JPS6029187B2 - electronic microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron microscope, and particularly to an electron microscope that makes it possible to keep the focus excitation of an objective lens substantially constant from high magnification to relatively low magnification.

From operational standpoints, it is desirable to keep the focus excitation of the objective lens of an electron microscope almost constant even when the magnification is varied.

In conventional electron microscopes, this condition is usually satisfied only by selected area magnification, and the range of magnification that can be used with this selected area magnification is usually from several thousand times to hundreds of thousands of times. An example using field magnification is shown in FIG. FIG. 1 is a diagram showing an electron path created to obtain a relatively high magnification image in an electron microscope equipped with an objective lens 3, a selected area diaphragm 4, intermediate lenses 5 and 6, and a projection lens 8. be.

In this case, the electron beam 2 scattered from the sample 1 is refracted by the objective lens 3 and is imaged as an image 9 on the selected area diaphragm 4 surface. In the medium and high magnification range from several thousand times to hundreds of thousands of times, the excitation of the intermediate lenses 5 and 6 and the projection lens 8 is changed so that the object plane of the intermediate lens 5 coincides with the surface of the selected area diaphragm 4, and the image 10 is Since the magnification is varied, the focus excitation of the objective lens can be kept almost constant even when the magnification is varied. However, similar to the above, when the image is formed at the selected area diaphragm 4 positions, the image 10 has a magnification lower than several thousand times.
However, in order to obtain such an image, it is necessary to reduce the image in several stages using the intermediate lens 6 or the like, which tends to cause large off-axis aberrations. Therefore, in conventional electron microscopes, in order to obtain images with a low magnification of several thousand times or less, the excitation of the objective lens 3 is changed as shown in FIG. A low magnification image 10 was formed. According to this, the electron beam 2 scattered by the sample 1 is refracted by the objective lens 3 and the intermediate lens 5, and after being imaged on the object surface of the projection lens 8 behind the intermediate lens 5, the electron beam 2 is 8 and forming squad 10 on the rear flank 13.

However, in this method, the imaging plane of the objective lens 3 is not on the selected area aperture 4 surface, but is located at a relatively large distance from this plane, so the focus excitation of the objective lens 3 is difficult when using the selected area magnification. is set to a value that differs by a few percent for the focus excitation of . Therefore, when switching the magnification of the electron microscope and moving from the former limited field magnification to the latter low magnification, it is necessary to readjust the focus excitation and also readjust the astigmatism correction.
There was a problem that the operation was complicated. Furthermore, the objective lens 3 has a C. 0. When a strongly excitation lens such as a condenser objective lens is used, there is a problem in that changing the focus excitation of the objective lens 3 causes an undesirable change in the irradiation conditions. The present invention was made in view of the problems of the prior art described above, and its purpose is to place another electron lens immediately after the objective lens between the objective lens and the selected area diaphragm, and to When you want to obtain a low-magnification image, you can change the excitation of this electron lens and set the imaging plane of the sample at a position closer to the objective lens than before the excitation change of the electron lens. An object of the present invention is to provide an electron microscope capable of obtaining an image at a lower magnification even when the magnification is kept almost constant. That is, in the present invention, an electron lens is additionally installed immediately after the objective lens as described above, and while the objective lens is excited to a predetermined strength during high magnification observation, the electron lens is not excited at zero or extremely low. Set to strength.

As a result, the sample is imaged by the objective lens at a predetermined position behind the objective lens, and further imaged by the intermediate lens and the projection lens to obtain a high-magnification observation image of the sample.
Next, when performing low magnification observation, the excitation of the electron lens is increased while keeping the excitation strength of the objective lens the same as above. Then, the sample is imaged by the objective lens at a position closer to the objective lens than the above-mentioned objective lens image formation position, and then imaged by the intermediate lens and projection lens to obtain a low-magnification observation image of the sample. . For this reason,
Over a wide magnification range from low magnifications of several thousand times to high magnifications of several tens of times, there is almost no need to change the focus excitation of the objective lens, and the occurrence of astigmatism when switching to low magnification operation is avoided. and deterioration of irradiation conditions can be prevented. Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 3 and FIG. 4 are diagrams showing an embodiment of the present invention.

Of these, FIG. 3 shows a sample observation state using selected field magnification, and is an example of a high magnification observation method in an electron microscope. The electron microscope according to this embodiment has an objective lens 3 disposed behind the surface of the sample 1, a selected area diaphragm 4 disposed behind the objective lens 3, intermediate lenses 5 and 6, and a projection lens 8. is similar to the conventional electron microscope described above. However, unlike the conventional example, the objective lens 3
An electron lens 12 is arranged between the diaphragm 4 and the selected area diaphragm 4, in addition to the objective lens 3, intermediate lenses 5, 6, etc.
The objective lens 3 is capable of refracting the imaged electron beam. This electron lens 12 includes an objective lens 3
It is arranged behind the objective lens 3, intermediate lenses 5, 6, etc., and is configured to be electrically turned on and off independently of the objective lens 3, intermediate lenses 5, 6, etc., and when turned on, further refracts the electron beam that has passed through the objective lens 3. be able to. When using selected field magnification for high magnification observation, the electronic lens 12 is turned off, and when low magnification observation is performed, the electronic lens 12 is turned on. Therefore, in the electron microscope according to the present invention, when the electron microscope is used in a magnification range from several thousand times to several tens of times, the electron lens 12 is not excited, and the electron beam 2 emitted from the sample 1 is transmitted as shown in FIG. On the same machine as Tano, objective lens 3
is refracted at and focused on a point 14 on the surface of the selected area diaphragm 4,
Thereafter, an image 7 is formed by intermediate lenses 5 and 6, and an image 10 is formed on an image recording surface 13 after passing through a projection lens 8.

Further, the magnification is changed by varying the excitation of the intermediate lenses 5 and 6 and the projection lens 8. On the other hand, when observing the sample 1 at low magnification, the electron lens 12 is also turned on and excited together with the objective lens 3, intermediate lenses 5, 6, etc. Therefore, the electron beam 2 emitted from the sample 1 is refracted by the objective lens 3 and the electron lens 12, and is focused on a point 15 between the electron lens 12 and the selected area aperture to form an image 16. In this case, the excitation of the objective lens 3 is the same as the excitation at the selected field magnification, and after passing through the objective lens 3, the electron beam 2 advances in the direction of a point 14 as shown by a dotted line 17 in FIG. Then, by exciting the electron lens 12 to an appropriate size, an image 16 is created at a predetermined position between the electron lens 12 and the selected area diaphragm 4. On the other hand, the intermediate lenses 5, 6 and the projection lens 8 are arranged so that the object surface of the intermediate lens 5 is always at the focal point 15 of the image 16 even if the magnification is varied within the low magnification region. The excitation of the projection lens 8 is set. By performing such excitation settings, the object surface of the intermediate lens 5 changes from the point 14 position on the selected area aperture plane to the point 1.
5 toward the objective lens 3 side, the traverse magnification by the intermediate lenses 5 and 6 and the projection lens 8 is lower than in the case of limited field magnification, and a low magnification image 10 is obtained. In the above description, the electronic lens 12 was turned off at the selected field magnification shown in FIG. 3 and turned on at the low magnification shown in FIG. 4, but it may be turned on in the former case as well. That is, at selected area magnification, the excitation of the electron lens 12 is relatively weakly excited so that the objective lens 3 and the electron lens 12 form a first image on the selected area aperture 4, and at low magnification, the electron lens 12 may be increased to move the wisteria surface to a point 15 in front of the selected area diaphragm 4. In this way, magnification ranging from several hundred times to several thousand times is obtained, but during the magnification change within this magnification range, the focus excitation of the objective lens 3 changes slightly due to the influence of the hysteresis of the intermediate lenses 5 and 6. However, it is almost the same as focus excitation at selected field magnification.

In the conventional low-magnification imaging method shown in Fig. 2, the excitation of the objective lens changes depending on the magnification, whereas in the electron microscope of the present invention, the objective lens excitation is changed not only in the high-magnification region but also in the low-magnification region. Lens excitation can be made constant. As explained above, according to the present invention, there is almost no need to change the focus excitation of the objective lens over a wide magnification range from several hundred times to several tens of times, and Since there is almost no change in astigmatism, there is no need for readjustment. The range of focus adjustment when changing the magnification can be minimized, making it possible to provide an electron microscope that is extremely simple to operate. Furthermore, C. 0. If the present invention is applied to an electron microscope that uses a strongly excited electron lens like a lens as an objective lens,
By changing the excitation of the objective lens, there is no change in the sample irradiation conditions that occurs due to the variation of the objective lens magnetic field on the focusing lens side from the sample, and effects such as good image observation can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a state in which a conventional electron microscope is operated at selected field magnification. FIG. 2 is a diagram showing a state in which a conventional electron microscope is operated to form a low-magnification image. FIG. 3 is a diagram showing the electron microscope according to the present invention being operated at selected field magnification. FIG. 4 is a diagram showing a state in which low magnification images are formed using the electron microscope according to the present invention. 1
...Sample, 2...Electron beam, 3...Objective lens, 4...Selected area aperture, 5, 6...Intermediate lens, 8... Projection lens, 12...
electronic lens. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In an electron microscope that has an objective lens, a selected area diaphragm and an intermediate lens placed behind the objective lens, and a projection lens placed behind the intermediate lens, an excitation variable An electron lens is placed, and when observing at high magnification, the imaging plane of the sample by the objective lens and the electron lens is set at a predetermined position behind the objective lens, while when observing at low magnification, this electron lens is , the excitation is changed to a different intensity from the intensity during high-magnification observation, and the imaging plane of the sample by the objective lens and the above-mentioned electron lens is closer to the objective lens than before the excitation change of the above-mentioned electron lens and is limited to the above-mentioned electron lens. By setting it at a position between the field stop and further forming an image on the image recording surface using an intermediate lens and a projection lens, the focus excitation of the objective lens can be kept almost constant in the magnification range from high magnification to low magnification. An electron microscope characterized by: