US3760180A

US3760180A - Electron-beam micro-analyzer with an auger electron detector

Info

Publication number: US3760180A
Application number: US00297017A
Authority: US
Inventors: U Weber
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1971-10-14
Filing date: 1972-10-12
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18
Also published as: CH547530A; DE2151167A1; FR2157476A5; DE2151167C3; DE2151167B2; GB1389119A

Abstract

An electron-beam micro-analyzer for investigating solid test specimens and radiation penetrable test specimens is disclosed. The micro-analyzer has an electron-beam generator for directing a focussed electron beam unto the test specimen to release Auger electrons therefrom. An electron spectrometer then separates the released Auger electrons according to the respective kinetic energies thereof and an electron detector detects the Auger electrons of specified energy separated in the spectrometer. The electron-beam generator has a field-emission point cathode having a small radius of curvature and an anode having an opening for passing the electron beam therethrough. A voltage supply applys a voltage to develop an electric field between the anode and the point cathode of sufficient strength to excite the cathode to electron field emission. A deceleration lens disposed intermediate the anode and the test specimen reduces the velocity of the electrons of the electron beam passing from the opening of the anode.

Description

United States Patent 11 1 Weber ELECTRON-BEAM MICRO-ANALYZER WITH AN AUGER ELECTRON DETECTOR [75] Inventor: Ulrich Weber, Karlsruhe, Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany 221 Filed: on. 12, 1972 211 App]. 190.: 297,017

[30] Foreign Application Priority Data 1451 Sept. 18, 1973 Primary Examiner-William F. Lindquist Attorney-Hugh A. Chapin et al.

[57] ABSTRACT An electron-beam micro-analyzer for investigating solid test specimens and radiation penetrable test specimens is disclosed. The micro-analyzer has an electronbeam generator for directing a focussed electron beam unto the test specimen to release Auger electrons therefrom. An electron spectrometer then separates the released Auger electrons according to the respective kinetic energies thereof and an electron detector Oct. 14,1971 Germany P 21 51 167.1

detects the Auger electrons of specified energy sepa- [52] (125M495 PE 250/495 A 250/495 AE rated in the spectrometer. The electron-beam genera- 51 1m. (:1. 60111 23/20 G01t-l/36 has a field'emissim having a 58 Field of Search 250/495 11 49.5 PE radius Curvature n having Pening for 256/495 passing the electron beam therethrough. A voltage sup ply applys a voltage to develop an electric field be- [56] References Cited tween the anode and the point cathode of sufficient UNITED STATES PATENTS strength to excite the cathode to electron field emission. A deceleration lens disposed intermediate the 3,191,028 6/1965 Crewe 250/495 anode and the test Specimen reduces the velocity of the 2,213? a" electrons of the electron beam passing from the open- 3:678:333 7 1972 Coates et al. 250 495 x mg the anode 15 Claims, 7 Drawing Figures 5 .v L -==:,.5 a

Q s e s 9 I s i Fig.1

PATENTEU SEP 1 8 I973 ELECTRON-BEAM MICRO-ANALYZER WITH AN AUGER ELECTRON DETECTOR BACKGROUND OF THE INVENTION The invention relates to an electron-beam microanalyzer for investigating a solid or radiationpenetrable test specimen. The micro-analyzer has an electron-beam generator whose focussed electron beam is directed onto the test specimen and has an electron spectrometer in which Auger electrons released at the test specimen by the electron beam are separated as to their kinetic energy. The microanalyzer further has an electron detector for the detection of the Auger electrons of defined energy which are separated in the electron spectrometer.

An electron-beam micro-analyzer with a gridelectron spectrometer is known, for example, from FIG. 1 of the article Auger Electron Spectroscopy of fcc Metal Surfaces in Journal of Applied Physics, Vol. 39, Apr. 1968, pages 2425 to 2432. Another electronincreasing the current of the primary electron beam.

beam micro-analyzer with a 127 cylinder spectrometer is disclosed in US. Pat. No. 3,461,306. Here an improvement of the ratio of the Auger-electron line intensity to the background intensity is obtained by electronic differentiation of the recorded electron energy spectrum; this ratio is of importance for the sensitivity of the analysis.

