical, frustoconical, or of any other convenient form.
The invention will now be further described by way of example with reference to the accompanying drawings, in which:
FIG. I is a diagrammatic illustration of the apparatus according to the invention;
FIG. 2 is a graph showing the energy distribution of secondary electrons; and
FIG. 3 is a graph showing the relationship between collector current and potential difference.
Referring first to FIG. 1, the probe-forming system is orthodox, comprising an electron gun G, an anode A, a first electron-optical lens LI and a final electron lens L2. The beam or probe of electrons formed by this system impinges on a specimen S and is caused to scan a small area of the specimen, for example a square measuring a fraction of a millimeter each way, by scanning coils C fed from a time base T which also controls the deflection plates of a cathode-ray tube CR. The brightness of the spot on the screen of the tube is controlled by the signal from a detector, indicated generally at D, so that there is reproduced on the screen an image of the scanned area of the specimen, the contrast in the image being determined by the change in signal at the detector D as the probe moves over the surface of the specimen.
Where the detector is simply picking up the secondary electrons from the specimen and the contrast to be displayed is potential contrast at the specimen surface, the known detectors suffer from the defects mentioned above. The changes that are to be detected are masked by backscattered highenergy primary electrons, by secondary electrons generated by impact of backscattered primary electrons on parts of the instrument around the specimen, and the by fact that the very potential contrast which one is seeking to detect produce fields above the surface of the specimen which themselves influence the paths of the low-energy secondary electrons and which thus mask unpredictably the contrast one is seeking to observe.
Normally the electron gun will be at a large negative potential, (for example -20 kv. and the specimen at earth potential, so that the electrons of the probe will have an energy (in the example quoted) of 20 kev. Any of these which are backscattered from the specimen will have energies of a similar order, i.e., of various values up to 20 kev. Consequently they will be fast and not easily deflected by small electric or magnetic fields. The true secondary electrons, on the other hand have low energies of varying values, mostly under 5 electron volts, with a peak around about 2% electron volts. This is shown diagrammatically in FIG. 2.
Those secondary electrons leaving a point in the specimen surface which is at earth potential have, on arriving at given grid or other surface of a certain potential an amount of energy represented by their intrinsic energy around 2% to 4 electron volts, to which is added (or from which is subtracted) that energy gained or lost as a result of the potential difference between the earthed specimen and the grid or other surface in question. Where the specimen surface is not at earth potential the energy gained or lost will be different.
In the detector illustrated we provide a grid G1 at a relative- 1y high-positive potential, a control grid G2, of adjustable low potential, and a third grid G3 for a purpose to be explained below, between the specimen surface and an electron collector in the form of a scintillator SC, the light from which is taken by a light pipe to a photomultiplier P to produce the electrical signal that is amplified and used to modulate the beam in the cathode-ray tube CR.
The grid G1 serves simply to attract the secondary electrons from the point of impact of the beam on the specimen surface towards the detector and has the additional function of producing an electrical field above the specimen surface that masks any field distortions caused in this region by the presence of potential differences in the specimen. in a typical example the grid G1 may be at a positive potential of 500 volts but the actual voltage will depend on the distance from the specimen; it is desirable that the potential gradient should be not less than 5,000 volts per meter. This would give a value of 25 volts where the grid is 5 millimeters from the specimen surface. Preferably the gradient is at least volts per meter. However, regardless of distance the potential on G1 should be at least 25 volts to have a worthwhile effect.
