DE1204350B - electron microscope - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α. ·.

Hölj

German class: 21g-37/01

Number: 1204 350

File number: N19846 VIII c / 21 g

Filing date: April 5, 1961

Opening day: November 4, 1965

The invention relates to an electron microscope in which, in addition to the imaging electron beam an additional beam generating system is provided, the beams of which the focusing device of the microscope against the direction of the imaging electron beam.

It is already known to have several electron guns in an electron beam microscope to be provided. For example, U.S. Patent 2928943 shows three in FIG. 7, each at 90 ° electron gun systems offset from one another. At the intersection of the electron beams generated the preparation is intended. Each electron beam has its own focusing device. These different electron beams all work simultaneously on the sample and serve primarily Line to illuminate the sample from different angles.

The German patent specification 692 336 shows an electron microscope in which the reflected from the sample Electron beam penetrates the same lens. The electron source is to the side of the microscope axis arranged. The electron beam is deflected into the microscope axis by a deflection system, the beam of reflected electrons is going through this refractor block in the opposite direction diverted. In this electron microscope, therefore, only one electron source is provided.

In the German patent specification 761 663, too, only one electron beam generation system is provided. After this electron beam has passed through the object, it passes through a central one Opening in a fluorescent screen and then hits an electron-optical mirror, the throws the beam back along its axis onto the fluorescent screen.

The Swiss patent specification 233 972 also made it known for an electron microscope with only one electron source by switching on different apertures in the beam path to generate either a strongly bundled beam or a weakly bundled beam.

The German patent specification 748 680 finally shows an electron microscope, in addition to the imaging Electron beam an additional beam generating system is provided, the beams of which Focusing device of the microscope runs through against the direction of the imaging electron beam. However, this additional beam generating system generates an ion beam, but not one second electron beam. In this arrangement, the ion beam is used to target certain substances electron microscope

Applicant:

Hilger & Watts Limited, London

Representative:

Dipl.-Phys. R. Kohler, patent attorney,

Stuttgart, Hohentwielstr. 28

Named as inventor:

William Charles Nixon, Fen Couseway,

Cambridge (Great Britain)

Claimed priority:

Great Britain 7 April 1960 (12 361)

to carry out destructive interventions or other changes in the preparation. This ion beam replaces a thin wire probe or glass probe commonly used for such procedures will. Electron beams are deflected much more strongly by magnetic lenses than ion beams, Strong electrostatic fields are required to influence the ions to some extent. It is therefore extremely difficult to accurately determine an ion beam and an electron beam focus when the two beams pass through the same optical system. This well-known Electron microscope is therefore extremely difficult to adjust and can therefore only be completely specially trained staff are served. This microscope can also do those tasks cannot be resolved in which it does not involve the destruction of a specific point of the object

+0 arrived, but on a non-destructive examination of a certain point.

The object on which the invention is based is therefore to develop an electron microscope, which can be operated easily and in which a point of one is imaged by an electron beam Object section can be examined more closely non-destructively.

This object is achieved according to the invention in that the additional beam generating system is also an electron gun, the electrons of which are on the object at one point are focused, which is a section of the through the

509 720/349

3 4

imaging electron beam is the image shown. Fig. 1 shows the outline of an electron micro-

The particular advantage is that the first telescope. This microscope contains an evacuable one

tronenstrahl, in the following "imaging beam" outer housing 15, at the upper end of an in

called, can serve to determine the point of the ob- its totality with 16 designated electrons-

to select the project and to set it precisely, the 5 source is arranged, which has a filament 17

by means of another electron beam which has a small opening 19 in its

is to be siert, be it that this point axis having cylinder 18 is surrounded. In

is to be enlarged much more or a cylinder 20 is arranged in the axial direction for this purpose,

by that one of the usual electron micro- has a small opening 21 through which the

Scopic examination methods for this an electron beam generated by the filament 17

Place should be applied. Another benefit passes through and along the axis of the housing 15

lies in the fact that it advances through the second electron.