Electron-beam micro-analyzers equipped for detec tion of Auger electrons will be referred to as auger analyzers in the following. In auger analyzers it has heretofore been customary to use electron-beam generators based on the principle of thermionic emission which have already been used in the field of electron-beam micro-analysis (ESMA) with X-ray spectrometers. In this connection, for example, tungsten wires, are heated up to a condition of thermal electron emission. In principle, this enables large currents in the primary electron beam to be obtained. In the known Auger analysers, currents of 10' to 10" A are produced with these thermionic electron-beam generators, so that the Auger-electron lines show sufficient contrast against the background in the recorded electron energy spectrum. These currents correspond to a diameter of the electron beam striking the test specimen of 50 to 1,000

beam generator of up to about 3 keV.

The electron-beam micro-analyzers with Augerelectron analysis, which have become known up to now, do not reach the signal intensity of the usual electron-beam micro-probes with X-ray spectrometers, this being the case even for the investigation of light chemical elements. The signal of the probe, that is, the number of Auger electrons leaving the surface of the test specimen, is smaller by a factor of about 1,000 than the number and the signal of the X-ray quanta leaving the surface of the specimen for the same diameter of the primary electron beam. This factor 1,000 is determined by the proportion of the emission depth of the X-ray quanta, which is some few u, to the emission depth of the Auger electrons, which is in the range of about 1 m t. Even in the case of the light chemical elements, which exhibit a lower X-ray fluorescence yield than heavy elements, still more X-ray quanta will leave the surface of the test specimen for this reason than Auger electrons. p

In principle it would be possible to increase the number of Auger electrons released at the test specimen by pt at an energy of the electrons emitted by the electron i With the electron-beam generators which are based on the principle of thermionic emission, however, this would automatically be accompanied by an increase of the diameter of the primary electron beam and therefore by poorer spot resolution.

However, the spot resolution achieved so far in Auger analyzers which is of the order of the diameter of the primary electron beam of 50 to 1,000 ,u,is already considerably poorer than the spot resolution in ESMA probes with X-ray quantum detection. There, the resolution is generally confined to a test specimen area of several um diameter, which is determined by the emission depth of the excited X-ray radiation and the diffusion of the exciting primary electrons in the test specimen. If the diameter of the primary electron beam is reduced to values below 1 IL, neither the emission depth nor the diameter of the diffusion circle of the primary electrons change. For Auger electrons, on the other hand, the size of the diffusion circle is about 10 to mg.

The invention is based on the recognition of the fact that in Auger analyzers, the resolution capability of electron-beam micro-analyzers with X-ray spectrometers is not only matched for solid or radiationpermeable test specimens, but can be improved substantially and the sensitivity of analysis (signal intensity) attained so far with regard to the light elements can be increased decisively if it is possible to find an electron-beam generator, in which the diameter of the primary electron beam can be further decreased below the values of the magnitudes of the emission depth of the X-ray radiation or the diffusion circle of the X-ray radiation, because the emission current density of the electron-beam generator per solid angle (directionality) and the Auger electron yield obtained therewith at the test specimen are considerably better than with known-electron-beam generators. The lowest possible spot resolution is desired particularly if the test specimen isto be scanned by the primary electron beam in raster fashion and the Auger electron measuring signal is to be used to produce an image of the distribution of chemical elements on the surface of the specimen.

If in the-known Auger analyzers merely the diameter of the primary electron beam would be reduced, one would admittedly obtain a finer, and therefore better spot resolution, but the measuring signal would be at the detection limit or below. The reason for this is that a reduction of the diameter d of the primary electron beam by a given factor, for example, by the factor 10 or 1,000, is accompanied, according to the equation I k U d 8/3 where k is a constant and U the accelerating voltage of the primary electrons, by a decrease of the current I by a considerably larger factor, in the present example by the factor 500 and 2.5 10 respectively. In order to reach in the known Auger analyzers the resolution capability of the ESMA probes or to improve it by a factor of 10, the diameter of the primary electron beam must be reduced by at least a factor of 10 or 100 to values between 0.5 and 10 1.1.. Reducing the diameter, however, is not sufiicient; at the same time, measures must be taken to cancel the loss in intensity of the measuring signal which occurs therewith.

