JPH0736353U - Ex B type mass spectrometer - Google Patents

Abstract

(57) [Summary] [Purpose] A T-shaped magnetic body having a central pole piece having a coil wound around it to generate magnetic flux from magnetic poles is opposed to generate a magnetic field. X Uniform magnetic flux density in B-type mass spectrometer. [Configuration] By changing the thickness of the magnetic pole stepwise or continuously,
The gap between the poles is wide in the central portion and the gap between the poles is short in both ends so that the magnetic flux density in the longitudinal direction is uniform.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement in which the strength of a magnetic field is made constant in an E × B type mass spectrometer. The EXB type mass spectrometer is used for selecting ions in a treatment device for an object using an ion beam such as an ion irradiation device or a measuring device using ions. The ion irradiation device using ions converts the raw material gas into plasma, extracts this as an ion beam, and applies it to an object. If it is necessary to remove impurities such as ions, a mass spectrometer is required.

There are two types of mass spectrometry, one that uses only a magnetic field and the other that uses a magnetic field and an electric field. In the case of using only a magnetic field, a fan-shaped magnet is used to separate ions having different masses due to the difference in the half-diameters of the arc trajectories of ions traveling between them.

E × B type mass spectrometry uses orthogonal electric and magnetic fields. When an ion beam is passed through them so as to be orthogonal to them, only ions with a velocity of v = E / B can go straight through this. Since the ions are accelerated with the same energy, the velocity v is different if the mass is different. Therefore, mass spectrometry can be performed. It is also called a Wien filter. The E × B type device is lightweight and compact, and is used as a simple mass spectrometer. Since ion beams are selected by E / B, uniformity of magnetic field and electric field is required.

[0004]

[Prior art]

 An outline of an E × B type device according to a conventional example will be described with reference to FIG. A pair of electromagnet coils 1 are wound around a pair of magnetic pole pieces 2. A parallel flat plate-shaped magnetic body 3 is fixed to the tip of the pole piece 2 at a right angle thereto. The magnetic body 3 and the pole piece 2 may be integrally formed of a magnetic body made of the same material. It may be a separate body. In any case, it is necessary to reduce the resistance of the magnetic circuit. Make sure there is no space between them.

A magnetic field can be generated by a combination of the electromagnet coil 1, the pole piece 2 and the flat plate magnetic body 3 as described above. Two equivalent sets are made to face each other so that the flat plate-shaped magnetic body is flat. Make the current directions of the coils the same. The magnetic field lines are generated in the same direction. A magnetic field is generated between the two parallel magnetic bodies 3 and 3 at right angles to them. The flat plate magnetic body functions as a magnetic pole. The electric field is applied perpendicular to the magnetic field. The electrodes are provided at positions orthogonal to the parallel magnetic bodies 3 and 3, but the illustration of the electrodes is omitted here for simplicity.

A coordinate system is defined. The flight direction of the ion beam 5 is the Z axis. The direction of the magnetic field is the X axis, and the direction perpendicular to both axes is the Y axis. The coil is wound in the YZ plane. The facing surface of the flat plate magnetic body (magnetic pole) is parallel to the YZ plane. The electrodes are provided separately in the Y direction. The direction of the electric field is the Y-axis direction.

Since the parallel plate magnetic bodies (magnetic poles) are opposed to each other, a magnetic field in the X direction exists between them. There is an electric field E at right angles to this. The ion beam traveling in the Z direction receives an electrostatic force in the Y direction due to the electric field E. The magnetic field B also receives a force in the Y direction. If both forces are equal, you can go straight in the Z direction. Ion beams of the desired type pass through them in the Z direction, and other ion beams bend in the Y direction. Impurities can be removed depending on the orbit.

[0008]

[Problems to be solved by the device]

 It is the current in the coil that produces the magnetic field. This causes a magnetic field to be generated in the pole piece, but the magnetic flux spreads from the pole piece to the flat plate-shaped magnetic body 3 and the magnetic force lines emerge in the space. Since the two pole pieces 2 are excited in the same direction, lines of magnetic force perpendicular to this are formed between the flat plate-shaped magnetic bodies. However, the density of magnetic field lines is not uniform. Since there is only one pole piece at the center, the magnetic field B becomes large at the center of the magnetic body. The magnetic field becomes weak at the front and rear ends of the flat plate magnetic body.

In FIG. 1, arrows indicate magnetic lines of force. The magnetic field strength is strong at the center and weak at both ends, as indicated by the density of the arrows. The electric field and the magnetic field do not necessarily have to be constant in order to perform the E × B analysis accurately. The electric field and magnetic field strength distributions must correspond to each other within a certain range. The electric field is easily and uniformly formed by parallel plates. Therefore, in this case, it is necessary to form the magnetic field uniformly. In the parallel plate magnetic body as shown in Fig. 1, the magnetic field becomes non-uniform. Therefore, even if the ion has a desired mass, it cannot go straight through this device. On the contrary, it is possible that impurities pass through here. In other words, mass separation cannot be performed accurately and there are many ion losses. In order to prevent such drawbacks, it is an object of the present invention to provide an E × B type separation device that generates a magnetic field with high uniformity.

[0010]

[Means for Solving the Problems]

 In the EXB type mass spectrometer of the present invention, the thickness of the parallel magnetic body connected to the pole piece is changed to widen the distance between the parallel magnetic bodies (distance between the poles) at the central portion and near the ends. Reduce the distance between parallel magnetic bodies. A magnetic material with geometrical anisotropy is used as the magnetic pole instead of a flat plate. In the central part, the distance between the two magnetic poles is large, which has the effect of weakening the magnetic field. At the ends, the distance between the magnetic poles is close, so there is an action of strengthening the magnetic field. That is, the geometrical anisotropy of the magnetic pole tends to reduce the magnetic flux density at the center and increase the magnetic flux density at both ends.

[0011]

[Action]

 Since the pole piece is originally connected to the center of the parallel magnetic poles, the magnetic flux density is high in the center and low near both ends. In the present invention, the pole piece is located at the center, so that the tendency of the magnetic flux to be concentrated at the center is canceled by the geometrical anisotropy of the magnetic pole. Due to the non-uniformity of the magnetic field caused by the pole piece, the magnetic field fluctuation due to the change in the thickness of the parallel magnetic poles is canceled out. The preferred magnetic pole thickness distribution is determined by calculation or by experiment. The magnetic pole thickness may be changed stepwise or continuously. The distance between the poles is wide at the center and short between the edges.

[0012]

【Example】

 FIG. 2 is a schematic view of an E × B type device according to an embodiment of the present invention. Two electromagnet coils 1 are wound around a pole piece 2 which is two magnetic bodies. The two pole pieces 2 and 2 are on the same straight line. Magnetic poles 4 and 4 of a magnetic material are connected to the inner end of the pole piece 2. The pole piece 2 and the magnetic pole 4 may be integrally formed of the same magnetic material. Alternatively, a separate magnetic body may be joined.

In order to reduce the loss due to the eddy current, it is effective to stack a plurality of thin silicon steel sheets having the same shape including the pole pieces and the magnetic poles to form a core. The pole pieces 2 and 2 are magnetically coupled by a magnetic ring 6 on the back. The magnetic lines of force pass from the pole piece 2 through the magnetic ring 6, enter behind the other pole piece 2, and emerge from the parallel magnetic poles 4 into the space. This becomes the magnetic flux in the X direction. After passing through the space, the magnetic flux enters the other magnetic pole 4. In such a magnetic circuit, the magnetic resistance is low because most of the paths are made of magnetic material.

The magnetic pole 4 is not a flat plate, but its thickness changes stepwise. It becomes thinner at the center and thicker at both ends. In this example, the thickness is changed in four steps, but more changes may be given. Further, in this example, the back surface of the magnetic pole is a flat surface, but the back surface may be changed in a stepwise manner.

In this way, the distance between the opposing magnetic poles is long at the center and short at both ends. In the central part where the distance is long, the magnetic flux density in space decreases. The magnetic flux density in the space increases at both ends where the distance is short. The magnetic flux density is originally high in the central part near the pole piece, but the magnetic flux density here decreases due to the wide gap. Since both tendencies cancel each other out, the magnetic flux density becomes constant in the traveling direction of the beam. Arrows indicate magnetic field lines. The density of the arrow indicates the magnetic flux density. It means that it is uniform in the traveling direction.

The traveling direction of the beam is the Z axis, and the direction of the pole piece is the X axis direction. The origin O is the intersection of the pole piece center line and the Z axis. The inter-electrode distance W is W (z) as a function of z. Since it is symmetrical about the Y axis, W (−z) = W (z). In the example of FIG. 2, since a step-like one is shown,

0 ≦ z <Z ₁ W (z) = D ₁ Z ₁ ≦ z <Z ₂ W (z) = D ₂ Z ₂ ≦ z <Z ₃ W (z) = D ₃ Z ₃ ≦ z <Z ₄ W (z) = D ₄ D ₄ <D ₃ <D ₂ <D ₁

It is as follows. There are four levels, but three, five or more levels may be used. Alternatively, the magnetic pole may be formed by an inclined surface and the thickness may be continuously changed. That is, W (−z) = W (z), and in the positive range

W (z) = K-Hz (H, K: constant) may be set. Furthermore, the facing surface of the magnetic pole may be determined by a quadratic curve.

W (z) = J−Lz ² (J, L: constant) The distance between the poles is directly related to the height M (z) of the facing surface of the magnetic poles.

From 2M (z) + W (z) = constant, the surface shape of the magnetic pole can be determined from W (z).

FIG. 3 shows the distribution of the magnetic flux density B in the traveling direction of the beam. The horizontal axis is the Z direction. The broken line is due to the flat magnetic pole as shown in FIG. The magnetic flux density is large at the center but small at the edges. The magnetic flux density is not uniform. The solid line indicates the embodiment of the present invention. It is constant up to near the edges. The present invention can make the magnetic flux density constant in the traveling direction of the beam.

[0023]

According to the present invention, in the E × B type separation device, the magnetic poles are made thin at the center and thick at both ends, and the distance between the magnetic poles is changed to make the magnetic flux density constant in the longitudinal direction of the magnetic poles. The geometrical peculiarities of the magnetic poles counteract the non-uniformity of the magnetic field due to the pole piece connecting only to the center of the magnetic pole. For this reason, in the E × B type separation device, an ion beam having a desired mass can be accurately moved straight, and an ion beam having a mass other than that can be bent. The accuracy of mass spectrometry is improved. It is optimal as an ion irradiation device, an ion source for measuring instruments that use ions, and a lightweight and compact mass spectrometer placed in the middle of the beam transport system.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a magnetic field generation unit of an E × B type mass spectrometer according to a conventional example.

FIG. 2 is a schematic sectional view of a magnetic field generating portion of the E × B type mass spectrometer of the present invention.

FIG. 3 is a distribution of magnetic flux density in the longitudinal direction of magnetic poles.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 electromagnet coil 2 pole pieces 3 flat plate parallel magnetic poles 4 step parallel magnetic poles 5 ion beam 6 magnetic ring

Claims (1)

[Scope of utility model registration request] 1. An apparatus for mass spectrometric analysis by changing a trajectory of an ion beam incident from a direction perpendicular to a uniform electrostatic field E and a static magnetic field B applied thereto at a right angle. , An electromagnetic coil including two magnetic poles facing each other and having a longitudinally varying gap, a pole piece of a magnetic body continuous at a right angle to the center of the magnetic pole, and an electromagnetic coil wound around the pole piece. A magnetic field is generated by passing a current through the magnetic poles so that the different poles face each other between the magnetic poles. The magnetic poles have a wide gap at the portion connected to the pole piece and a narrow gap at both ends. An E × B-type mass spectrometer characterized in that the magnetic field in the longitudinal direction is uniform.