JPS6113540A - Electron microscope - Google Patents

Abstract

PURPOSE:To prevent any decrease in the visual field which might be caused by a movable diaphragm and produce high contrast images by enabling an electron ray flux to be focused upon the movable diaphragm even when the excitation of a focusing lens is changed by enabling the excitation of an objective or an intermediate lens to be varied within a given range. CONSTITUTION:When a focusing lens 1 is strongly excited and the cross over point of an electron microscope is adjusted to be point (A) in the figure, an electron ray flux 3 extends over the surface of a sample 5. The electron ray flux 3 is then focused upon a movable diaphragm 6 by a weakly excited objective 4. In contrast, when the focusing lens 1 is more weakly excited than above and the cross over point is adjusted to be point (B), an electron ray flux 5 extends within a smaller area than above on the surface of the sample 5 (the area surrounded by a dotted line). The electron ray flux 7 is then focused upon the movable diaphragm 6 by the objective 4 which is excited in a degree different from above.

Description

Detailed Description of the Invention [Technical Field of the Invention 1] The present invention relates to an electron microscope in which an electron beam transmitted through a sample is focused on a movable diaphragm behind an objective lens even when the excitation of a focusing lens is changed. It is.

[Prior art and its problems] In the past, specimens were observed using an electron microscope at a low magnification of about 1,000 times or less! 'j:'') in the case ll-
In order to increase the image quality by increasing the contrast and reducing the 11t2 difference of 1000/Z, an example λ is shown in FIG. U/, f electron optical system is adopted, I, = 1. From this electron optical system (, t, 1- side (electron beam source side) aligned with the electron beam axis O), the focusing lens 1 (fftj spinning "01J Mi middle 1,
・Installed adjacent to the top concentrating lens 1
l"'+ l'L /, -, 'il Sen diaphragm: ? and movable diaphragm 2 installed behind (J,: χ・l 1jrl l nozzle 4, ] and 11. A sample 'l r) is installed inside the single object lens 4.The electron beam exiting from the concentrating lens 1 and the movable diaphragm 2J The electron beam 3 is once focused (crossover) at Δ':, then diverges, and illuminates the sample 5 placed within the objective lens 4.Trial 1:', The divergent electron beam 3 is The objective lens 4 is set to a weak constant excitation so that the movable aperture 6E1 placed at the rear focuses I.From this state, the excitation of the focusing lens 1 is changed, and the dotted line in the figure If the diameter of the sample irradiation beam is changed so that the trajectory 5M of the electron beam 7 shown in FIG. expands and has a small diameter (e.g. λ
If an aperture with a diameter of 20t] is inserted, the field of view will be reduced by 1 to 1. The same applies to the case where an intermediate non-zero is installed ('J1) to focus the electron beam onto the movable aperture 6 and strengthen the scattering contrast (Fig. 71) by exciting it (Fig. 71). It is 1.

Figure 2 [1, this] - The objective lens 4 is normally excited (), and the back focal plane of (a) "A more divergent electron beam is created between the objective lens 1 and the aperture 6 of 1n ohm. A conventional example is shown in which the electron beam is focused on the movable diaphragm 6 by an intermediate lens 8 provided.In this figure, when the excitation of the focusing lens 1 is changed and the irradiated electron beam of 1'I+5 is changed, the objective One crossover point in front of the lens moves from C to D, and one crossover point behind the objective lens moves from E to ". In this case, if the excitation of the intermediate lens 8 is constant, the electron beam flux 3
is focused on the movable aperture 6. Therefore, when using a diaphragm with a small diameter as the movable diaphragm 6, 1. Jl,
This can lead to a decrease in visual field.

On the other hand, i7i 1 figure and 1 yen! Figure 2 Smell]+・
l'l! /I The excitation limit of the lens 4 or (,1, intermediate 1, 8) is kept constant, and the movable diaphragm 6-1- has an electric current of 1J.1, U11, middle 1. Connect the nons system and maintain the relationship Kl of C and I. 1.'r 7.1)
If so, the above deficiency 1:,! 4.1 or i "rikai 7'4"
3" PI Lono) \, focusing lens Visler - 11 cis and b!) fixed translation; A" etc. 1 + 1 ° (there is, small diameter diaphragm E) is used to create a wide field image A, 111 A) - :In some cases, it is important to finely adjust the excitation of the objective lens and the L intermediate lens.