SUMMARY OF THE INVENTION It is an object of the invention to provide an electronbeam micro-analyzer with an Auger electron detector of the kind mentioned above that is equipped with a beam generator of high directivity for low-energy electrons for obtaining the highest possible yield of Auger electrons at the test specimens.

The electron-beam micro-analyzer of the invention for investigating solid test specimens and radiation penetrable test specimens has as a feature an electronbeam generator that directs a focussed electron beam unto the test specimen to release Auger electrons therefrom. An electron spectrometer is provided for separating the released Auger electrons according to the respective kinetic energies thereof and an electron detector detects the Auger electrons of specified energy separated in the spectrometer. The electron-beam generator defines a space for containing an ultrahigh vacuum and includes a field-emission point cathode disposed in said space, the point cathode having a small radius of curvature. An anode has an opening for passing the electron-beam therethrough and a voltage supply applys a voltage to develop an electric field between the anode and the point cathode in the vacuum of sufficient strength to excite the cathode to electron field emission to produce the electron-beam. An electrostatic device in the form of a deceleration lens disposed intermediate the anode and the test specimen reduces the velocity of the electrons of the electron-beam passing from the opening of the anode.

With such an Auger analyzer, it is possible to obtain a spot resolution which is at the theoretical limit and which is given by the size of the diffusion circle of the Auger electrons of about to 100 m ,u.

As investigations described by A.V.Crewe, J.Wall and L.M.Walter in the Journal of Applied Physics (1968), Vol. 39, pages 5861 to 5868 have shown, directivity values can be achieved with field-emission cathode systems which are superior to thermal electron-beam generators with tungsten hairpin cathodes for the same accelerating voltage of 20 kV by a factor of approximately 10 Whereas in the conventional electron-beam generators the electrons are emitted from a relatively large area (crossover diameters of 30 to 100 p. at about 30 kV to 3 kV), the electrons in a point cathode with a point having, for example, a radius of curvature of 50 m y. are apparently field-emitted from the center of a sphere whose diameter is only about 3 m [L because of the electric field which emanates radially from the tip. Depending on the choice of the radius of curvature of the point cathode, its distance from the anode and the diameter of the aperture of the anode, the high voltage required for field emission is between about 3 and 10 kV. Currents of 10' A can be obtained in the primary electron-beam with field-emission point cathodes. The use of a fieldemission point cathode generally necessitates an ultrahigh vacuum with a pressure of 10" to at mostlO' Torr.

As other investigations have shown, optimum Augerelectron yield is not obtained if the electrons of the primary electron beam impinging on the test specimen have the highest possible energy, and therefore also not at the high, optimal accelerating voltages of electronbeam micro-analysis (ESMA) in the energy range between 10 and 50 keV. The primary-beam energy required for optimal excitation of the Auger electrons is much lower and is given by three times the energy which is required to ionize an atom of an element for releasing an Auger electron in an atom shell; it is therefore between 0.5 and 3 keV. This optimum excitation energy is achieved by focussing the primary electron beam onto the test specimen by means of an electrostatic deceleration lens. The deceleration lens reduces the energy of the electrons in the primary electron beam which, due to the high accelerating voltage required for field emission at the electron-beam. generator,.is too high for optimal excitation. The energy of these electrons is reduced by the deceleration lens to values in the range of a few keV in the space in front of the test specimen. The high directivity of an electron-beam generator with a field-emission point cathode can thereby be utilized for an electron-beam micro-analyzer with Auger-electron detection.

According to a further embodiment of the invention, a field-free space is provided between the anode and the deceleration lens. This affords the advantage that the field emission current can be adjusted. independently of the operating condition of the deceleratin lens.

In still another embodiment of the invention, at least one first electrode having an aperture is arranged between the anode 'and the test specimen. The first electrode is combined with the anode to form a decelerating lens; this embodiment is distinguished by its simple configuration.

