JPS6314814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for observing a sample with an electron microscope by applying a magnetic field along the surface of the sample.

In order to investigate the magnetic domain structure, etc., samples are observed with an electron microscope while a magnetic field is applied along the sample surface. Conventionally, the magnetic field application device for this purpose has the configuration shown in Figure 1. Ta.

In FIG. 1, reference numeral 1 designates a first magnetic pole for generating a magnetic field in a direction perpendicular to the plane of the paper and applying the magnetic field to the sample 2 along its surface. A magnetic pole 3 is arranged at a certain distance l from the first magnetic pole 1, and a magnetic pole 4 is arranged at a further distance l. 5 is an objective lens.

Now, if there is no magnetic field of the first magnetic pole for applying a magnetic field to the sample, the electron beam passing through the tip of sample 2 indicated by the arrow will take a trajectory as indicated by the dotted line in the same figure. A transmission image and a diffraction image are formed at the positions indicated by 7, respectively. However, if there is a magnetic field to apply a magnetic field to sample 2,
Because the electron beam transmitted through the sample 2 is deflected by a certain angle α due to this magnetic field, the transmitted image and the diffraction image will not be formed at the positions indicated by 6 and 7, but at the optical axis 8. The images will be greatly shifted in the right angle direction, making it impossible to observe these images. The second and third magnetic poles 3 and 4 are arranged to avoid such a situation. That is, as is clear from the ray diagram indicated by the thin line in FIG. If we pay attention to the electron beam that is supposed to travel in the direction forming the angle (expressed by adding a + sign), we find that
As shown by the thin line A, this electron beam is deflected by an angle α by the magnetic field of the first magnetic pole 1, so it travels in the direction of the optical axis 8, and is deflected by an angle −2α by the second magnetic pole 3 to the third is deflected by an angle α by the magnetic pole 4 of the first magnetic pole 4, and travels along the dotted line in the same direction as when there is no magnetic field of the first magnetic pole 1. Therefore, it can be seen that the transmitted image is formed at the position indicated by 6. Next, in order to investigate the position of the diffraction image, we pay attention to the so-called straight beam that does not change its traveling direction at all when passing through the sample 2 unless the magnetic field of the first magnetic pole 1 exists. 1, the magnetic field of the first magnetic pole 1 deflects an angle α, the second magnetic pole 3 deflects an angle −2α, and the third magnetic pole 4 deflects an angle α. As a result, it is incident on the objective lens 5 parallel to the optical axis 8, and the first beam shown by the dotted line
It progresses through the same trajectory as in the absence of the magnetic field of magnetic pole 1. Therefore, it can be seen that a diffraction image is also formed at position 7.

However, in such conventional devices,
In addition to the first magnetic pole 1, second and third magnetic poles 3 and 4 must be placed between the sample 2 and the objective lens 5, so the distance between the sample 2 and the objective lens 5 becomes large. Compared to the case of observing a sample without applying a magnetic field, the magnification decreases and the spherical aberration coefficient and chromatic aberration coefficient increase.

The present invention solves the drawbacks of such conventional devices,
The purpose of this device is to provide a magnetic field application device for an electron microscope that is improved in terms of magnification and aberrations, and uses a magnetic field application device between a magnetic field application device for applying a magnetic field to a sample and an objective lens. A first deflection means for deflecting the electron beam deflected by angle α by angle α is arranged, and an objective lens is disposed between the imaging position of the diffraction image and the imaging position of the transmission image after the objective lens. a second deflection for moving the image formation position of the transmission image formed by the optical axis in a direction perpendicular to the optical axis so as to match the image formation position when the magnetic field application means and the first deflection means do not operate; It is characterized by having the means.

Hereinafter, one embodiment of the present invention will be described in detail based on FIG. 2, and the same parts in FIG. 2 as in FIG. 1 are given the same numbers.

In Fig. 2, the difference from the conventional one is that only a second magnetic pole 9 is arranged between the first magnetic pole 1 and the objective lens 5, and this second magnetic pole 9 is passed through the sample 1 by the first magnetic pole. The deflection angle that the electron beam receives is the angle α
, a diffraction image is formed at the point where the third magnetic pole 10 generates a magnetic field that deflects the electron beam by an angle α (deflects −α), and the third magnetic pole 10 forms a diffraction image after the objective lens 5. The magnetic field formed by the third magnetic pole 10 changes the imaging position of the transmitted image formed by passing through the objective lens. The point is that a magnetic field is generated to move the optical axis 8 in a direction perpendicular to the optical axis 8 so that the first magnetic pole 1 and the second magnetic pole 9 coincide with the imaging position when they are not operated.