source-generated electron beam, which in the following are called several focusing EIe "analysis beam", in many cases elements are arranged, which in the example shown are already optimally placed on the object is when the imaging beam is surrounded by the shields 28, which are optimally adjusted on the inner same optical system, or have circumferential gaps that serve as pole shoes for generating a strong magnetic field. Since both the imaging beam and the analysis beam can be electron beams as a condenser lens, 20 are sought and this is followed by a diaphragm through the optical system in the same way plate 23, which serves as a condenser diaphragm and influences one . This makes it very easy to adjust the micro-intensive electron beam to a specimen fall scope. Because of the small opening, which is arranged on a carrier 24, which is supported by the angle of the suitable object micrometer device used in electron microscopes, and because the focusing effect is unsuccessful. This is shown schematically as a slide 25 depending on the direction of the electron beam and allows the sample to be in the axis of the anist, the analysis beam has a relatively order without significant vacuum loss within a large depth of focus in the object plane, so that the housing 15 can be introduced. The device 25 second electron source is not exactly in the image is movable in a known manner in two directions, plane of the imaging beam must be arranged, 30 so that any section of the sample can be selected for the test, for example through a fluorescent screen. To the sample can be formed without. To be able to use this electron source of the vacuum loss, an analysis beam can be provided at a small distance from a suitable lock; Of course, both sides of this imaging plane of the loan have the arrangement in the usual image beam, the fluorescence mode can have a vacuum pump that maintains a small recess in the center of the necessary screen so that it maintains a vacuum within the arrangement the analysis beam from behind.
jective lens and projector lens of the imaging beam 40 The device also contains further focussing and also serves to focus the oppositely directed elements, namely an objective lens 26 and a running analysis beam on a point of the projector lens 27, which again consists of electromagnets in the objective plane. consist of suitable shields 29 and

With the aid of the analysis beam, it is possible to surround and in a known manner be so limited Carry out examination procedures that are 45 measure that they are on a fluorescent screen a local examination or analysis of a specific 31 an enlarged image of the illuminated area Allow location from a portion of the sample that will assist with the sample placed on slide 24 of the imaging beam enlarged on a witness. This screen can be seen through a window Screen or on a photographic 32 in a suitable housing at the lower end would appear. These devices can be viewed at 50 of the outer housing 15. Of the Include pointing devices pointing to the reac screen 31 has a central recess 33 and tion addressed by the analysis beam on can be shown in the dashed lines at 34 Object is triggered. drawn rest position from the beam path

F i g. 1 shows the outlines which must be swiveled out for understanding when photographic elaborate Parts of an electron microscope in 55 were supposed to be made. To this end Cut; can, as shown schematically, a photo

Fig. 2 shows a circuit diagram of the electron graphically sensitive element 35 on a ge

microscope; suitable carriages or other similar carriers 36

Fig. 3 shows another embodiment of the arrangement, which can be loaded from outside the device.

Order of the second electron source for processing 60 is operable.

Twist in microscopes that have a different supply. With the exception of opening 33, the

photographic plate chamber; the written arrangement is already known. The con-

FIGS. 4 to 9 show schematically the various densor lenses 22 used to illuminate the sample

Method for testing transilluminated samples on the carrier 24, whereas the lenses 26 and 27

with the help of the analysis beam, and the 65 can be viewed as image lenses that are a

FIGS. 10 to 13 schematically explain methods, greatly enlarged images of the illuminated area with which the specimen is checked with the help of reflection, the specimen with HiKe of the image electron beam, witness. The reproduction of this image is the sample

visible on the fluorescent screen 31 or, if necessary, can be photographed through the device 35, 36 will.

In accordance with the present invention, a second electron source 38 is on the opposite side of the fluorescent screen 31 is provided. This electron source is in the same way as the electron source 16 arranged and works the same. The electron source 38 generates an electron beam

beam generated, so that both electron sources receive a high negative voltage. Apart from that the microscope is constructed in a known manner by setting up a second electron source.

Fig. 3 illustrates a modification in the arrangement the second electron source 38, which is suitable when e.g. B. several photographic Plates 35 are stacked on top of one another in a holding device 36 in the vicinity of the image field. In

(the analysis beam) that is in the image beam from io in this case, the second electron source 38 the source 16 can be arranged laterally in the opposite direction, so that its axis is as stepped. The analysis beam is characterized by the effect, runs obliquely to the main axis, and a of the lenses 26 and 27 are bundled and directed so that deflection means 39 are provided. A fluoreser A certain small section of the reference screen 31 is in the same position as in FIG. 1 rich of the sample 15 arranged on the carrier 24 is arranged and the deflection device 39 is pivotable, which is checked and arranged on the screen 31 so that it can be seen above the screen, so that it is cash. with normal microscopic observation of the

Of course, the holder of the object sample can be removed from the path of the image beam can be swiveled in two at right angles by means of fine drives. The fluorescent screen 31 mutually extending directions can be set, ao can by an externally actuated lever or so that certain areas of the sample are shielded on the image using an electromagnet 31 appear enlarged when it pans in to be turned on for analysis the position shown in the drawings. and is switched off for normal viewing.