It also reduces the field of view of an electron microscope (11).
! The cause of -4= was the occurrence of astigmatism for the electron beam transmitted through Trial 1. Conventionally, in both high and low magnification modes, the astigmatism correction device is used to correct the astigmatism of the image, and is used to correct the astigmatism of the electron beam focused on the movable aperture. It had not been done. Therefore, when a small-diameter aperture is used, problems such as an elliptical shadow appearing on the aperture may occur during image formation, reducing the field of view for observation.

In the examples shown in Figures 1 and 2, due to the factors of )Ta.

[Object 1 of the Invention] Since the present invention (1) was made in view of the problems of the conventional armor T, its first purpose is to reduce the culm by 1,000 times or less; '[-do, or 1;1. The movable diaphragm provided behind the intermediate lens is changed to 11 (1, 2 to obtain random convergence 1 to last!), and the excitation of the focusing lens system is changed with a3 to 1.I. The movable diaphragm installed behind the objective lens does not reduce the field of view, and the movable diaphragm can be used to improve the image quality from 161 to 11.
1) Providing 4 electron microscopes that can be used - Cc)
Ru.

Book! 111 related to 1! Approximately 41, 1,000 fi
+[+' ll: I, low magnification mode below 1 SO, [・v
l is the result of the upper j i (911 need's?h''i't'l-3 to the optical system 7, mu+0::l transmitted/, = electron beam jl +,', mi's To suppress the occurrence as much as possible, add 1ktl of L field of view to 11 [φj1 school (]) [1J11- Then, turn the possible lI + width to Ij effect, and make the image to 1' u l'7 truss 1. ?'7 (To 1) (Saru Denryomicroscope (Scattered Mirror)/,, 1.1 To provide. l [Structure 1 of the Invention The first and second inventions 1J Note 1]
In order to achieve this goal, a sample in front of the objective lens is illuminated by an electron beam passing through a concentrating lens, and a movable diaphragm placed behind the weakly excited objective lens or intermediate lens is used to collect the electron beam divergent from the sample. Focused on I! In the electron microscope, the electron beam flux can be focused on the movable aperture even if the excitation of the focusing lens is changed by varying the excitation of the objective lens or the intermediate lens around a constant value. This is a summary. Such embodiment lJ1 is adopted when the observation magnification of the electron microscope is low, and the objective lens or (
, I The intermediate lens immediately behind this objective lens has an excitation strength of 0 or 4! iv) is set to a weak value, and the sample light! J
The first 77 [1 s A-bar after passing through the 4'O electron beam 151 objective lens is tied onto the movable aperture. The movable aperture is generally an aperture whose hole i"- is located at 201149rα, and a swarm is formed on the movable aperture. It can be cut to enhance the height of the statue.

Furthermore, t, = ;Jl,: As another embodiment of the present invention, an intermediate lens is placed between the objective lens of the electron microscope and a movable aperture at the rear, the objective lens is set to normal excitation, and the intermediate lens is In order to refocus the electron beam diverged from the focal plane behind the objective lens onto the movable aperture,
The main point is that the excitation of the intermediate lens is made variable around a constant value, and the excitation of the intermediate lens is changed as the excitation of the focusing lens changes, so that the electron beam flux is focused η on the movable aperture. do.

Furthermore, the invention of this I'1 13, 17'I [J]
1. Place the electron beam that has passed through the test tube using the method described above into the movable diaphragm 1 behind the objective lens. In addition to 1.1, a new astigmatism correction device between the sample and the movable diaphragm has been added.
91 (), a movable diaphragm t) 1- corrects the astigmatism of the electric i' ray flux, and prevents a decrease in the field of view due to the 11 [moveable diaphragm t]. ] FIG. 3 and FIG. 4 are diagrams showing an embodiment of the first invention. In the embodiment shown in FIG. 3, in the low magnification mode, the electron beam divergent from the sample is focused onto a movable diaphragm placed at the rear by a weakly excited objective lens, and the objective lens 4 is The excitation can be varied around a certain value. In this embodiment, the distance from the focusing lens 1 to the objective lens 4 and the sample placed therein is set to 150IIIIIIl, and the distance from the objective lens 4 to the movable aperture 6 is set to 150w1IIl.