The heart of the invention lies in the control grid G2, which forms a potential barrier of variable height to discriminate between secondary electrons emanating from regions of the specimen surface of different potential. The grid G2, like the grids G1 and G3 can be in the form of a mesh of wires and its effective potential is not that on the wires themselves but that of the field in the gaps between the wires, which is largely determined by the potential on the wires but is also influenced to some extent by potentials of surrounding electrodes. if this effective potential is zero, secondary electrons coming from a point on the specimen surface which is at zero potential will get through the grid G2 as they will have a potential energy of about 2% electron volts or more. Electrons coming from a region of the specimen surface which is at, say, 5 volts will get through it easily as they will have the added energy of 5 electron volts derived from their acceleration in the field from 5 volts up to zero. Electrons coming from a region at +5 volts, on the other hand, are retarded and only those which started with an intrinsic energy of greater then 5 electron volts will get through the grid. As will be seen from FIG. 2, this will only be a small proportion. Thus the signal picked up by the detector will vary as the probe scans over a region of the specimen surface that varies in potential, those portions which are more negative producing a larger signal in the detector than those which are more positive.
in practice the absolute potentials are influenced by the work function potential of the elements of which the specimen is made but as this is the same all over the specimen it will not affect the reasoning above.
The detector is thus able to discriminate between regions of the specimen surface of different potential and a potential contrast image is formed on the screen of the cathode-ray tube CR. By adjusting the potential of the grid G2 it is possible to vary the mean potential level at which the scanned region just produces no signal in the detector, and so one can discriminate at will between regions of positive and negative potential or between regions having different levels of potential of the same sign. Effectively the grid G2 forms a barrier B as indicated in FIG. 2, all those electrons which lie to the right of the barrier being able to pass through it. For maximum discrimination the barrier will normally be set approximately to the peak of the curve, or to the point of the curve of steepest slope, or the point of inflexion, to the right of the peak, or somewhere between these two points. Linearity of response is also desirable, i.e., a uniform change in signal at the detector for a uniform change in potential at the specimen surface, and this is best achieved by working at the point of inflexion. FIG. 3 shows approximately how the collector current [c varies with the value of the difference between the effective potential Vg on the grid G2 and the potential Vs on the specimen surface. Effectively this represents the integral of the curve of FIG. 2, but with the zero of the horizontal axis shifted by approximately 5 volts to allow for the fact that the potential difference in question has to be up to 5 volts negative to overcome the intrinsic energy of the secondary electrons. it is desirable to work over the nearly linear part of the curve around 2% volts.
A scintillator is preferably used to pick up the electrons. as it has a very low-noise factor. its potential is unimportant to the above reasoning and is of any typical value used for scintillators for example 10 kv. The grid G3 has the function of a suppressor grid to avoid the signal being upset by secondary emission from the collector itself, resulting from impact of high-energy backscattered primary electrons. For convenience we connect this third grid to the first grid G1, so that it has the same potential of 500 volts in the present example.
in order to improve linearity of response we may vary the potential on the control grid G2 cyclically in a sinusoidal .or other manner about its mean value. As the absolute value of sensitivity varies to some extent with the potential on the control grid, i.e., away the straight part of the curve of FIG. 3, the cyclic variation does itself introduce some distortion and so its amplitude should be not more than necessary.
In the example illustrated the grids and the scintillator are arranged in line on an axis which is normal to the surface of the specimen, and the electron probe is brought in at an angle to clear them but it would be possible for the probe to be normal to the surface, the detector then being to one side. The grids need not be flat but could, for example be part-spherical or even cylindrical, surrounding the normal to the specimen, and in that case the collector may be other than a scintillator, since a scintillator is generally necessarily flat.
In the example illustrated we provide a window W defining the area of scintillator exposed. The purpose of this window is to increase the proportion, in the collected electron current, of electrons emitted with small energies (and thus contributing to the voltage contrast) to the proportion of electrons emitted with high energies. The positive first grid G1 will tend to pull in towards the normal to the specimen the preferred low-energy secondaries, more than it does high-energy electrons. Again, the high-kinetic energy of these preferred electrons at the first grid G1 means they are less bent by the retarding field between the grids G1 and G2 than they would be without the additional kinetic energy given by the first grid. Finally, the positive third grid G3 will again pull in towards the specimen normal those electrons penetrating the grid G2 with a low energy. At the other extreme, an electron emitted with high energy will be much less deflected from its course by the various grid potentials. The window W allows through to the collector only those electrons which are close to the normal to the specimen. Hence the net effect is that electrons from a larger solid angle of emission are collected for low-emission energies than for high-emission energies.