By means of a special configuration of the anode and the electrodes in the region of their respective apertures and/or their thickness, it is possible to achieve a minimal imaging error of the electrostatic'device. The configuration required therefor can be calculated theoretically. Applicable calculations for a two-electrode lens of the acceleration type have already been carried out. In this connection, reference may be had to J.W.Butler, Sixth International Congress for Electron Microscopy (Kyoto),l9l (1966).

Although the invention is illustrated and described herein as an electron-beam micro-analyzer with an Auger electron detector, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein within the scope and the range of the claims. The invention, however, together with additional objects and advantages will be best understood from the following description and in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the electron-beam micro-analyser of the invention together with potential diagrams are illustrated in the following FIGS. described below. Similar or like components are designated by the same reference numeral in each FIG. in which they appear.

FIG. 1 is a schematic diagram of an electron-beam micro-analyzer according to the invention wherein the electron beam generator is equipped with a fieldemission point cathode. An anode and a diaphragm conjointly define a decelerating lens.

FIG. 2 is a schematic diagram of an alternate embodiment of the micro-analyzer of the invention. This diagram depicts a field-emission point cathode, an anode and a test specimen as well as two electrodes arranged between the anode and the test specimen.

FIG. 3 shows the electric potential distribution between the field-emission point cathode and the test specimen for the micro-analyzer according to FIG. 2.

FIG. 4 is a schematic diagram of another embodiment of the micro-analyzer of the invention. There, three electrodes are arranged between the anode and the test specimen.

FIG. 5 shows the electric potential distribution be- DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 illustrates an electron beam micro-analyzer in which a primary electron beam 1 is generated by field emission at a field-emission point cathode 2. The point cathode 2 consists, for example, of tungsten and has, at its tip, a radius of curvature of only 50 mu. The point cathode 2 is welded to a wire loop 3 which can be connected via leads 4 and a switch 5 to a heater-current source 6. By turning on the heater-current source 6 contamination on the point cathode 2 can be heated out.

The point cathode 2 is situated in a space 7 kept at ultra-high vacuum. The space 7 is bounded by electric insulators 8 and 9 which can be of ceramic material for example and an anode 10 having an aperture 11. The diameter of the aperture 11 can be adjusted by means of a diaphragm, now shown, to 100 y. for example. The diaphragm determines the aperture error of the imaging system which is formed by the

electrodes

10 and 17. The electron beam focus attainable on the test specimen is determined, as far as its lower limit is concerned, by the aperture error.

The point cathode 2 is connected to a voltage supply means comprising the adjustable bias source 12. The

point cathode 2 is connected to the minus terminal of source 12. The positive terminal of the source 12 is grounded. The voltage of the bias source 12 can be adjusted, for example, (to a value of between 0.5 kV and 3kV). The point cathode 2 is therefore at a potential which is negative relative to ground.

The voltage supply means can also comprise an adjustable high-voltage source 13. The anode 10 is connected to the positive terminal of the adjustable highvoltage source 13. The negative terminal of source 13 is tied to ground. The high-voltage source 13 is adjustable, for example, to a value between 3 kV and IOkV; this enables a value to be obtained between 3.5 kV and 13 kV for the voltage between the anode 10 and the point cathode 2, this value of voltage is sufficient to obtain a field strength of at least 10 V/cm directly at the tip of the point cathode and to thereby produce coldfield emission at the point cathode 2.

The electron beam 1 leaving the point cathode 2 because of the field emission arrives in the further space 14 through the aperture 11 of the anode 10 with a kinetic energy between 3.5 keV and 13 keV. The space 14 is enclosed by a spacer 15 of insulating material and a diaphragm which serves as an electrode 17 having an aperture 16. The diaphragm 17 can be set to an electric potential which can be adjusted to any value, for example, between +200 and -200 V relative to ground by means of decelerating voltage supply means in the form of an adjustable decelerating-voltage source 18. The diaphragm 17 is therefore at least approximately at ground potential, that is, at an electric potential between that of the point cathode 2 and that of the anode 10. The electrons entering the space 14 through the aperture ll of the anode 10 are thereby greatly decelerated. The anode 10 and the diaphragm 17 are combined in this manner to form a decelerating lens. Whereas the electrons still have a. kinetic energy in the range between 3.5 keV and 13 keV when they pass through the aperture 11, their energy after passing the aperture 16 has only a value in the range between 0.5 and 3 keV, if the diaphragm is, for example, exactly at ground potential. This, however, is the energy range of the primary electron beam, at which an optimum Auger-electron yield can be obtained.