Further, the diameter of the aperture 2 of the condensing lens is set to 200μ, so that =8-. Under such a 4% concentration, the electron beam 3 spreads over the surface of the sample 5 when the focusing lens 1 is strongly excited (6) and one crossover point is set at a position in the figure. With objective lens 1, electron beam flux 3 is possible 111 comparison VI G
It is focused on the On the other hand, the converging lens is expanded to a point where (J, weaker excitation, crossover is rarer) than in the case of ten. In the case of A, this electron beam flux 7 is generated by the objective lens 4 which is excited with a different value of T than v1.
focused on. FIG. 6 shows "A 5°/II? of one crossover point (Δ or B) on the focusing lens 1 that enters the electron distribution optical system. It is a figure which shows the relationship between Zc and the diameter d of the electron beam flux on test rI5.

ZC is a trial tl',! The position of l 5 is the origin, the focusing lens side is indicated as -, and the movable aperture side is indicated as 10. According to this figure, if one point A of lossover is Zc=-125, the irradiation diameter on the sample F15 is 1 mm.

FIG. 6 shows the position 7 of a crossover point formed on the focusing lens 1. The excitation of the objective lens focused on a and the movable aperture G is 1.11 strong. Power 1: Aisu・1 theory supplementary W! Please check the actual relationship with acceleration voltage ('
I) In the righorn diagram showing r”.This graph is
The distance between the magnetic poles of the pole piece of the λj object lens 4 is S, and the hole 1 is
When changing y to b, s + b = 1 (1 (mm)).

In this case, the excitation strength of the objective lens 4 is as shown in Figure 6: J/B -1,9 (ΔT/V±). Next, by changing the excitation of the focusing lens and moving one crossover point from 8 to B, that is, to the 150 mm point in FIG. 6, the electron beam irradiation diameter on specimen 5 becomes 100 μ.
Therefore, from FIG. 7, the excitation strength of the objective lens is 070-2,6 (ΔT/\l+).

Even if the illumination rod changes, the excitation of the objective lens 4 will continue.
By changing the node, the electron beam flux can always be focused on the variable fj+ aperture 6.

FIG. 4 shows a tree ('I) showing another embodiment of the first invention (
・A<)1. The electron optical system related to this actual fdlj example includes a focusing lens 1, a movable aperture 2, an objective lens 4, and a movable aperture 6.
What R'! This embodiment has the same features as the embodiment shown in FIG. Then, similarly to the embodiment shown in Fig. 3, when the focusing lens 1 is strongly excited Q&S and one crossover point is set at the Δ' position, the electron beam 3 spreads over the surface of the sample 1915. .

In this embodiment, the excitation of the objective lens 4 is set to zero, and the electron beam 3 is focused onto the movable diaphragm 6 by low-magnification excitation of the intermediate lens 8. Also, the excitation of the focusing lens 1 is weaker than described above. and move one crossover point from A' position to B
When moved to the ' position, the electron beam flux 7 spreads over a smaller area on the surface of the sample 5 (the area surrounded by the dotted line). Then, set the intermediate lens to a different excitation from the above case!
The electron beam bundle 7 is focused onto a movable aperture 6. By excitation of the intermediate lens 8, the third Ij7 in the electron beam is placed above the aperture 6 at a low magnification.
The relationship between the 7th [tsu1 ()] and the strength of moxibustion is broken! (
2) Show (\Ladle, A1 point: 7C--125mm) / P = :!, 0 (△-r '\/z
) Point V': 7c -! -i r) mm,
J/, /TP 2.2<Δ'T-,,,'V completion)
becomes. However, the distance between the magnetic poles of the pole piece of the intermediate lens 8 is S, the hole 1Y a, 1) and 7I rod \, 3 +b -
1()(mm).

As mentioned above, a change in the excitation of the objective lens 4 or the intermediate lens 8 naturally causes a change in lens magnification and a change in image focus. It is possible to correct the JZ error in the subsequent intermediate lens during the subsequent focusing process.

FIG. 5 is a diagram showing an embodiment of the second invention.

In this embodiment as well, the same logic as in the imaging structure of the electron microscope of the first invention is applied. In this embodiment, an intermediate lens 8 is installed between the objective lens 4 and the rear aperture 6, and the objective lens 4 is set to normal excitation. The divergent electron beam flux is then refocused onto ijφ116. The configuration of such an electron optical system is such that, while the A1'1 ratio mode according to the first invention is a low magnification mode of 1,000 times or less, this J: d is a large magnification mode. i'R7i' IA culm+! This realizes a magnification mode of . Now, when the focusing lens 1 is relatively strongly excited and one crossover point is set to 0, the electron beam 3 passes through the sample 15 and is focused by the objective lens 4 at a point E, and after the point A, the electron beam 3 is focused at a point E. It is focused by lens 8. At this time, if the excitation of the intermediate lens 8 is set to a predetermined value, the electron beam 3 is focused onto the movable aperture 6.

