JPH10237657A - Plasma treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma treating device in which the contamination and corrosion of a discharge preventing board are eliminated. SOLUTION: In a plasma treating device 1 in which the object 70 to be treated is arranged on a susceptor 2 arranged in a reaction tank 10, the inside of the reaction tank 10 is evacuated, a treating gas is introduced thereinto, and at the time of executing plasma treatment, voltage is applied to the susceptor, purge gases are flowed into the gaps 6 and 7 between discharge preventing boards 31 and 32 around susceptor 2 and the susceptor 2. Since reaction products do not infiltrate into the gaps 6 and 7, the contamination and corrosion of the insides of the gaps 6 and 7 do not occur. The discharge preventing boards 31 and 32 shall be composed so as to be movable up and down together with the main body of the susceptor. Furthermore, if the purge gases are released into the reaction tank 10, the piping of an exhaust system can be made needless.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for processing the surface of a processing object using plasma, and more particularly to a plasma processing apparatus for applying a voltage to a susceptor on which a processing object is arranged.

[0002]

2. Description of the Related Art Among plasma processing apparatuses, a CVD apparatus is an apparatus for introducing a film forming gas into a reaction tank and forming a thin film on a substrate surface to be processed. By heating the substrate to a high temperature, a CVD reaction is caused, and a reaction product is deposited to form a thin film. In contrast, in a plasma CVD apparatus, a film formation gas is activated by plasma generated on
Since a thin film is formed by causing a VD reaction, normal pressure CVD
As compared with an apparatus or a low-pressure CVD apparatus, there is an advantage that a thin film can be formed while the substrate is kept at a low temperature.

[0003] A conventional plasma CVD apparatus is indicated by reference numeral 101 in FIG. This plasma CVD apparatus 101 includes a chamber 131, a gas shower head 121, a support plate 11
1. A support 134 is provided, and a chamber 131 and a gas shower head 121 are air-tightly fixed to each other via an insulator 141 to constitute a reaction tank 110 capable of evacuating. The support plate 111 is fixed in the upper end portion of the support 134 and is disposed in the reaction tank 10, and the support plate 111 and the support 134 constitute the susceptor 102.

When a thin film is formed by the plasma CVD apparatus 101, first, a substrate 170 to be processed is placed on a support plate 111, and then the reaction plate 110 is evacuated while the support plate 111 is evacuated. When the heater disposed in the chamber is energized, the inside of the reaction tank 110 reaches a predetermined pressure, and when the temperature of the substrate 170 reaches a predetermined temperature, a film forming gas is introduced from the gas shower head 121 into the reaction tank 110, and the pressure is reduced. Is stable, the high-frequency power source 182 is activated, and a high-frequency voltage is applied to the gas shower head 121 to apply
A plasma of a film forming gas is generated on zero.

When the film-forming gas is excited by the plasma, a plasma CVD reaction proceeds, and when a reaction product is deposited on the surface of the substrate 170, a thin film containing the elements in the film-forming gas is formed on the surface of the substrate 170. .

Conventionally, when generating plasma,
Although the susceptor 102 is grounded together with the chamber 131, in recent years, a plasma CVD apparatus that insulates the susceptor 102 from the chamber 131 and applies a DC voltage or a high-frequency voltage to the susceptor 102 has appeared. By improving the quality, the quality of a thin film formed by a CVD reaction is improved.

However, since the inside of the reaction vessel 10 is placed in a vacuum atmosphere, when a voltage is applied to the susceptor 102, a discharge is easily generated between the susceptor 102 and the chamber 131.

Therefore, measures have conventionally been taken, and a discharge prevention plate 103 placed at the ground potential is arranged close to the susceptor 102 to which a voltage is applied, as shown in FIG.
According to Paschen's rule, the discharge prevention plate 103 and the susceptor 10
2 is increased, and the chamber 131 is increased.
And the occurrence of discharge between them was prevented.

In this case, the susceptor 102 and the discharge prevention plate 1
03, the gap 107 is formed.
A hole 108 is provided in the discharge prevention plate 103 so that the gap 107 is opened to the inside of the reaction tank 110 so that the inside of the gap 107 is evacuated when the inside of the reaction tank 110 is evacuated. I was

However, such a discharge prevention plate 10
In the method (3), when a thin film is formed by a plasma CVD reaction, there is a problem that a reaction product enters through the hole 108 and accumulates in the gap 107. When the reaction products accumulate and the inside of the gap 107 is contaminated, it forms particles when forming the thin film, or causes the degree of vacuum in the reaction tank to be deteriorated due to the released gas, and is formed. The quality of the thin film is deteriorated.

Gases generated when performing plasma etching and gases generated when cleaning a plasma CVD apparatus are corrosive, and such corrosive gases enter the gap 107 and stay there. In this case, the discharge prevention plate 103 is corroded.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages of the prior art, and an object of the present invention is to provide a plasma processing apparatus free from contamination and corrosion of a discharge prevention plate. .

[0013]

According to a first aspect of the present invention, there is provided an apparatus having a reaction tank, a susceptor disposed in the reaction tank, and an object to be treated on the susceptor. The plasma processing is configured to apply a voltage to the susceptor when performing a plasma processing by evacuating the inside of the reaction tank and introducing a processing gas to generate a plasma on the processing target. An apparatus, wherein the susceptor has a discharge prevention plate disposed in proximity to the susceptor body in an electrically insulated state, so that gas can flow into a gap formed between the susceptor body and the discharge prevention plate. It is characterized by comprising.

In this case, as in the invention according to claim 2,
A bellows may be provided on the susceptor so that at least the susceptor body and the discharge prevention plate can move up and down together while maintaining the vacuum atmosphere and the gap in the reaction tank.

In the plasma processing apparatus according to the second aspect, the gas flowing into the gap is introduced after flowing between the bellows and the discharge prevention plate, as in the third aspect of the invention. It can be configured to be.

In the plasma processing apparatus according to any one of the first to third aspects described above, the gas flowing into the gap is discharged into the reaction tank as in the fourth aspect of the invention. It can be configured to be.

The plasma processing apparatus having the above-described configuration has a reaction tank and a susceptor disposed in the reaction tank. An object to be processed is disposed on the susceptor, and the inside of the reaction tank is evacuated. Since a voltage can be applied to the susceptor when a processing gas is introduced and plasma is generated, controllability and processing speed of plasma processing such as thin film formation by plasma CVD reaction and etching by plasma etching reaction are high.

However, the susceptor is placed in a vacuum atmosphere,
Since the reaction tank is usually placed at the ground potential, when a voltage is applied to the susceptor, a discharge easily occurs between the susceptor and the reaction tank.

Here, the pressure in the reaction tank is p, the distance between objects to which a voltage is applied in the reaction tank is d, and the voltage at which discharge occurs is V _S, and a graph of FIG. Value and V _S
The relationship with the size of is shown. The graph of FIG. 2 shows the law of spark discharge called Paschen's law. The discharge starting voltage that causes a discharge between objects placed in a vacuum atmosphere is a product of the pressure and distance, which is a specific value ( in the graph the minimum value when the value) indicated by the reference numeral a ₀ (here is shown to take the size) indicated by symbol V _sm.

A place where an undesirable discharge is likely to occur in the plasma processing apparatus is between the susceptor and the reaction tank. The product of the distance between the susceptor and the reaction tank and the pressure in the reaction tank is the above-mentioned symbol a _0. If the size is close to the above, a discharge will occur even when a relatively small voltage is applied to the susceptor.

In this case, if the value of p × d is reduced by disposing a discharge prevention plate placed at the ground potential close to the periphery of the susceptor and shortening the distance between objects to which voltage is applied, the discharge generation voltage V _S rises, making it difficult for discharge to occur.

If a reaction product or a corrosive gas generated by the plasma CVD reaction enters the gap formed between the discharge prevention plate and the susceptor, the gap is contaminated or corroded. Or progress.

In the plasma processing apparatus according to the present invention, a reaction product and a corrosive gas enter the gap by flowing a gas into the gap and making the pressure in the gap higher than the pressure in the reaction tank. Since the reaction product and the corrosive gas which have entered once are washed away by the introduced gas, the above-mentioned problem does not occur.

Further, regarding the problem that the degree of vacuum in the reaction tank is deteriorated due to the gas released in the gap and the quality of the formed thin film is deteriorated, the purge gas is supplied into the gap to purge the gas released as impurities. It is removed so that the degree of vacuum and the quality of the vacuum do not deteriorate, and the quality of the thin film is improved.

