JPH10199458A - Energy filter and transmission type electron microscope having this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy filter whose vacuum inside exposed surface area is small and by which positioning accuracy of magnetic pole pieces is enhanced and whose cost can be reduced and by which the edge magnetic field distribution is reduced and whose manufacturing and assembling accuracy can be enhanced, and a transmission type electron microscope having this. SOLUTION: Magnetic pole pieces 2a, 3a (2b, 3b) to constitute magnetic poles are integrally molded in a projecting shape in yoke members 1a and 1b. An exciting coil arranged in the atmosphere and vacuum packing 8a, 8b, 9a and 9b, are arranged on the magnetic pole pieces. Grooves 81 and 82 to pass an electron beam are arranged in a yoke between the magnetic poles. Passing holes of the electron beam are arranged in intermediate rings 35 and 36 to press down the vacuum packing around the magnetic poles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy filter and a transmission electron microscope having the same, and more particularly, to dispersing electrons transmitted through a sample and selectively extracting electrons having a specific energy to form an image. More particularly, the present invention relates to an energy filter suitable for obtaining an element distribution image of a minute region and a transmission electron microscope including the energy filter.

[0002]

2. Description of the Related Art An energy filter is a device used for dispersing the energy of an electron beam transmitted through a sample and extracting only electrons in a specific energy region, and is used in combination with a transmission electron microscope. Electrons that have passed through the sample lose their intrinsic energy due to inelastic scattering due to inelastic scattering, so an electron microscope image obtained with only electrons that have undergone a specific energy loss shows a two-dimensional distribution according to the sample constituent elements. Will be. In addition, by restricting the energy that has greatly spread after transmission through the sample to a specific range for observation, an image with less chromatic aberration and good contrast can be obtained.

[0003] Such an energy filter is composed of a plurality of magnetic poles formed by arranging magnetic pole pieces at regular intervals, and there is no magnetic field between adjacent magnetic poles.
It is a free space where electrons travel straight. Electrons that enter the energy filter along the optical axis of the electron microscope exit the filter and then return to the original optical axis of the electron microscope.
Behind the energy filter, an energy spectrum is obtained, where a specific energy is selected.

After the energy is selected, a two-dimensional distribution image of the elements is obtained using an imaging electron lens. An energy filter having such a shape is called an in-column type energy filter, for example, an Ω-type energy filter described in JP-A-62-66553 or an α-type energy filter described in JP-A-62-69456. A shape energy filter and the like are known.

In order to manufacture this type of energy filter, it is necessary to form and position the pole pieces facing each other with high precision. This is described in 294044.

FIG. 5 shows an energy filter according to a conventional embodiment and a transmission electron microscope having the same (first prior art). FIG. 5A is a cross-sectional view of the energy filter, and FIG. FIG. 2B is a cross-sectional view taken along the line AA ′ in FIG. 2A, and FIG. 2C is a cross-sectional view of a transmission electron microscope having the energy filters in FIGS. 1A and 1B.

This energy filter is constructed by sandwiching a pair of outer plates 21 and 22 and a pair of inner plates 23a and 23b in a sandwich shape, and has four magnetic poles 51, 52, 53 and 53 for deflecting an electron beam. 54 are pole pieces (51a, 51b), (52a, 52
b), (53a, 53b) and (54a, 54b). Magnetic pole piece
51a, 52a, 53a and 54a are all positioned on the outer plate 21 with the pin 26a as a guide, and are fixed by screws 25.
Similarly, the pole pieces 51b, 52b, 53b, and 54b are all positioned on the outer plate 22 with the pins 26b serving as guides, and fixed by screws 25. Each pole piece 51a, 52a, 53a, 54a and 51b, 52b, 5
Excitation coils 71a, 72b, 73b, 74a and 7
1b, 72b, 73b and 74b are attached.

In the Ω-type energy filter having such a configuration, the electron beam 100 incident from the electron beam incident hole 61 is
1 guides the optical axis 67 in the filter, and the magnetic poles 52, 53 and 5
After being deflected by 4, it is guided again on the optical axis 66 and is emitted from the electron beam emission hole 62.

The energy filter is fixed to the flange 29 so that the electron beam incident hole 61 coincides with the optical axis of the electron microscope as shown in FIG. 1C (the fixing jig is not shown).
Vacuum chambers 27 and 28 that double as electron microscope tubes
Is mounted inside. The vacuum chambers 27 and 28 are provided with energy filter position adjusting mechanisms 17 and 18, respectively, so that the optical axis of the electron microscope and the optical axis of the energy filter can be matched.

Regarding another configuration of the conventional energy filter (second prior art), see, for example, Japanese Patent Application Laid-Open No. 58-323.
No. 47 has been described, as shown in FIG. 6,
The entire electron beam path inside the energy filter is isolated by the analysis tube 24 made of a non-magnetic material, and a magnetic field is applied from outside the electron beam path by the fan-shaped magnetic poles 51, 52, and 53.

In the first prior art, the entire energy filter is housed in vacuum chambers 27 and 28 and evacuated. In this case, the outer plates 21, 22, the inner plates 23a, 23b, the magnetic field exciting coils 71, 72, 73, 74, the magnetic poles 51, 52, 5
The volume and surface area of the portion to be evacuated are extremely large because all of the components 3, 54, the screw 25, the fitting pin 26, and the like are in a vacuum.

On the other hand, the vacuum exhaust holes inside the energy filter are only the electron beam entrance / exit holes 61 and 62. For this reason, it takes a long time to evacuate until the desired degree of vacuum is reached, and the gas released from the entire energy filter lowers the degree of vacuum and contaminates the sample. In particular, when observing the surface structure of a sample or when observing a biological sample embedded in ice, the emitted gas adheres to the surface of the sample at a low temperature, which makes observation difficult. Further, in order to obtain a high vacuum, it is necessary to heat and degas the entire energy filter with a heater or the like. However, in such a structure, the heater itself must be housed in the vacuum, so that a large degassing is required. There is also a problem that the gas effect cannot be expected.

Further, in the first prior art, each of the magnetic pole pieces 51a, 52b, 53b and 54b is separate from the outer plates 21 and 22, and both are positioned using the fitting pins 26 and screwed. ing. Also, each plate 21 and 22 is an inner plate 23
They are mutually positioned by fitting pins (not shown) via a and 23b.

That is, since the relative positioning of the magnetic pole pieces (for example, the magnetic pole pieces 51a and 51b) constituting each magnetic pole is indirectly performed through each section, the parallelism of each magnetic pole is determined by the plates 21 and 22. , The flatness of the pole piece, the parallelism of the plate and the pole piece, and the parallelism of the plate 21 and the plate 22. Therefore, the positioning accuracy and the parallelism of the pole piece are reduced in consideration of the play of the fitting pin, the surface accuracy and the flatness of the plate and the pole piece. On the other hand, in order to ensure the necessary positioning accuracy and parallelism, extremely high processing accuracy and assembly accuracy are required, which is disadvantageous in terms of price.

On the other hand, in the above-mentioned second prior art, only the inside of the electron beam passage is independently evacuated, so that there is no problem with respect to the degree of vacuum as in the first prior art. However, the electron beam path of such a shape is manufactured by welding a tube of a non-magnetic material bent along the path of the electron beam,
Alternatively, it is necessary to weld a plate having a groove processed in accordance with the path of the electron beam. However, in such a processing method, since heat is applied, deformation such as partial distortion may occur, or some materials may be magnetized to change the trajectory of the electron beam.

Further, since the electron beam passage is formed by welding, vacuum leakage is liable to occur. Further, since the vacuum vessel of the electron beam passage is disposed in the gap between the pole pieces, the electron beam passage at the magnetic pole interval is provided. The part that can be used as a device is reduced by about half. On the other hand, when the inner diameter of the electron beam path is increased and the magnetic pole gap is widened to improve the transmittance of electrons, the coil current for obtaining a magnetic field of a required strength increases in proportion to the magnetic pole gap. There is a problem that drift occurs due to heat generation of the coil and the position of electrons changes.

