JPH02213024A - Ion source - Google Patents

Abstract

PURPOSE:To improve ionization efficiency in simple structure without adding a new power source by providing a Wehnelt electrode arranged on the rear part of a plasma production chamber and an anode provided between the Wehnelt electrode and the plasma production chamber. CONSTITUTION:A first electron beam 10 projected into a plasma production chamber 15 passes through a second anode 6 and is injected into a second Wehnelt 7, which is electrically insulated and thus whose electric potential is enhanced according to the incidence of the first electron beam 10. When the electric potential of the second Wehnelt 7 is enhanced and approaches that of a cathode 1, plasma is generated in a second plasma production region 13 in the Wehnelt 7. Discharge does not occur in other region than in the Wehnelt 7 and in the anode 6 by means of a shield electrode 8. A plasma electron gun is formed, whose cathode surface is the generated plasma, whereby an electron is extracted by the difference between the electric potential of the Wehnelt 7 and of the anode 6, and is accelerated and injected into the plasma production chamber 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to ion sources, and more particularly to electron beam excited ion sources.

[Conventional technology]

Conventionally, there is an electron beam-excited ion source as an ion source that generates plasma and obtains an ion beam through the interaction of an electron beam and an ionized substance ([Patent Publication (A)]
This ion source uses the same electric field to generate and accelerate an electron beam, as well as extract and accelerate an ion beam. In order to increase the ion production rate, it is necessary to increase the electron beam current, but in order to obtain a large amount of electron beam current, it is necessary to increase the electron beam acceleration voltage, and it is also necessary to increase the practical current from the plasma. In order to extract a large amount of ions, it is desirable that the extraction voltage be high.

Therefore, the accelerating voltage of the electron beam needs to be at least several KV.

[Problem to be solved by the invention]

In order to ionize an ionized substance by the impact ionization effect of an electron beam, the ionization efficiency is often highest when the energy of the electron beam is several hundred eV, although it depends on the type of the ionized substance. However, for the reasons mentioned above, in electron beam excited ion sources, the accelerating voltage of the electron beam is at least several KV, so the ionization efficiency of the ionized substance is relatively low, and therefore it is difficult to obtain a large amount of ion beam current. There were drawbacks.

The purpose of the present invention is to eliminate such drawbacks, increase ionization efficiency with a relatively simple configuration without adding a new power source, and
An object of the present invention is to provide an electron beam-excited ion source that can obtain a relatively large current.

[Means to solve the problem]

The configuration of the present invention includes an electron gun having a cathode with a pore in the center, and a plasma generation chamber into which the electron beam emitted from the electron gun enters and generates plasma. An electron beam-excited ion source has a structure in which an ion beam extracted from the plasma flows backward through the path of the electron beam and is ejected from the pores of the cathode. a Wehnelt electrode that is electrically insulated and has a hole that extends therein; an anode that is provided between the Wehnelt electrode and the plasma generation chamber; and a shield electrode that is kept at the same potential as the anode and surrounds the Wehnelt electrode. It is characterized by having

[Effect]

In the configuration of the ion source of the present invention, when the electron beam is incident on the Wehnelt electrode electrically insulated at the rear of the plasma generation chamber, the Wehnelt tvfl becomes a floating potential, and a discharge occurs due to the potential difference between the Wehnelt electrode and the anode. A plasma is then generated within the Wehnelt electrode. Therefore, a plasma electron gun is formed using this plasma as a cathode, and the electron beam generated by this plasma electron gun enters the plasma generation chamber and participates in ionization, increasing the t-separation rate within the plasma generation chamber and increasing the ion current. can be increased. In addition, since the electron beam of the plasma electron gun has relatively high energy, it can reach the vicinity of the ion extraction electrode, increasing the number of space charges in ion extraction, and extracting even more ions. be able to.

〔Example〕

Next, the present invention will be explained in detail using the drawings.

FIG. 1 is a sectional view schematically showing an embodiment of the present invention. The cathode 1 having a pore (not shown) in the center is a directly heated ribbon filament made of W. The thermoelectrons generated by heating this cathode 1 are
The potential difference between the acceleration voltage formed by the first Wehnelt 2 and applied to the cathode 1 by the acceleration power source 17 and the extraction voltage applied to the extraction voltages 11!3 by the extraction power source 16, and the first anode 4 and The electron beam is accelerated by two steps due to the potential difference with the extraction electrode 3, and further focused by the electromagnetic lens 5, and enters the plasma generation chamber 15 as the first electron beam 10.

At this time, the ionized substance introduced as a gas from the ionized substance introduction port 9 (hereinafter referred to as ionized gas) is collided with 11 and separated by the first electron beam 10 to generate plasma in the first plasma generation region 14.

The first electron beam 10 entering the plasma generation chamber 15 passes through the second anode 6 and enters the second Wehnelt 7 . Since this Wehnelt 7 is electrically insulated, its potential increases according to the amount of incidence of the first electron beam 1o.

When the potential of the second Wehnelt 7 increases and approaches the potential of the cathode 1, the second anode 6 uses the ionized gas as a medium.
A discharge occurs between the two and a plasma is generated in the second plasma generation region 13 within the Wehnelt 7. shield electric w18
prevents discharge from occurring in areas other than Wehnelt 7 and anode 6. Therefore, a plasma electron gun is formed with the plasma generated here as the cathode surface, and the Wehnelt 7
Electrons are extracted by the potential difference between the anode 6 and the anode 6, are accelerated, and enter the plasma generation chamber 15.

In the present invention, since the energy of the first electron beam 10 is used to provide a potential when forming the plasma electron gun, a special power source for forming the plasma electron gun is not required.

The second electron beam 11 incident on the plasma generation chamber 15 also participates in ionization in the plasma generation chamber 15, so that the ionization efficiency can be increased. The energy of the second electron beam 11 is determined by the potential of the Wehnelt 7, and since this potential is close to the potential of the cathode 1, it has a relatively high energy.
Therefore, the second electron beam 11 can reach the vicinity of the extraction electrode 3.

The ion beam 12 is formed by ions generated in the first plasma generation region 14 being extracted according to the electric field created by the extraction electrode 3 and the first anode 4. However, the second electron beam 11 is formed near the extraction electrode 3. By being present in , the space charge of ions is relaxed, the space charge relaxation coefficient in ion extraction is increased, and a larger amount of ions can be extracted.

〔Effect of the invention〕

As described above, according to the present invention, ionization efficiency can be increased by adding an electrode with a relatively simple structure that does not require a power source to a conventional electron beam-excited ion source. Since the space charge can be relaxed, a larger amount of ion current can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing an embodiment of the present invention. 1... cathode, 2... first Wehnelt, 3...
- Extraction electrode, 4... First anode, 5... Electromagnetic lens, 6... Anode B, 7... Second Wehnelt, 8... Shield electrode, 9... Ionized substance introduction mouth, 10... first electron beam, 11... second electron beam, 12... ion beam, 13... first plasma generation region, 14... second plasma generation region , 15... plasma generation chamber, 16... drawer power supply,
17... Acceleration power supply, 18... Bias power supply, 19.
...Insulated tube.

Claims (1)

[Claims] an electron gun having a cathode with a pore in the center;
It consists of a plasma generation chamber into which an electron beam emitted from the electron gun enters and generates plasma, and an ion beam extracted from the plasma in this plasma generation chamber flows backward along the path of the electron beam and reaches the narrow end of the cathode. In an electron beam-excited ion source having a structure in which the electron beam is emitted from a hole, an electrically insulated Wehnelt electrode is arranged at the rear of the plasma generation chamber and has a hole through which the electron beam is incident, and the Wehnelt electrode and the plasma generation An ion source comprising: an anode provided between a chamber and a shield electrode that is kept at the same potential as the anode and surrounds the Wehnelt electrode.