JPH0673319B2 - Plasma equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plasma device that utilizes microwave discharge to generate plasma for laser excitation and for plasma processing.

[Conventional technology]

Conventionally, there are various types of plasma devices using microwave discharge such as laser devices, light source devices, plasma processing devices, and ion sources.

Figure 8 shows, for example, the Journal of Applied Physics Vol.49, N
O.7, July 1978, P.3753, which is a sectional view showing a conventional gas laser device as a plasma device, and FIG. 9 is a sectional view taken along line BB in FIG. In the figure, (3) is a waveguide that transmits microwaves, (31) is a waveguide taper provided in a part of this waveguide, and (32) is installed in the space of this waveguide taper portion. Laser discharge tube made of pyrex glass, (33) laser glass inlet provided at the end of the laser discharge tube, (34) laser gas outlet,
(35) is a cooling gas supply pipe arranged so as to enclose the laser discharge pipe (32), (36) is a cooling gas inlet provided at the end of the cooling gas supply pipe, and (37) is the same cooling gas. The discharge port, (38) is a Brewster window provided at both ends of the laser discharge tube (32), (39) is a cathode for DC discharge, (4)
0) is also an anode.

In the conventional gas laser device as described above, a CO gas is introduced from the laser gas inlet port (33) into the laser discharge tube (32).
₂ Laser gas such as laser gas is introduced, while TE ₁₀ mode microwave is excited in the waveguide (3). This waveguide (3) has a waveguide taper (31) inside, and the inner diameter of the waveguide (3) is minimized at the position where the laser discharge tube (32) is installed. The electric field of the microwave becomes maximum at the position. Due to this strong microwave electric field, the laser gas in the laser discharge tube (32) is discharged and destroyed,
Plasma is generated and the laser medium is excited. At this time,
For example, a low-temperature N ₂ gas or the like is caused to flow at high speed in the cooling gas supply pipe (35) to cool the laser discharge pipe (32) from the outside, and the discharge conditions such as the pressure of the laser gas are appropriately selected. Laser oscillation conditions are obtained, and laser oscillation is performed by providing a laser oscillation mirror (not shown) outside the Brewster window (38).

[Problems to be solved by the invention]

In the conventional gas laser device as described above, since the closed laser discharge tube (32) is used, when a plasma having conductivity is generated, the plasma in the laser discharge tube (32) is used as an inner conductor. The microwave mode of the mode becomes dominant, and the microwave electric field in the plasma becomes a laser discharge tube (32).
An electric field whose main component is a component parallel to the tube wall of the
It is a mode that is incident perpendicularly to the tube wall of 2), that is, the plasma boundary. Thus, in the discharge generated by the microwave incident perpendicularly to the plasma electric field, the microwave electric field decreases from the wall of the discharge tube toward the inside.
Since the discharge plasma has a constant-voltage characteristic, a slight difference in the electric field causes a large change in the current density, resulting in the generation of extremely nonuniform plasma concentrated near the wall of the discharge tube. This situation is shown in the sectional view of FIG. In the figure, (31) is the waveguide taper, (32) is the laser discharge tube,
(69) is the electric field line of the microwave electric field, and (70) is the plasma. In a conventional gas laser device using microwave discharge, it is difficult to put the entire discharge into a state suitable for laser excitation because of the non-uniform plasma generation as shown in Fig. 10. The mode and plasma did not overlap, and the laser output and efficiency were low. In fact, the device shown in Fig. 8 uses a pulse microwave of 132Hz at 2.45GHz and a peak width of 2.6KW with a pulse width of 1µs, and only an average output of 15mW is obtained. It is considered that this is because it was possible to operate only at a very low pulse duty of 1 μs 132 Hz, that is, about 1 / 10,000, because of the non-uniformity of the discharge described above.

The above description has been made by taking a gas laser device as an example of a conventional plasma device, but other plasma devices also have various problems due to nonuniform discharge.