By further adjusting the sample, any- If the analysis beam is used

a special section of this area via which the deflection device 39 is brought into the working opening 33 of the fluorescent screen shown, pivoted position so that the analysis beam in so that then this particular section of the sample is reversed along the axis of the microim The area of the finely focused analysis beam is, the scope runs. In this case the fluoresder zenzschirm generated by the second electron source 38 can be appropriately marked or to be will. The reaction of the sample to these electrons - the setting of the desired section to shine can then be facilitated by any suitable display, which is shown by the analysis beam from the or measuring device are displayed. Beam generating system 38 is to be tested.

Below are various methods of examining a section of the sample using

Microanalysis described. It is first pointed out, however, with the aid of the analysis beam emitted by a second electron source 38, that the preparation of the analysis beam emitted can be carried out, depending on the sample, for the examination of a sample in the known manner with the aid of a transmission method or a RE while the screen 31 is being observed . The various corrections, the centering used depending on the particular analytical method and the like of the lenses will be able to be performed during the viewing of the for the implementation of the sub-image on the screen, so that the 40 search is preferred or is suitable.
The best possible reproduction of the sample is guaranteed. The F i g. 4 and 5 show devices for

is. When the optimal conditions are found, the characteristic X-rays are receptive so are thus in many cases the optimal ones, which are determined by the various elements in the Conditions for the analysis beam to be emitted from the second section of the sample to be tested, Electron source 38 found. The maximum intensity when the section is bombarded with electrons sity of the analysis beam can be determined by observation. The emitted x-rays are in the a display device 40 can be set, which is determined in a known manner and give exactly the type is located near the sample. The image beam and amount of each element present. In from the electron source 16 is switched off for so long. all F i g. 4 to 9, the objective lens 26 is schematic Sometimes it is possible to check whether the 50 is shown and the trajectory of the image beam is through Area analyzed by the analysis beam indicated with arrows /, whereas the path of the analysis

the area to be tested coincides that the increase in contamination of the sample on the The point at which the electron beam strikes the sample is observed.

In some cases, both electron beams, namely that from the electron source 16 and the from the second electron source 38, work simultaneously. But if there is an interaction between

Ray is shown by arrows y4. In no case do the two beams have to be used at the same time, the image beam is mainly used to select a certain part of the sample for testing a small section of it with the aid of the analysis beam A.

Fig. 4 shows that the X-rays emanating from the sample 24 through a curved crystal

the rays enters or if the main ray from 60 reflector 41 onto a display tube 42 (counter) reflekder Electron source 16 benefits a background radiation, which in a known manner with an amplifier and a counting or display device is connected. Fig. 4 explains a spectrographic

cal X-ray dispersion analysis, the specific

generated on the rest of the sample, the analysis beam can be used alone or the two electron beams in quick succession

applied intermittently one after the other. 65 specific methods are known.
Fig. 2 shows the connection of a high voltage Fig. 5 explains another display device,

in which the display or counting device 42 acts on the sample under the action of the analysis beam

source P with the electron source 16 and also with the second electron source 38, which the analysis

immediately responds to emitted X-rays, giving an X-ray spectrographic analysis with no dispersion. In these arrangements, the display device responds to the X-ray emission of the sample and not to the electron beams / or A.

Figs. 6 and 7 illustrate methods using visible, ultraviolet or infrared radiation emitted from some samples when they are subjected to the action of the analysis beam A. Figs. In Fig. 6, a prism or other corresponding diffraction device 44 is arranged in the path of the emitted radiation and a device 45 which transmits the radiation leads to a photoelectron multiplier so that the wavelength and the size of the radiation emitted by the sample 24 can be determined. Similar results can be achieved by the arrangement shown in FIG. 7, in which a number of light filters, one of which is designated at 46, are provided. The radiation is passed through the device 45 to the photomultiplier.

8 explains the examination of a crystalline sample by diffraction of the electrons of the analyzer Beam, whereby a diffraction image is obtained, which on a suitably arranged photographic Plate 47 can be held. This image can be used to determine the amount, type and genus of the Material are evaluated, which is arranged in the small selected section of the sample that has been exposed to the analysis beam.

