JPS6335065B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam device, and particularly to an electron beam device in which a tunnel is formed in the magnetic pole piece of an objective lens, and an objective aperture can be inserted through the tunnel.

An example of an electron beam device is a transmission electron microscope, and an example of its structure is shown in FIG. 1, for example. This is electron gun 3 and
A microscope main body 1 has a built-in focusing lens 5, an objective lens 9 having excitation coils 8 and 10 is disposed below the focusing lens 5, and an intermediate lens 11 and a projection lens 12 below the objective lens 9; It consists of an observation chamber 2 which is disposed below the microscope body 1 and is fixed to the microscope body 1, forming a hollow chamber 13 in which a projection screen 14 is arranged. A hollow hole 7 is formed in the center of the microscope body 1 and extends in the longitudinal direction along an axis 6 of an electron beam emitted from an electron gun 3 (hereinafter referred to as an optical axis). The objective lens 9 includes an upper magnetic pole piece 16 that is excited by the excitation coil 8 and a lower magnetic pole piece that is arranged downwardly from the upper magnetic pole piece 16 at a predetermined interval and that is excited by the excitation coil 10. 17, and a sample holding device 18 and an objective aperture 19 are arranged between the upper magnetic pole piece 16 and the lower magnetic pole piece 17 so that they can be inserted and pulled out.

A transmission electron microscope configured in this way is
Its performance has improved year by year, and its resolution has reached the level where it can image the atomic structure of solid samples.
It is generally referred to as a high-performance electron microscope. In order to further improve the performance of such a high-performance electron microscope, such as the resolution, it is possible to reduce the gap between the magnetic pole pieces of the objective lens 9, but on the other hand, various technical problems arise. That is, as shown in Figure 1,
A sample holding device 18 and an objective aperture 1 are located within the magnetic pole piece gap.
As for the objective aperture 19, it is provided close to the top of the lower pole piece 17, so if the gap between the pole pieces is made small, the sample holding device 18 and the objective aperture can be removed. 19, and the movement or tilting movement of the sample holder in the X and Y directions may be hindered.

In order to solve this problem, a tunnel communicating with the hollow hole 7 is formed in the middle part of the lower magnetic pole piece 17 in a direction perpendicular to the optical axis 6 (that is, horizontally in FIG. 1), and a tunnel is formed along this tunnel. A method of inserting an objective aperture 19 has been considered. By the way, the objective diaphragm 19 should originally be set at the back focal plane position of the objective lens 9, and if it deviates from this position, the restriction on the observation field increases, and when observing at low magnification, the objective diaphragm 19 should be set at the back focal plane position of the objective lens 9. This results in only a very partial image being obtained. Therefore, the tunnel needs to be provided as close to the top of the lower pole piece 17 as possible. However, in a high-performance electron microscope, the objective lens 9 is designed to minimize spherical aberration, so the magnetic flux density in the magnetic pole pieces 16, 17 is different from that of the magnetic pole pieces 16, 17. The magnetic saturation region of the magnetic material has been reached. If a tunnel is formed in the lower magnetic pole piece 17 under such circumstances, the magnetic flux density will increase due to the volume defect in the magnetic material and exceed the magnetic saturation region. There was resistance.

There was a solution to this problem, as seen in Japanese Patent Publication No. 47-28539, for example, but in that case, the lower magnetic pole piece 17 was made into a two-part structure, with a thin U on one side. Although the volume loss of the magnetic material can be kept low by providing the letter-shaped grooves, the structure of the magnetic pole piece becomes complicated, which poses a problem that it is not suitable for practical use.

The present invention was developed by focusing on these conventional problems, and its purpose is to have a relatively simple structure,
Moreover, the above-mentioned conventional problems are solved by providing an objective lens for an electron beam device in which a tunnel is formed while minimizing volume defects, and the objective aperture can be inserted and removed through the tunnel.

In the present invention, near the top of the lower magnetic pole piece of the objective lens, a predetermined equal angular interval is placed in the circumferential direction,
The first feature is that a passage is provided so as to extend toward the central axis and be axially symmetrical with respect to this axis, and the objective aperture is inserted into the hollow hole of the electron beam device through this passage. . The width and height of the passage for inserting the objective diaphragm are set to dimensions that allow the objective diaphragm to be inserted leaving a slight gap, and the volume of the lower magnetic pole piece due to the provision of the passage is Deficiencies are kept to a minimum. Therefore, in the objective lens according to the present invention, the objective aperture can be placed at a position away from the magnetic pole piece gap, and only the sample needs to be placed within the magnetic pole piece gap. Therefore, the gap between the magnetic pole pieces of the objective lens can be set to an even smaller dimension, which is useful for improving the performance of the electron beam device. On the other hand, since the volume loss of the lower pole piece is minimized, the magnetic saturation of the objective lens pole piece exhibits similar characteristics to a normal objective lens pole piece without a passage.

Hereinafter, embodiments of each invention will be described in detail with reference to the accompanying drawings.

FIG. 2 to FIG. 5 are diagrams showing an embodiment of the first invention. The objective lens 29 of the electron beam device according to this embodiment has a truncated conical structure, and the optical axis 6
It consists of an upper magnetic pole piece 16 and a lower magnetic pole piece 17, which are arranged with a predetermined gap in the direction and with their heads facing each other. A tunnel 20 is provided near the head of the lower pole piece 17, extending from the outer peripheral surface of the pole piece in a direction perpendicular to the central axis, that is, the optical axis 6, and reaching the hollow hole 7. This tunnel 20 is connected to the lower pole piece 1 as shown in FIG.
Four pieces are provided at equal angular intervals of 90 degrees in the circumferential direction of 7, and the cross section thereof is formed into a substantially circular shape.

Furthermore, a sleeve 21 having substantially the same length as the tunnel 20 is inserted and fixed into the tunnel 10 . This sleeve 21
In this method, split rods 22 and 27 each having a semicylindrical cross-sectional shape, which are formed by dividing a round bar made of a magnetic material into halves along an axis extending in the longitudinal direction, are separated at a predetermined interval so that the cut surfaces face each other. A spacer member 23 having a small thickness and approximately the same length as the split rods 22, 27 is interposed on both sides of the gap formed between the split rods 22, 27. , the split rods 22, 27 and the spacer member 23 are integrated by adhesion or other means, and a width of 4 mm is formed in the center part.
A slit-like passage 24 is formed having a substantially rectangular cross-sectional structure of ~6 mm (millimeters) and a height of 0.2~0.5 mm. Therefore, the lower magnetic pole piece 17 is
As shown in FIG. 2, a slit-like passage 24 extending from the outer circumferential portion toward the central axis is formed in a substantially cross shape, and the other portion is a truncated cone formed of magnetic material into a real structure. .

Note that the slit-shaped passage 24 may be directly dug in the lower magnetic pole piece 17, or the passage 24 may be directly formed in a rod having a circular cross section for the sleeve 21 to be inserted into the tunnel 20. It may be dug. However, it is extremely difficult to form the above-mentioned slit-shaped passage 24 through a block structure such as the lower magnetic pole piece 17 or the rod in the longitudinal direction. It is preferable to use the structure as described above.

In the objective lens 29 having such a structure,
An objective diaphragm 19 is inserted through one passage 24 of the lower pole piece 17 . The objective diaphragm 19 consists of a support rod 26 and an aperture plate 25 attached and fixed to the tip of the support rod 26 with screws 28, and an aperture hole 30 is provided at the tip of the aperture plate 25. . The aperture plate 25 has a thickness that allows it to be inserted into the passage 24, and is slightly movable in the horizontal plane (ie, the XY plane) with the aperture hole 30 aligned with the optical axis 6.

With such a configuration, the objective lens of the electron beam apparatus according to this embodiment is such that the electron beam irradiated from the electron gun 3 is focused by the focusing lens 5, and the magnetic pole pieces 16, 17 of the objective lens 29 are focused. After passing through the sample placed in the gap, the scattered electron beam is cut by the objective diaphragm 19 and refracted by the intermediate lens 11 and the projection lens 12. In this case, the excitation in the objective lens 29 is performed without the magnetic flux density greatly exceeding the magnetic saturation region of the magnetic material constituting the lower magnetic pole piece 17 because the volume defect in the lower magnetic pole piece 17 is extremely small. . Further, since the tunnel 20 and the passage 24 are provided in a symmetrical relationship with respect to the optical axis 6, the lower magnetic pole piece 17 has a substantially uniform magnetic flux density over its entire cross section, and the lower magnetic pole piece 17 has a substantially uniform magnetic flux density over its entire cross section. It is possible to prevent the bending of the optical axis 6 and the occurrence of astigmatism of the objective lens.

In this embodiment, as shown in FIGS. 2 and 3, the base end of the sleeve 21 protrudes outside the outer peripheral surface of the lower magnetic pole piece 17; The side magnetic pole piece 17 may be cut obliquely along the slope. Alternatively, in order to excavate the tunnel 20, a cut is made in the slope of the lower magnetic pole piece 17 to form a vertical surface, and a cut is made from the vertical surface. A tunnel 20 may be formed in the direction of the optical axis 6 so that the base end of the sleeve 21 inserted into the tunnel 20 coincides with the vertical plane.

FIG. 6 and FIG. 7 are diagrams showing an embodiment of the first invention. In this example, objective lens 2
Tunnels 20 are formed in the lower magnetic pole piece 37 of 9 at equal angular intervals of 90 degrees, as in the first embodiment. At or near the opening 20a of this tunnel 20, the lower magnetic pole piece 37
The outer inclined surface of the is shaped to expand outward,
A shoulder portion 37a is formed in this enlarged portion. In one of the tunnels 20, an objective diaphragm 19 is removably arranged, as in the first embodiment. In addition, inside the tunnel 20,
The sleeve 21 is not disposed as in the above embodiment, and the tunnel 20 directly serves as a passage for inserting the objective aperture 19.

