JP2897168B2 - Microwave introduction window for vacuum vessel - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a microwave introduction window of a vacuum container, and more particularly to a vacuum container that generates plasma in an internal space based on a discharge action. The present invention relates to an improvement of a microwave introduction window of a vacuum vessel having a vacuum seal structure, which is a window for introducing microwave power.

[Conventional technology]

Conventionally, an ECR (Electron Cyclotron Resonance) apparatus configured to generate plasma using microwaves has been proposed (Japanese Patent Laid-Open No. 55-141729). In these apparatuses, a microwave introduction window is formed at one location on the wall of the vacuum vessel to introduce the microwave into the vacuum vessel forming the plasma generation chamber. Such a microwave introduction window is made of a material having a small loss with respect to microwaves, has a low generation of reflected waves of microwaves in the window, is easy to clean and replace, and has a small window. There are demands such as sufficient safety measures at the time of breakage, simple structure and inexpensive fabrication. FIG. 8 to FIG. 10 show an example of the structure of a conventional microwave introduction window in response to these requirements. These figures show only the microwave introduction window.

The microwave introduction window shown in FIG. 8 is a window having the most general structure. In FIG. 8, reference numeral 101 denotes a part of the vacuum vessel of the microwave discharge device, 102 denotes a waveguide for introducing a microwave into the vacuum vessel 101, and 103 denotes a material having a small microwave loss such as quartz. Window disk, 104 is an O-ring for performing vacuum sealing, 105 is a groove for fixing the O-ring 104, 106 is a micro-hole formed in the vacuum vessel 101 for introducing microwaves to generate electric discharge. Wave coupling hole. In the microwave introduction window, an annular concave portion 107 is formed on the outer surface of the vacuum vessel 101 in the microwave coupling hole 106, and a window disk 103 is provided in the concave portion 107. Since the groove 105 is formed in a portion corresponding to the bottom of the concave portion 107, the O-ring 104 fixed to the groove 105 is in contact with the lower surface of the window disc 103. Vacuum container 101 of waveguide 102
A mounting flange 102a is formed at the end on the
The reference numeral 102 is attached to a wall around the microwave coupling hole 106 of the vacuum vessel 101 via a mounting flange 102a by coupling means (not shown). In FIG. 8, a microwave generation source is provided on the upper end side of the waveguide 102, and an exhaust device is provided below the vacuum vessel 101.

In the structure of the microwave introduction window shown in FIG.
1, the waveguide 102 and the window disk 103 are the same as the conventional example shown in FIG. In this conventional example, a groove 105 is formed in the side surface of the concave portion 107 so that the O-ring 104 comes into contact with the peripheral surface of the disk 103, and the O-ring 104 is provided in the groove 105.

In the microwave introduction window shown in FIG. 10, the window disk 103 is sealed to the inner wall of the waveguide 102 by brazing or the like, thereby performing vacuum sealing. Also, the mounting flange 102 of the waveguide 102
a is formed with a large thickness, and a ring-shaped groove 108 is formed on the outer surface of the mounting flange 102a.
104 are arranged. In this state, the mounting flange 102a is fixed to a portion around the hole 106 of the vacuum vessel 101.

[Problems to be Solved by the Invention] The above-mentioned conventional microwave introduction windows have the following problems.

Although the window shown in FIG. 8 has a simple structure and can be manufactured at low cost, it is relatively large as a place for forming a groove 105 for fixing the O-ring 104 on the atmosphere side of the microwave coupling hole 106. It is necessary to provide a step. Since the microwave current flowing on the wall surface flows only on the surface of the waveguide 102, the groove 1
05 has a disadvantage that current loss is increased and a reflected wave is easily generated due to mismatching of characteristic impedance. In particular, since the inner end of the groove 105 is vacuum, there is a disadvantage that abnormal discharge is likely to occur due to concentration of the microwave electric field. Further, when the microwave power is large, the heat generation due to the dielectric loss of the O-ring 104 increases. Therefore, according to the structure of the microwave introduction window shown in FIG. 8, heat is generated near the microwave coupling hole 106 due to microwave loss, particularly when the applied power is several hundred W or more. It is disadvantageous in that it is easy and the reliability as a window is poor.

In the window shown in FIG. 9, the O-ring 104 is brought into close contact with the peripheral surface of the window disk 103 to perform vacuum sealing. In this conventional example, the microwave coupling hole 106 also has a projection edge 109 which forms a step for the purpose of preventing the window disk 103 from being sucked into the vacuum vessel 101,
Since it can be made smaller than the conventional example shown in FIG. 8, it is effective to reduce the reflected wave of the microwave. . However, since the window disc 103 is usually formed using quartz, alumina, or the like, it is difficult to process the peripheral surface of the window disc 103 with high dimensional accuracy and as finely as possible for vacuum sealing. In addition, in order to ensure a vacuum seal in this conventional example, it is necessary to install the window disc 103 with the O-ring 104 crushed,
In a microwave discharge device in which the use of lubricating oil is restricted, it is very difficult to dispose the window disk 103 at a predetermined position, so that the practicality of this configuration is low.