The present invention has been made to solve the above problems, and an object thereof is to obtain a plasma device that generates a microwave discharge plasma that is spatially uniform.

[Means for solving problems]

The gas laser device according to the present invention is a space formed between a conductor wall forming a part of a microwave circuit, such as a waveguide, and a dielectric provided so as to face the conductor wall. A laser gas is enclosed in the interior of the chamber, and plasma is generated by microwave discharge using pulsed microwaves.

[Action]

In the plasma device according to the present invention, since there is a conductor wall having a conductivity higher than that of the plasma facing the dielectric material which is the microwave entrance window, the terminal current of the incident microwave flows through this conductor wall. , A current that penetrates between the dielectric and the conductor wall flows in the plasma, so that a spatially uniform plasma is generated and the plasma is further spatially separated by the pulsed microwave. Like

〔Example〕

FIG. 1 is a schematic view showing a gas laser device according to an embodiment of the present invention. (1) is a magnetron which is a microwave oscillator, (2) is a waveguide, (3) is a waveguide (2). A horn waveguide that expands the width of the microwave, (4) is a microwave coupling window,
(5) is a mirror for laser oscillation, (6) is a laser head portion, and FIG. 2 is a sectional view taken along the line AA in FIG. 1 showing the details of the laser head portion (6). As shown in FIG. 2, the laser head portion (6) has a structure of a ridge waveguide type microwave cavity which is a kind of microwave circuit. Second
In the figure, (61) is a cavity wall following the microwave coupling window (4), (62) and (63) are ridges formed in the center of the cross section of this cavity wall, and (64) is one of these. Ritsuji (62)
And (65) is a conductor wall forming a part of the microwave circuit. In this embodiment, the groove (64) is formed.
Walls of are used. (66) is a dielectric such as alumina provided facing the conductor wall (65),
(67) is a discharge space formed between the conductor wall (65) and the dielectric (66) by covering the groove (64) with the dielectric (66). (67) for example CO
₂ Laser gas such as laser gas is enclosed. Also (6
8) is the cooling water channel formed in the ridges (62) and (63).

On the other hand, the power source for driving the magnetron (1) is constructed as shown in FIG. In FIG. 3, the commercial frequency AC power source E is converted into DC by the rectifying and smoothing circuit (11), and this DC is converted into high frequency AC such as 20 KHz by the DC-AC inverter circuit (12). This high-frequency alternating current is boosted by the transformer (13), and the capacitor C, diodes D ₁ , D ₂
Is converted into a high-voltage pulsating flow by the half-wave voltage doubler rectifier circuit (14) and applied to the magnetron (1). (1
5) is the filament power supply for the magnetron (1).

