JPH0715838B2 - Plasma generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The application fields of plasma generators are expanding year by year.
From the plasma generator, it is possible to generate electrons, ions, ion radicals, etc., especially in the electronics industry,
The extracted ion beam is applied in various fields such as ion implantation, ion plating, crystal growth, sputtering, etching, and compound synthesis.

The present invention relates to a plasma generator that supplies microwave power to generate plasma and extracts an ion beam.

[Conventional technology]

Electron cyclotron resonance absorption (ECR) is used in various fields as a plasma generator because microwave power effectively heats electrons to create high-density plasma by the interaction of magnetic fields and electrons, but it is still 100 mm. It is difficult to generate plasma as flat as possible with the above large diameter.

[Problems to be Solved by the Invention] Conventionally, various methods have been announced as plasma generators using ECR, but all of them are single-mode excitations, and therefore large-diameter plasma cannot be generated. .

The present invention performs TE _on mode excitation by microwave power in a large-diameter metal cylinder, and generates a cyclotron resonance by applying a magnetic field corresponding to this frequency to generate a plasma as flat as possible with a large diameter. It is an object of the present invention to provide a plasma generator that enables the above.

[Means for Solving the Problems]

The present invention relates to a metal cylinder into which an ionized substance is injected, a microwave power supply means for exciting a TE _on mode from one axial end surface of the cylinder through a plurality of loop coils or slits, and the cylinder. And a magnetic field generation means for generating an electron cyclotron resonance absorption by applying a magnetic field corresponding to a microwave frequency from the outside of the plasma generator.

[Action]

There are TE waves and TM waves in the resonance modes in the metal cylinder. In the former, the electric field does not contact the conductor, but in the latter, the electric field cuts the conductor, resulting in large loss and inefficiency. Therefore, in the present invention, TE _on mode excitation, which is a higher mode of TE wave, is adopted. The o at the beginning of the subscript of the mode signal indicates that there is no change in the electromagnetic field in the circumferential direction, and the next n indicates the number of changes in the radial direction. When both ends of the metal cylinder in the axial direction are closed by metal plates, a resonator is formed and this mode is shown in the form of TE _onm , where m is the number of changes in the electromagnetic field in the axial direction. Is showing. A longitudinal sectional view of the electromagnetic field of the TE ₀₂₁ resonator is shown in FIG. 2, and a transverse sectional view thereof is shown in FIG. 2 and 3, 1 is a plasma chamber, 2 is an input terminal for microwave power, 71 and 72 are electric field distributions, 8 is a magnetic field distribution, 12 ...
13 indicates a metal plate. The plasma chamber 1 has a structure of a metal cylinder, and both end surfaces in the axial direction of the cylinder are closed by metal plates 12 and 13. Since neither the electric field distribution nor the magnetic field distribution touches the metal wall surface, the loss for that is small. Although the drawing shows the case where n is 2, generally n layers are formed. In the present invention, TE
_{Since the} microwave power is applied by the _on- mode excitation, the plasma excitation portion becomes n times as large as the single-mode excitation and spreads in the large-diameter metal cylinder, so that the object can be achieved.

In the case of a TE _{on1 type} resonator, when the diameter D becomes less than the minimum value, it will be attenuated and propagation in the axial direction will not be possible.
The diameter D must be greater than or equal to the minimum value. The cutoff wavelength λ _c for each propagation mode and the minimum diameter D _min for the frequency 2.45 GHz have the relationship shown in the following table.

Assuming that the used frequency is 2.45 GHz, the wavelength λ ₀ is λ ₀ = 122.364 mm, and the resonance length Lmm of the resonator is (1/2) of the guide wavelength, so it can be calculated by the following formula.

_{L = λ 0/2 / {} 1- (λ 0 / λ c) 2} 0.5 Accordingly, when choosing several points above the minimum diameter D _min the diameter D of the cavity of the used frequency 2.45 GHz, the resonant length Lmm Is calculated as shown in the table below.

As shown in the above table, when the diameter D is thickened in TE _{on 1} mode,
Since the resonance length L becomes short, if the TE _onm mode is used to make L longer, it can be expanded m times.

In electron cyclotron resonance, plasma electrons can be selectively heated by the interaction between a magnetic field and microwave power to create high-density plasma. There is the following relationship between the electron cyclotron frequency f (GHz) and the magnetic field strength B (kGauss).

f = 2.8B That is, at f = 2.45 (GHz), B = 0.875 (kGauss). However, this magnetic field strength does not have to be set to this value over the entire surface of the plasma generation chamber, and in particular, the portion where the plasma is ignited near the ionized substance introduction port and the magnetic mirror action is performed near the plasma generation chamber outlet. Therefore, the magnetic field strength may be adjusted.

〔Example〕

FIG. 1 is a vertical cross-sectional view for explaining the outline of the present invention.

