JPH0448596A - Window for microwave introduction of vacuum vessel - Google Patents

Abstract

PURPOSE:To provide a practical window of a vacuum vessel for microwave introduction which is economical, highly reliable, and able to introduce high electric power by sticking a conductive thin film to prescribed parts of a disk plate for the window. CONSTITUTION:A conductive thin film l is stuck to at least contacting part of a window plate part 8 of a vacuum vessel into which microwave electric power is introduced through the window plate part 8 with a vacuum seal part 7. The conductive thin film 11 prevents a microwave electromagnetic file from invading a groove 8 part for fixing the vacuum seal part 7 and the thin film. The thickness of the conductive thin film 11 should be thicker than the thickness 6 of surface thickness defined by delta (2/ musigmaomega)<1/2> where omega is angular frequency, sigmais conductivity of the conductive substance, and mu is permeability and may be about 2mum.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a window for introducing microwaves into a vacuum container, and is particularly applicable to a vacuum container in which plasma is generated in the internal space based on an electric discharge action. The present invention relates to an improvement of a window for introducing microwave power into a vacuum container, which is a window for introducing microwave power and is equipped with a vacuum seal structure.

[Conventional technology]

BACKGROUND ART Conventionally, an ECR (electron cyclotron resonance) device configured to generate plasma using microwaves has been proposed (Japanese Patent Application Laid-open No. 141729/1983, etc.).

In these devices, in order to introduce microwaves into a vacuum container that forms a plasma generation chamber, a window for introducing microwaves is formed at one location on the wall of the vacuum container. Such windows for introducing microwaves must be made of materials with low microwave loss, have low microwave reflection waves, be easy to clean and replace, and have the following features: Sufficient safety measures in the event of damage are taken;
There are demands for a simple structure and for manufacturing at low cost. Examples of structures of conventional microwave introduction windows that meet these requirements are shown in FIGS. 8 to 10. These figures only show the microwave introduction window.

The microwave introduction window shown in FIG. 8 is a window having the most general structure. In FIG. 8, 101 indicates a part of the vacuum vessel of the microwave discharge device, 102 a waveguide for introducing microwaves into the vacuum vessel 101, and 10
3 is a window disc made of a material such as quartz with low microwave loss; 104 is an O-ring for vacuum sealing;
105 is a groove for fixing the O-ring 104, and 106 is a vacuum vessel 1 for introducing microwaves to generate electric discharge.
This is the microwave coupling hole formed in 01. In this microwave introduction window, an annular recess 107 is formed on the outer surface of the vacuum container 101 at the microwave coupling hole 106, and a window disc 103 is disposed in the recess 107. Said groove 1
05 is formed at a portion corresponding to the bottom of the recess 107, so the O-ring 104 fixed in the groove 105 is attached to the window disc 1.
It is in contact with the lower surface of 03. Vacuum vessel 1 of waveguide 102
A mounting flange 102a is formed at the end on the 01 side, and the waveguide 102 is mounted via the flange 102a to the wall around the microwave coupling hole 106 of the vacuum container 101 by a coupling means (not shown). It is being In FIG. 8, a microwave generation source is provided at the upper end of the waveguide 102, and an exhaust device is provided at the bottom of the vacuum container 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 in the conventional example shown in FIG. In this conventional example, a groove 105 is formed in the side surface of the recess 107 so that the O-ring 104 comes into contact with the circumferential surface of the disc 103, and the O-ring 104 is disposed in this groove 105.

In the microwave introducing window shown in FIG. 10, a window disk 103 is sealed to the inner wall of the waveguide 102 by brazing or the like, thereby performing vacuum sealing. Further, the waveguide 102 is mounted by increasing the thickness of the flange 102a, and by forming a ring-shaped groove 108 on the outer surface of the flange 102a, and disposing an O-ring 104 in this groove 108. There is. In this state, the flange 102a is attached to the vacuum vessel 1.
It is fixed around the hole 106 of No. 01.

[Problem to be solved by the invention]

Each of the conventional microwave introduction windows described above poses the following problems.

The window shown in FIG. 8 has a simple structure and can be manufactured at low cost, but it is relatively large as it is used as a location for forming the groove 105 for fixing the O-ring 104 on the atmosphere side of the microwave coupling hole 106. It is necessary to provide a stepped portion. Since the microwave current flowing through the wall surface flows only through the surface of the waveguide 102, the groove 105 causes a large current loss, and the problem is that reflected waves are likely to occur due to characteristic impedance mismatch. In particular, since the inner end of the groove 105 is in a vacuum, it has the disadvantage that abnormal discharge is likely to occur due to concentration of the microwave electric field. Furthermore, when the microwave power is large, heat generation due to dielectric loss of the O-ring 104 increases. Therefore, according to the structure of the microwave introduction window shown in FIG. 8, heat generation due to microwave loss occurs near the microwave coupling hole 106, especially when the applied power is several hundred W or more. It has the drawback of being easy to use and lacking in reliability as a window.