After passing through the aperture 16, the electron beam 1 arrives at a deflection system 36, which is shown in FIG. 1 as a magnetic deflection system and is controlled by a deflecting arrangement (not shown). An electrostatic deflecting system can, of course, also be used. The deflection system 36 deflects the decelerated electron beam 1 in raster fashion over a test specimen 19. This specimen 119 is attached on a movable specimen manipulator 20 and is connected essentially to ground potential. The test specimen 20 is therefore practically at the same potential as the diaphragm 17.

Through the incidence of the electron beam 1, Auger electrons 21 as well as back-scatter and secondary electrons. 22 are released at the surface of the test specimen 19, the normal of which, different from the position shown, is preferably inclined with respect to the primary electron beam 1. The kinetic energy of the Auger electrons 21, which are used for the analysis, is in the energy range below about 1,000 eV, and that of the other electrons isin the energy range of O to E,,, where E, is the energy of the primary electrons at the test specimen 19. The released electrons 21 and 22 get into an electron spectrometer, which in FIG. 1 is shown as a hemispherical spectrometer 23. Any type of electron spectrometer can be used inthe invention. The hemisphere spectrometer 23 comprises a first grid 24 which is at ground potential as is the test specimen 19. The spectrometer 23 also has a second grid 25 to which a negative potential, relative to ground, can be applied by means of an adjustable voltage source 26. This voltage source 26 is adjusted to a fixed voltage value in the range of 0 to 1 kV, so that Auger electrons and other electrons with an energy which is lower than the adjusted voltage value, cannot overcome the second grid 25. The voltage source 26 is adjusted for the Augerelectron line in the energy sepctrum of that chemical element, the distribution of which on the surface of the test specimen 19 is to be determined and recorded.

Electrons which overcome the second grid 25, arrive at a hemispherical detector surface: 27 which is kept at a positive potential relative to the second grid 25. For this purpose a voltage source 28 with a collecting voltage of, for example 0.2 kV is provided.

A modulation oscillator 29 generates an altematingcurrent voltage of, for example, 2 kHz which is superimposed by means of a transformer 30 on the potential of the test specimen with an amplitude of, for example, 1 to V. The load resistor 31 thereby receives a modulated signal, which is fed via a blocking capacitor 32 to a detection apparatus 33. The latter comprises a phase-sensitive rectifier whose reference input is fed with the alternating-current voltage of the modulation oscillator 29. The measuring signal determined by the detection apparatus 33 is fed to a picture tube 34; this measuring signal now originates essentially from Auger electrons and the voltage source 26 is adjusted to the energy of these electrons. Here the measuring signal is used for displaying the distribution on the surface of the test specimen of that chemical element, to the Aug er-electron energy of which the voltage source 26 is adjusted. The line scan of the picture tube 34 is synchronized with the motion of the electron beam 1 (not shown) via the leads 35 by the deflection arrangement which controls the deflection system 36.

FIG. 2 is a schematic diagram of an Auger analyzer in which, in contrast to the Auger analyzer according to FIG. 1, a second electrode 37 having an aperture 38 is additionally arranged between the first electrode 17 and the test specimen. As in the Auger analyzer according to FIG. 1, the first electrode 17 is combined with the anode 10 to form a deceleration lens. This hecomes clear from FIG. 3 where the electric potential P(d) of the Auger analyzer according to FIG. 2 is shown as a function of the distance d; for simplicity, straightline segments are shown. Negative potential values are plotted in the upward direction.

The point cathode 2 is again at a negative potential relative to the ground potential of the test specimen 19, for example, at -O.5 kV. A positive potential of, for example, +3 kV is applied to the anode 10. The first electrode 17 can now be at a negative potential of 0.4 kV for example. This potential can be adjusted toward larger values, which is indicated by the vertical arrow.

