JP2834147B2 - Method of forming charged particle beam - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for forming a charged particle beam. More specifically, the present invention relates to a method for forming a charged particle beam composed of an electron beam and / or an ion beam, which enables extraction of an electron beam, which has been difficult so far, and an apparatus therefor.

(Background Art) In recent years, as a charged particle beam forming device has been developed, a technology that uses a charged particle beam and has a long life capable of stably supplying a large current electron beam or ion beam has been required. However, since the conventional charged particle beam forming apparatus uses a metal filament as a charged particle source, it is impossible to meet the above-mentioned demands.

On the other hand, an ion source using a plasma cathode has been proposed (Tokai University, Faculty of Engineering, Vo1.26, No.2, p.115,
1986). In this ion source, arc discharge is performed using a plasma cathode in an ion source container to form highly ionized and high-density plasma, and the plasma is extracted by applying a voltage.

Although the proposal of this ion source is important for the future charged particle beam technology, the charged particles that can be extracted from this ion source are limited to ions, and have the drawback that electrons cannot be extracted. This is because electrons are strongly captured by the magnetic field and cannot be extracted simply by applying an extraction voltage.

Although the service life of this ion source is longer than that using a conventional metal filament, a high-density plasma is generated by arc discharge.
In the case of / cm ² it is only 90 hours.

For this reason, this ion source cannot be used as an electron beam forming device at all, and the ion source does not have a sufficient life to meet future demands.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and it is possible to extract an electron beam, form a high-current charged particle beam, and extend the life. It is an object of the present invention to provide a new method of forming a charged particle beam and a device therefor.

DISCLOSURE OF THE INVENTION In order to achieve the above object, the present invention generates plasma in a multipolar magnetic field by electron cyclotron resonance discharge, superimposes a multipolar electric field, and draws plasma out of a discharge space by an electromagnetic field drift. A method for forming a charged particle beam is provided.

Further, as an apparatus for implementing the method of forming a charged particle beam, the apparatus has a multi-pole magnetic field for generating plasma by electron cyclotron resonance discharge and an electric field superimposed on this magnetic field, and converts the plasma generated in the multi-pole magnetic field to an electromagnetic field. Provided is a charged particle beam forming apparatus characterized in that the charged particle beam is drawn out of a discharge space by field drift.

The electron cyclotron resonance discharge method employed in the present invention is a method of forming plasma as an electrodeless discharge. That is, in the space of the magnetic field configuration satisfying the electron cyclotron resonance condition f = eB / 2πm (where f is the frequency of the electromagnetic wave used, m is the mass of the electron, e is the electric charge, and B is the magnetic flux density), the frequency f To generate plasma. For example, when f = 2.45 GHz and B = 875 gauss, this resonance condition is satisfied.

Plasma generated by this electron cyclotron resonance discharge is
Ion beam sources have already been used for publicity such as semiconductor etching, surface treatment, and multiply charged ion sources, and it has been demonstrated that the lifetime of the ion beam source is infinite.

The present invention is characterized in that plasma is generated in a multi-pole magnetic field by the electron cyclotron resonance discharge, and a multi-pole electric field is superimposed on the magnetic field.

For example, a multi-pole electric field is superimposed on a multi-pole magnetic field such as four poles or six poles.

FIG. 1 shows the relationship between the magnetic field and the plasma for an example of a quadrupole magnetic field. Electrons in the plasma (2) generated in the quadrupole magnetic field (1) are strongly captured by the lines of magnetic force and cannot be normally extracted, but in order to enable this, an electric field is superimposed on the magnetic field and the electromagnetic field ( E × B) Drift motion. As a result, not only ions but also electrons can be extracted in the same direction at the speed of E / B.

To increase the drift speed, a multi-pole electric field is applied to the magnetic field. For example, as shown in FIG. 2, a quadrupole magnetic field (1) is made orthogonal to a quadrupole electric field (3). Particles constituting the plasma drift from the back of the paper to the front in a direction perpendicular to the paper.

As described above, in the present invention, both electrons and ions are extracted from the plasma, and the extracted electrons and ions can be separated by utilizing the difference in charge and mass. Therefore, in the present invention, an electron beam or an ion beam can be separated and formed by using a magnetic field or an electric field applying means with respect to plasma in which electrons and ions drawn out of the discharge space are mixed. FIG. 3 shows an example in which an electron beam (5) and an ion beam (6) are separated and formed by using a magnetic field applying means (4).

For example, when an electron beam is formed by using a device in which a quadrupole electric field is superimposed on the electron cyclotron resonance discharge device having a quadrupole magnetic field shown in FIG. 2, a magnetic field of 2.45 GHz is set as an operating condition of the electron cyclotron resonance discharge device. And microwave, electron density 2 × 10 ¹⁰ cm ^-3 , electron temperature 5e
Plasma of about V can be easily generated. In this case, an electron beam of 100 mA · cm ⁻² is obtained.

An electron density of about 5 × 10 ⁹ to 1 × 10 ¹² cm ⁻³ can be easily realized.

(Effects of the Invention) According to the present invention, plasma is generated in a multipole magnetic field by electron cyclotron resonance discharge, and the plasma is used as a charged particle beam source, so that highly ionized and high-density plasma can be generated. Its generation life is extremely long. Further, according to the present invention, the generated plasma is extracted to the outside of the discharge space by the E × B drift, so that not only ions but also electrons can be extracted.

[Brief description of the drawings]

FIG. 1 is a front view showing a positional relationship between a quadrupole magnetic field and plasma generated therein. FIG. 2 is a front view showing a superposed quadrupole magnetic field and quadrupole electric field. FIG. 3 is a perspective view when an electron beam and an ion beam are separated and formed. DESCRIPTION OF SYMBOLS 1 ... Multi-pole magnetic field, 2 ... Plasma 3 ... Multi-pole electric field, 4 ... Magnetic field applying means 5 ... Electron beam, 6 ... Ion beam

Claims (2)

(57) [Claims] 1. A method for forming a charged particle beam, comprising generating plasma in a multi-pole magnetic field by electron cyclotron resonance discharge, superposing a multi-pole electric field, and extracting re-plasma out of a discharge space by an electromagnetic field drift. . 2. The method for forming a charged particle beam according to claim 1, wherein a magnetic field or an electric field is applied to the plasma drawn out of the discharge space to separate and form an electron beam and an ion beam.