JPH02100251A - Electron beam device - Google Patents

Abstract

PURPOSE:To enable the easy switching between high magnification and low magnification and reduce the distortion of an image by providing an auxiliary lens for focusing an electron beam on a sample between the focusing lens and the objective lens. CONSTITUTION:An auxiliary lens 20 for focusing electron beams on a sample 17 is provided between focusing lenses 13, 14 and an objective lens 16. In the use at a high magnification, an electron beam generating source 11, focusing lenses 13, 14 for focusing the electron beams from the generating source 11, the objective lens 16 for focusing the electron beams on the sample 17, and a deflecting means 15 for scanning the electron beams on the sample 17 are used. In the use at a low magnification, by switching the objective lens 16 to the auxiliary lens 20 newly provided, the distance between the objective lens and the sample 17 is considerably lengthened to reduce the magnification, but the distortion of the image is never increased as the radiation angle of the electron beams to the sample 17 is not so much increased. Hence, the switching between high magnitude and low magnitude can be easily carried out, and the distortion of the image can be reduced.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention makes it possible to obtain images with high resolution and less distortion not only in high magnification ranges but also in low magnification ranges in electron microscopes, etc. Related to electron beam equipment.

(Prior Art) In a conventional scanning electron microscope or the like, as shown in FIG. The beam is focused by the scanning coil 5, scanned by the scanning coil 5, and focused by the objective lens 6 so as to form a point image on the sample, and the sample 7 is irradiated. In order to obtain high resolution, the working distance is shortened and the sample is observed closer to the objective lens. When increasing the magnification of the microscope to observe at high magnification, the scanning range of the electron beam is narrowed, and when lowering the magnification and observing at low magnification, the scanning range of the sample surface is widened. It will be scanned.

(Problem to be solved by the invention) By the way, when the magnification of the microscope is set to low, the scanning range on the sample surface is widened, but when the working distance is short, the electron beam is emitted at the edge of the scanning range. There is a drawback that the irradiation angle becomes considerably large with respect to the optical axis, resulting in large distortion of the observed image. Therefore, as shown in Figure 5, there is a method to move the sample placement position from Ll to L2 in the figure, so that even if the scanning range becomes larger, the irradiation angle does not increase, thereby reducing image distortion. When switching from a high magnification to a low magnification, the sample must be moved up and down, and moving it up and down is time-consuming and impractical.

Moreover, FIG. 6 shows a state in which the excitation of the objective lens 6 is turned off.
The same members as in FIG. 5 are shown with the same symbols, but since there is no objective lens 6, the electron beam is focused on the sample 7 by the second focusing lens 4, and the irradiation angle of the electron beam is set at right angles. It is designed to be held at an angle close to . Although an image with small distortion can be obtained in this way, the distance between the second focusing lens 4, which is the last of the focusing lenses, and the sample 7 becomes long, and spherical aberration and chromatic aberration become very large. There was a problem that low magnification images with good resolution could not be obtained.

The present invention has been made by focusing on such conventional problems, and provides an electron beam device that can easily switch between high magnification and low magnification and can reduce image distortion. Its purpose is to

(Means for Solving the Problems) As a means for solving the above problems, the present invention has a configuration including an electron beam generation source, a focusing lens that focuses the electron beam from the generation source, and the electron beam generation source. In an electron beam device comprising an objective lens that focuses an electron beam onto a sample, and a deflection means that scans the electron beam on the sample, an aid for focusing the electron beam on the sample is provided between the focusing lens and the objective lens. I decided to install a lens.

(Function) Next, the present invention will be explained in detail. When this electron beam device is used at high magnification, it must include an original electron beam generation source, a focusing lens that focuses the electron beam from the source, an objective lens that focuses the electron beam on a sample, and the electron beam and a deflection means for scanning the sample on the sample. When using this electron beam device at low magnification, by switching the objective lens to a newly installed auxiliary lens, the distance between the objective lens and the sample becomes considerably longer and the magnification becomes smaller. Since the irradiation angle of the electron beam is not very large,
Image distortion will not increase.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram of the present invention, showing a scanning electron microscope. From the top: electron gun 11, anode 12, first focusing lens 1
3. There are a second focusing lens 14, a scanning coil 15, and an objective lens 16, which allow the electron gun 11 to be placed on the sample 17.
focuses the electron beam from Here, the second focusing lens 14
An auxiliary lens 2 that focuses the electron beam on the sample 17 is placed between the scanning coil 15 and the objective lens 16.
0 (indicated by a broken line).