On the other hand, if the focusing lens 1 is excited more weakly than in the case of 10 and one crossover point is set at position D, the electron beam 7 passes through the sample 1) 4/, -ju 2.1 object 1 nonce 4 J.

(17 of tl21i of single object lens 4)
．． By setting the excitation of the intermediate lens 8 to a predetermined value l+1", the electron beam is focused at 7 (1) of the movable aperture 6. Each excitation of the intermediate 1 nonsense in this 1-simple case can be obtained by using the Graph J: as in Figure 7.

Even if the excitation of the focusing lens 1 changes and the diameter of the electron beam 3 or 7 that irradiates the sample changes, the movable aperture 6
A predetermined electron beam flux is focused on 451. at a low magnification or a slightly higher magnification. high contrast)
It is possible to image the image in four different ways.

In the structure and imaging mode of the electron microscope described above,
In particular, when the diameter of the test cap is large and the movable aperture 6 is small, it is necessary to set the circle of least confusion of the focused electron beam strictly above the movable aperture 6, so that the irradiated electrons Fine adjustment of the objective lens 4 or the intermediate lens 8 is required as the diameter of the beam changes. When using a movable diaphragm 6 with a small diameter (for example, 20 μm or less in diameter), even if the minimum 1j random circle is set at 11"l [1] exactly above the aperture, due to lens aberrations, etc. If there is a point I1 in the electron beam flux at the position of the movable aperture 6, an elliptical shadow will be generated and the field of view will be reduced. It turns out.

FIG. 8 is a diagram showing an embodiment of the third invention relating to an electron optical system configured to correct such astigmatism. As shown in this figure, in the low magnification mode using the electron optical system having the same dimensions as shown in FIG. 3, the astigmatism correction devices 10 and 11 are installed. The astigmatism correction device 11 is
This astigmatism correction device 1 is commonly used in conventional low magnification mode electron optical systems.
1 to correct image astigmatism. On the other hand, the non-l:a correction device 10 is newly activated according to the present invention in the low magnification mode d3, and the astigmatism correction device 10 corrects the astigmatism of the electron beam 3 on the movable aperture 6. It is designed to be corrected. Here, in FIG. 8, a dotted line 12 indicates a scattered electron beam diverged from the sample 5.

As a result, in this invention, degree (II +,'
When A is 7 correct, it is concentrated towards the movable diaphragm G. Therefore, for example, the shape of this focused electron beam will not become a round circle, and even if the aperture 6 with a relatively small diameter is used, the field of view will not become narrow.

FIG. 9 shows an embodiment of the fourth invention showing a method for astigmatism correction of an electron beam in an imaging mode in which scatter contrast is obtained by a movable diaphragm installed behind an intermediate lens. FIG. The electron microscope according to this embodiment consists of an electron optical system similar to the electron optical system shown in FIG. These astigmatism correction devices 101 and 111 have the same functions as the astigmatism correction devices 10.11 in the third invention, respectively.
The astigmatism of the electron beam bundle 3 on the movable aperture 6 is corrected by
The astigmatism of the image is corrected by the astigmatism correction device 111. For this reason, even in the electron microscope of the present invention, astigmatism correction of the image is performed. If the maximum /Is ff1i random circle is 11
There is no longer a problem that the field of view becomes narrow due to protruding from the hole of the dynamic diaphragm 6. For an electron microscope having an electron optical system as in the present invention, the image forming astigmatism correction device 111 is arranged so that the image forming astigmatism correction device 111 is fixed to Electron beam astigmatism correction device 10
1 is preferably installed near the focal point 11 of the scattered electron beam 12.

Note that this method of improving the field of view according to the present invention can also be applied to the case where the electron microscope uses a fixed aperture instead of the movable aperture 6.

[Effects of the Invention] As explained above in Section 1, according to the present invention, the objective lens or the intermediate lens is excited very weakly, and the electron beam that has passed through the sample in 1 is focused on the fj+ aperture. , a low-magnification imaging mode to obtain a high-contrast image, or a mode in which the objective lens is normally excited and the electron beam exiting from the focal plane after the objective lens is refocused onto a movable aperture using an intermediate lens. In the imaging mode in which a high-contrast image is obtained by excitation of the focusing lens, the electron beam is directed forward to sample r1 in response to the excitation of the focusing lens, and the objective lens and intermediate lens are excited and changed to around a predetermined value, thereby changing the focusing lens system. Even if a change in excitation occurs, the divergent electron beam can be focused on the movable aperture compared to test 1, so the aperture can be
, decrease in visual field. A movable diaphragm with a small diameter can be used, and there is a high 1!I!

[Brief explanation of drawings]

Figure 1 shows a low-magnification -T-F imaging method for concentrating the electric current at the rear movable diaphragm 1 by excitation of the λ1 object lens in the prior art. 'j <) o second
The figure shows that the objective 1 and 4 are normally excited, and the P Ilk 1 and L irradiation lines are fired from the back focus of the objective lens. A conventional imaging method is shown in which the image is focused again on the movable diaphragm 1- by an intermediate lens placed at the lens I'G Ij.
Figures 3 and 3 show an electron microscope with an imaging lens system similar to that shown in Figure 1, in which the electron beam passing through the sample is focused on a movable aperture by varying the excitation of the objective lens. Diagram showing the first embodiment of the first invention, No. 4
The figure shows a tree (!1 1st
FIG. 5 is a diagram showing a second embodiment of the invention, and FIG. 5 is an electron microscope using an imaging system similar to that shown in FIG. 1) 3J to focus the electron beam on the movable aperture 6
: Diagram showing an embodiment of the second invention of the sea urchin IC, No. 6
Fig. 11 is a graph showing the relationship between the radius formed by the focusing lens in the first invention and the diameter of the beam of illumination light of the sample and the position of one point of superposition @7C.
, in the imaging lens system shown in Fig. 3 or Fig. 4 [1
The electron beam flux for one point 7G of the bus is focused on the ffl+diaphragm 1! FIG. 8 is a graph for determining the excitation strength of the objective lens and the intermediate 1 non-sense for the objective lens, and the diagram shown in (1) for the objective lens and (2) for the intermediate lens. FIG. 3 shows a means for correcting astigmatism of a sample-transmitting electron beam focused on a movable aperture in an electronic type microscope having a similar imaging system as shown in FIG. FIG. 9, a diagram showing an embodiment, relates to a means for correcting astigmatism in a sample r1 transmission electron beam focused on a movable aperture in an electron microscope having an imaging lens system similar to that shown in FIG. It is a figure which shows one Example of this invention 4th. 1...Focusing lens 2...(Focusing lens) diaphragm 3.7.12...Electron beam flux 4...Objective lens 5...Test F16...Movable diaphragm 8...Intermediate lens 10. 101...Stigmatism correction device (for astigmatism correction of electron beam flux)

Claims (1)

[Claims] 1) A sample is irradiated with an electron beam using a focusing lens at low magnification, and the electron beam transmitted through the sample is focused onto a movable aperture placed at the rear using a weakly excited objective lens or intermediate lens. In the electron microscope, the electron beam can be focused on the movable aperture even if the excitation of the focusing lens is changed by varying the excitation of the objective lens or the intermediate lens around a constant value. An electron microscope featuring: 2) An intermediate lens is provided between the objective lens of the electron microscope and the rear movable aperture, and the objective lens is set to normal excitation.
In an electron microscope in which the electron beam diverged by the focal plane after the objective lens is refocused on the movable aperture by excitation of an intermediate lens, the focusing lens is An electron microscope characterized in that an electron beam flux is focused on the movable aperture even when the excitation of the movable aperture is changed. 3) An electron microscope in which a sample is irradiated with an electron beam using a focusing lens at low magnification, and the electron beam transmitted through the sample is focused onto a movable aperture placed at the rear using a weakly excited objective lens or intermediate lens. In addition to the astigmatism correction device that corrects the astigmatism of the image between the sample and the movable aperture, a new astigmatism correction device was installed to correct the astigmatism of the electron beam on the movable aperture. An electron microscope characterized by: 4) An intermediate lens is provided between the objective lens of the electron microscope and the rear movable aperture, and the objective lens is set to normal excitation.
An objective lens for correcting astigmatism in a normal image between a sample and the movable aperture in an electron microscope in which an electron beam diverged from a focal plane after the objective lens is refocused onto the movable aperture by an intermediate lens. Apart from the astigmatism correction device,
An electron microscope characterized in that a stigma correction device is newly provided to correct stigma of an electron beam flux on a movable aperture.