A technique for solving these problems is disclosed in Japanese Patent Application Laid-Open No. 8-36.
No. 990. As shown in FIG. 7, a pair of yoke members 55a and 55b in which a plurality of integrally formed magnetic pole pieces 2 and 3 are overlapped so as to face each other while maintaining a fixed gap, and A pair of provided electron beam input / output holes 61a, 61b, an analysis container 30 made of a non-magnetic material mounted between the yoke members, and respective magnetic poles provided on respective opposing surfaces of the respective yoke members. A plurality of openings 4 and 5 through which pieces are inserted, a communication hole 81 that allows the openings 4 and 5 to communicate with each other, and a yoke member that is provided around each opening surface of each of the openings and faces each other. Hermetic shield members 7 and 8 that are in close contact with the opposing surfaces, and magnetic pole pieces 2 and 3 that are provided on the outer peripheral portion of the hermetic shield member and are inserted from each opening surface into each opening.
And excitation coils 11 and 12 for respectively exciting Magnetic shield cylinders 29 and 30 are mounted between the pole pieces 2 and 3 to shield the edge magnetic field.

However, with respect to the energy filter having this configuration, the following points to be improved upon implementation have been clarified.

(1) The production of the analysis container 27 made of a nonmagnetic material sandwiched between the yoke members leads to an increase in cost.

(2). The excitation coils 11 and 12 of the magnetic poles are vacuum-sealed.
Since it must be installed outside of 7 and 8, the distribution of the edge magnetic field increases.

(3). Magnetic pole shield cylinder 29, 3 mounted between magnetic poles
It is difficult to manufacture and assemble 0 with high precision.

[0022]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a small exposed surface area in a vacuum, high positioning accuracy of a pole piece,
An object of the present invention is to provide an energy filter which can reduce the cost, has a small edge magnetic field distribution, and has high manufacturing and assembling accuracy, and a transmission electron microscope including the same.

[0023]

According to the present invention, there are provided a yoke having an electron beam entrance hole and an electron beam exit hole, and a plurality of pairs formed integrally with the yoke so as to face each other and form a gap therebetween. A magnetic pole piece, an exciting coil arranged to generate an energy dispersing magnetic field in a gap between each pair of the magnetic pole pieces, and a vacuum packing for vacuum-sealing a gap between the exciting coil and the gap. The yoke has a groove arranged around the pole piece, the vacuum packing is installed in the groove, and an electron beam incident from the electron beam entrance hole passes through the gap from the electron beam exit hole. Is emitted.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiments of the present invention, the following characteristic means are taken.

(1). Conventional analysis container 27 and magnetic shield tube 2
Omitting 9, 30 as shown in FIG. 1, a pair of yoke pairs 1 a and 1 b of a new shape in which the magnetic pole pieces 2 and 3 disposed opposite to each other are integrally formed.
And the combination of the excitation coils 11, 12 and the vacuum seal 7.

(2) As shown in FIG. 2, a pair of yoke members 1a and 1b constituting a yoke form a vacuum container via a vacuum seal 7, and an exciting coil 11, which is wound around a pole piece, Numeral 12 is set to the atmospheric pressure through holes 43 and 44 provided in the yoke member, and another vacuum packings 8 and 9 are used to maintain the magnetic pole gaps 50 and 51 through which the electron beams pass, in a vacuum.

(3) In order to vacuum seal the passage of the electron beam from the exciting coils 11 and 12 in the atmosphere, a pair of rings 31 and 32 and intermediate rings 35 and 6 for holding vacuum packings 8 and 9 around magnetic poles are provided. The electron beam entrance / exit holes 61a, 6 through which the electron beam 100 enters / exits
1b is provided on the yoke member 1b.

(4) The yoke members 1a, 1b are formed by cutting the passages 81, 82 through which the electron beam 100 passes, the magnetic pole gaps 50, 51, the exciting coils 11, 12 and the portions of the vacuum packings 8, 9; Portions are left for magnetic shielding.

According to such a configuration, since the magnetic pole pieces 2, 3 opposed to each other are integrally formed with the yoke members 1a, 1b, if the respective yokes are accurately positioned, each magnetic pole piece will inevitably be formed. Is also accurately positioned. Therefore, the relative positioning of each pole piece can be performed accurately and easily.

The exciting coils 11, 12 are vacuum-packed 8, 9
Therefore, the vacuum pumping speed, the degree of vacuum, and the quality of the vacuum are all improved to prevent sample contamination.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings. Referring to FIGS. 1, 2 and 3, a pair of opposed yoke members 1a, 1b constituting a yoke are made of an integrally formed ferromagnetic material, the main parts of which are substantially mutually separated. Has a mirror-symmetrical shape.
Conventionally, the yoke is made of pure iron, but is made of permalloy to reduce the residual magnetic field and the hysteresis effect.

At the respective opposing positions of the opposing surfaces of the yoke members 1a and 1b, magnetic pole pieces 2a, 3a and 2b and 3b constituting the magnetic poles 2 and 3 of the energy filter are respectively formed in a convex shape with the yoke members 1a and 1b. When the yoke members 1a and 1b are superimposed on each other, they are integrally formed, and the outer peripheral portions thereof are in close contact with each other.
Are formed.

A vacuum packing 7 is provided around the yoke member 1b.
Is mounted, and the yoke members 1a and 1b form a vacuum container. Excitation coils 11a, 11b and 12a, 12b for exciting the pole pieces 2a, 2b and 3a, 3b of the yoke member are arranged.

In order to dispose these exciting coils outside the vacuum, press rings 31a, 32a and 31b and 32b having the same shape as the exciting coils, vacuum packings 8a, 8b and 9a and 9b, and intermediate rings 35 and 36 are provided. Are located. The intermediate ring has through holes 38a, 38b, 38c and 38d and through holes 39a, 39d at the entrance and the exit so that the electron beam can pass through the gap (electron beam passage) between the pole pieces.
b is provided.

Grooves 81a, 81b and 82a, 82b through which electron beams pass are provided between the pole pieces 2a, 2b and the pole pieces 3a, 3b.
It is provided in. Also, the yoke members 1a, 1b are provided with processing grooves 40, 41 having a fixed width so as to be arranged around the pole piece, and these are provided with excitation coils 11, 12, holding rings 31, 32,
Vacuum packings 8, 9 and intermediate rings 35, 36 are installed, and vacuum packings 8, 9 are holding rings 31, 32 and intermediate rings 35, 36.
It is sandwiched and held by. Of machining grooves 40, 41,
The surface of the yoke member facing the magnetic pole serves as a magnetic shield.

In such a configuration, the yoke members 1a, 1a
b are mutually positioned in the lateral direction by inserting the fitting pin 26, and are fixed by the screw 25.

As shown in FIG. 2, the excitation coils 11, 12
Are connected to the connector 46 through wires 43a, 44a and 43b, 44b provided in the yoke members 1a, 1b. As is clear from FIG. 2, the passage portion of the electron beam is sealed from the atmospheric pressure portion by vacuum packings 7 and 31a and 32a and 31b and 32b. The electron beam enters and exits through the electron beam entrance / exit holes 61a, 61b, which are openings on the side surface of the yoke member, and the openings 61a, 61b are also used for evacuation.