The energy loss of the electrons in the sample can also be used for a determination. For this purpose, the in FIG. 9, wherein 48 is a magnetic device which generates an energy loss spectrum (shown at S) which is characteristic of the small, selected section of the sample which is under the action of the analysis beam. Other analytical methods, for example investigation methods based on secondary electron emission or the emission of field electrons, can also be used.

The F i g. 10 to 13 explain methods of electron microscopy in which a thin sample is not irradiated. F i g. 10 illustrates a reflection microscopy method in which the surface of a solid sample is disposed obliquely to the axis and it receives the image beam transverse to the axis. The analysis beam A hits a certain section of the sample surface and is made visible on a fluorescent screen.

11 explains the use of mirror field methods, a deflection device 50 deflecting the image beam onto the surface of the sample 49 and then rotating it into the longitudinal axis of the microscope. In this case, the analysis beam A is not shown because it cannot be used at the same time as the image beam. This is because the deflection device must be reversed if the analysis of a certain area is to be carried out by the analysis beam.

In some cases, the surface of a sample can be examined by the emission of thermal electrons from the surface when it is heated (Fig. 12). Such an emission forms the image beam / and sections of the sample surface can be examined with the analysis beam A. In other cases, the emission of electrons from the surface of the sample can be stimulated by other methods. 13 shows an emission excited by ions, an ion beam B being directed against the sample 49, the surface of which emits electrons which generate the image beam. Part of the image can be examined more closely by the analysis beam A. In the arrangement according to FIG. 12, the thermal electron-emitting surface can be arranged perpendicular to the microscope axis ″, whereas in the arrangements according to FIGS. 10, 11 and 13 the surface is arranged obliquely to the axis 13 through 13 can be determined or estimated by one or more of the methods described with reference to FIGS. 4-9.

Claims (13)

Patent claims: 1. Electron microscope, in which, in addition to the imaging electron beam, there is an additional Beam generating system is provided, the beams of which the focusing device of the microscope runs counter to the direction of the imaging electron beam, characterized in that that the additional beam generating system is also an electron gun is whose electrons are focused on the object in a point that is a section of the electron beam imaging shown image is. 2. Electron microscope according to claim 1, characterized in that the second electron source (38) is arranged in the axis of the microscope (Fig. 1). 3. Electron microscope according to claim 1, characterized in that the second electron source (38) is arranged to the side of the microscope axis and that the electron beam generated is steered into the microscope axis by means of a deflection device (39) (FIG. 3). 4. Electron microscope according to claim 1, 2 or 3, wherein a fluorescent screen for viewing of the enlarged image of part of the sample is provided, characterized in that the screen (31) at least when not in use outside the beam path of the second, for Analysis of the section from the illustrated sample section serving electron beam arranged is. 5. Electron microscope according to claim 4, characterized in that the fluorescent screen has a central recess (33) through which the second electron beam passes. 6. Electron microscope according to claim 3 and 4, characterized in that the fluorescent screen is marked at a point corresponding to the microscope axis. 7. Electron microscope according to one of claims 4 to 6, characterized in that the Fluorescent screen (31) can be moved out of the path of the second beam. 8. Electron microscope according to one or more of claims 1 to 7, characterized in that that devices for display or registration of by the second electron beam caused electron beams, ion beams or secondary emitted electrons are provided. 9. Electron microscope according to one of the preceding claims 1 to 8, characterized in that that the imaging beam is formed by thermal electron emission from the sample. 10. Electron microscope according to one or more of claims 1 to 7, characterized in that that devices for the spectrographic display and / or registration of by X-rays with or without dispersion analysis emitted the second electron beam from the sample are provided. 11. Electron microscope according to one or more of claims 1 to 7, characterized in that that a diffraction device and a photoelectron multiplier or a light filter are provided in connection with a photoelectron multiplier if a light IO emission in the visible, ultraviolet or infrared region of the spectrum under action of the second electron beam is caused. 12. Electron microscope according to one or more of claims 1 to 7, characterized in that that when using a crystalline sample a device for the determination and / or recording of the Debye-Sherrer diagram is provided. 13. Electron microscope according to one or more of claims 1 to 7, characterized in that that a device for displaying and / or recording the energy loss spectrum which has electrons that are characteristic of the sample material. Considered publications:
German patent specifications No. 692336, 748 680,
761663, 893 104;
U.S. Patent No. 2928,943. 1 sheet of drawings 509 720/349 10.65 © Bundesdruckerei Berlin