The detector arrangement in accordance with the invention may be used in conjunction with AC sorting methods, or in conjunction with the stroboscopic scanning methods disclosed in our copending U.S. Pat. application Ser. No. 813,176 filed on Apr. 3, 1969.
We claim:
1. Electron beam apparatus comprising electron gun means for forming a high-energy probe of electrons having an energy of the order of thousands of electron volts, lens means focusing said probe, a specimen having a surface thereof in the path of said probe for impact thereon of said probe, a detector adapted to receive secondary electrons emerging from said specimen surface as a consequence of the impact thereon of said probe said detector subtending a restricted solid angle at said specimen surface, image display means connected to said detector to receive signals therefrom generated by said secondary electrons, deflection means acting on said probe to deflect said probe laterally, said image display means being synchronized with said deflection means such as to produce an image of a region of said specimen surface in terms of said secondary electrons, a first grid between said specimen surface and said detector, said first grid being at a substantial positive electric potential with respect to said specimen; such as to create a voltage gradient between said first grid and specimen surface which is not less than 5,000 volts per meter, and said potential being not less than 25 volts, a second grid between said first grid and said detector, said second grid being at a potential which is negative and low but variable with respect to the specimen, the potential of said second grid being of the order of between zero and 5 volts.
2. Electron beam apparatus as set forth in claim 1 including a third grid between said second grid and said collector.
Claims (6)
1. Electron beam apparatus comprising electron gun means for forming a high-energy probe of electrons having an energy of the order of thousands of electron volts, lens means focusing said probe, a specimen having a surface thereof in the path of said probe for impact thereon of said probe, a detector adapted to receive secondary electrons emerging from said specimen surface as a consequence of the impact thereon of said probe said detector subtending a restricted solid angle at said specimen surface, image display means connected to said detector to receive signals therefrom generated by said secondary electrons, deflection means acting on said probe to deflect said probe laterally, said image display means being synchronized with said deflection means such as to produce an image of a region of said specimen surface in terms of said secondary electrons, a first grid between said specimen surface and said detector, said first grid being at a substantial positive electric potential with respect to said specimen, such as to create a voltage gradient between said first grid and specimen surface which is not less than 5,000 volts per meter, and said potential being not less than 25 volts, a second grid between said first grid and said detector, said second grid being at a potential which is negative and low but variable with respect to the specimen, the potential of said second grid being of the order of between zero and -5 volts.
2. Electron beam apparatus as set forth in claim 1 including a third grid between said second grid and said collector.
3. Electron beam apparatus as set forth in claim 2 wherein said third grid is electrically connected to said first grid.
4. Electron beam apparatus as set forth in claim 1 wherein each of said grid and said collector are planar and are mutually parallel.
5. Electron beam apparatus as set forth in claim 4 wherein said grids and collector lie perpendicular to a normal to the specimen surface.