In FIG. 3, after the electron microscope image is formed by the intermediate lens system 15, the aperture angle of the electron beam incident on the γ-type energy filter is restricted by the stop 20, and the electron beam 100 incident on the energy filter is After passing through the electron beam incident hole 61a, the gap between the magnetic poles 2 (pole pieces 2a and 2b) is deflected and the traveling direction is changed by about 90 degrees, then the magnetic pole 3 (pole piece 3
a, 3b). At the magnetic pole 3, the traveling direction of the electron beam 100 is changed by about 180 degrees, and then passes through the groove 81 to reach the magnetic pole 2 again. At the magnetic pole 2, the traveling direction of the electron beam 100 is changed by about 90 degrees again, passes through the electron beam exit hole 61b, travels again along the optical axis of the electron microscope, and is emitted outside the energy filter. After that, the electron beam 100 passes through the aperture 14 and the projection lens system 1
Proceed to 5. Thus, the energy of the electron beam 100 is selected by the energy dispersing magnetic field formed in the magnetic pole gap, and an electron beam having a specific energy is obtained.

As described above, according to the embodiment of the present invention, since the magnetic poles 2 and 3 are integrally formed with the yoke, the relative positioning of the magnetic pole pieces disposed to face each other can be performed accurately and easily. Become like In addition, the exciting coils 11 and 12 are vacuum-packed 7 and 8 without the need for a conventional analysis vessel.
Since it can be installed outside the vacuum via a, 8b, 9a, 9b, holding rings 31a, 31b, 32a, 32b and intermediate rings 35a, 35b, 36a, 36b, the electron beam path is kept at a high vacuum. Further, since a large vacuum chamber is not required unlike the related art, the size and weight of the apparatus can be reduced.

As shown in FIG.
In the configuration that keeps confidentiality through, it is possible from atmospheric pressure to adjust the position of the energy filter in a plane perpendicular to the axial direction of the electron beam so that the optical axis of the energy filter matches the optical axis of the electron microscope. is there. That is, the energy filter is moved in the direction orthogonal to the energy dispersion direction 47 by the moving screw 17 directly attached to the lens barrel 11, and the energy filter is moved in the energy dispersion direction 47 by the screw 18 and the base 19 fixing the screw. Can be done.

In the above embodiment, the present invention has been described as applied to a two-pole γ-type energy filter. However, the present invention is not limited to this. For example, Japanese Patent Application Laid-Open No. Sho 62-66553
The present invention can also be applied to an Ω-type energy filter as described in Japanese Patent Application Laid-Open Publication No. H11-260, 1988.

FIG. 8 shows an Ω-type energy filter according to another embodiment of the present invention, which shows the same or equivalent parts as described above. In this embodiment, the magnetic pole 3 is 2
The two yoke members 1a and 1b are made into a vacuum container via a vacuum packing 7, and the exciting coils 11 and 1b are provided.
The structure in which 2, 13 is installed outside the vacuum section by another vacuum packing 8, 9, 10 remains unchanged. Thus, the present invention can be applied to any type of energy filter as long as it is an energy filter using a magnetic field.

As described above, according to the embodiment of the present invention, the following effects are achieved.

(1) Since each magnetic pole piece is integrally formed with the yoke, the relative positioning of the magnetic poles disposed opposite to each other can be performed accurately and easily.

(2) Since only the portion through which the electron beam passes is evacuated, the evacuation speed, the ultimate vacuum degree, and the quality of the vacuum are all improved, thereby preventing the sample from being contaminated. Further, since a large vacuum vessel is not required, the size and weight of the device can be reduced.

(3) The mechanical position adjustment of the energy filter can be performed from the atmosphere side without providing a complicated vacuum mechanism.

(4) Since all the gaps between the pole pieces that are arranged to face each other can be used as passages for the electron beam, the gap can be reduced to the divergence width of the electron beam. Therefore, a coil current for generating a magnetic field can be reduced, and heat generation can be suppressed.

(5) The structure does not require a non-magnetic analysis container sandwiched between the yokes, and the manufacturing cost can be reduced.

(6) Since the excitation coil of the magnetic pole is mounted along the shape of the magnetic pole, the distribution of the edge magnetic field can be minimized.

(7) Since the structure does not require a magnetic shield tube mounted between the magnetic poles, the manufacturing and assembling accuracy is improved.

[0051]

According to the present invention, there is provided an energy filter having a small exposed surface area in a vacuum, a high positioning accuracy of a pole piece, a low cost, a small edge magnetic field distribution, and a high manufacturing and assembling accuracy. A transmission electron microscope provided with the same.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an energy filter showing one embodiment according to the present invention.

FIG. 2 is a sectional view through an energy filter showing one embodiment according to the present invention.

FIG. 3 is a longitudinal sectional view of a main part of a transmission electron microscope showing an embodiment according to the present invention.

FIG. 4 is a cross-sectional view of FIG.

FIGS. 5A and 5B show a conventional energy filter and a transmission electron microscope having the same, wherein FIG. 5A is a cross-sectional view of the energy filter, and FIG. FIG. 3C is a cross-sectional view of the transmission electron microscope having the energy filters of FIGS.

FIG. 6 is a cross-sectional view of another conventional energy filter.

FIG. 7 is an exploded perspective view of another conventional energy filter.

FIG. 8 is an exploded perspective view of an energy filter showing another embodiment according to the present invention.

[Explanation of symbols]

1: Yoke member, 2, 3: magnetic pole piece, 4, 5: magnetic pole insertion opening, 6: electron beam path, 7, 8, 9, 10, 48: vacuum packing, 1
1, 12, 13: Excitation coil, 14: Slit for energy selection, 15: Intermediate lens system, 16: Projection lens system, 17: Screw for axis adjustment, 18: Screw for filter movement, 19: Screw fixing stand, 2
0: aperture, 21, 22: outer plate, 23: inner plate, 2
4: analysis tube, 25: screw, 26: mating pin, 27: analysis container, 2
9, 30: Magnetic shield tube, 31, 32, 33: Holding ring, 35, 3
6, 37: intermediate ring, 38, 39: electron beam passage hole, 40, 41, 42:
Coil groove, 43, 44, 45: Exciting coil lead wire outlet, 46: Connector, 47: Energy dispersion direction, 49, 50:
Pole gap, 51, 52, 53, 54: pole piece, 55: pair of yokes, 6
1: Electron beam entrance / exit hole, 67: Optical axis in filter, 71, 72, 7
3, 74: magnetic field excitation coil, 81, 82: groove for electron beam passage, 100:
Electron beam.

Claims (7)

[Claims] A yoke having an electron beam entrance hole and an electron beam exit hole; a plurality of pairs of pole pieces integrally formed with the yoke so as to face each other to form a gap therebetween; An exciting coil arranged to generate an energy dispersing magnetic field in a gap between the pole pieces, and a vacuum packing for vacuum-sealing the exciting coil and the gap, wherein the yoke is provided around the pole piece. Energy, wherein the vacuum packing is disposed in the groove, and the electron beam incident from the electron beam entrance hole is emitted from the electron beam exit hole through the gap. filter. 2. The energy filter according to claim 1, wherein said exciting coil is provided in said groove. 3. The energy filter according to claim 2, further comprising an intermediate ring disposed in said groove so as to be disposed between said vacuum packings for each pair of pole pieces. 4. A holding ring disposed between said exciting coil and said vacuum packing, wherein said holding ring and said intermediate ring hold said vacuum packing therebetween. Item 7. An energy filter according to Item 3. 5. The energy filter according to claim 1, wherein said yoke and said pole piece are made of permalloy. 6. An energy filter according to claim 1, having a space that is exposed outside a vacuum to be inserted, and is opposed to each other that is exposed to the space and through which an electron beam passes. A transmission electron microscope having an opening, wherein the energy filter is inserted into the space such that the electron beam entrance and exit holes respectively correspond to the openings facing each other, and wherein the electron beam entrance / exit portion is provided. A transmission electron microscope characterized in that a part where the opening and the opening coincide with each other is vacuum-sealed. 7. A transmission electron microscope according to claim 6, further comprising means for moving said energy filter in a plane perpendicular to an axis of said electron beam in said space.