The second electrode 37 is preferably at ground potential. Its potential can, however, likewise be varied within narrow limits, which is indicated by the double arrow. As the potential of the second electrode 37 is higher than that of the first electrode 17, it acts as a post-acceleration electrode. The velocity of the electrons in the beam 1 emanating from the aperture 16 of the first electrode 17 is therefore again increased somewhat. The deciding factor for the optimum kinetic energy of the electrons in the electron beam 1 at the point of the test specimen 19 is only the potential difference between the point cathode 2 and the test specimen 19.

If the aperture 16 in the first electrode 17 is chosen large enough, the potential of the first electrode 17 can also be made smaller, that is, more negative than the potential of the point 2 cathode because of the field penetration which takes place in that case.

In FIG. 2, the anode 10 is combined with the first and the second electrodes, 17 and 37, to form an electrostatic lens. If the aperture 16 of the first electrode 17 is chosen smaller than the apertures 11 and 38 of the anode l0 and the second electrode 37, respectively, and if short mutual spacings are chosen, an asymmetrical three-electrode lens is obtained which is known per se and in which the field emission current can be adjusted via the potential of the anode 10, and the deceleration via the potential of the first electrode 17.

The advantage of the Auger analyzer shown in FIG.

2 with the potential pattern P(d) shown in FIG. 3 over 1 the Auger analyzer according to FIG. 1 is that the prop erties of the beam generating system can be varied to a larger extent; these properties include the field emission potential, energy of the primary beam and focal length.

In FIG. 4, an associated electrostatic lens is shown between the anode l0 and the test specimen 19; this lens consists of three

electrodes

17, 37 and 39 with approximately equally large

respective apertures

16, 39 and 40, which in turn are larger than the aperture 11 of the anode 10. This arrangement is provided for a large working distance between the third electrode 39 and the test specimen 19. As will be seen from the corresponding potential distribution P(d) in FIG. 5, the first electrode 17, which may have selectively a slightly positive or a slightly negative potential, as desired, but preferably ground potential, again acts as a decelerating electrode. The third electrode 39 has preferably the same potential as the first electrode 17, that is, ground potential. The potential of the second electrode 37, which is shown in FIG. 5 as negative, can be varied. Thereby, the focal length of the

electrostatic lens

17, 37, 39 can be adjusted. If the potential of the second electrode 37 is chosen more positive, a longer focal length results, but if it is chosen more negative the focal length is shortened.

The anode 10 and the first electrode 17 can image the point electrode 2 electron-optically in the aperture 38 of the second electrode 37. Additionally, the lens system consisting of the

electrodes

17, 37 and 39 can image the point cathode 2 on the test specimen 19 through focussing. Focussing on the test specimen 19 is thereby largely independent of the potential of the anode 10 adjusted to obtain field emission and the decelerating potential adjusted between the anode l0 and the first electrode 17. The arrangement then functions according to the principle of a light-optical elastic lens. The arrangement shown in FIG. 2 can also be configured in the manner of a light-optical elastic lens.

It is fundamental for the configuration of the electrostatic arrangement as an elastic lens that it consists of at least two, separately adjustable electrostatic lenses and that the electron beam 1 emanating from the point cathode 2 is focussed within the second lens in such a manner that the focal length of the overall electrostatic arrangement is virtually not influenced if the emission potential at the first lens is varied.

In FIG. 6, the electron-beam generator of an Auger analyzer isshown schematically which corresponds with respect to the electric circuit arrangement and also otherwise in large measure 'to the Auger analyzer shown in FIG. 1. At the anode 10, a cylindrical tube 41 is attached here in an electrically conducting manner. The tube 41 and a cylindrical tube 42 as the first electrode conjointly define a decelerating lens. The cylindrical tube 42 is aligned with the tube 41 and is arranged at a distance a as shown in FIG. 6. The corresponding potential plot in FIG. 7 shows that the electrons of the primary electron beam 1 are accelerated and are also decelerated again over a relatively short distance. By changing the potential of the anode 10, the focal length of the decelerating lens can be adjusted. Deviating from the arrangement of FIG. 6, the interior space 43 of the cylindrical tube 42 and the interior space 44 of the tube 41 can be made non-cylindrical, although rotation-symmetrical with respect to the electron beam l, to obtain minimum imaging errors.