6. Electron beam apparatus as set forth in claim 1 wherein said voltage gradient is not less than 105 volts per meter.
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB300/69A GB1246744A (en) | 1969-01-02 | 1969-01-02 | Electron beam apparatus |
Publications (1)
Publication Number | Publication Date |
---|---|
US3646344A true US3646344A (en) | 1972-02-29 |
Family
ID=9701950
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US889762A Expired - Lifetime US3646344A (en) | 1969-01-02 | 1969-12-31 | Scanning electron beam apparatus for viewing potential distribution on specimen surfaces |
Country Status (4)
Country | Link |
---|---|
US (1) | US3646344A (en) |
DE (1) | DE2000217B2 (en) |
FR (1) | FR2027656A1 (en) |
GB (1) | GB1246744A (en) |
Cited By (15)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3775610A (en) * | 1972-06-20 | 1973-11-27 | Us Air Force | Method and system for secondary emission detection |
US3786268A (en) * | 1971-04-12 | 1974-01-15 | Hitachi Ltd | Electron gun device of field emission type |
US3845304A (en) * | 1972-03-21 | 1974-10-29 | Hitachi Ltd | Ion microanalyzer |
US3894233A (en) * | 1972-10-27 | 1975-07-08 | Hitachi Ltd | Ion microprobe analyzer |
US4292519A (en) * | 1979-01-23 | 1981-09-29 | Siemens Aktiengesellschaft | Device for contact-free potential measurements |
US4355232A (en) * | 1979-05-28 | 1982-10-19 | Hitachi, Ltd. | Apparatus for measuring specimen potential in electron microscope |
US4554455A (en) * | 1982-08-16 | 1985-11-19 | Hitachi, Ltd. | Potential analyzer |
US4629889A (en) * | 1983-06-24 | 1986-12-16 | Hitachi, Ltd. | Potential analyzer |
US4721909A (en) * | 1985-08-16 | 1988-01-26 | Schlumberger Technology Corporation | Apparatus for pulsing electron beams |
US4864228A (en) * | 1985-03-15 | 1989-09-05 | Fairchild Camera And Instrument Corporation | Electron beam test probe for integrated circuit testing |
EP0949653A2 (en) * | 1991-11-27 | 1999-10-13 | Hitachi, Ltd. | Electron beam apparatus |
EP1049132A1 (en) * | 1999-03-31 | 2000-11-02 | Advantest Corporation | Method and apparatus for imaging a surface potential |
US6359451B1 (en) | 2000-02-11 | 2002-03-19 | Image Graphics Incorporated | System for contactless testing of printed circuit boards |
US6621274B2 (en) | 2000-02-14 | 2003-09-16 | Image Graphics Incorporated | System for contactless testing of printed circuit boards |
US20180082829A1 (en) * | 2016-01-21 | 2018-03-22 | Japan Synchrotron Radiation Research Institute | Retarding potential type energy analyzer |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2823642A1 (en) * | 1978-05-30 | 1980-01-03 | Siemens Ag | METHOD FOR CONTACTLESS POTENTIAL MEASUREMENT ON AN ELECTRONIC COMPONENT |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3461306A (en) * | 1967-04-27 | 1969-08-12 | Gen Electric | Electron probe microanalyzer for measuring the differential energy response of auger electrons |
-
1969
- 1969-01-02 GB GB300/69A patent/GB1246744A/en not_active Expired
- 1969-12-31 FR FR6945615A patent/FR2027656A1/fr not_active Withdrawn
- 1969-12-31 US US889762A patent/US3646344A/en not_active Expired - Lifetime
-
1970
- 1970-01-02 DE DE19702000217 patent/DE2000217B2/en active Pending
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3461306A (en) * | 1967-04-27 | 1969-08-12 | Gen Electric | Electron probe microanalyzer for measuring the differential energy response of auger electrons |
Non-Patent Citations (3)
Title |
---|
Electronics; Vol. 37, No. 16; May, 1964; pp. 119. * |
Lander et al.; Review of Scientific Instr; Vol. 33, No. 7; July 1962, 782, 783. * |
Tharp et al; Journal of Applied Physics; Vol. 38, No. 8; July, 1967; pp. 3320 3330. * |
Cited By (17)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3786268A (en) * | 1971-04-12 | 1974-01-15 | Hitachi Ltd | Electron gun device of field emission type |
US3845304A (en) * | 1972-03-21 | 1974-10-29 | Hitachi Ltd | Ion microanalyzer |
US3775610A (en) * | 1972-06-20 | 1973-11-27 | Us Air Force | Method and system for secondary emission detection |