In the window shown in FIG. 9, vacuum sealing is achieved by bringing an O-ring 104 into close contact with the circumferential surface of the window disc 103. In this conventional example as well, a protruding edge 109 forming a step is formed in the microwave coupling hole 106 for the purpose of preventing the window disk 103 from being sucked into the vacuum container 101. Since it can be made into a smaller shape than the conventional example shown, it is effective in reducing reflected waves of microwaves. However, the window disc 10
3 is usually formed using quartz or alumina, etc., so it is difficult to process the circumferential surface of the window disk 103 finely to the extent that it can be vacuum-sealed with good dimensional accuracy. In addition, in order to ensure vacuum sealing in this conventional example,
The window disc 103 must be installed with the O-ring 104 crushed, and in a microwave discharge device where the use of lubricating oil is restricted, it is extremely difficult to place the window disc 103 at a predetermined location. This configuration is difficult to implement, so the practicality of this configuration is low.

In the window shown in FIG. 10, the window disk 103 is connected to the waveguide 1.
It has a structure in which it is directly bonded to the inner surface of 02, and has been used in many applications such as microwave heating devices and accelerators. Usually, alumina is used for the window disk 103, and the circumferential surface of the window disk is sealed to the inside of a metal waveguide by brazing. Although this window can achieve a complete vacuum seal and minimize loss, the material of the waveguide is usually limited to steel or Kovar, and highly reactive gas cannot be introduced into the vacuum vessel, and the window must be replaced. What must be done for each waveguide,
There are some practical problems because it is difficult to double the window disc 103 as a safety measure in case of damage, and the manufacturing cost is high.

In view of the above-mentioned problems with conventional microwave introduction windows, an object of the present invention is to provide a practical microwave introduction window for a vacuum container that is inexpensive, highly reliable, and capable of introducing large amounts of electric power. There is a particular thing.

[Means to solve the problem]

The microwave introducing window of the vacuum container according to the present invention is constructed by disposing a window plate member in a hole formed in the wall of the vacuum container via a vacuum sealing member, and is supplied from the outside by a waveguide or the like. A microwave introduction window of a vacuum container that introduces microwave power into a vacuum container through a window plate member is characterized in that a conductive thin film is attached to at least the contact portion of the window plate member with the vacuum seal member. .

The microwave introduction window of the second vacuum container according to the present invention is
The first configuration is characterized in that the area of the portion of the window plate member to which the conductive thin film is not attached is greater than or equal to the opening area of the hole.

The microwave introduction window of the third vacuum container according to the present invention is
In the first configuration, the area of the portion of the window plate member to which the conductive thin film is not attached is made smaller than the opening area of the hole, and the microwave coupling hole is defined by the portion to which the conductive thin film is not attached. Have it as a feature point.

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

[Effect]

In the microwave introduction window of the vacuum container according to the present invention, a conductive thin film is attached to a part of the window disk in a predetermined range that does not block the transmission of microwaves, thereby forming the vacuum seal member. A microwave electromagnetic field no longer exists in the ring and the groove for arranging it.

〔Example〕

Embodiments of the present invention will be described below 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 introducing window of a vacuum container. In FIG. 1, reference numeral 1 denotes a part of the wall of a vacuum container, and the vacuum container 1 is configured to be supplied with microwaves and to generate microwave discharge therein. In FIG. 1, the lower side of the wall 1 of the vacuum container is the inside of the vacuum container, and the upper side is the atmosphere side. 2
is a waveguide for introducing microwaves into the inside of the vacuum container, and the upper part thereof is not shown.

A microwave generator 3 is disposed at the upper end of the waveguide 2 . A flange 2a having predetermined radial dimensions and wall thickness is formed at the end of the waveguide 2 on the vacuum vessel side.

A stepped hole 4 is formed in the wall portion 1 of the vacuum vessel at a location where the waveguide 2 is connected, and thereby an annular recess 4a with a large diameter is formed on the outer surface side of the wall portion 1, and an annular recess 4a with a large diameter is formed on the inner surface side. 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 vacuum container, and in this embodiment, the microwave coupling hole has a small diameter. Hole 4b
defined by. Reference numeral 5 denotes a circular protruding edge created by forming the stepped hole 4 in the wall portion 1. Further, an annular groove 6 is formed at a location on the outer surface of the protruding edge 5 corresponding to the bottom of the annular recess 4a, and an O-ring 7 that functions as a vacuum seal member in the microwave introduction window is housed in the groove 6.・It is arranged.