What is claimed is:

1. An electron-beam micro-analyzer for investigating solid test specimens and radiation penetrable test specimens comprising an electron-beam generator for directing a focussed electron beam onto the test specimen to release Auger electrons therefrom; an electron spectrometer for separating the released Auger electrons according to the respective kinetic energies thereof; and an electron detector for detecting the Auger electrons of specified energy separated in said spectrometer, said electron-beam generator defining a space for containing an ultra-high vacuum and comprising a field-emission point cathode disposed in said space, said point cathode having a small radius of curvature, an anode having an opening for passing the electron beam therethrough, voltage supply means for applying a voltage to develop an electric field between said anode and said point cathode in the vacuum of sufficient strength to excite said cathode, to electron field emission to produce the electron beam, and a deceleration lens disposed intermediate said anode and the test specimen for reducing the velocity of the electrons of the electron beam passing from said opening of said anode.

2. The electron-beam micro-analyzer of claim 1, comprising means for providing a field-free space intermediate said anode and said decelerating lens.

3. The electron-beam micro-analyzer of claim 1 comprising a first electrode disposed between said anode and the test specimen and having an opening for passing the beam therethrough, said electrode and said anode conjointly constituting said deceleration lens.

4. The electron-beam micro-analyzer of claim 3 wherein the test specimen is at a given potential, and wherein the analyzer comprises decelerating voltage supply means connected to said electrode for adjusting the electric potential of said electrode to at least approximately the electrical potential of the test specimen.

5. The electron-beam micro-analyzer of claim 3 wherein said first electrode is configured as a single apertured diaphragm, said diaphragm being connected to ground potential.

6. The electron-beam micro-analyzer of claim 3 wherein said first electrode is configured as a single apertured diaphragm and said voltage supply means ap-' plies respective potentials to said anode and said point cathode to establish said electric field, the microanalyzer comprising deceleration voltage supply means connected to said diaphragm for applying thereto an electric potential between the potential on said anode and the potential on said point cathode.

7. The electron-beam micro-analyzer of claim 6 wherein the test specimen is at a given potential, said deceleration voltage supply means comprising adjusting means for adjusting the potential applied to said diaphragm to the potential of the test specimen.

8. The electron-beam micro-analyzer of claim 6, said deceleration voltage supply means comprising adjusting means for adjusting the potential applied to said diaphragm to ground potential.

9. The electron-beam micro-analyzer of claim 3 comprising decelerating voltage supply means connected to said first electrode for applying a potential thereto, and

a second electrode disposed between said first electrode and the test specimen and having an opening for passing the beam therethrough, and second electrode voltage supply means connected to said second electrode for applying a potential thereto selected to have a value compared to the value of the potential on said first electrode to cause the velocity of the electrons of the electron beam passing from said opening of said first electrode to increase.

10. The electron-beam micro-analyzer of claim 3 comprising a second electrode disposed adjacent said first electrode in beam direction, and a third electrode disposed adjacent said second electrode in beam direction, said second and third electrodes having respective openings for passing the electron beam therethrough, said first, second and-third electrodes constituting a three electrode electrostatic lens.

11. The electron-beam micro-analyzer of claim 3 comprising a cylindrical tube attached to said anode so as to be electrically conductive therewith and to be concentric with said opening thereof, said first electrode being a cylindrical tube spaced an distance a from and axially aligned with said tube attached to said anode, said cylinder tubes conjointly constituting said deceleration lens. a

12. The electron-beam micro-analyzer of claim 3, said anode and said electrode each being configured in the respective regions of said openings thereof respectively to obtain a minimal imaging error for said deceleration lens.