US3894233A (en) * | 1972-10-27 | 1975-07-08 | Hitachi Ltd | Ion microprobe analyzer |
US4292519A (en) * | 1979-01-23 | 1981-09-29 | Siemens Aktiengesellschaft | Device for contact-free potential measurements |
US4355232A (en) * | 1979-05-28 | 1982-10-19 | Hitachi, Ltd. | Apparatus for measuring specimen potential in electron microscope |
US4554455A (en) * | 1982-08-16 | 1985-11-19 | Hitachi, Ltd. | Potential analyzer |
US4629889A (en) * | 1983-06-24 | 1986-12-16 | Hitachi, Ltd. | Potential analyzer |
US4864228A (en) * | 1985-03-15 | 1989-09-05 | Fairchild Camera And Instrument Corporation | Electron beam test probe for integrated circuit testing |
US4721909A (en) * | 1985-08-16 | 1988-01-26 | Schlumberger Technology Corporation | Apparatus for pulsing electron beams |
EP0949653A2 (en) * | 1991-11-27 | 1999-10-13 | Hitachi, Ltd. | Electron beam apparatus |
EP0949653B1 (en) * | 1991-11-27 | 2010-02-17 | Hitachi, Ltd. | Electron beam apparatus |
EP1049132A1 (en) * | 1999-03-31 | 2000-11-02 | Advantest Corporation | Method and apparatus for imaging a surface potential |
US6359451B1 (en) | 2000-02-11 | 2002-03-19 | Image Graphics Incorporated | System for contactless testing of printed circuit boards |
US6621274B2 (en) | 2000-02-14 | 2003-09-16 | Image Graphics Incorporated | System for contactless testing of printed circuit boards |
US20180082829A1 (en) * | 2016-01-21 | 2018-03-22 | Japan Synchrotron Radiation Research Institute | Retarding potential type energy analyzer |
US10319578B2 (en) * | 2016-01-21 | 2019-06-11 | Japan Synchrotron Radiation Research Institute | Retarding potential type energy analyzer |
Also Published As
Publication number | Publication date |
---|---|
FR2027656A1 (en) | 1970-10-02 |
DE2000217A1 (en) | 1970-07-09 |
DE2000217B2 (en) | 1972-01-13 |
GB1246744A (en) | 1971-09-15 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US3646344A (en) | Scanning electron beam apparatus for viewing potential distribution on specimen surfaces | |
US3678384A (en) | Electron beam apparatus | |
US4751393A (en) | Dose measurement and uniformity monitoring system for ion implantation | |
US3626184A (en) | Detector system for a scanning electron microscope | |
US6667476B2 (en) | Scanning electron microscope | |
US3103584A (en) | Electron microanalyzer system | |
JP3836519B2 (en) | Electron detector | |
US4292519A (en) | Device for contact-free potential measurements | |
US3569757A (en) | Acceleration system for implanting ions in specimen | |
EP0328869B1 (en) | Electron beam testing of electronic components | |
US4587425A (en) | Electron beam apparatus and electron collectors therefor | |
US5408098A (en) | Method and apparatus for detecting low loss electrons in a scanning electron microscope | |
JP6124679B2 (en) | Scanning charged particle microscope and image acquisition method | |
JPH0736321B2 (en) | Spectrometer-objective lens system for quantitative potential measurement | |
US4958079A (en) | Detector for scanning electron microscopy apparatus | |
US4032787A (en) | Method and apparatus producing plural images of different contrast range by x-ray scanning | |
US2288402A (en) | Television transmitting tube | |
US4831267A (en) | Detector for charged particles | |
US6291823B1 (en) | Ion-induced electron emission microscopy | |
US3694652A (en) | Electron probe apparatus using an electrostatic field to cause secondary electrons to diverge | |
GB2081501A (en) | Device for detecting secondary electrons in a scanning electron microscope | |
US3792263A (en) | Scanning electron microscope with means to remove low energy electrons from the primary electron beam | |
US20200273665A1 (en) | Scanning electron microscope | |
US3337729A (en) | Method and apparatus for investigating variations in surface work function by electron beam scanning | |
Seah et al. | Energy and spatial dependence of the electron detection efficiencies of single channel electron multipliers used in electron spectroscopy |