Reference numeral 1 is a plasma chamber made of a metal cylinder, and one end face in the axial direction of the metal cylinder is sealed with a metal plate 12, and microwave power is supplied from a terminal 2 to perform TE _on mode excitation. . 3 is an exciting coil or a permanent magnet, and is a plasma chamber 1
Set the inside to the required magnetic field strength. Reference numeral 4 denotes a plasma substance introduction port for feeding gaseous substances into the plasma chamber 1 from multiple directions, and the inside of the plasma chamber 1 is set to about 10 ^{-2 to} 10 ^-3 Torr.
In the vicinity of the plasma substance input port 4, a magnetic field having a strength that causes cyclotron resonance absorption is applied, so that the plasma is ignited and diffused inside the plasma chamber 1 according to the flow of gas to be averaged. This plasma flow
Since it is excited by the microwave power of TE _on mode, it has a large diameter. On the other end surface of the plasma chamber 1, many small holes are made in the metal plate 13, and a thick ion beam 6 is taken out to the outside due to the potential difference with the ion extraction electrode 5.

FIG. 4 shows a state in which microwave power is supplied by the loop coil as viewed from the inside of the plasma chamber 1. In the TE _on mode excitation, the magnetic field around the end face is oriented in the diametrical direction as shown in Fig. 2 and Fig. 3, so make sure that the strips of the loop coils 21 and 22 are perpendicular to the magnetic field. Moreover, they are attached so that the adjacent excitation phases are reversed. Further, since the plasma chamber is in a low vacuum state, the loop mounting portion of the metal plate 12 is sealed with the heat resistant insulator 9. That is, in FIG. 4, the loop coil 21 is located at the position 21 of the heat resistant insulator 9.
After being drawn into the plasma chamber from 1, it is bent to the left side in the drawing, and further bent and then joined to the metal plate 12. The loop coil 22 is retracted from the opposite direction to the loop coil 21, and therefore is retracted from the position 221 into the plasma chamber.

When microwave excitation is performed from the waveguide through the slit, microwave power is supplied from the waveguide 11 through the slit 10 formed at right angles to the magnetic field as shown in FIG. In this case also, the adjacent slits 10 are constructed so that the excitation phases thereof are opposite to each other, and the slits are sealed with a heat-resistant insulating material to maintain airtightness.

In the present invention, the problem when using a large resonator is how to suppress the TM mode. Although it is a heterogeneous mode resonance, it is a problem in the TE _on mode because the dimensions are the same as the TM _1n mode.

In the TM _1n mode, the electric field and the magnetic field of TE _on are opposite to each other, so that the microwave current flows in the resonator wall and the loss increases. Therefore, in the present invention, the sixth mode suppressor is used as a heterogeneous mode suppressor.
I tried to construct the figure. FIG. 6 is a partial vertical cross-sectional view of the end face portion of the cylinder of the plasma chamber, in which a heat-resistant insulating ring 91 is inserted between the cylinder 101 and the metal plate 121 to increase the electrical loss of TM mode resonance. The heat-resistant insulating ring 91 is used as a suppressor for TM mode of different mode resonance.

In this embodiment, a microwave power source of 2.45 GHz and 5 kW is used, and the plasma chamber dimensions are 320 mm in diameter and 235.7 mm in length.
(TE022 mode) was used, and a magnetic field of 875 gauss was applied from the outside by an exciting coil. As a result, it was confirmed that a large number of samples generated plasma with high efficiency and large diameter.

〔The invention's effect〕

According to the present invention, plasma with a large diameter of 200 mm to 500 mm can be generated substantially uniformly with high efficiency.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a plasma generator of the present invention, and FIG.
The figure shows a longitudinal cross-sectional view of the electromagnetic field of the TE ₀₁₂ resonator, FIG. 3 shows its cross-sectional view, and FIG. 4 shows an embodiment using a loop coil.
FIG. 5 is a view showing an embodiment using microwave excitation by a slit, and FIG. 6 is a vertical sectional view of a suppressor. 1 is a plasma chamber, 2 is an input terminal, 21 and 22 are loop coils, 3 is an exciting coil or a permanent magnet, 4 is a plasma substance inlet, 5 is an ion extraction electrode, 6 is an ion beam,
71 and 72 are electric field distribution, 8 is magnetic field distribution, 9 is heat resistant insulator, 10
Is a slit, 11 is a waveguide, 12/13/121 is a metal plate, 91 is a heat-resistant insulating ring, and 101 is a cylinder.

Claims (2)

[Claims] 1. A metal cylinder into which an ionized substance is injected,
Microwave power supply means for exciting the TE _on mode from one axial end surface of the cylinder through a plurality of loop coils or slits, and an electron cyclotron by applying a magnetic field corresponding to the microwave frequency from the outside of the cylinder. A plasma generator comprising magnetic field generating means for causing resonance absorption. 2. The plasma generator according to claim 1, further comprising a suppressor provided between the cylinder and the axial end face for suppressing the TM mode supply of microwave power.