8 placed in the recess 4a of the wall 1 of the vacuum container is
This is a window disk for introducing the microwave supplied by the waveguide 2 into the vacuum container and vacuum-sealing the vacuum container. The window disk 8 is made of alumina or the like. The diameter of the window disc 8 is smaller than the diameter of the large diameter hole of the stepped hole 4, that is, the diameter of the recess 4a, and is formed so that it can be installed within the recess 4a. Furthermore, as is clear from FIG. 1, the window disk 8 and the flange 2a of the waveguide 2 are placed within the recess 4a, and the combined thickness of both is set to be approximately equal to the depth of the recess 4a. has been done. A ring plate 9 is placed in contact with the window disk 8 disposed in the outer recess 4a of the stepped hole 4 and the flange 2a of the waveguide 2 from the outside. It is fixed to the wall 1 with a plurality of bolts 10. A hole 9a at the center of the ring plate 9 is a hole through which the waveguide 2 is inserted. The above assembly depends on the structure of the window disc 8 forming the microwave introduction window and the waveguide flange 2a.
The assembly portion is supported on one side by the end face of the protruding edge 5 and the O-ring 7, and is pressed down on the other side by a ring plate 9. Note that the waveguide 2 can also be directly attached to the vacuum vessel 1 by making the flange 2a larger.

In the above assembly structure, the window disc 8 has a conductive thin film 11 attached to a region facing the bottom of the recess 4a. The surface of the window disk 8 to which the conductive thin film 11 is attached is shown in FIG. In the figure, 11 is a ring-shaped conductive thin film, and the outer diameter of the conductive thin film 11 is approximately equal to the diameter of the window disk 8, and its inner diameter is approximately equal to the diameter of the small diameter hole 4b, or the same as the O ring 7. It is set to be large within the range that satisfies the condition of contact.

In the vacuum container 1 having the microwave introduction window having the above structure, a predetermined gas is introduced into the vacuum container at a predetermined pressure, and the microwave power generated by the microwave generator 3 is transmitted through the waveguide 2. The vacuum container 1
be introduced within. As a result, gas plasma is generated within the vacuum vessel 1 due to the discharge. This plasma is used for etching, plasma CVD, etc. in the manufacturing process of semiconductors, electronic parts, etc. Generation of such plasma has also been put to practical use in an ECR device that also uses a magnetic field.

Next, the conductive thin film 11 provided on the window disk 8 which functions as a window for introducing microwaves will be described in detail. As described above, the conductive thin film 11 is attached to the surface of the vacuum container.

The area to be attached is the area that does not overlap the stepped hole 4 and overlaps the groove 6 for fixing the O-ring 7 in the assembled state. Under the condition that the stepped hole 4 is circular, the conductive thin film 11 is attached concentrically to the window disk 8 as shown in FIG. Further, when the stepped hole 4 is other than circular, for example rectangular, it is attached in a shape as shown in FIG.

The thickness of the conductive thin film 11 described above is determined as follows. The conductive thin film 11 is provided to prevent microwave electromagnetic fields 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. ) is larger than the epidermal thickness δ given by I/2. If the thickness of the conductive thin film 11 satisfies the above conditions, microwaves cannot pass through the conductive thin film 11.

Next, calculate δ for typical conductive materials.

However, it is assumed that f=2.45 GHt and ω=2yrf. In addition, the value of σ is 1 considering the temperature rise of the window disc 8.
The value of 00°C is used.

Copper: a-4,5X 10'/m: j-*o1.26
X 1O-6H/a: 6-1.54m Aluminum: a-1.3 X IO'U/m: a-jo
:δ~1.9B total 1. ~3.5 X IO'U/n+ 1~go
:δ~1.7ja Iron: a~6.8 X l07U/s: r200
no: δ~0. 3. As is clear from the data for one or more layers, the thickness of the conductive thin film 11 should be at least about 2 μm.

Further, the material of the conductive thin film 11 must be selected from a material that does not react with a predetermined gas such as oxygen or chlorine that is turned into plasma inside the vacuum container and does not generate oxides, chlorides, etc. be. Furthermore, methods for attaching the conductive thin film 11 to the disk 8 include vacuum evaporation, ion blating, sputtering, electroless plating, and powder metal baking. Any method may be used as long as there is sufficient adhesion between the two and the surface roughness is sufficiently smooth for the vacuum sealing action of the O-ring 7.

