JPH05128986A - Magnetic field type lens - Google Patents

Abstract

PURPOSE:To reduce power consumption and to make lens control easier. CONSTITUTION:A permanent magnet 10 and an electromagnetic coil 11 are set along an optical axis, and they are surrounded by a yoke 12 except for the parts of gaps G1 and G2. The yoke 12 forms a magnetic circuit common to the permanent magnet 10 and the electromagnetic coil 11, and lenses are formed at the positions of the gaps G1 and G2. Since the lenses are formed at the positions of the gaps G1 and G2 by the composits magnetic field of the magnetic fields by the permanent magnet 10 and the electromagnetic coil 11, the two lenses can be controlled simultaneously by regulating the direction and the amount of the exciting current fed to the electromagnetic coil 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a magnetic field type lens used in an irradiation system of an electron microscope.

[0002]

2. Description of the Related Art Conventionally, two electromagnetic lenses are generally used as an irradiation system lens of a transmission electron microscope (TEM) as shown in FIG. In FIG. 3, the first condenser lens CL ₁ is formed by the electromagnetic coil 1 and is mainly used for adjusting the spot size of the electron beam. The second condenser lens CL ₂ is formed by the electromagnetic coil 2 and is mainly used for adjusting the spread of the electron beam. In FIG. 3, reference numeral 3 is a sample, O is an optical axis, and the yokes of the electromagnetic coils 1 and 2 are omitted.

When observing an image at a low magnification,
In order to irradiate a wide range of the sample 3 with the electron beam and obtain brightness, the electromagnetic coil 1 is relatively weakly excited, and the electromagnetic coil 2 is
Is relatively strongly excited, and a converged state as shown in FIG. 4A is obtained. Further, when observing an image at a high magnification, the electromagnetic coil 1 is relatively strongly excited, and the electromagnetic coil 2 is compared in order to irradiate the electron beam in a narrow area of the sample 3 and to enhance the parallelism of the electron beam. Weakly excited, and a converged state as shown in FIG. 4B is obtained. 4A and 4B, 4 indicates an electron gun.

[0004]

[Problems to be Solved by the Invention] However, in the past,
As the irradiation system lens of the electron microscope is composed of all electromagnetic lenses as shown in FIG. 3, there is an advantage that each lens can be controlled independently, but the electromagnetic coils for forming each lens are respectively excited. It needs to supply an electric current and consumes a very large amount of power. Further, when observing an image, it is usually necessary to set the exciting currents to be supplied to the respective electromagnetic coils in association with each other. Therefore, not only is the operation troublesome, but the operation requires skill. However, if the operation is mistaken, there is a problem that the sample is irradiated with an excessive amount of electron beams and the sample is destroyed. This is especially noticeable when observing biological samples.

An object of the present invention is to solve the above problems, and an object thereof is to provide a magnetic field type lens capable of reducing power consumption and easily controlling the convergence condition. It is a thing.

[0006]

In order to achieve the above object, the magnetic field type lens of the present invention includes a permanent magnet, an electromagnetic coil, the permanent magnet and the electromagnetic coil which are arranged along the optical axis. It is characterized in that a common magnetic circuit is formed and a yoke having a gap at the position of the permanent magnet and the electromagnetic coil is provided.

[0007]

The lens is formed at the position of each gap. Since a magnetic field by a permanent magnet and a magnetic field by an electromagnetic coil are formed in each gap, each lens has a magnetic field by a permanent magnet and a magnetic field by an electromagnetic coil. It will be formed by the synthetic magnetic field. Therefore, the two lenses can be easily controlled simultaneously by adjusting only the exciting current supplied to the electromagnetic coil.

[0008]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an embodiment in which a magnetic field type lens according to the present invention is applied to an irradiation system lens of a TEM, in which 10 is a permanent magnet, 11 is an electromagnetic coil, and 12 is a yoke. The same components as those in FIG. 3 are designated by the same reference numerals.

In FIG. 1, the permanent magnet 10 and the electromagnetic coil 11 are arranged along the optical axis O.
The electromagnetic coil 11 is surrounded by a yoke 12 except for the gaps G ₁ and G ₂ . Therefore, the yoke 12 forms a common magnetic circuit for the permanent magnet 10 and the electromagnetic coil 11, and the lens is formed at the positions of the gaps G ₁ and G ₂ .

Next, a magnetic field formed by the permanent magnet 10 and the electromagnetic coil 11 along the optical axis O will be described. First, the magnetic fields formed by the permanent magnets 10 are formed in the mutually opposite bendability at the positions of the gaps G ₁ and G ₂ , as shown by the solid line in FIG. This magnetic field distribution changes the magnetic field strength from -∞ to + ∞
It has the property of becoming zero when integrated up to.

[0011] In contrast, the magnetic field generated by the electromagnetic coil 11, as indicated by the broken line in FIG. 2, the gap G ₁ in the same polarity,
It is formed at the position of G ₂ . In FIG. 2, the permanent magnet 10 and the electromagnetic coil 11 are omitted, and only the positions of the gaps G ₁ and G ₂ of the yoke 12 are shown.

Therefore, since the magnetic field strength of the lens formed at the positions of the gaps G ₁ and G ₂ is determined by the combined magnetic field of the magnetic field of the permanent magnet 10 and the magnetic field of the electromagnetic coil 11, the magnetic field supplied to the electromagnetic coil 12 is excited. The intensity of the two lenses can be controlled simultaneously by adjusting the direction and magnitude of the current. For example, when observing an image at a high magnification, an exciting current is supplied so that the magnetic field generated by the electromagnetic coil 11 at the position of the gap G ₁ is formed in the same direction as the magnetic field generated by the permanent magnet 10 as shown in FIG.
The state shown in FIG. 4B can be achieved by adjusting the size, and when the image is observed at a low magnification, the magnetic field generated by the electromagnetic coil 11 at the position of the gap G ₂ is shown in FIG. On the contrary, the state shown in FIG. 4A can be achieved by supplying the exciting current so as to be formed in the direction opposite to the magnetic field by the permanent magnet 10 and adjusting the magnitude thereof.

According to this structure, when one lens is strongly excited, the other lens is always weakly excited, and neither is weakly excited, and the sample is not irradiated with an excessive electron beam. , It does not destroy the sample.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. For example, in the above embodiment, the present invention is
The case where the present invention is applied to the EM irradiation system lens has been described, but it is needless to say that the present invention can be applied to various cases without being limited to this. Further, in the above-mentioned embodiment, the permanent magnet and the electromagnetic coil are arranged in this order along the optical axis, but it goes without saying that the reverse order is also possible.

[0015]

As is apparent from the above description, according to the present invention, since the permanent magnet and the electromagnetic coil are combined, the power consumption can be greatly reduced to 1/10 or less as compared with the conventional one. Not only that, the two lenses can be controlled simultaneously by simply adjusting the direction and magnitude of the exciting current supplied to the electromagnetic coil, so that the intensity and spread of the electron beam can be controlled simultaneously and continuously. .

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining a magnetic field distribution in the configuration of FIG.

FIG. 3 is a diagram showing a configuration example of an irradiation system lens of a conventional TEM.

FIG. 4 is a diagram showing a converged state of an electron beam at low magnification and high magnification.

[Explanation of symbols]

 10 ... Permanent magnet, 11 ... Electromagnetic coil, 12 ... Yoke.

Claims (1)

[Claims] 1. A permanent magnet arranged along an optical axis, an electromagnetic coil, a magnetic circuit common to the permanent magnet and the electromagnetic coil is formed, and a gap is formed between the permanent magnet and the electromagnetic coil. A magnetic field type lens comprising: a yoke.