By the way, in such a plasma processing apparatus, a bellows is provided around the susceptor, and when the substrate to be processed is carried in and out, the susceptor body composed of the support plate and the support is placed inside the reaction tank. It is often possible to move up and down while maintaining the vacuum atmosphere. Therefore,
In the plasma processing apparatus of the present invention, when the susceptor main body moves up and down, the discharge prevention plate also moves up and down together, so that the size of the gap described above may not be changed.

In this case, the gas flowing into the gap is bellows.
(Inner wall surface) and the discharge prevention plate (outer periphery), and then introduced into the gap, the impurity gas can be purged when released from the bellows inner wall surface or the outer periphery surface of the discharge prevention plate. .

Furthermore, if the gas flowing through the gap is discharged into the reaction tank, it is not necessary to provide a piping for an exhaust system, and the configuration of the plasma processing apparatus can be simplified.

[0028]

Embodiments of the present invention will be described with reference to the drawings. Referring to FIG. 1, reference numeral 1 denotes a plasma CVD apparatus showing one embodiment of the plasma processing apparatus of the present invention, which includes a chamber 31 made of a metal material, a gas shower head 21, discharge prevention plates 3 ₁ , 3 ₂ , Support plate 11, pillar 3
Four.

The chamber 31 is formed in a container shape.
A gas shower head 21 is hermetically fixed on the chamber 31 in a state in which the gas shower head 21 is electrically insulated by an insulator 41. Is configured. An exhaust port 32 is provided on a side wall of the chamber 31, and the inside of the reaction tank 10 can be evacuated when a vacuum pump (not shown) is started.

The support plate 11 is formed in a rectangular shape, the discharge prevention plate 3 ₁ and its support plate 11 is formed in substantially the same size in the same shape, the discharge prevention plate 3 _1, the back surface of the supporting plate 11 , Are arranged in a non-contact state with the support plate 11, and the periphery thereof is fixed to an insulator 45 provided around the support plate 11. Therefore, the support plate 11 and the discharge prevention plate 3 ₁
Are electrically insulated from each other, and a gap 7 of 2 mm is formed therebetween.

The column 34 has a hollow cylindrical shape (outer diameter 6 mm).
Is formed on the 0 mm), the discharge prevention plate 3 ₂ cylindrical (inner diameter 6
Is formed on the 4 mm), post 34 is inserted into the discharge prevention plate 3 _2, discharge prevention plate 3 ₂ is configured to be positioned in a state of non-contact with the periphery of the strut 34, in between 2
A mm gap 6 is formed.

[0032] At the center of the discharge prevention plates 3 _1, discharge prevention plate 3 ₂
Has been opened in the inner diameter and the same diameter of the hole, the upper end portion of the discharge preventing plate 3 ₂ inserted struts 34 has, in its bore, the support plate 1
1 is a discharge preventing plate 3 ₁ of the back are inserted in a non-contact state,
The susceptor is fixed to the back surface of the support plate 11, and the support plate 11 and the support 34 constitute a susceptor body.

[0033] On the other hand, the upper end portion of the discharge preventing plate 3 ₂ is hermetically fixed to the hole around the discharge preventing plate 3 _1, the susceptor body constituted by the support plate 11 and the support 34, the discharge preventing plate 3
_1, 3 ₂ are arranged close, the susceptor indicated by reference numeral 2 is formed.

A through hole is provided on the bottom surface of the chamber 31. A gas introduction plate 61 having a through hole having substantially the same diameter as the through hole is arranged outside the reaction tank 10 on the bottom surface of the chamber 31. Are fixed in an airtight manner by communicating through holes. Of the susceptor 2, discharge prevention plate 3 ₂ are inserted in a non-contact state to the through hole with struts 34,
The support plate 11 and the discharge preventing plate 3 ₁ is configured to be positioned within the reaction vessel 10.

[0035] the lower end of the lower portion and the discharge prevention plate 3 ₂ struts 34 includes a seal plate 56 and mounting plate 57 are respectively fixed, and its sealing plate 56 and the mounting plate 57, an insulator 43 The seal plate 56 and the mounting plate 57 are configured so as to be airtightly fixed to each other while being sandwiched and electrically insulated, so that the air does not enter between the seal plate 56 and the mounting plate 57.