When performing high-magnification observation using this scanning electron microscope, the auxiliary lens 20 is turned off (
), and the first and second focusing lenses 1
3.14, the sample 17 is irradiated with an electron beam using the objective lens 16. Since the distance between the objective lens 16 and the sample 17 is short, an image with good resolution can be obtained.
Even if the distance between the sample 17 and the sample 17 is short, since the observation is performed at a high magnification, the range over which the electron beam scans the sample 17 is small, so the observed image will not be distorted.

When performing low-magnification observation, as shown in FIG. 2, the excitation of the objective lens 16 is turned off or extremely weak (this state is shown by the broken line), and the auxiliary lens 20 (shown by the solid line) is used to collect electrons. The line is focused onto the sample 17 and scanned over the sample 17 by the scanning coil 15. The distance between the auxiliary lens 20 and the sample 17 in this case is considerably shorter than the distance between the second focusing lens 4 and the sample 7 in FIG.
The spherical aberration and chromatic aberration are reduced and the resolution is improved, but the distance between the auxiliary lens 20 and the sample 17 becomes considerably longer than in the case of high magnification using the objective lens 16, and the irradiation angle of the electron beam becomes smaller. Therefore, an image with less distortion can be obtained.

FIGS. 3 and 4 show an embodiment in which an auxiliary lens 20 is attached to the objective lens 16, which is close to the actual state. An objective lens excitation coil 19 is wound around the magnetic pole 18 of the objective lens 16 shown in FIG. 3. The magnetic pole 18 has an upper magnetic pole 18a and a lower magnetic pole 18b. and an auxiliary lens excitation coil 22 are attached.

An objective lens excitation coil 24 is wound around the magnetic pole 23 of the objective lens 16 shown in FIG. 4, and the magnetic pole 23 has an upper magnetic pole 23a and a lower magnetic pole 23b. and an auxiliary lens excitation coil 26. In the above embodiment, a part of the magnetic pole of the objective lens 16 is shared to form the auxiliary lens 20, but the auxiliary lens 20 can also be formed independently.

Note that when operating the auxiliary lens 20, the objective lens 1
Instead of turning off the lens 6 completely, it may be possible to excite it weaker than when it is used alone, change the excitation of the auxiliary lens 20, and thereby perform focusing. In addition, the auxiliary lens 20 is placed under the normal magnetic field strength, and the objective lens 1
6 may be excited weaker than when used alone, and the excitation may be changed to perform focusing.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain images with good resolution and little distortion at both high and low magnifications in a scanning electron microscope or the like. Moreover, when switching the magnification, only the objective lens and auxiliary lens are required.
It is only necessary to change the excitation, and there is no need to perform the troublesome operation of moving the position of the sample. Furthermore, the first and second
Since there is no need to change the excitation of the focusing lens, there is also the effect that the operation of the switching stop becomes extremely simple.

[Brief explanation of drawings]

Fig. 1 shows an embodiment of the present invention, a configuration diagram for high magnification observation, Fig. 2 shows the same as Fig. 1 but with a lower magnification, Fig. 3,
Figure 4 is a cross-sectional view of the objective lens with an auxiliary lens attached, showing a state close to the actual situation. Figure 5 is a configuration diagram of the case where a sample is moved up and down using the electron optical system of a conventional scanning electron microscope. Figure 6 is FIG. 2 is a configuration diagram of a conventional scanning electron microscope electron optical system in which a second focusing lens is used as an objective lens. 11... Electron gun (electron beam source) @1 Figure 2 Figure 2 15... Scanning coil 16... Objective lens 17... Sample 20... Auxiliary lens Patent applicant Akashi Beam Technology Co., Ltd.← 11

Claims (4)

[Claims] (1) Comprising an electron beam generation source, a focusing lens that focuses the electron beam from the source, an objective lens that focuses the electron beam on a sample, and a deflection means that scans the electron beam on the sample. An electron beam apparatus characterized in that an auxiliary lens for focusing an electron beam on a sample is provided between the focusing lens and the objective lens. (2) The electron beam device according to claim 1, wherein the electron beam device weakly excites the objective lens when using the auxiliary lens, and performs focusing by changing the excitation of the auxiliary lens. (3) The electron beam device according to claim 1, wherein the electron beam device performs focusing by changing the excitation of the objective lens with the objective lens in a weakly excited state when using the auxiliary lens. (4) The electron beam apparatus according to claim 1, wherein the electron beam apparatus sets the excitation of the objective lens to zero when using the auxiliary lens, and performs focusing by changing the excitation of the auxiliary lens.