In such a configuration, when the objective lens 29 is excited, a tunnel 20 is formed in the lower magnetic pole piece 37, and since no insertion rod such as the sleeve 21 is loaded in this tunnel 20, the lower magnetic pole piece 37 is energized. The pole piece 37 experiences significant volume loss. However, as described above, since the diameter of the lower pole piece 37 is expanded stepwise near the tunnel 20 position midway from the top to the base, the diameter of the lower pole piece 37 is expanded stepwise in the vicinity of the tunnel 20 position. The cross section of the magnetic pole piece (assuming that there is no magnetic pole piece) is shown by the solid line A in FIG. Even if a volume defect occurs due to the tunnel 20 in the lower magnetic pole piece 37, the cross section of the magnetic pole piece when the volume defect occurs falls within the range shown by the two-dot chain line B in the figure. As is clear from a comparison with FIG. 4, this range corresponds to the lower magnetic pole piece 1 in the first embodiment.
7 (the sleeve 21 is inserted into the tunnel 20 and the volume loss is suppressed to a minimum). Therefore, in this second embodiment as well, excitation in the objective lens 29 is performed without the magnetic flux density greatly exceeding the magnetic saturation region of the magnetic material constituting the lower magnetic pole piece 27. That is, in this embodiment, by expanding the diameter of the inclined surface of the lower magnetic pole piece 27 at its intermediate position, the volume loss due to the tunnel 20 is reduced by the solid line A and the two-dot chain line B in FIG. It can be seen that this is compensated for by an increase in volume of the enclosed area (indicated by mesh-like diagonal lines).

Here, when considering the embodiment of the first invention and the embodiment of the second invention, the tunnel 2 of the lower magnetic pole piece 37 in the second embodiment
By inserting the sleeve 21 having the structure as shown in FIG. The objective lens 37 can be Therefore, by such means, the diameter of the tunnel 20 opened in the lower magnetic pole piece 37 is made even larger, and the diameter of the passage 24 for inserting the objective aperture 19 is made larger, so that the objective aperture 19 can be moved in and out. can be done easily. Also, tunnel 20
may be provided axially symmetrically with an interval of 180 degrees.

As explained above, according to the present invention, a tunnel is provided in the lower magnetic pole piece of the objective lens, extending in a direction perpendicular to the optical axis, and extending in a predetermined circumferential direction from the outer inclined surface of the lower magnetic pole piece to the hollow hole. are formed axially symmetrically at equal angular intervals, and this tunnel allows the objective diaphragm to be moved in and out to the optical axis position.
There is ample space between the magnetic pole pieces of the objective lens, and it becomes possible to easily insert and remove the sample or tilt the sample.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a typical structural example of a conventional electron microscope. FIG. 2 is a perspective view of a lower magnetic pole piece employed in an objective lens of an electron beam apparatus according to an embodiment of the first invention. FIG. 3 is a sectional view showing the structure of the above embodiment. Figure 4 shows
FIG. 4 is a cross-sectional view taken along the line ``--'' in FIG. 3, showing a cross section of the lower magnetic pole piece of the objective lens according to the above embodiment. FIG. 5 is a diagram showing the cross-sectional structure of the sleeve inserted into the tunnel in the above embodiment. FIG. 6 is a sectional view showing the structure of an objective lens of an electron beam apparatus according to an embodiment of the second invention.
FIG. 7 is a cross-section of the lower magnetic pole piece of the objective lens according to the second embodiment of the invention in FIG. 6.
FIG. 1... Microscope body, 9, 29... Objective lens, 16
...Upper magnetic pole piece, 17...Lower magnetic pole piece, 18...Sample holding device, 19...Objective aperture, 20...Tunnel, 21
... Sleeve, 23... Spacer member, 24... Passage.

Claims (1)

[Claims] 1. In an objective lens for an electron beam device comprising an upper magnetic pole piece and a lower magnetic pole piece disposed at a predetermined gap from the upper magnetic pole piece and facing the upper magnetic pole piece. , a plurality of tunnels extending perpendicularly to the optical axis and reaching the hollow hole from the outer inclined surface of the lower magnetic pole piece are formed in the lower magnetic pole piece in an axially symmetrical manner with respect to the optical axis. Each sleeve is fitted with a sleeve made of a ferromagnetic material and having a passage for inserting the objective diaphragm, and the objective diaphragm can be inserted into and taken out of the hollow hole through one passage of these sleeves. Objective lens for electron beam equipment. 2. The objective lens for an electron beam apparatus according to claim 1, wherein the lower magnetic pole piece is formed by expanding the slope of the magnetic pole piece outward in diameter at a position near the tunnel. 3. In an objective lens of an electron beam device consisting of an upper magnetic pole piece and a lower magnetic pole piece disposed at a predetermined distance from the upper magnetic pole piece and facing the upper magnetic pole piece, the lower magnetic pole piece forms a plurality of tunnels extending perpendicularly to the optical axis and reaching the hollow hole from the outer inclined surface of the lower magnetic pole piece, axially symmetrical to the optical axis, and the lower magnetic pole piece 1. An objective lens for an electron beam apparatus, characterized in that the diameter of a slope of a magnetic pole piece is expanded outward at a nearby position, and an objective aperture is inserted into and taken out of a hollow hole through one of the tunnels.