4. Regarding the adhesion of the conductive thin film 11 to the window disc 8
Other embodiments will be described based on FIGS.

In FIG. 4, 8 is the window disk described above, and 21 is a conductive thin film. In this embodiment, the thin film 21 is attached to the outer edge and outer peripheral surface of the lower surface in the figure of the vacuum vessel side. Also the fifth
The conductive thin film 31 according to the illustrated embodiment is attached to the outer edge and outer peripheral surface of the lower surface on the vacuum vessel side and the outer edge of the upper surface on the atmosphere side. Although it is desirable that the adhesion range on the atmosphere side surface be the same as the internal shape of the waveguide 2, it is not limited to this and may have other shapes. Furthermore, the window disk equipped with the conductive thin film according to the embodiments shown in FIGS. 4 and 5 can also be applied to the microwave introducing window structure shown in FIG. Can be applied.

In the embodiment of FIG. 6, the conductive thin film 4 in the window disc 8 is
On the lower surface of the vacuum vessel side to which the conductive thin film is attached, the area of the portion to which the conductive thin film is not attached is smaller than the opening area of the small diameter hole 4b. Therefore, in this embodiment, the microwave coupling hole is not the small diameter hole 4b of the stepped hole 4, but the conductive thin film 41 attached to the window disk 8.
will be substantially defined by. Further, 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 determined by the thickness of the protrusion edge 5 forming the small diameter hole 4b.

Therefore, if the thickness of the protruding edge 5 cannot be made sufficiently small compared to the wavelength of the microwave used,
That is, when using very high frequency microwaves, microwave coupling holes are formed by the conductive thin film 41 deposited as in this embodiment, thereby reducing reflected waves and improving the efficiency of microwave power usage. It becomes possible to improve the

Note that in the configuration of the above embodiment, there is a slight gap between the window disk 8 and the vacuum container due to the O-ring 7, but the width of this gap is the same as the wavelength of the microwave. If it is sufficiently short in comparison, the effect will be fully demonstrated.

Furthermore, if the conductive thin film 11 is charged up by being set to a DC floating potential and an abnormal discharge occurs between the conductive thin film 11 and the vacuum vessel 1, the conductive thin film 11 and A metal spring 12 is used to short-circuit between the vacuum container 1 and the vacuum container 1. This makes it possible to maintain the conductive thin film 11 and the vacuum container 1 at the same potential and prevent abnormal discharge from occurring. Note that the metal spring 1
Any conductor (for example, an aluminum plate, etc.) that can make the conductive thin film 11 and the vacuum container 1 have the same potential can be used as the conductor 2. Furthermore, the shape of the window disc 8 is not limited to a disc, but may be square or the like depending on the shape of the waveguide 2 and the stepped hole 4.

Further, by making a hole in the center of the window disk 8 and attaching a conductive thin film to the inside thereof, the present invention can also be applied to a coaxial type microwave introducing device.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, by attaching a conductive thin film to a predetermined location of a window disc, reflected waves that conventionally occur at a location where a vacuum sealing O-ring is provided can be reduced. Since it is eliminated, the reliability of the microwave introduction window in a microwave discharge vacuum apparatus to which high-power microwaves are supplied can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the structure of the microwave introduction window of the vacuum container according to the present invention, FIG. 2 is an end view of the window disk, and FIG. 3 is another embodiment of the window disk. Diagram similar to Figure 2, Figure 4
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 other examples of the structure of the microwave introduction window of the vacuum container, and FIG. 8 to 10 are sectional views showing the structure of a conventional microwave introduction window. [Explanation of symbols]

Claims (4)

[Claims] (1) A window plate member is arranged in a hole formed in the wall of the vacuum container via a vacuum seal member, and microwave power supplied from the outside is introduced into the vacuum vessel through the window plate member. In the microwave introduction window of the vacuum container,
A window for introducing microwaves into a vacuum container, characterized in that a conductive thin film is attached to at least a portion of the window plate member that contacts the vacuum seal member. (2) In the microwave introduction window for a vacuum container according to claim 1, the area of the portion of the window plate member to which the conductive thin film is not attached is larger than the opening area of the hole. Window for introducing microwaves into the container. (3) In the microwave introduction window for a vacuum container according to claim 1, the area of the portion of the window plate member to which the conductive thin film is not attached is made smaller than the opening area of the hole, and the microwave coupling hole is . A microwave introduction window of a vacuum container, characterized in that the window is defined by a portion to which the conductive thin film is not attached. (4) The window for introducing microwaves into a vacuum container according to any one of claims 1 to 3, wherein the conductive thin film has a thickness of 2 μm or more. window.