The window shown in FIG. 10 has a structure in which the window disc 103 is directly joined to the inner surface of the waveguide 102, and has many uses in microwave heating devices, accelerators, and the like. Usually a window disc
Alumina is used for 103, and the circumferential surface of the window disk is sealed inside the metal waveguide by brazing. With this window, complete vacuum sealing and minimization of loss can be achieved, but the material of the waveguide is usually limited to copper or Kovar, and it is not possible to introduce a highly reactive gas into the vacuum vessel. There are various practical problems from the fact that it must be performed for each waveguide, that it is difficult to double the window disk 103 as a safety measure in case of breakage, and that the manufacturing cost is high.

An object of the present invention is to provide a microwave introduction window of a practical vacuum vessel which is inexpensive, has high reliability, and can introduce a large amount of electric power, in view of the above-mentioned problems of the conventional microwave introduction window. It is in.

[Means for solving the problem]

The microwave introduction window of the vacuum vessel according to the present invention has a window plate member provided in a hole formed in the wall of the vacuum vessel via a vacuum seal member, and is supplied from outside by a waveguide or the like. The microwave introduction window of the vacuum vessel for introducing microwave power into the vacuum vessel through the window plate member has a feature that a conductive thin film is attached to at least a contact portion of the window plate member with the vacuum seal member. .

The microwave introduction window of the second vacuum vessel according to the present invention is characterized in that, in the first configuration, an area of a portion of the window plate member where the conductive thin film is not attached is equal to or larger than an opening area of the hole. Have as a point.

In the microwave introduction window of the third vacuum vessel according to the present invention, in the first configuration, the area of the window plate member to which the conductive thin film is not attached is smaller than the opening area of the hole, and The feature is that the coupling hole is defined by a portion where the conductive thin film is not attached.

The microwave introduction window of the fourth vacuum vessel according to the present invention is characterized in that, in any one of the first to third configurations, the conductive thin film has a thickness of 2 μm or more.

[Action]

In the microwave introduction window of the vacuum vessel according to the present invention, a conductive thin film is adhered to a part of the window disk within a predetermined range that does not prevent the transmission of microwaves, thereby forming a vacuum sealing member. The microwave field does not exist in the ring and the groove for disposing the ring.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention, and shows a cross section of a main part of a microwave introduction window of a vacuum vessel. In FIG. 1, reference numeral 1 denotes a part of the wall of the vacuum vessel, which is configured so that a microwave is supplied into the vacuum vessel 1 and a microwave discharge is generated therein. In FIG. 1, the lower side of the vacuum vessel wall 1 is the inside of the vacuum vessel, and the upper side is the atmosphere side.
Reference numeral 2 denotes a waveguide for introducing microwaves into the vacuum vessel, and the upper part thereof is not shown. A microwave generator 3 is provided at an upper end of the waveguide 2. A flange 2a having a predetermined radial dimension and thickness is formed at an end of the waveguide 2 on the vacuum vessel side. A stepped hole 4 is formed in a portion of the vacuum vessel wall 1 where the waveguide 2 is connected, thereby forming a large-diameter annular recess 4a on the outer surface side of the wall 1 and an inner surface thereof. A small diameter hole 4b is formed on the side. In the embodiment shown in FIG. 1, the stepped hole 4 has a function as a microwave coupling hole for introducing microwaves into the inside of the vacuum vessel. In this embodiment, the microwave coupling hole has a small diameter. It is defined by the hole 4b. Reference numeral 5 denotes a circular protruding edge formed by forming the stepped hole 4 in the wall portion 1. Further, an annular groove 6 is formed at a position on the outer surface of the projection edge 5 corresponding to the bottom of the annular concave portion 4a, and an O-ring 7 functioning as a vacuum sealing member in the microwave introduction window is housed in the groove 6.・ It is arranged.

