JPS61183899A - Fast atomic beam source - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of application in the pot industry> The present invention relates to a fast atomic beam source capable of generating a large amount of fast atomic beams with a high neutralization rate of 771-+.

<Prior Art> Conventionally, a high-speed atomic beam is generated using a radiation source shown in FIG. As shown in the figure, this radiation source has cold cathodes 3.4 on both end faces (diameter 30 mm) of a cylinder made of M, and a ring-shaped anode 2 is arranged concentrically within this cylinder, while one cold cathode 3 is provided with a gas introduction hole 1, the collar of the cold cathode 3 is grounded, and a beam extraction hole with a diameter of 1i111j is bored in the center of the other cold cathode 4. The beam 5 extracted from the radiation source having such a configuration is a mixed beam consisting of ions and atoms. Experiments have shown that the ratio of the ion beam to the atomic beam in this case is 50%.

That is, the beam neutralization rate is 50%.

Conventionally, the method shown in FIG. 4 or 5 has been employed to increase or control the neutralization rate of this beam. What is shown in FIG.
By irradiating the ion beam in the mixed beam 7? It is partially neutralized and converted into an atomic beam. With this method, it is difficult to convert all of the ions into atoms, and only a few percent of the ions convert into atoms. Therefore, the mixed beam can only increase the neutrality rate to a beam consisting of about 51-52% atoms and 48-49% ions, and this method cannot obtain a large amount of high-speed atomic beams. . In the system shown in FIG. 5, a mixed beam 7 extracted from a radiation source 6 is obliquely incident on a Neutralizer 11.
This is a method of converting the charge of ions in the mixed beam 7 to form an atomic beam. In this method, the mixed beam 7 is
When colliding with tralizer 11, many are absorbed,
It disappears, and a large amount of atomic beams cannot be created.

Furthermore, since the mixed beam collides with Neutralizer II and sputters the Neutralizer itself, Ne is added to the beam obtained by charge conversion.
There is also a possibility that atoms of the ultralizer 11 may be mixed in and reduce the purity of the beam.

<Problems to be solved by the invention> As described above, in the conventional technology, the neutralization rate is about 50%, it is difficult to obtain a large amount of high-speed atomic beams, and it is difficult to obtain high-speed atomic beams with high purity. The disadvantage was that it could not be done. An object of the present invention is to provide a high-speed atomic beam source that solves the problems of the prior art by adding a thermionic source and a magnet.

Means for Solving the Problems〉 The structure of the fast atomic beam source of the present invention that achieves the above object comprises arranging cold cathodes on both sides of an annular anode and interposing a gas between these electrodes. While generating a low-pressure gas discharge, a thermionic source is placed close to the cold cathode, and magnets are placed around the anode and the cold cathode to form an electric field between the anode and the cold cathode. A beam emitting hole is provided in the center of one of the cold cathodes for applying a magnetic field in the direction along the anode and extracting a high-speed atomic beam consisting of electrons and ions oscillating between the two cold cathodes with the anode as the center. It is characterized by:

Effect〉 When a gas is interposed between the annular anode and the cold cathodes on both sides to cause a low-pressure gas discharge, the electrons emitted from the cold cathode oscillate between the two cold cathodes with the anode as the center, and on the way, It collides with many gas molecules and atoms to produce ions. The vibrating electrons become slow near the cold cathode, which is the turning point, and recombine with ions to form a high-speed atomic beam, which is then extracted from the beam emission hole in the center of the cold cathode. Ions are also taken out from the beam emission hole.

When the thermionic source is ignited to generate thermoelectrons, the probability that ions and electrons combine to form a high-speed atomic beam increases, and the neutralization rate of the beam extracted from the beam emission hole increases. becomes.

In addition, among the oscillating electrons, those that do not move parallel to the electric field are affected by the Lorentz force due to the magnetic field, so
These electrons move in a spiral motion as if entangled with magnetic lines of force, and their radius becomes smaller on both sides, so they do not diverge, but instead concentrate at the beam emission hole, where they combine with ions in large numbers to form high-speed atomic beams.

<Example> 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 4, a cold cathode 3 is attached to the other end surface of the container, and an annular anode 2 is concentrically arranged in the center of the container. placed,
It is contained within a discharge space with a diameter of 551 m and a length of 6021 m. The cold cathodes 3 and 4 are both made of graphite and are grounded, while the cold cathode 3 is connected to a gas inlet 1, and the cold cathode 4 is provided with a beam discharge hole 14 at its center. Further, in the present invention, a thermionic source 16 is inserted into the discharge space from the center of the cold cathode 3, and a DC stabilized power source 17 is connected to the thermionic source 6.

As the thermionic source 16, for example, a tungsten filament, a tungsten thorium filament, etc. can be used. Furthermore, an annular magnet 18 is arranged concentrically around the outer periphery of the anode 2 and the cold cathodes 3 and 4.
As shown in FIG. 1, a magnetic field B is generated along an electric field E formed between the anode 2 and the cold cathodes 3 and 4. magnet 18
As a magnet, a direct current electromagnet, a father current electromagnet, a permanent magnet, etc. can be used, and an electromagnet whose magnetic field strength can be changed is convenient.

A fast atomic beam source with such a configuration 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 DC positive voltage of about several kV to 10 kV is applied to the anode 2.

Then, a glow discharge occurs between the anode 2 and the cold cathodes 3 and 4 on both sides of it, and at this time, the electrons 12 emitted from the cold cathode 3 or 4 accelerate toward the anode 2 and strike the center of the annular anode 2. It passes through and reaches the cold cathode 4 or 3 on the opposite side, where it loses speed and once stops, is accelerated again toward the anode 2, and repeats the same process thereafter. In other words, the 'seiko 12 emitted from the cold cathode 3°4 performs a frequency motion called Lukhausen-Kurz vibration (hereinafter referred to as B-vibration) around the anode 2, and along the way, many gases are generated. gas, molecules,
A large amount of ions 13 are generated by colliding with atoms. In this case, the gas pressure within the source is lO=~1O-3 Torr, and the source is designed so that vibrations in the extraction direction are dominant based on Paschen's law in discharge. Near the beam emission hole 14, electrons 12 vibrating in B-
It is also a space where a large number of electrons 12 with low velocity exist at the turning point. Since the electrons 12 have a low velocity and a large collision cross section, they combine with ions 13 flying near the cold cathode 4 to form a high-speed atomic beam 15. In addition, the ions 13 that have arrived at the cold cathode 4 have a kinetic energy of several kV.
Some of them collide with the cold cathode 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, and these also combine with subsequent ions 13 to form high-speed atomic beams 15. Therefore, as the anode 2 and the cold cathode 3.4, graphite, which is a material with a secondary electron emission ratio of about 0.1 and has excellent heat resistance, is preferable. However, at this level, the neutralization rate of the entire beam of the high-speed electron beam 15 is only improved to about 70%. That is, the number of ions 13 incident on the cold cathode 3゜4 is N
+ (pcs/al sea), B- near cold shade @3,4
The number of oscillating electrons and secondary electrons is n (pieces/ad sec)
, the number of atoms 15 generated k No (pieces/aAsec)
, the secondary electron emission ratio fr due to ion bombardment of the cold cathode 4, the aperture ratio of the beam emission hole, Ar! If the collision cross section of the oscillating electrons is Qn (cyd) and the collision cross section of the secondary electrons is Qs, the beam neutralization rate No/(N
o1N+)=δ can be approximately expressed as follows.

As a specific value, QB-=10-” al , Qs
Medium 10-17- is given as the literature value. In addition, if graphite is used as the cold cathode material like the main source, γ
Make a discharge hole so that Ki0.1 and =0.3 and n=3
If a discharge of
2). In other words, a beam containing about 30% of ions is emitted from the emission port 15. As can be seen from equation (1), if 'nt- increases, the neutralization rate will be improved.

Therefore, in the present invention, a thermionic source 16 is added within the radiation source. When a maximum current of about 10 A is applied to the thermionic source 16 by the DC stabilizing source 17, the surface temperature of the thermionic source 16 increases and a large amount of electrons are emitted. Therefore, by igniting the electron source 16, the number of ions 13 generated within the source can be increased, and the number of low-speed electrons near the cold cathode 4 can be increased, so that the ions 13 and electrons 12 are combined. Therefore, the probability of becoming a high-speed atomic beam 15 increases. For example, if the number n of electrons increases 10 times, δ=1, and almost all ions become atoms and are emitted. However, by changing the magnitude of the current flowing through the thermionic source 16,
It becomes possible to control the amount of electrons 12 emitted from the thermionic source 16 and arbitrarily select the probability that ions 13 and electrons 12 recombine. In the above embodiment, the thermionic source 16 is attached to the cold cathode 3 provided with the gas inlet 1, but the invention is not limited to this. Alternatively, the thermionic source 16 may be attached to both the cold cathodes 3 and 40. In either case, the same effect is achieved.

Furthermore, in the present invention, since the magnetic field B is applied along the electric field EK, the electrons 12 behave as if they are concentrated in the emission hole 14 without being diverged. That is, electrons vibrating to B-], 2 is the electric field E
Although it is subjected to nine accelerations along K, its direction of motion is not necessarily parallel to the electric field because it collides with other atoms, molecules, or walls.

When the angle between the direction of movement of the electron 12 and the electric field is θ, the Lorentz force F that the electron 12 receives from the force B is expressed by the following formula.

F=v-sinθ-e, 3
-(3) However, V is the velocity of the electron, and e is the charge of the electron.

This Lorentz force F acts perpendicularly to the direction of movement of the electrons 12 and the direction of the magnetic field B, and is balanced by the centrifugal force, so the following equation holds true.

However, m is the mass of the electron, r is the electron moving in a circle It is the radius.

Also, the kinetic energy of an electron can be expressed as follows.

±mv"=.■ 2...(5)
However, ■ is the voltage applied to the anode.

Therefore, from these three equations, the radius r of the circular motion of the electrons is expressed by the following equation.

Equation (6) shows that when electrons move in a spiral around magnetic lines of force, the radius is large at the center and becomes smaller as it approaches both sides. for example,
If the dimensions of the anode cold cathode 3 and 4 are 3cn1 in major axis and the inner diameter of the anode 2 is 2cn1, then due to this spiral movement, the electrons will not be diverged inside the electrode system but will be concentrated in the beam emission hole 14, In the vicinity of the beam emitting hole 14, the ions and the sterons combine to generate a large amount of high-speed atomic beams.

Next, experimental results using the fast atomic beam source of the present invention will be explained. Figure 2 shows the fast atomic beam radiation characteristics of the fast atomic beam source of the present invention. The fast atomic beam is emitted from the emission hole at an opening angle of about 15°, and the current density at the exit of the emission hole is shown on the vertical axis of FIG. A constant current (6 A) was applied to the thermionic source 16 to change the magnetic flux density of the magnet 18, and the beam current extracted at that time was measured. The beam current is calculated by converting the number of fast atomic beams into ion current, and the beam current when using the fast atomic beam source of the present invention is expressed as (thermionic source + magnet). For comparison, the beam current (beam' at the point of magnetic flux density O) when only the thermionic source 16 is used is shown.
The beam current when only the magnet 18 is used is also shown. As is clear from FIG. 2, the beam current using the fast atomic beam source of the present invention includes a thermionic source 16 and a magnet 18.
A synergistic effect is seen when each is used alone. That is, when the thermionic source 16 and the magnet 18 are used together, a beam current that is 3 to 5 times as much as when only the thermionic source 16 is used and 1.5 times as much as when only the electromagnet 18 is added is obtained.

<Effects of the Invention> As described above in detail based on the examples, the fast atomic beam source of the present invention increases the probability of bonding between ions and electrons by generating electrons from the thermionic source. The carbonation rate can be increased and freely controlled. Furthermore, since a magnet can be added to focus electrons without causing them to diverge, a large number of high-speed atoms can be detected.

Further, if the high-speed atomic beam source of the present invention is applied to sputtering, material processing can proceed efficiently without being affected by charge-up on the surface of an insulator, which is particularly advantageous when forming a thin film.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the correlation between beam current density and magnetic flux density, and Fig. 3 is a graph showing the correlation between beam current density and magnetic flux density.
Figures (a) and (b) are schematic configuration diagrams and front views showing conventional radiation sources, Figure 4 is an explanatory diagram showing how a mixed beam is irradiated with an electron beam, and Figure 5 is a diagram showing how a mixed beam is neutralized.
FIG. 3 is an explanatory diagram illustrating oblique incidence on r. In the drawing, 1 is the gas inlet, 2 is the anode, 3.4 is the cold cathode, 5 is the beam, 6 is the radiation source, 7 is the mixed beam, 8 is the electron source, 9 is the electron beam, and 10 is the remaining ion Atomic beam; 11 is Neutralizer. 12 is an electron, 13 is an ion, 14 is a beam emission hole, 15 is a diurnal atomic beam, 16 is a thermionic source, 17 is a DC stabilized power source, and 18 is a magnet.

Claims (1)

[Claims] Cold cathodes are placed on both sides of the annular anode, and a gas is interposed between these electrodes to generate a low-pressure gas discharge.A thermionic source is placed close to the cold cathode, and the anode and the cold cathode are placed close to each other. A magnet is arranged around the outer circumference of the cathode to apply a magnetic field in a direction along the electric field formed between the anode and the cold cathode, and electrons and ions that oscillate between the two cold cathodes centering on the anode are generated. A fast atomic beam source characterized in that a beam emission hole for extracting the combined fast atomic beams is provided in the center of one of the cold cathodes.