13. The electron-beam micro-analyzer of claim 1 comprising a plurality of electrodes disposed one adjacent the other intermediate said anode and the test specimen, each of said electrodes having an opening for passing the beam therethrough, said plurality of electrodes and said anode conjointly constituting said deceleration lens.

14. The electron-beam micro-analyzer of claim 13 wherein the test specimen is at a given potential, and wherein the analyzer comprises decelerating voltage supply means connected to the one electrode of said plurality of electrodes disposed adjacent the test specimen for adjusting the electric potential of said one electrode to at least approximately the electrical potential of the test specimen.

15. The electron-beam micro-analyzer of claim 1 comprising an electrostatic arrangement having a focal length and including at least two electrostatic lenses, one of said lenses being said deceleration lens and the other one of said lenses being an associated electrostatic lens disposed between said deceleration lens and the test specimen, associated electrostatic supply means connected to said associated electrostatic lens to focus the same independently of said deceleration lens,

and deceleration voltage supply means connected to.

said deceleration lens for adjusting the potential thereon independently of said associated electrostatic lens for in turn focussing the electron beam emanating from said point cathode in said associated electrostatic lens so that any change in said potential on said deceleration lens will cause no appreciable change in the focal length of said electrostatic arrangement.

Claims

1. An electron-beam micro-analyzer for investigating solid test specimens and radiation penetrable test specimens comprising an electron-beam generator for directing a focussed electron beam onto the test specimen to release Auger electrons therefrom; an electron spectrometer for separating the released Auger electrons according to the respective kinetic energies thereof; and an electron detector for detecting the Auger electrons of specified energy separated in said spectrometer, said electron-beam generator defining a space for containing an ultra-high vacuum and comprising a field-emission point cathode disposed in said space, said point cathode having a small radius of curvature, an anode having an opening for passing the electron beam therethrough, voltage supply means for applying a voltage to develop an electric field between said anode and said point cathode in the vacuum of sufficient strength to excite said cathode to electron field emission to produce the electron beam, and a deceleration lens disposed intermediate said anode and the test specimen for reducing the velocity of the electrons of the electron beam passing from said opening of said anode.

6. The electron-beam micro-analyzer of claim 3 wherein said first electrode is configured as a single apertured diaphragm and said voltage supply means applies respective potentials to said anode and said point cathode to establish said electric field, the micro-analyzer comprising deceleration voltage supply means connected to said diaphragm for applying thereto an electric potential between the potential on said anode and the potential on said point cathode.

9. The electron-beam micro-analyzer of claim 3 comprising decelerating voltage supply means connected to said first electrode for applying a potential thereto, and a second electrode disposed between said first electrode and the test specimen and having an opening for passing the beam therethrough, and second electrode voltage supply means connected to said second electrode for applying a potential thereto selected to have a value compared to the value of the potential on said first electrode to cause the velocity of the electrons of the electron beam passing from said opening of said first electrode to increase.

10. The electron-beam micro-analyzer of claim 3 comprising a second electrode disposed adjacent said first electrode in beam direction, and a third electrode disposed adjacent said second electrode in beam direction, said second and third electrodes having respective openings for passing the electron beam therethrough, said first, second and third electrodes constituting a three electrode electrostatic lens.

11. The electron-beam micro-analyzer of claim 3 comprising a cylindrical tube attached to said anode so as to be electrically conductive therewith and to be concentric with said opening thereof, said first electrode being a cylindrical tube spaced an distance a from and axially aligned with said tube attached to said anode, said cylinder tubes conjointly constituting said deceleration lens.

15. The electron-beam micro-analyzer of claim 1 comprising an electrostatic arrangement having a focal length and including at least two electrostatic lenses, one of said lenses being said deceleration lens and the other one of said lenses being an associated electrostatic lens disposed between said deceleration lens and the test specimen, associated electrostatic supply means connected to said associated electrostatic lens to focus the same independently of said deceleration lens, and deceleration voltage supply means connected to said deceleration lens for adjusting the potential thereon independently of said associated electrostatic lens for in turn focusSing the electron beam emanating from said point cathode in said associated electrostatic lens so that any change in said potential on said deceleration lens will cause no appreciable change in the focal length of said electrostatic arrangement.