8 arranged in the recess 4a of the wall 1 of the vacuum vessel
This is a window disk for introducing the microwave supplied by the waveguide 2 into the vacuum vessel and performing vacuum sealing of the vacuum vessel. The window disk 8 is formed of alumina or the like. The diameter of the window disk 8 is smaller than the large diameter hole of the stepped hole 4, that is, the diameter of the concave portion 4a, and is formed so as to be installed in the concave portion 4a. Further, as is apparent from FIG. 1, the window disk 8 and the flange 2a of the waveguide 2 are disposed in the recess 4a, and the combined thickness thereof is set to be substantially equal to the depth of the recess 4a. Have been. A ring plate 9 is disposed from the outside in contact with the window disk 8 and the flange 2a of the waveguide 2 disposed in the outer recess 4a of the stepped hole 4, and the ring plate 9 is attached to the vacuum vessel. It is fixed to the wall 1 with a plurality of bolts 10. Ring plate 9
The center hole 9a is a hole for inserting the waveguide 2.
With the above assembly structure, the assembly portion of the window disk 8 and the waveguide flange 2a forming the microwave introduction window is supported on one side by the end face of the protruding edge 5 and the O-ring 7, and on the other side. Is held down by the ring plate 9. In addition,
The waveguide 2 can be directly attached to the vacuum vessel 1 by making the flange 2a larger.

In the window disk 8, the conductive thin film 11 is attached to a region facing the bottom of the concave portion 4a in the above-described assembly structure. FIG. 2 shows the surface of the window disk 8 to which the conductive thin film 11 is attached. In the figure, reference numeral 11 denotes a ring-shaped conductive thin film. The outer diameter of the conductive thin film 11 is substantially equal to the diameter of the window disk 8, and the inner diameter thereof is substantially equal to the diameter of the small-diameter hole 4b, or is equal to the O-ring 7. It is set to be large within a range that satisfies the condition of contact.

In the vacuum vessel 1 having the microwave introduction window having the above structure, a predetermined gas is introduced into the vacuum vessel at a predetermined pressure, and the microwave power generated by the microwave generator 3 is transmitted through the waveguide 2. Being guided and passing through the window disk 8,
It is introduced into the vacuum vessel 1 through the stepped hole 4 which is a microwave coupling hole. As a result, gas plasma is generated in the vacuum vessel 1 by discharge. This plasma is used for etching, plasma CVD, and the like in a manufacturing process for semiconductors, electronic components, and the like. Such plasma generation has been put to practical use in an ECR device using a magnetic field.

Next, the conductive thin film 11 provided on the window disk 8 functioning as a microwave introduction window will be described in detail. Conductive thin film
11 is attached to the surface on the vacuum vessel side as described above. The area to be attached is set so as not to overlap the stepped hole 4 and to overlap the groove 6 for fixing the O-ring 7 in the assembled state. The condition that the stepped hole 4 is circular is
As shown in FIG. 2, the conductive thin film 11 is concentrically attached to the window disk 8. Also, the stepped hole 4 is not circular,
For example, in the case of a rectangle, it is attached in a shape as shown in FIG.

The thickness of the conductive thin film 11 is determined as follows. The conductive thin film 11 is provided for preventing the microwave electromagnetic field from entering the O-ring 7 and the groove 6 for fixing the O-ring. Therefore, in order to achieve this function, the thickness of the conductive thin film 11 is determined based on the angular frequency ω of the microwave, the conductivity σ of the conductive material, and the magnetic permeability μ, as follows: δ = (2 / μσω) ^{1 / It} is larger than the skin thickness δ given in ² . If the thickness of the conductive thin film 11 satisfies the above condition, microwaves cannot pass through the conductive thin film 11.

Next, δ for a typical conductive material is calculated. However, f = 2.45 GHz and ω = 2πf. As the value of σ, a value of 100 ° C. is used in consideration of the temperature rise of the window disk 8.

Copper: σ-4.5 × 10 ⁷ / m: μ-μ0 = 1.26 × 10 ^-6 H / m: δ-1.5 μm Aluminum: σ-1.3 × 10 ⁷ / m: μ-μ0: δ-1.9 μm Gold: σ ~ 3.5 × 10 ⁷ / m: μ-μ0: δ-1.7 μm Iron: σ-6.8 × 10 ⁷ / m: μ-200 μ0: δ-0.3 μm Thickness of the conductive thin film 11 as evident from the above data Should be at least 2 μm.

Further, as the material of the conductive thin film 11, it is necessary to select a material which does not react with a predetermined gas such as oxygen, chlorine or the like, which is turned into plasma inside the vacuum vessel, to generate oxides, chlorides and the like. is there. Further, methods for attaching the conductive thin film 11 to the disk 8 include vacuum evaporation, ion plating, sputtering, electroless plating, and baking of powdered metal. Any method may be used as long as there is a sufficient adhesive force therebetween and the surface roughness is sufficiently smooth for the vacuum sealing action of the O-ring 7.

Adhesion of conductive thin film 11 to window disk 8
Another embodiment will be described with reference to FIGS.

In FIG. 4, reference numeral 8 denotes the window disk, and reference numeral 21 denotes a conductive thin film. In this embodiment, the thin film 21 is attached to the outer edge and the outer peripheral surface of the lower surface in the figure on the vacuum vessel side. In the conductive thin film 31 according to the embodiment shown in FIG. 5, it is attached to the outer edge of the lower surface on the vacuum vessel side, the outer peripheral surface, and the outer edge of the upper surface on the atmosphere side. It is desirable that the adhesion range of the surface on the atmosphere side be the same as the internal shape of the waveguide 2, but is not limited to this, and may be another shape. The window disk provided with the conductive thin film according to the embodiment shown in FIGS. 4 and 5 is also applicable to the above-described microwave introduction window structure shown in FIG. 9 by improving the finishing accuracy of the thin film on the outer peripheral surface. Can be applied.

In the embodiment of FIG. 6, the conductive thin film on the window disk 8 is shown.
On the lower surface on the vacuum vessel side to which 41 is attached, the area of the portion where the conductive thin film is not attached is configured to be smaller than the opening area of the small diameter hole 4b. Therefore, in this embodiment, the microwave coupling hole is the small-diameter hole 4b of the stepped hole 4.
Instead, it is substantially defined by the conductive thin film 41 attached to the window disk 8. The thickness of the microwave coupling hole defined by the conductive thin film 41 is the thickness of the conductive thin film 41, that is, at least about 2 μm. On the other hand, the thickness of the microwave coupling hole of the window structure in the above embodiment was defined by the thickness of the projection edge 5 forming the small diameter hole 4b. Therefore, when the thickness of the projection edge 5 cannot be made sufficiently small as compared with the wavelength of the microwave to be used, that is, when a microwave having a very high frequency is used, A microwave coupling hole is formed by the conductive thin film 41 adhered as described above, whereby the reflected wave can be reduced, and the utilization efficiency of the microwave power can be improved.

In the configuration of the above embodiment, there is a small gap between the window disk 8 and the vacuum vessel due to the arrangement of the O-ring 7, and the width of this gap is smaller than the microwave wavelength. If it is short enough, the effect will be fully realized.

When the conductive thin film 11 is charged up by being set to a floating potential in a DC manner and abnormal discharge occurs between the conductive thin film 11 and the vacuum vessel 1, as shown in FIG. A short circuit is formed between the vacuum vessel 1 and the vacuum vessel 1 using a metal spring 12. Thereby, the conductive thin film 11
And the vacuum vessel 1 can be kept at the same potential to prevent occurrence of abnormal discharge. In addition, as the metal spring 12, any conductor can be used as long as it is a conductor (for example, an aluminum plate or the like) that can make the conductive thin film 11 and the vacuum vessel 1 have the same potential. Further, the shape of the window disk 8 is not limited to a disk, and may be a square or the like depending on the shapes of the waveguide 2 and the stepped hole 4.

In addition, a hole is made in the center of the window disk 8 and a conductive thin film is adhered inside the hole, so that the present invention can be applied to a coaxial microwave introduction device.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the reflected wave which has conventionally occurred at the place where the O-ring for vacuum sealing is disposed is eliminated by attaching the conductive thin film to the predetermined place of the window disk. As a result, it is possible to improve the reliability of the microwave introduction window in the microwave discharge vacuum device to which the high-power microwave is supplied.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a microwave introduction window of a vacuum vessel according to the present invention, FIG. 2 is an end view of a window disk, and FIG. 3 shows another embodiment of the window disk. FIG. 4 similar to FIG.
5 and 5 are cross-sectional views showing other examples of adhesion of the conductive thin film, FIG. 6 is a cross-sectional view showing another embodiment of the structure of the microwave introduction window of the vacuum vessel, and FIG. 7 is a conductive thin film. 8 to 10 are cross-sectional views showing the structure of a conventional microwave introduction window. [Explanation of References] 1 ... wall of vacuum vessel 2 ... waveguide 3 ... microwave generator 4 ... stepped hole 5 ... projection edge 6 ... groove 7 ... o-ring 8 ... window Disk 11,21,31 …… conductive thin film

Claims (4)

(57) [Claims] 1. A window plate member is provided in a hole formed in a wall of a vacuum container via a vacuum seal member, and microwave power supplied from the outside is supplied to the inside of the vacuum container through the window plate member. A microwave introduction window of a vacuum vessel, wherein a conductive thin film is attached to at least a portion of the window plate member that contacts the vacuum seal member. 2. The microwave introduction window of a vacuum vessel according to claim 1, wherein an area of a portion of said window plate member to which said conductive thin film is not attached is larger than an opening area of said hole. Window for microwave introduction of vacuum vessel. 3. The microwave introduction window of a vacuum vessel according to claim 1, wherein an area of a portion of said window plate member to which said conductive thin film is not attached is smaller than an opening area of said hole, and microwave coupling is performed. A microwave introduction window of a vacuum vessel, wherein a hole is defined at a portion where the conductive thin film is not attached. 4. The microwave introduction window for a vacuum vessel according to claim 1, wherein said conductive thin film has a thickness of 2 μm or more. Introductory window.