In the gas laser device according to the present invention constructed as shown in FIGS. 1 to 3, the microwave generated by the magnetron (1) is propagated through the waveguide (2) and spread by the horn waveguide (3). Then, impedance matching is performed in the microwave coupling window (4) to efficiently couple the laser head portion (6). The laser head portion (6) is in the shape of a cavity of the ridge as shown in the sectional view of FIG. 2, and the microwave is concentrated between the ridges (62) and (63). Due to the strong electromagnetic field of this concentrated microwave, the discharge space (67)
The laser gas enclosed in the lamp is destroyed by discharge, plasma is generated, and the laser medium is excited. Where the cooling channel (68)
Laser oscillation conditions are obtained by flowing cooling water to cool the discharge plasma and appropriately selecting discharge conditions such as the pressure of the laser gas, and the mirror (5) in FIG. Laser oscillation light can be obtained by forming a laser resonator with one mirror. At this time, in the gas laser device according to the present invention, the conductor wall (65) forming a part of the microwave circuit and the dielectric wall which is provided so as to face the conductor wall (65) and serves as a microwave incident window. Since the microwave discharge is generated in the discharge space (67) formed between the body (66) and the microwave, the microwave is incident only from one surface of the plasma, and the coaxial mode of the plasma is used as the inner conductor. The phenomenon in which the microwave mode is dominant does not occur, and the desired microwave mode discharge can be performed. In addition, when the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric (66) and the plasma like the ridge cavity shown in FIG. Since the walls (65) are installed to face each other, the electric conductor wall (65) also has a vertical electric field component, and an electric field penetrating the plasma can be generated. At this time, even if a conductive plasma is generated, there is a conductor wall (65) that is several orders of magnitude more conductive than the plasma, facing the dielectric (66) that is the microwave entrance window. The end current of the wave is the conductor wall (65)
The electric field in the vicinity of the conductor wall (65) is forced to be perpendicular to the surface of the conductor wall (65) and the electric field penetrating the plasma is maintained. For this reason, microwaves penetrate into the plasma, and a current flows through the plasma, resulting in a spatially uniform discharge plasma due to the continuity of the current. This state is shown in the enlarged sectional view of FIG. In the figure, (69) is the electric field lines of the microwave electric field, and (70) is the discharge plasma. According to the gas laser device of the present invention, a uniform discharge as shown in FIG. 4 can be obtained. However, perpendicular to the plane of Fig. 4,
That is, a discharge node is generated in the discharge length direction in accordance with the microwave mode.

In the embodiment of the present invention, the power source of the magnetron, which is a microwave oscillator for generating microwaves, is shown in FIG. The microwave generated by the magnetron driven by this power supply has a waveform as shown in FIG. That is, pulsed microwaves intermittently generated at a high frequency are generated. The pulse duty of this pulse microwave can be set to a very large value such as 0.1 to 0.4 as compared with the conventional pulse microwave. Also, the pulse frequency is several
Can be very high like 10KHz. When the apparatus of FIGS. 1 and 2 is operated by the pulsed microwave as described above, the length of the discharge cut at the node of the microwave electromagnetic field in the length direction becomes short, and the discharge becomes more uniform in the length direction. It was confirmed that If the pulse frequency is about 500Hz or more,
The temporal modulation of plasma parameters is suppressed, and a uniform plasma is generated in terms of time.

By obtaining a uniform discharge as described above, it becomes easier to put the entire discharge in an optimal state for laser excitation, and the laser cavity mode and plasma overlap are good, and the gas using conventional microwave discharge is used. It is possible to obtain laser oscillation with high efficiency and high output, which is orders of magnitude higher than that of laser devices. Here, the sixth example of the experiment by the present inventors is shown.
The figure shows the structure shown in Figs. 1 to 3 and the discharge length is 300 mm.
Fig. 5 is a graph of the experimental results when the device in Fig. ₂ was applied to a CO ₂ laser, where the horizontal axis is the microwave input and the vertical axis is the CO ₂ laser output and efficiency. Here, as a magnetron, 2M 120
(Hitachi) was used to generate a microwave of about 2.45 GHz. The pulse frequency is 20 KHz and the pulse duty is 0.4. As shown in Fig. 6, the maximum output is 24W and the maximum efficiency is 10.5.
%, A high output of 3 digits or more was obtained for the CO ₂ laser output of 15 mW reported in the conventional example shown in FIG. In the device, it was confirmed that the microwave can be pulsed but the laser can oscillate CW.

In the above embodiment, an inverter is used as the power source of the magnetron, but a pulsed microwave may be generated from a high voltage DC power source using a tipper type power source applied to the magnetron through a switching element.
Further, although the laser device is shown as the plasma device in the above-mentioned embodiment, even if the present invention is applied to the ion source or the light source plasma processing device, the effect of making the discharge spatially and temporally uniform is similar.

