JPH067464B2 - Fast atom beam source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is suitable for material processing such as sputtering and etching and for a neutral beam source such as a secondary ion mass spectrometer. The present invention relates to a fast atom beam source capable of generating an atom beam.

[Summary of Disclosure] The present invention has a high neutralization rate and is suitable for a material processing such as sputtering and etching and a neutral beam source such as a secondary ion mass spectrometer, and can generate a large amount of high-speed atomic beams. In the atomic beam source, the opposite end surfaces are respectively cold cathodes, and a gas discharge chamber having a beam emission hole at the center of at least one of the two cold cathodes and two cold cathodes in the gas discharge chamber A ring-shaped anode provided in the middle, a magnetic field generating means provided outside the gas discharge chamber for generating a magnetic field in a direction along an electric field formed by two cold cathodes and the anode in the gas discharge chamber, and a gas Disclosed is a technique for generating a large amount of high-speed atomic beam having a high neutralization rate by including a thermionic source provided outside the discharge chamber and close to the beam emission hole.

It should be noted that this outline is provided only for quick access to the technical contents of the present invention, and has no influence on the technical scope and the interpretation of rights of the present invention.

[Prior Art] Conventionally, a high-speed atomic beam has been formed using the radiation source shown in FIG. As shown in the figure, this radiation source is provided with both ends (diameter 30 mm) of an Al cylinder as a cold cathode, and the anode 2 is arranged concentrically in this cylinder, while one cold cathode 3 has a gas introduction hole. 1 is provided, the cold cathodes 3 and 4 are grounded, and a beam extraction hole having a diameter of 1 mm is bored in the center of the other cold cathode 4. The beam extracted from the radiation source having such a configuration is a mixed beam composed of ions and atoms. In this case, the ratio of ion beam and atomic beam is the result of the experiment.
It is known to be 50% and 50%. That is, the neutralization rate of the beam is 50%.

Conventionally, the method shown in FIG. 6 has been adopted to increase or control the neutralization rate of this beam.

In FIG. 6, the mixed beam 7 extracted from the radiation source 6 is obliquely incident on the Neutralizer 8,
This is a method of exchanging charges of ions in the mixed beam 7 to form an atomic beam. In this method, the mixed beam 7 is Neu
When colliding with tralizer8, most of them are absorbed and disappear, and a large amount of atomic beam cannot be obtained. Further, since the mixed beam sputters the Neutralizer itself, Ne in the beam 9 obtained by charge exchange is
There is a possibility that the atoms of the extralizer 8 are mixed and the purity of the beam is lowered.

[Problems to be Solved by the Invention] As described above, the conventional technique has a defect that the neutralization rate is about 50% and a large amount of high-speed atomic beams cannot be obtained.

It is an object of the present invention to provide a high-speed atomic beam source that solves the above-mentioned problems of the conventional art by adding a magnet and a thermoelectron source.

[Means for Solving the Problems] In the high-speed atomic beam source of the present invention which achieves such an object, a cold cathode is arranged on both sides of an annular anode, and a gas is interposed between these electrodes to cause low-pressure gas discharge. Generate. Also,
Magnets are arranged around the outer periphery of the anode and the cold cathode to apply a magnetic field in the direction along the electric field formed between the anode and the cold cathode, and electrons and ions oscillate between the cold cathode using the anode as a communication. A beam emission hole for taking out a high-speed electron beam by combining with and is provided in the center of any of the cold cathodes, and a thermoelectron source is installed immediately after the beam emission hole to change the magnitude of the current flowing to the thermoelectron source and emit it. The neutralization rate of the beam is controlled by changing the number of thermoelectrons that are generated.

[Operation] When gas is interposed between the annular anode and the cold cathodes on both sides to cause low-pressure gas discharge, electrons emitted from the cold cathode vibrate between the cold cathodes around the anode, and in the middle of the process. Collisions with many gas gas molecule atoms to produce ions. Also,
For oscillating electrons that do not move in parallel with the electric field, the Lorentz force due to the magnetic field acts, so that the electrons make a spiral motion as if they are entwined with the magnetic field lines, and the radius becomes smaller as they approach the cold cathode. Without concentrating, it concentrates in the emission hole and combines with a large amount of ions to form a fast atom beam. At this time, ions are similarly extracted from the beam emission hole. Here, if a thermoelectron source is installed immediately after the beam emission hole and the filament is heated to generate thermoelectrons, the probability that the ions and electrons will combine to form a high-speed atom beam will increase the neutralization rate of the beam. Can be improved.

[Examples] Examples of the present invention will be described in detail below.

FIG. 1 shows an embodiment of the present invention. As shown in the figure, one end surface of a cylindrical container serves as a cold cathode 3 and the other end surface of the container has a cold cathode 4, and an annular anode 2 is concentrically arranged in the central portion of the container. ing. The cold cathodes 3 and 4 are grounded, the gas introduction hole 1 is connected to the cold cathode 3, and the beam emission hole 5 is provided in the center of the cold cathode 4.

Further, in the present invention, the thermoelectron source 10 is installed immediately after the cold cathode 4. The thermoelectron source 10 is connected to a transformer such as a sliderac. As the thermoelectron source 10, for example, a tungsten filament, a thorium-tungsten filament, or the like can be used.

Further, a ring-shaped magnet 11 is concentrically arranged on the outer periphery of the cold cathodes 3 and 4, and as shown in FIG.
A magnetic field B is generated along the electric field E formed between the cold cathodes 3 and 4. As the magnet 11, a DC electromagnet, an AC electromagnet, a permanent magnet, or the like can be used, but an electromagnet that can arbitrarily change the magnetic field strength is convenient.

The fast atom beam source having such a structure is used as follows.
First, an inert gas such as Ar is introduced into the discharge space through the gas inlet 1, and then a positive DC voltage of about several kV to 10 kV is applied to the anode 2. Then, the anode 2 and the cold cathodes 3 on both sides of the anode 3,
A glow discharge is generated between the cold cathodes 4, and at this time, the electrons 12 emitted from the cold cathodes 3 and 4 accelerate toward the anode 2 and penetrate the center of the ring-shaped anode 2 or the cold cathode 3 or the opposite side. 4, where the vehicle loses its speed, stops, temporarily accelerates toward the anode 2 again, and so on. That is, the electrons 12 emitted from the cathodes 3 and 4 perform high-frequency vibration called Barkhausen-Kurz vibration (hereinafter referred to as BK vibration) around the anode 2, and many gas gas molecules and atoms are included in the middle of the high-frequency vibration. Collides with and produces a large amount of ions 13. In this case, the gas pressure in the radiation source is 10 ⁻² to 10 ⁻³ torr.
Moreover, in the radiation source, the vibration in the drawing direction is designed to be dominant based on Paschen's law in the discharge. The vicinity of the beam discharge hole 5 is a turning point of the electrons 12 that vibrate in BK, and is a space where many electrons 12 having a low velocity exist.

Since the electrons 12 are slow and have a large collision cross-section, they combine with the ions 13 flying near the cold cathodes 3 and 4 to form a fast atom beam.
14 Also, the ions 13 flying to the cold cathodes 3 and 4 are
It has a kinetic energy of several kV, part of which is cold cathode 3,
4 and emit secondary electrons. Since the emitted secondary electrons have a low initial velocity of several tens of eV, they have a large collision cross section.
Becomes

Further, in the present invention, since the magnetic field B is applied along the electric field E, the electrons 12 behave as shown in FIG.

That is, the BK-oscillating electron 12 is accelerated in the direction along the electric field E, but other atoms and molecules collide with the wall surface, so that the direction of movement is not always parallel to the electric field.

Let θ be the angle between the moving direction of the electron 12 and the electric field E.
Lorentz force F that 12 receives from magnetic field B is expressed by the following equation.

 F = v · sin θ · eB (1) where v is the velocity of the electron and e is the charge of the electron.

This Lorentz force F acts in the direction perpendicular to the direction of movement of the electrons 12 and the direction of the magnetic field B, and balances with the centrifugal force, so the following equation holds.

However, m is the mass of the electron and r is the radius of the circular motion of the electron.

The kinetic energy of electrons can be expressed as follows.

However, V is the voltage applied to the anode. Therefore, from these three equations, the radius r in which the electrons make a circular motion is represented by the following equation.

Equation (4) shows that, as shown in FIG. 2, when the electron 12 spirals so as to be entwined around the magnetic field lines, its radius becomes larger toward the center and becomes smaller toward both sides. For example, if the dimensions of the anode 2, the cold cathode 3 and 4 are 3 cm in the major axis and the inner diameter of the anode 2 is 2 cm, the electrons do not diverge inside the electrode system due to this spiral motion, and the beam emission hole 5
In the vicinity of the beam emission hole 5, ions and electrons are combined to generate a large amount of fast atom beam. Ions 13 are similarly extracted from the beam emission hole 5.

Therefore, a thermoelectron source 10 is installed immediately after the beam emission hole 5 to heat the filament and emit thermoelectrons. Ions 13 in the beam extracted from the beam emission hole 5 have a high probability of being combined with electrons to become a high-speed electron beam, and the neutralization rate in the beam is improved.

Next, the test results of the fast atom beam source of the present invention will be described. Since the beam extracted from the radiation source is an atomic beam, it was converted into an io current to obtain a current value.

FIG. 3 shows the correlation between the beam current and the discharge current of the fast atom beam extracted from the fast atom beam source of the present invention. In the figure, the beam currents with and without the electromagnet are shown for comparison. By using an electromagnet, about 2
A beam current that is twice as large can be obtained. That is, according to the present invention, it is possible to improve the beam current.

FIG. 4 shows the relationship between the proportion of fast atoms in the total beam when the electromagnet is added to the radiation source, that is, the neutralization rate and the filament current. As shown in the figure, the neutralization rate when the electromagnet is attached is about 50%. That is, the residual ion rate is 50%. At this time, it can be seen that the neutralization rate can be increased to almost 100% by causing a current to flow in the thermionic source 10 to emit thermions. Further, the beam current also doubles as the neutralization rate increases.

By attaching an electromagnet and a thermoelectron source to the above-mentioned radiation source, the beam current can be increased four times as compared with the case where it is not used, and a beam with a neutralization rate of almost 100% can be obtained.

[Effects of the Invention] As described specifically above with reference to the examples, the fast atom beam source of the present invention can generate a large amount of ions in the source by adding a magnet, and can also generate electrons. Can be focused without diverging, so that a large amount of high-speed atomic beam can be generated, and thus material processing such as sputtering and etching can be advanced at high speed. Further, since the neutralization rate of the beam can be improved by mounting the thermionic source, the irradiation portion of the beam is not charged, which is particularly effective for processing and analyzing the insulating material.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing trajectories of electrons in the electric and magnetic fields of FIG. 1, and FIG. 3 is beam current density discharge current. Figure 4 shows the correlation between beam current density, neutralization rate and filament current, and Figures 5 (a) and 5 (b) are schematic diagrams showing conventional radiation sources. so
(a) is a cross-sectional view, (b) is a front view, and FIG. 6 is a view showing how the mixed beam is obliquely incident on the Neutralizer. DESCRIPTION OF SYMBOLS 1 ... Gas introduction hole, 2 ... Anode, 3,4 ... Cold cathode, 5 ... Beam emission hole, 6 ... Radiation source, 7 ... Mixed beam, 8 ... Neutralizer, 9 ... Beam, 10 ... Thermoelectron source, 11 ... Electromagnet , 12… electrons, 13… ions, 14… high-speed electron beams.

Claims (3)

[Claims] 1. A gas discharge chamber having a beam emission hole in the central portion of at least one of the two cold cathodes, the opposite end faces being cold cathodes, respectively, and the two gas discharge chambers in the gas discharge chamber. A magnetic field in a direction along an electric field formed by an annular anode provided in the middle of the cold cathode and the two cold cathodes provided outside the gas discharge chamber and the anode is generated in the gas discharge chamber. And a thermoelectron source provided outside the gas discharge chamber and in the vicinity of the beam emission hole. 2. The fast atom beam source according to claim 1, wherein said magnetic field generating means is an electromagnet which makes the strength of said magnetic field variable. 3. The fast atom beam source according to claim 1, wherein the thermionic source has a variable number of emitted thermoelectrons.