The discharge preventing plate 3 ₂ is inserted together with the strut 34 to the bellows 60, the bellows 60 around the discharge prevention plate 3 ₂ are to be positioned in a non-contact state,
The upper and lower ends of the bellows 60 is welded and fixed respectively to the gas introducing plate 61 and the mounting plate 57, constructed as air does not penetrate into the gap 5 formed between the bellows 60 and the discharge prevention plate 3 ₂ Have been.

The upper end of the gap 6 formed by the discharge preventing plate 3 ₂ and the support 34 is in communication with the gap 7 formed in the support plate 11 discharge preventing plate 3 _1, a lower end portion, the seal plate 56 And the space formed between the mounting plate 57 and
The hole provided in the discharge prevention plate 3 _2, the space and the gap 5 and has been through, and is configured such that each gap 5-7 is communicated with each other.

The gas introduction plate 61 is provided with a gas introduction nozzle 4, which is configured so that a desired type of gas can be introduced into the gap 5 from the gas introduction nozzle 4, while being located near the exhaust port 32. the portion of the discharge preventing plate 3 _1, is provided with a purge gas discharge holes 8, the reaction vessel 10 at the time of evacuation, the introduction of gas into the gap 5 through the gas introducing nozzle 4, introduced gas is the The gas flows through the gaps 5 to 7, is discharged from the purge gas discharge hole 8 into the reaction tank 10, and is then discharged from the exhaust port 32.

Outside the reaction tank 10, a substrate lifting mechanism 50 having a fixed plate 51, a movable plate 52, a shaft 53, and a ball screw 54 is disposed below the chamber 31.
The above-mentioned seal plate 56 is fixed to the movable plate 52 while being electrically insulated by the insulator 42.
The lower end of the support 34 is moved to the movable plate 52 via the seal plate 56.
It will be fixed to.

On the other hand, the upper end and lower end of the shaft 53 are
The bottom surface of the chamber 31 and the fixed plate 51 are respectively rotatably mounted. The ball screw 54 is mounted on the shaft 53, and the movable plate 5 is mounted on the ball screw 54.
2 are installed.

The fixed plate 51 is fixed relative to the chamber 31. When the shaft 53 is rotated, the ball screw 54 reciprocates on the shaft 53 by the movable plate 52 whose rotational movement is restricted. It is configured to move. The reciprocating motion of the ball screw 54 causes the movable plate 5
2 moves up and down, the support 34 becomes a vertical axis, and the support plate 11
Is configured to be able to move up and down in the reaction tank 10.

The chamber 31 of the discharge prevention plate 3 ₂ is inserted
The through-hole, the packing 37 and is projected, and is configured to seal 37 contacts the outer peripheral surface of the discharge prevention plate 3 _2. Therefore, when the support plate 11 moves up and down,
Packing 37 slides and that the lateral movement is restricted, the discharge prevention plate 3 ₂ is configured so as not to contact with the chamber 31 and the gas introducing plate 61.

In the reaction tank 10, the surface of the support plate 11
The substrate 70 is arranged, but are exposed to allow heat, sides and back, the discharge prevention plates 3 ₁ and is covered by insulator 45, not exposed to the reaction vessel 10, the support plate Reference numeral 11 does not directly oppose the wall surface of the chamber 31.

[0044] Further, struts 34 is covered with the discharge prevention plate 3 ₂ not exposed in the reaction vessel 10, the chamber 3
1. The gas introduction plate 61 and the bellows 60 are not directly opposed to each other.

Therefore, the discharge prevention plates 3 ₁ and 3 ₂ are grounded,
When a voltage is applied to the support 34 and the support plate 11 is set to the same potential as the support 34, the discharge prevention plate 3 is provided between the support plate 11 and the support 34 (susceptor body) and the chamber 31 placed at the ground potential. It is configured to be electrically shielded by ₁ , 3 ₂ .

When a thin film is formed by using the plasma CVD apparatus 1 having such a configuration, first, the substrate 70 to be processed is loaded into the reaction tank 10 and the substrate elevating mechanism 50 is operated. Is placed on the support plate 11. Next, a vacuum pump (not shown) is started, and the inside of the reaction tank 10 is evacuated from the exhaust port 32. At this time, if the gas introduction nozzle 4 is kept closed, the gaps 5 to 7 are also evacuated.

A heater is arranged in the support plate 11, and after the inside of the reaction tank 10 reaches a predetermined degree of vacuum, the support 34
A voltage is applied to the wiring 35 led out from the lower end of the substrate to energize the heater, and the substrate 70 is heated via the surface of the support plate 11. When the temperature of the substrate 70 reaches a predetermined temperature, a film formation gas (processing gas) is introduced into the gas shower head 21 from a gas introduction pipe.

A shower plate 22 having a plurality of holes is provided on the inside of the reaction tank 10 of the shower head 21.
The introduced film-forming target gas is evenly dispersed on the surface of the substrate 70 by the shower plate 22.

When the deposition gas is sprayed, a purge gas (an inert gas such as an argon gas or a nitrogen gas) is introduced from the gas introduction nozzle 4, flows through the gaps 5 to 7, and flows through the discharge holes 8 into the reaction tank 10. To the reaction tank 10
The purge gas released into the chamber 32 together with the deposition gas
It is exhausted from.

In this state, when the pressure in the reaction tank 10 is stabilized at a predetermined value, the high-frequency power source 82 is started, and a high-frequency voltage of 40 MHz is applied to the gas shower head 21 to generate a plasma of a film forming gas. . At this time, when the high-frequency power supply 81 is activated at the same time and a high-frequency voltage of about 1 MHz is applied to the susceptor body from the lower end of the column 34,
The high-frequency voltage is superimposed on the voltage applied to the gas shower head 21, and a uniform plasma of the film forming gas is generated on the surface of the substrate 70. When the CVD reaction proceeds by the plasma and a reaction product is deposited on the surface of the substrate 70, a thin film containing an element in the deposition gas is formed.

During such a CVD reaction, the purge gas is supplied from the purge gas discharge hole 8 to the reaction tank 10.
The pressure in each of the gaps 5 to 7 is positive with respect to the pressure in the reaction tank 10. Therefore, CV
The reaction product generated by the D reaction is supplied to the purge gas discharge hole 8.
It is impossible to enter the gaps 5 to 7 from inside, and the insides of the gaps 5 to 7 are not contaminated with particles.

The size of the gaps 6 and 7 as described above
(2 mm) is a distance at which no discharge occurs when the high-frequency voltage of 1 MHz is applied to the susceptor 2.

After the thin film has been formed to a predetermined thickness, the operation of the high-frequency power supplies 81 and 82 and the supply of the film forming gas are stopped, the substrate lifting / lowering mechanism 50 is operated, and the substrate 70 is delivered and received. After being carried out, the untreated substrate is removed from the reaction tank 10.
Then, the thin film forming operation of the new substrate by the plasma CVD reaction is restarted.

When such a process is repeated and a thin film is formed on the surface of a predetermined number of substrates, the inside of the reaction tank 10 is evacuated without loading the substrates, and the gas shower head 2 is evacuated.
From 1, a fluorine-based cleaning gas is sprayed, and one or both of the high-frequency power supplies 81 and 82 are activated to generate a plasma of the cleaning gas, thereby gasifying and removing the reaction products attached to the reaction tank 10.

By the cleaning operation, the reaction tank 10
The particles adhered to the wall surface of the substrate and the surface of the support plate 11 are removed. Therefore, a periodic cleaning operation is performed every time a predetermined number of substrates are subjected to plasma processing, so that the particles are continuously attached without adhering to the substrate surface. Thus, a thin film can be formed.

[0056] Incidentally, fluorine-based cleaning gas enters the gap 5-7, when staying in the discharge prevention plates 3 _1, 3 ₂ and the bellows 60 is corroded.

Therefore, when the plasma of the cleaning gas is generated, the purge gas flows from the gas introduction nozzle 4 into each of the gaps 5 to 7, and the reaction tank 1 is discharged from the purge gas discharge hole 8.
If it is set to be released within 0, the fluorine-based cleaning gas cannot enter each of the gaps 5 to 7, and
Corrosion can be prevented.