Further, in the above-described embodiment, the case where the ridge cavity is used as the microwave circuit, the groove is formed in the ridge, and the groove is covered with the dielectric to form the discharge space is described. A coaxial line as shown in FIG. 7 may be used. In Fig. 7, (67) is the discharge space and (6
1) and (65) are the outer and inner conductors that make up the coaxial line, and (66) is a dielectric such as a quartz glass tube. With such a structure, even if plasma is generated in the discharge space by the pulsed microwave, the discharge becomes uniform as in the case of FIG. In addition to this, a discharge space is formed between a conductor wall forming a part of the microwave circuit and a dielectric provided so as to face the conductor wall, and the boundary between the dielectric and the discharge space, that is, plasma is formed. Any configuration that excites a microwave mode having an electric field component perpendicular to the
The same effect as that of FIG. 7 and FIG. 7 can be obtained in which the discharge becomes more uniform.

Further, in the above embodiment, the case where the conductor and the plasma contact each other has been described, but even if a thin dielectric layer such as a dielectric coating layer is provided on the surface of the conductor, this dielectric layer has a large electric field distribution of microwaves. Needless to say, the above effects are not impaired because they have no effect.

[Advantages of the Invention] As described above, according to the present invention, the plasma device is formed between the conductor wall forming a part of the microwave circuit and the dielectric provided so as to face the conductor wall. The plasma generation medium is enclosed in the space defined by the microwave circuit, and the microwave circuit forms a microwave mode having a component perpendicular to the boundary with the dielectric so as to excite pulsed microwaves in the microwave circuit. Therefore, there is an effect that a spatially uniform plasma can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view showing a gas laser device as a plasma device according to an embodiment of the present invention, and FIG. 2 is an AA of FIG.
3 is a power supply circuit diagram of a microwave oscillator according to an embodiment of the present invention, FIG. 4 is an enlarged cross-sectional view of an essential part for explaining the state of discharge in FIG. 2, and FIG. The figure which shows the waveform of the microwave generated using the power supply of the figure, 6th
1 is a graph showing laser oscillation characteristics in the embodiment shown in FIGS. 1 to 3, FIG. 7 is a sectional view showing another embodiment of the present invention, and FIG. 8 is a sectional view showing a conventional gas laser device. , FIG. 9 is a cross-sectional view of FIG. 8B-, and FIG. 10 is a cross-sectional view illustrating the state of discharge in a conventional gas laser device. In the figure, (65) is a conductor wall forming a part of the microwave circuit, (66) is a dielectric, (67) is a discharge space, and (70) is a discharge space.
Is discharge plasma. The same reference numerals in each figure indicate the same or corresponding parts.

Front page continuation (72) Inventor Yoshihiro Ueda 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture Sanryu Electric Co., Ltd. Applied Equipment Laboratory (72) Inventor Tadashi Yanagi 8-1-1 Tsukaguchi Honcho, Amagasaki City, Hyogo Prefecture No. 1 Sanritsu Electric Co., Ltd. Applied Equipment Laboratory

Claims (4)

[Claims] 1. In a plasma device for generating plasma by microwave discharge in a microwave circuit, a conductor wall forming a part of the microwave circuit, and a dielectric provided so as to face the conductor wall. A plasma generation medium that generates the plasma is enclosed in a space formed between the microwave circuit and the microwave circuit, and the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric and the plasma. , A plasma device characterized by exciting pulsed microwaves in the microwave circuit. 2. The pulse frequency of the pulse microwave is 500 Hz.
The plasma apparatus according to claim 1, characterized in that the above is the case. 3. The pulse microwave converts direct current into alternating current having a frequency higher than the commercial frequency by an AC-DC inverter,
2. The plasma device according to claim 1, wherein the plasma is generated by a microwave oscillator driven by a power source that generates a high voltage of pulsating current in a half-wave voltage doubler circuit after boosting by a transformer. 4. The plasma device according to claim 1, wherein the pulse microwave is generated by a microwave oscillator driven by a high-voltage pulse power source in which a high-voltage direct current is intermittently connected by a switching element.