In an apparatus having such a configuration, first, positions where a transmission image and a diffraction image are formed when no magnetic field is applied to the sample are determined. Therefore, when considering the optical path of the electron beam traveling in a direction parallel to the optical axis 8 from the tip of the sample 2, it becomes as shown by the dotted line D. Similarly, if we consider the optical path of the electron beam traveling from the tip of the sample 2 in a direction passing through the center of the objective lens 5, it becomes as shown by the dotted line C. Therefore, from the position of the intersection of dotted lines D and C,
It is clear that when no magnetic field is applied to the sample, a transmission image is formed as shown at 11 in FIG. In addition, since the diffraction image is formed on the back focal plane of the objective lens, the optical path of the beam indicated by the dotted line D, which indicates the optical path of the electron beam traveling from the tip of the sample 2 in a direction parallel to the optical axis 8, is aligned with the optical axis. It can be determined by finding the position where it intersects with 8. From this, it is clear that the diffraction image is formed at the position indicated by 12 in the figure. Note that the dotted line H in FIG. 2 is shown because it is necessary for the explanation that will be given later.
It shows the optical path of an electron beam traveling from the tip in a direction forming an angle -α with respect to the optical axis 8. Next, due to the action of the second magnetic pole 9 and the third magnetic pole 10, the positions of the transmission image and the diffraction image become the positions indicated by 11 and 12 despite the presence of the magnetic field of the first magnetic pole 1. Explain that.

When the electron beam passing through the sample 2 passes through the tip of the sample 2 (the tip of the arrow) and the sample is observed without applying a magnetic field, the electron beam should be at an angle of - to the optical axis 8 as shown by the dotted line H. Focusing on the electron beam traveling in the direction α, this electron beam is deflected by the angle α by the magnetic field of the first magnetic pole 1, so it is actually parallel to the optical axis 8 as shown by the thin line in FIG. and is deflected by an angle −α by the second magnetic pole 9,
After passing through the objective lens 5, the beam is deflected by an angle β by the third magnetic pole 10 and proceeds. Also, when observing sample 2 without applying a magnetic field, we note that the electron beam does not receive any deflection when passing through sample 2 and takes a trajectory like the dotted line D. When a magnetic field is applied to sample 2, this electron beam is deflected by the angle α by the magnetic field of the first magnetic pole 1, deflected back by the angle α by the second magnetic pole 9, and after passing through the objective lens 5, the third magnetic pole is deflected by the angle α.
It is deflected by an angle β by the magnetic pole 10, and travels while taking a trajectory as shown by the thin line D. Trajectory portions A and D indicated by dashed-dotted lines indicate the trajectories H and G would take, respectively, in the absence of the magnetic field of the third magnetic pole 10, and 11' indicates the sample image formed in that case. As can be seen from this figure, the position of the sample image formed by the objective lens 5 is moved in the direction perpendicular to the optical axis by the magnetic field of the third magnetic pole 10.
Matches 1. Therefore, even when a magnetic field is applied to sample 2, it is clear that the positions of the diffraction image and transmission image coincide with images 11 and 12 when no magnetic field is applied, and it is clear that the positions of the diffraction image and transmission image match those of images 11 and 12 when a magnetic field is applied to the sample. It can be observed.

In the apparatus based on the present invention described above, only one magnetic pole is disposed between the magnetic pole for applying a magnetic field to the sample and the objective lens to eliminate the effect of deflection of the electron beam due to this magnetic field. , the distance a′ between the sample and the objective lens is the distance a in the conventional device.
It can be made smaller. Therefore, since the distance b between the objective lens 5 and the transmitted image is usually fixed as a size specific to the device, the observation magnification M'=b/a' of the device in the present invention is the same as the observation magnification M=b/a in the conventional device. You can make it bigger.

Additionally, as the focal length of the objective lens becomes smaller than in the case of conventional devices, the magnetomotive force of the objective lens must be increased compared to the conventional device, which reduces the spherical aberration coefficient and chromatic aberration coefficient. can be made smaller.

Note that the above-described embodiment is only one embodiment of the present invention, and other embodiments may be adopted when implementing the present invention. For example, two stages of electrostatic deflection type deflection means may be used in place of the second and third magnetic poles in the above embodiment.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a conventional device,
FIG. 2 is a diagram for explaining one embodiment of the present invention. 1... First magnetic pole, 2... Sample, 3... Second magnetic pole,
4... Third magnetic pole, 5... Objective lens, 6... Transmitted image,
7... Diffraction image, 8... Optical axis, 9... Second magnetic pole, 10...
Third magnetic pole, 11...Transmission image, 11'...Transmission image, 1
2...Diffraction image.

Claims (1)

[Claims] 1 A magnetic field applying means 1 for applying a magnetic field along the sample surface, and a magnetic field applying means 1 arranged between the magnetic field applying means 1 and the objective lens 5, transmitting through the sample 2 and being deflected by the angle α by the magnetic field applying means 1. a first deflecting means 9 for deflecting the electron beam by an angle α; and a first deflection means 9 for deflecting the electron beam by an angle α; a second deflection means 10 for moving the image in a direction perpendicular to the optical axis 8 so that the image formation position coincides with the image formation position 11 when the magnetic field application means 1 and the first deflection means 9 are not operated; A magnetic field application device for an electron microscope, comprising: