JPH0935650A - Ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion source which enables the ionization efficiency of gas within a second plasma generating container to be raised more. SOLUTION: The material of a middle electrode 8 is made of high fusing point metal, and the tip 8a of this middle electrode 8 is projected into the second plasma generating container 10, being protruded from the face on the side of the second plasma generating container 10 of an insulator 34. Besides, this middle electrode 8 is provided with a Dc power source 40 to apply negative voltage to the second plasma generating container 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a cathode, an intermediate electrode, an anode, and a reflective electrode, and a so-called Duo-PIGatron type, which performs two-stage discharge by compressing plasma by the intermediate electrode. Regarding the ion source.

[0002]

2. Description of the Related Art An ion source obtained by improving the above-mentioned duopigatron type ion source has been previously proposed by the same applicant. (For example, Japanese Patent Application No. 5-306816).

This will be described with reference to FIGS. 3 and 4. The ion source is composed of a first plasma generating container 2 having a gas inlet 4 and a cathode provided in the first plasma generating container 2. Filament 6, a second plasma generation container 10 provided adjacent to the first plasma generation container 2 and also serving as an anode, and a nozzle for communicating the inside of the first plasma generation container 2 with the inside of the second plasma generation container 10. -Shaped intermediate electrode 8, a reflection electrode 12 provided in the second plasma generation container 10 so as to face the tip portion 8a of the intermediate electrode 8, and an ion extraction port 14 provided in the second plasma generation container 10. It is provided in the vicinity of the outlet of the ion extraction port 14 and from inside the second plasma generation container 10 (more specifically, from the plasma 16 generated therein).
A magnetic field B is generated in a direction along the central axis of the intermediate electrode 8 in the region extending from the inside of the first plasma generation container 2 to the inside of the second plasma generation container 10 and the extraction electrode 20 that extracts the ion beam 22 through the ion extraction port 14. And a magnetic field generator 24. 32-36 are insulators.

The magnetic field generator 24 is a coil, a magnetic pole around which the coil is wound, a permanent magnet, or the like. The direction of the magnetic field B may be opposite to that shown.

A filament power source 26 is connected to both ends of the filament 6. A DC arc power supply 28 is connected between one end of the filament 6 and the second plasma generation container 10 with the former being the negative side.

The intermediate electrode 8 is made of a non-magnetic material,
It is kept at the same potential as the plasma generation container 2. The tip portion 8a of the intermediate electrode 8 is substantially flush with the surface of the insulator 34 on the second plasma generation container 10 side in this prior art example. A resistor 30 is connected between the second plasma generation container 10 and the first plasma generation container 2, and thus the intermediate electrode 8.

The reflective electrode 12 may be connected to the floating potential without being connected to any part as in the illustrated example, or may be connected to the intermediate electrode 8 or the filament 6 and fixed to the intermediate electrode potential or the filament potential. Even with a floating potential, light and highly mobile electrons in plasma 16, which will be described later, are much more incident on the reflection electrode 12 than ions and are charged to a negative potential, so that the electrons are repelled. .

The operation of this ion source will be described. When the filament 6 is heated and gas is introduced into the first plasma generating container 2 from the gas inlet 4, thermoelectrons emitted from the filament 6 collide with gas molecules. And ionizes it, whereby arc discharge occurs between the filament 6 and the first plasma generation container 2, whereby gas molecules are further ionized and plasma 7 is generated.

When the above-mentioned arc discharge occurs, a current flows through the resistor 30, which causes a potential difference across the resistor 30, and the potential of the second plasma generating container 10 becomes higher than that of the intermediate electrode 8 by that amount. Therefore, the potential increases in the order of the filament 6, the intermediate electrode 8, and the second plasma generation container 10.

The electrons in the plasma 7 are drawn out into the plasma generation container 10 through the intermediate electrode 8 due to the above potential difference, vibrate between the intermediate electrode 8 and the reflection electrode 12, and in the meantime, the first plasma generation container 2 The gas molecules collide with the gas molecules flowing in from the side through the intermediate electrode 8 to generate a plasma 16 having a higher density in the second plasma generation container 10.

An ion beam 22 is extracted from the plasma 16 by the action of the electric field generated by the extraction electrode 20.

In this ion source, the plasma 7 can be compressed by the nozzle-shaped intermediate electrode 8, and the PIG (Pennin) is provided between the intermediate electrode 8-the anode 10 and the reflective electrode 12.
By adopting the g Ionization Gauge) structure, the ionization efficiency of the gas in the second plasma generation container 10 can be increased. That is, the electrons extracted into the second plasma generation container 10 through the intermediate electrode 8 are the magnetic field B in the axial direction applied thereto and the anode 10 perpendicular to the magnetic field B.
Under the action of the electric field due to, the magnetic field B reciprocates between the intermediate electrode 8 and the reflective electrode 12 while rotating around the magnetic field B.
As a result, the probability of collision between the electrons and the gas molecules is increased, the ionization efficiency of the gas is increased, and the second plasma generation container 1
The plasma 16 having a higher density than that of the plasma 7 in the first plasma generation container 2 can be generated in the space 0.

As described above, in this type of ion source, the density of the plasma 7 generated in the first plasma generation container 2 may be relatively low, and therefore, the sputtering of the filament 6 by the plasma 7 can be suppressed, so that it is high. It is also effective as a multiply-charged ion source that requires a discharge voltage.

[0014]

However, in reality, some ions in the plasma 16 generated in the second plasma generation chamber 10 pass through the intermediate electrode 8 and are incident on the filament 6 to sputter it. . Generally, the rate of sputtering the cathode (filament 6 in this example) increases as the discharge voltage and discharge current increase. In particular, in the case of extracting multivalent ions having a valence of 2 or more, the discharge voltage and the discharge current are large, and in addition, the density of neutral particles that prevent the ions from reaching the cathode is low in order to reduce the gas pressure. The consumption of the cathode becomes faster than that of the above operation.

Therefore, in order to extend the life of the cathode and increase the beam amount, it is necessary to further enhance the ionization efficiency of the gas in the second stage, that is, in the second plasma generation container 10.

Therefore, the main object of the present invention is to provide an ion source capable of further enhancing the ionization efficiency of gas in the second plasma generating container.

[0017]

The ion source of the present invention comprises:
A material of the intermediate electrode is a high melting point metal, a tip portion of the intermediate electrode is projected into the second plasma generation container, and a DC power source for applying a negative voltage to the second plasma generation container is provided to the intermediate electrode. It is characterized by that.

According to the above structure, the ions in the plasma generated in the second plasma generation container are accelerated by the potential difference between the second plasma generation container and the intermediate electrode (which is given by the DC power supply), It collides with the tip of the intermediate electrode protruding into the second plasma generation container, and secondary electrons are emitted from it. The secondary electrons also ionize the gas while vibrating between the intermediate electrode and the reflective electrode, and contribute to the generation of plasma in the second plasma generation container.

In this way, in addition to the electrons extracted from the first plasma generating container side through the intermediate electrode, the secondary electrons also contribute to the ionization of the gas, so that the ionization efficiency of the gas in the second plasma generating container is increased. Will be higher.

The intermediate electrode becomes extremely hot due to the collision of ions, but since the material of the intermediate electrode is a refractory metal in the present invention, it can withstand the high temperature due to the collision of ions.

[0021]

1 is a sectional view showing an example of an ion source according to the present invention as viewed from the front side. The same or corresponding portions as those of the preceding example of FIG. 3 are designated by the same reference numerals, and the differences from the preceding example will be mainly described below. Also in this example, the side cross section around the ion extraction port is shown in FIG.
As shown in.

In this embodiment, the tip portion 8a of the intermediate electrode 8 mentioned above is projected from the surface of the insulator 34 on the side of the second plasma generation container 10 to form the second plasma generation container 1
It is projected in 0. In this way, plasma 1
Ions in 6 collide with the tip portion 8a due to the potential difference given by the DC power supply 40 described later.

With the above arrangement, the intermediate electrode 8 becomes extremely hot due to the collision of ions, so that the material of the intermediate electrode 8 is a refractory metal to withstand it.
This refractory metal is, for example, Ti, Zr, Hf, V, N.
b, Ta, Cr, Mo and W. The material of the intermediate electrode 8 is preferably a material having a low work function in order to improve the efficiency of secondary electron emission therefrom. Therefore, for the intermediate electrode 8, it is preferable to use a metal having a relatively low work function and a high melting point, more specifically Ta, W, Mo or the like, which is used for the cathode of the ion source.

The tip portion 8a of the intermediate electrode 8 may have a cylindrical shape as shown in FIG. 1, a conical shape as shown in FIG. 2, or any other shape. The conical shape allows the plasma 7 to be more compressed, and
Ions in the plasma 16 are less likely to enter the filament 6.

Between the second plasma generation container 10 and the first plasma generation container 2 and thus the intermediate electrode 8, the intermediate electrode 8
A DC power supply 40 that applies a negative voltage to the second plasma generation container 10 is connected to the. Arc power supply 28 described above
Of the output voltage V ₁ of the DC power supply 40 and the output voltage V ₂ of the DC power supply 40 are such that the electrons in the plasma 7 generated in the first plasma generation container 2 can be easily drawn into the second plasma generation container 10. is set to _1> V _2.

The operation of this ion source will be described. As in the case of the prior example, the electrons in the plasma 7 generated in the first plasma generation chamber 2 are generated by the output voltage V ₂ of the DC power supply 40 and the intermediate electrode 8 is discharged. Through the second plasma generation container 10
While being vibrated between the intermediate electrode 8 and the reflective electrode 12, the gas is ionized in the second plasma generation container 10 to generate a high density plasma 16.

Further, the ions in the plasma 16 generated in the second plasma generation container 10 are accelerated by the potential difference V ₂ between the second plasma generation container 10 and the intermediate electrode 8, which is provided by the DC power supply 40. , And collides with the tip portion 8a of the intermediate electrode 8 which is projected into the second plasma generation container 10, and secondary electrons are emitted from the tip portion 8a. The secondary electrons also ionize the gas while vibrating between the intermediate electrode 8 and the reflective electrode 12, and contribute to the generation of the plasma 16 in the second plasma generation container 10.

Thus, in this ion source, the first
In addition to the electrons extracted through the intermediate electrode 8 from the plasma generation container 2 side, the secondary electrons also contribute to the ionization of the gas, so that the ionization efficiency of the gas in the second plasma generation container 10 is further increased.

As a result, the power to be applied between the filament 6 and the second plasma generating container 10, that is, the arc power source 2
Since the high density plasma 16 can be generated in the second plasma generation container 10 even if the power output from 8 is reduced, the power can be suppressed to a low level,
As a result, the proportion of the ions in the plasma 7 that sputter the filament 6 is reduced, so that the life of the filament 6 can be extended. In addition, the second plasma generation container 1
Since the density of the plasma 16 within 0 can be kept high, the beam amount of the ion beam 22 extracted therefrom can be increased.

The second plasma generation vessel 10 is provided with a vapor introduction port 18 as in the example shown in FIG. 4, and metal vapor is introduced into the second plasma production vessel 10 from there, thereby making It is also possible to ionize the metal vapor using the electrons extracted from the plasma generation container 2 side and the secondary electrons emitted from the tip portion 8a of the intermediate electrode 8 to extract metal ions as the ion beam 22.

The extraction electrode 20 may be composed of a plurality of electrodes.

The first plasma generation container 2, the second plasma generation container 10, and the extraction electrode 20 and the tip of the magnetic field generator 24 are also housed in a vacuum container in some cases. Is omitted.

Also, unlike the above example, the ion extraction port 1
4 is provided on the reflection electrode 12, and the extraction electrode 2 is provided near the outside thereof.
0 may be provided to extract the ion beam 22 in the axial direction of the second plasma generation container 10 or the like.

[0034]

As described above, according to the present invention, the ions in the plasma in the second plasma generating container collide with the tip of the intermediate electrode and secondary electrons are emitted from the tip. In addition to the electrons extracted from the side of the first plasma generation container through the intermediate electrode, the secondary electrons also contribute to the ionization of the gas, so that the ionization efficiency of the gas in the second plasma generation container can be further increased. As a result, it is possible to suppress the power applied between the filament and the second plasma generation container to be small, thereby reducing the ratio of ions sputtering the filament, so that the life of the filament can be extended. Further, since the plasma density in the second plasma generation container can be kept high, the beam amount can be increased.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an ion source according to the present invention when viewed from the front direction.

FIG. 2 is a cross-sectional view showing another example of the intermediate electrode.

FIG. 3 is a cross-sectional view showing an ion source of a prior art example as viewed from the front direction.

FIG. 4 is a cross-sectional view showing the periphery of an ion extraction port of the ion source of FIGS. 1 and 3 as seen from a side direction.

[Explanation of symbols]

 2 First Plasma Generation Container 6 Filament 8 Intermediate Electrode 8a Tip 10 Second Plasma Generation Container 12 Reflective Electrode 14 Ion Extraction Port 20 Extraction Electrode 24 Magnetic Field Generator 40 DC Power Supply

Claims (1)

[Claims] 1. A first plasma generation container, a filament as a cathode provided in the first plasma generation container, and a second plasma generation container provided adjacent to the first plasma generation container and also serving as an anode. A nozzle-shaped intermediate electrode having the same potential as that of the first plasma generation container and connecting the inside of the first plasma generation container and the inside of the second plasma generation container, and the intermediate electrode in the second plasma generation container. It is provided facing the tip and has a floating potential,
A reflection electrode maintained at the intermediate electrode potential or the filament potential, an ion extraction port provided in the reflection electrode or the second plasma generation container, and a second plasma generation container provided in the vicinity of the outlet of the ion extraction port. An extraction electrode for extracting an ion beam from the inside through the ion extraction port, and a magnetic field generator for generating a magnetic field in a direction along the central axis of the intermediate electrode in a region from the first plasma generation container to the second plasma generation container. In the ion source, the material of the intermediate electrode is a refractory metal, the tip of the intermediate electrode is projected into the second plasma generation container, and a negative voltage is applied to the intermediate electrode with respect to the second plasma generation container. An ion source characterized by being provided with a DC power supply for applying.