JP2904439B2 - High power microwave introduction device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-power microwave introduction device for introducing a microwave from a microwave source into a discharge chamber from a waveguide through a microwave introduction window. This high-power microwave introduction apparatus can be used for a microwave plasma or ion beam generation apparatus used for an etching apparatus, a vapor deposition apparatus, an ion implantation apparatus, and the like.

[Prior Art] A conventional microwave or ECR plasma generator is shown in FIG. 3 of the accompanying drawings, in which microwaves are guided to a discharge chamber B by a rectangular or circular waveguide A. A microwave introduction window C is provided at the entrance of the discharge chamber B. The microwave introduction window C is usually made of ceramic, boron nitride, or the like. It is introduced into the discharge chamber B in a vacuum state through the window C. The microwaves introduced into the discharge chamber B form a plasma in the discharge chamber B under the action of the external magnetic field generated by the magnetic field generating means D provided outside the discharge chamber B. The microwave plasma thus formed is irradiated on the substrate E,
It is used for processing such as sputtering, etching, and deposition. Further, an ion beam extraction electrode is placed at the position of the substrate E, and is used as an ion source.

[Problem to be Solved by the Invention] In such a conventional microwave plasma generator,
In order to introduce microwaves, a JIS standard rectangular waveguide [for microwave frequency f = 2.45 GHz, WRJ-2 (cross section)
109.22 mm × 54.61 mm)], and ceramic, boron nitride, quartz, or the like slightly larger than this size is used for the microwave introduction window, and microwaves are introduced into the discharge chamber. In this case, the size of the microwave introduction window is about 120 mm × 60 mm when f = 2.45 GHz,
There is a problem that this window is broken during plasma discharge or during extraction of the ion beam. The main causes of breakage of the microwave introduction window are (1) heat generation due to dielectric loss of the microwave introduction window, (2) heat generation due to plasma irradiation from the discharge chamber to the microwave introduction window, and (3) ions. In the case of the source, the impact of the back-flow electron beam generated at the extraction electrode portion is applied, resulting in a serious heat load. When the effects of (1), (2) or (1), (2), and (3) act simultaneously, the central portion of the window is heated, and the temperature difference from the peripheral portion increases, leading to destruction. Become.

In order to avoid the destruction of the microwave introduction window due to heat generation and heat load caused by the above (2) and (3), the conventional window is formed in a triple structure, and the surface of the ceramic window is prevented from being charged up. TiN less than thickness, for example, about 50mm
Coating measures have been taken. However, the triple window structure increases the microwave dielectric loss, and the TiN coating is also effective for charge-up, but it is ineffective at heat load of electrons and when exposed to plasma when the thickness is about 50 mm. There is a problem that the TiN film is immediately peeled off.

Therefore, the present invention solves the problems associated with the prior art as described above, that is, removes the heat and heat load caused by the above (2) and (3), and further increases the microwave output to about 5 kW or even higher. It is an object of the present invention to provide a high-power microwave introduction device for a plasma generator capable of stably introducing the microwave.

[Means for Solving the Problems] In order to achieve the above object, in the high-power microwave introduction apparatus according to the present invention, as shown in FIG.
A microwave introduction waveguide 5 having a small cross-sectional area is inserted between the standard waveguide 1 and the magnetic field in this portion, as shown in FIG. The invention is characterized in that a distribution is formed, and the waveguide 1 and the window 3 are connected by a tapered waveguide 2.

The cross section of the waveguide 5 is made larger than the shape that blocks microwaves. For example, in the case of a rectangular waveguide, the waveguide width a needs to be equal to or greater than the cut-off waveguide width c / 2f. Where c is the light speed of 2.998 × 10 ¹⁰ c
m and f are microwave frequencies. The height b of the rectangular waveguide is set as long as the window 3 is not damaged by the heat generated by the above (1), as long as there is no discharge between the upper and lower walls of the waveguide 5, or as long as the creeping discharge does not occur in the window 3. , As small as possible. The cross-sectional shape of the waveguide 5 is not particularly limited as long as it can be reduced without blocking the microwave. For example, it may be square or elliptical.

Although the magnetic field distribution inside the waveguide 5 is a magnetic field distribution diverging from the discharge chamber toward the window as described above, the inside of the waveguide 5 corresponds to electron cyclotron resonance (ECR) (f = (B = 875G for 2.45GHz) Avoid generating points with magnetic field strength.

[Operation] In the high power microwave introduction device according to the present invention thus configured, since the taper waveguide is connected to the JIS standard waveguide to reduce the cross section, the microwave introduction window is The cross section can be reduced to a diameter corresponding to the cutoff wavelength of the fundamental mode wave of the waveguide used, and thus the cooling efficiency of the window by the cooling tube (FIG. 1) wound around the window is improved. As a result, the temperature difference between the central part and the peripheral part of the window is about 1/5 or less as compared with the case of the JIS standard window.

In addition, since a diverging magnetic field exists in the region of the conduction waveguide 5, electrons and ions from the plasma and further backflow electrons from the ion extraction electrode portion are prevented from traveling by this magnetic field.
It collides with the direction of the diverging magnetic field lines, that is, the metal wall of the waveguide 5, and does not reach the window 3. Therefore, the causes (2) and (3) of the above-described window destruction can be eliminated.

When the plasma is generated inside the waveguide 5, the window 3 is damaged in a short time by the plasma irradiation, but this possibility is eliminated by the following operation. As described above, since no ECR point is formed in this region, plasma generation by ECR discharge cannot occur. Although it is a normal non-microwave discharge, the distance b between the walls is sufficiently small and the diverging magnetic field causes electrons to collide with the neutral gas and collide with the wall before ionization. That is, the breakdown condition for generating the plasma is not satisfied. The reason why the distance b between the walls is made sufficiently small and the divergent magnetic field is used in the present invention is to eliminate the causes (1) and (2) of the window damage, and at the same time, satisfy the conditions for preventing plasma from being generated in this region. That's why.

By the way, it is conceivable that the window is charged up by the impact of electrons on the window, causing a potential difference from the peripheral portion to discharge and destroy the electrode. Even if it is raised, the current in the direction parallel to the surface of the window can be forcibly induced by the E × B force of the electric field in the surface direction and the magnetic field in the axial direction, thereby eliminating the charge-up.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2 of the accompanying drawings.

1 and 2 show an embodiment in which the present invention is implemented as a microwave introduction device for an ECR plasma generator, and an example of a magnetic field distribution thereof. In the drawing, 1 is a rectangular waveguide for microwaves of 2.45 GHz (JIS standard WRJ-2, dimensions 109.22 mm x 54.6
1 mm), and the microwave introduction window 3
A tapered waveguide 2 whose cross section is reduced to 80 mm × 10 mm is connected. Successively, quartz window 3, cross section 80mm
A 10 mm guide waveguide 5 and a discharge tube 6 are connected. Is for the width a of the waveguide 5, but the following relationship holds between the width a of the fundamental mode TE ₁₀ wave of cutoff frequency f _c and the microwave introduction waveguide of the rectangular waveguide.

f _c = c / 2a Now, if the incident microwave is 2.45 GHz, a
It becomes 6.12cm. Thus the width a microwave introduction waveguide can be set up theoretically a = c / 2f _c, for example, when using a rectangular waveguide commercial JIS standard introducing a 2.45GHz microwave is the frequency band corresponding long and 1.7～2.6GHz, in the present invention of 2.45GHz this case, and since it is sufficient introduced the fundamental mode TE _10, the width a of the introduction waveguide is very small to 6.12cm that Can be. The height b of the waveguide 5 is determined in consideration of the creeping discharge in the quartz window 3 due to the microwave electric field,
In this embodiment, it is set to 10 mm. Even if the height b is infinitely small, the microwave is not cut off. However, as described above, the limit of the smaller height b is the above-described surface discharge,
Alternatively, it is set according to the condition of the dielectric breakdown discharge between the upper and lower walls of the waveguide 5 whichever is weaker.

As shown, a cooling pipe 4 for cooling the microwave introduction window 3 is provided around the microwave introduction window 3. A magnetic field generating coil 7 is provided around the microwave introduction waveguide 5 and the discharge chamber 6, and the maximum point of the magnetic field strength is in the discharge chamber in the example of FIG. A divergent magnetic field distribution is formed in the region between the maximum point and the window 3 all over the ECR magnetic field strength (875 G) and toward the window. Plasma is generated from the maximum point on the irradiation section 8 side, and most of the plasma flows to the irradiation section, and a part of the plasma leaks to the window side beyond this point.

In the operation of the illustrated apparatus configured as described above, the cross-section of the waveguide before and after the microwave introduction window can be reduced to a cross-sectional dimension close to the cutoff wavelength of the microwave. The cooling pipes 4 provided in the vicinity of the vicinity can efficiently cool the microwave introduction window 3, thereby effectively suppressing the heat generation of the window and increasing the size of the microwave introduction window 3 between the central portion and the peripheral portion. The occurrence of a temperature difference can be prevented.

Further, the diverging magnetic field formed in the region of the waveguide 5 works to diffuse plasma leaking from the discharge chamber 6 beyond the maximum point of the magnetic field and backflow electrons from the extraction electrode to the metal wall, and these scattered magnetic fields are generated. The particles are prevented from colliding with the introduction window 3. By setting the magnetic field in this region to be greater than the ECR magnetic field intensity of 875 gauss, the occurrence of ECR discharge in this region is prevented. Furthermore, the charge-up of the microwave introduction window 3 that can be caused by the impact of electrons is minimized by the effect of the diverging magnetic field. Even if the charge-up occurs, the E × B force due to the electric field in the surface direction and the magnetic field in the axial direction is obtained. This induces a current in a direction parallel to the surface of the window, and the resulting charge-up can be substantially eliminated. The material of the window 3 is not limited to quartz as in this embodiment as long as the material of the window 3 has a small dielectric loss with respect to microwaves and is strong against heat load.

By the way, in the illustrated embodiment, the microwave frequency is 2.45.
Although the case of GHz has been illustrated, the present invention is naturally applicable to microwaves of any frequency.
In addition, the present invention can be applied to a waveguide having an arbitrary cross-sectional shape.
For example, in a rectangular waveguide, the minimum value a _c of the width a of the microwave introduction waveguide 5 is defined as a _c = c / 2f (c = 2.998 × 10 ¹⁰⁾ as described above, where f is the frequency of the microwave used. cm).

Although a rectangular waveguide is used in the illustrated embodiment, a circular waveguide or an elliptical waveguide may be used instead. For circular waveguide, the fundamental mode is TE _11, the minimum value of the diameter a microwave introduction waveguide a _c = _c / 3.4125f
Becomes

[Effects of the Invention] As described above, in the present invention, a tapered waveguide, a microwave introduction window having a small cross-sectional area, and a microwave guided waveguide having a small cross-sectional area are provided between a microwave waveguide and a discharge tube. Means are provided for attaching the tube and generating a divergent magnetic field in the microwave introduction waveguide region. According to the present invention, the microwave introduction window can be efficiently cooled to reduce the temperature difference between the central portion and the peripheral portion thereof, and the introduction window can be protected from plasma and backflow electron impact. It can be counteracted by the current induced in the direction parallel to the surface of the microwave introduction window by the action of the electric field in the direction of the window surface and the magnetic field in the axial direction. High-power microwave of 5KW or more can be stably introduced into plasma.

[Brief description of the drawings]

1 (a) is a schematic horizontal sectional view showing an embodiment of the present invention, FIG. 1 (b) is a side view thereof, FIG. 2 is an example of a magnetic field distribution applied to the apparatus of FIG. 1, and FIG. It is the schematic which shows an example of the conventional microwave plasma generator. In the figure, 1: Waveguide 2: Tapered waveguide 3: Microwave introduction window 4: Cooling tube 5: Microwave introduction waveguide 6: Discharge tube 7: Magnetic field generating coil 8: Plasma irradiation target or ion extraction electrode

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideo Tsuboi 2500 Hagizono, Hagizono, Chigasaki City, Kanagawa Prefecture (72) Inventor Akira Hoshino 2500 Hagizono, Hagizono, Chigasaki City, Kanagawa Prefecture, Japan 56) References JP-A-63-289799 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05H 1/46

Claims (3)

(57) [Claims] 1. A high-power microwave introduction apparatus for introducing microwaves from a microwave source through a microwave introduction window into a plasma discharge chamber from a microwave source, wherein the microwave power supply apparatus is mounted between the waveguide and the plasma discharge chamber. A tapered waveguide for reducing the cross-sectional area toward the microwave introduction window, a microwave introduction window having a small cross-sectional area and a microwave introduction waveguide having a small cross-sectional area, and a microwave introduction waveguide region A high-power microwave introduction apparatus characterized in that a magnetic field diverging from the discharge chamber toward the microwave introduction window is distributed to reduce the area of the microwave introduction window. 2. The cross-sectional area of the microwave introducing waveguide is smaller than the cross-sectional area of the JIS standard waveguide corresponding to the frequency used, and the cross-sectional shape of the microwave introducing waveguide corresponds to the frequency used. 2. The high power microwave introduction device according to claim 1, wherein the high power microwave introduction device has a microwave cutoff shape. 3. The high power microwave introducing apparatus according to claim 1, wherein no point having an electron cyclotron resonance magnetic field intensity corresponding to the microwave frequency to be used exists in the microwave introducing waveguide region.