JPH0720838Y2 - Ion source - Google Patents

Description

[Detailed description of the device] [Industrial applications]

The present invention relates to an ion source for confining plasma by a cusp magnetic field, which has a high electron confinement efficiency.

[Prior art]

A bucket-type ion source configured to confine plasma by a cusp magnetic field basically has the following structure. Anode chamber consisting of cylindrical part and lid plate, cathode filament for generating thermoelectrons Permanent magnets provided on the outer periphery of the anode chamber to generate cusp magnetic fields inside the anode chamber with alternating polarities, anode An arc power supply that causes arc discharge by supplying a voltage with the chamber positive and the cathode filament negative, a power supply for heating the filament of the cathode filament, a plasma electrode provided at the outlet of the anode chamber for extracting the ion beam to the outside . To generate an ion beam with such a configuration, the following is performed. A gas composed of an element to be ionized or a gas containing the element is introduced into the vacuumed vacuum arc chamber. The cathode filament is heated and a voltage is applied between the cathode filament and the arc chamber. When the cathode filament becomes hot, thermoelectrons are generated. The thermoelectrons are accelerated by the voltage applied between the cathode filament and the arc chamber, collide with neutral atoms and molecules in the gas and ionize them. Ions and electrons are generated, which are heated again to ionize other neutral molecules. In this way, arc discharge is generated. Plasma is generated by the arc discharge. Since a large number of permanent magnets are arranged to form a cusp magnetic field, charged particles are confined by the cusp magnetic field and therefore hardly contact the wall surface of the arc chamber.

[Problems to be solved by the device]

When ionizing an element that is originally in a gaseous state, such a bucket type ion source can sufficiently ionize the element. However, there is a demand to obtain a metal ion beam that is solid at room temperature. For example, metal ions may be implanted as impurities in the semiconductor manufacturing process. For example, suppose you want to obtain ions of metals such as Al, Cr, Si, and Ti. These solids are heated by another evaporation source to form metal vapor and introduced into this ion source in a gaseous state. Then, the metal atoms are ionized by the arc discharge. This should be good, but not always enough. Because it vaporizes what is solid at room temperature,
The inside of the arc chamber must be kept at a higher temperature than in the case of targeting a gas at room temperature. Therefore, it is conceivable to enhance the cathode filament to increase the radiant energy from this filament. Further, in order to reduce heat dissipation, it may be possible to provide a lining such as Ta or W inside the arc chamber. Radiant energy is reflected by the metal lining to keep the inside high heat. But this is still not enough. It is desired that there be another heat generating mechanism in the arc chamber. Although there are different purposes, some arc chambers are provided with something other than the above-mentioned cathode filament. (Japanese Patent Application No. 63-326433, S63.12.23) In order to improve the confinement of electrons, an anode wire having an anode potential is provided at the cusp portion, which is a break in the cusp magnetic field.

[Means for Solving the Problems]

In order to further increase the temperature inside the arc chamber, another set of filaments is provided as a heating element other than the cathode filament. This is at the same potential as the anode chamber. Therefore, it is called an anode filament here.
The amount of heat generated is increased by energizing the anode filament to keep the metal vapor at a higher temperature. Further, the anode filament is set in the region where the cusp magnetic field exists. That is, the anode filament is located near the wall surface of the anode chamber and at an intermediate position between the adjacent magnets.

[Action]

Since the anode filament is energized to heat the anode filament, the amount of heat generated is increased, and the vapor state can be maintained even with metal vapor. When the cathode filament is heated, thermoelectrons are generated, ionizing gas molecules and converting them into plasma. Since electrons and positive ions are charged particles, they are confined by the cusp magnetic field created by the permanent magnet, and the plasma density becomes sufficient. The electrons collide with the arc chamber wall at the cusp portion corresponding to the break of the cusp magnetic field, so that they disappear here. Since the positive ions are separated from the wall of the arc chamber by an electrostatic force, it is only the cusp portion where electrons can exist that disappear by colliding with the wall of the arc chamber. Now, with the newly installed anode filament, this has only the function of heating. Of course, thermoelectrons may be emitted, but since they are at the anode potential, they are reabsorbed. The question is whether the anode filament will absorb the electrons present in the plasma. If the anode filament absorbs the electrons, the electron confinement efficiency becomes low. High density plasma cannot be maintained. However, this is not a concern. The anode filament is in the cusp field created by the magnet. Therefore, the plasma does not come close to the anode filament. The electrons also come very close to the anode filament. Therefore, the probability of electrons colliding with the anode filament is low. Therefore, in the present invention, the high-density plasma can be maintained without impairing the electron confinement efficiency despite the presence of the anode filament.

【Example】

Embodiments will be described with reference to the drawings. FIG. 1 is a central longitudinal sectional view of an ion source according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG. The arc chamber 1 includes a cylindrical portion 10 and a cover plate 11. The cylindrical portion 10 is made of Cu, Al, stainless steel or the like. It has flanges 12 and 13 on both sides. One flange 12 has a lid plate 11
Is fixed. There is also a case where the both are directly contacted with each other and the cover plate 11 is also set to the anode potential. In this case, it is necessary to insulate the lining 4 from the anode potential. Also, an insulating member may be interposed between the two to insulate them. In this case, the potential of the lid plate can be set independently of the anode potential. Also the lid plate
Made of Cu, Al and stainless steel. Since the arc chamber 1 is heated, it has a structure (not shown) for cooling it by passing cooling water around it. A plurality of permanent magnets 2 having a magnetization direction in the radial direction are provided on the outer periphery of the cylindrical portion 10 of the arc chamber 1. These permanent magnets are arranged so that the magnetization directions thereof are alternately opposite to each other. Therefore, a magnetic field existing only near the wall surface is created inside the arc chamber. Since the magnetization directions are different between the adjacent magnets, the magnetic field does not reach far away. A strong magnetic field is created only near the magnet. When the lines of magnetic force are drawn, it becomes a curve that connects adjacent magnets. This curve is called a cusp (cusp) magnetic field because it creates a sharp portion on the end face of the magnet. When the charged particles come to the part where the cusp magnetic field exists, they receive the Lorentz force by the magnetic field and make a half rotation back to the original. Therefore, it cannot effectively enter the cusp magnetic field. The star-shaped region in the center of the arc chamber is the part where there is almost no magnetic field. This is the region where plasma exists. The end face magnetic flux density of the permanent magnet is, for example, 5000 Gauss
It is ~ 10000 Gauss. This may be replaced by an electromagnet. The cathode filament 5 is held by the introduction terminal 21 at a portion relatively close to the center of the lid plate 11. Introduction terminal 21
Consists of a metal sheath and an insulator. The cathode filament 5 is insulated from the lid plate 11 by the insulator. The metal sheath is Mo inside and Cu outside. The cathode filament 5 is a cathode filament power supply 7
It is heated by and produces thermoelectrons. The anode filament 6 is held by the introduction terminal 22 in a portion near the peripheral edge of the lid plate 11. The introduction terminal 22 insulates the anode filament 6 from the lid plate. The anode filament 6 is an anode filament power supply 8
Heated by. The arc chamber 1 and the anode filament 6 are grounded. An arc power supply 9 having an arc chamber 1 as an anode and a cathode filament 5 as a cathode is provided. As a result, an arc discharge is generated between the cathode filament 5 and the arc chamber 1. On the end surface of the arc chamber 1 on the opposite side of the lid plate 11, a plasma electrode 3 having a single hole, a multi-hole, a single slit, a multi-slit or the like for extracting an ion beam is attached. An inner lining 4 is provided inside the cylindrical portion of the arc chamber 1, inside the lid plate 11, and inside the outer edge portion of the plasma electrode. This is made of heat resistant metal plate such as Ta and Mo. This is for keeping the inside of the arc chamber at a high temperature. The arc chamber 1 has a gas inlet 23 for introducing a gas containing atoms to be ionized. The anode filament 6 is in a cusp field near the wall of the anode chamber as shown in FIG. It is outside the plasma (electron, positive ion) existence area. The anode filament 6 attracts electrons by electrostatic force, but since the surrounding magnetic field is strong, the electrons are repelled. For this reason, the effective collision cross-sectional area of the electron becomes small, and the life of the electron becomes long. Therefore, high density plasma can be maintained. The space surrounded by the lining becomes the region where plasma exists. In this example, this space has a length of about 10 cm and a diameter of 15 cm. Can withstand high heat of 1400 ℃ or higher.

[Effect of device]

It is an ion source that generates plasma by arc discharge and confine electrons in the radial direction of the cylinder by a cusp magnetic field and in the axial direction by an electrostatic field.It has an anode filament, so it is possible to keep the arc chamber at a higher temperature. it can. It is most suitable for generating an ion beam of metal or the like. Since the anode filament is surrounded by the cusp magnetic field, the loss of electrons due to the addition of the anode filament is small. Therefore, the electron confinement efficiency is not impaired.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view of an ion source according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line II-II in FIG. 1 ... Arc chamber 2 ... Permanent magnet 3 ... Plasma electrode 4 ... Lining 5 ... Cathode filament 6 ... Anode filament 7 ... Cathode filament power supply 8 ... Anode filament power supply 9 ... Arc power supply 10 ... Cylinder Part 11 …… Lid plate 12,13 …… Flange 21,22 …… Introduction terminal 23 …… Gas inlet

Claims (1)

[Scope of utility model registration request] 1. An arc chamber which can be evacuated by a container composed of a cylindrical portion and a cover plate and serves as an anode, a plasma electrode provided on the opposite side of the cover plate of the arc chamber for extracting ions, and an arc. A plurality of magnets that are provided on the outer periphery of the chamber with alternating polarities to generate a cusp magnetic field inside the arc chamber, a cathode filament inserted from the lid plate into the arc chamber, and an arc with the same potential as the arc chamber. An ion source comprising an anode filament inserted from a cover plate for heating the inside of the chamber into a portion where a cusp magnetic field exists inside the arc chamber.