In the plasma CVD apparatus 1, a heater 66 is provided around the bellows 60, so that the bellows 60 can be heated. Therefore, if the bellows 60 is heated while the purge gas is flowing from the gas introduction nozzle 4 to perform the cleaning operation or the degassing operation, the gas released from the bellows 60 is evacuated together with the purge gas, so that the released gas is reduced. It is easy to return the inside of the reaction tank 10 to a high vacuum state without staying in the gaps 5 to 7. Therefore, when forming a thin film, the inside of the reaction tank 10 can be kept in a state where the amount of emitted gas impurities is small.

The plasma CVD apparatus 1 described above can be variously modified. For example, although the purge gas discharge hole 8 of the above was arranged in the discharge prevention plate 3 _1, may be provided in the insulator 45. Further, the purge gas is not limited to the case of flowing during the plasma processing. The purge gas is not supplied when performing the plasma CVD reaction, and the purge gas is introduced from the gas introduction nozzle 4 when cleaning the reaction tank 10. You may do so.

The above-mentioned support 34 is made of a metal material and has the same potential as the support plate 11, but the support may be made of an insulating material. In that case no discharge without placing discharge prevention plate 3 ₂ around the post of the insulator.

Although the plasma CVD apparatus 1 for forming a thin film has been described above, the present invention is not limited to the CVD apparatus, but includes a wide range of apparatuses for processing an object to be processed using plasma. For example, for a plasma etching apparatus, if a purge gas is allowed to flow in a gap formed when a susceptor is formed by a susceptor body and a discharge prevention plate, corrosion of the discharge prevention plate due to an etching gas is effectively prevented. can do.

The film formation target is not limited to a substrate such as a silicon wafer or a glass substrate, but may be formed of various materials and shapes such as jigs and tools to be subjected to surface treatment, works such as dies, and resin films. Widely include things.

In the above-described plasma CVD apparatus 1, a high-frequency voltage is applied to the susceptor 2. However, the present invention is not limited to this, and it is possible to apply a DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage. What is applied is also included. In short, the present invention is configured such that a desired type of gas such as a purge gas can be flowed into a gap formed between a discharge prevention plate provided to prevent discharge and a susceptor body to which a voltage is applied. Widely includes plasma processing equipment.

[0064]

According to the present invention, particles do not adhere to the inner peripheral surface of the discharge prevention plate or corrosion does not occur. Since the life of the discharge prevention plate is prolonged, cleaning or replacement work is not required, and the throughput of the plasma processing apparatus is improved.

[Brief description of the drawings]

FIG. 1 shows an example of a plasma processing apparatus according to the present invention.

FIG. 2 is a graph showing Paschen's law

FIG. 3 shows an example of a conventional plasma processing apparatus.

[Explanation of symbols]

1 ... Plasma treatment device 3 ₁ , 3 ₂ ... Discharge prevention plate
2 ... susceptor 10 ... reaction tank 11 ... susceptor body 60 ...
Bellows 70 …… Object to be processed (substrate)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05H 1/46 H01L 21/302 B (72) Inventor Susumu Arai 2500 Hagizono, Higazono, Chigasaki City, Kanagawa Pref. Japan Vacuum Engineering Co., Ltd. (72) Inventor Kuniaki Kurokawa 2500 Hagizono, Chigasaki-shi, Kanagawa Japan Vacuum Engineering Co., Ltd.

Claims (4)

[Claims] A susceptor disposed in the reaction vessel; a processing target placed on the susceptor; a process gas introduced by evacuation of the inside of the reaction vessel; A plasma processing apparatus configured to apply a voltage to the susceptor when performing plasma processing by generating plasma on a processing target, wherein the susceptor is in close proximity to a susceptor body in an electrically insulated state. A plasma processing apparatus, comprising: a discharge prevention plate arranged; and configured to allow gas to flow in a gap formed between the susceptor body and the discharge prevention plate. 2. The susceptor has a bellows, and at least the susceptor body and the discharge prevention plate can be moved up and down together while maintaining a vacuum atmosphere and the gap in the reaction tank. Claim 1 characterized by the following:
The plasma processing apparatus as described in the above. 3. The plasma processing apparatus according to claim 2, wherein the gas flowing in the gap flows between the bellows and the discharge prevention plate and then is introduced. . 4. The plasma processing apparatus according to claim 1, wherein the gas flowing into the gap is discharged into the reaction tank.