JPH10317150A - Formation of coating and coating forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the bad influence of fine particles composed of reaction products on coating quality in coating formation by a plasma CVD method. SOLUTION: In a plasma CVD method using silane as a coating forming gas, in a state in which high frequency discharge is held, the feed of the gaseous silane is stopped, and instead, the feed of gaseous hydrogen composed of a discharge gas is executed. Then, plasma which does not execute coating formation by the cracking of gaseous hydrogen for a prescribed time is formed. In this state, since a negative self-bias is applied to the face to be formed, negatively charged fine particles do not stick to the face to be formed. Then, the discharge is stopped in a state in which the fine particles in the atmosphere are exhausted. Thus, the state in which the fine particles do not stick to the face to be formed can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD [0001] The invention disclosed in the present specification is:
The present invention relates to a film forming method using a plasma CVD method and a film forming apparatus capable of performing the film forming method.

[0002]

2. Description of the Related Art As a method for forming an amorphous silicon film or a silicon oxide film, a plasma CVD method is known.

In the formation of various thin films by the plasma CVD method, fine particles such as particles and flakes generated at the time of film formation pose a problem.

[0004] The microparticles are as follows: (1) A reaction product formed on the inner wall of the reaction chamber or on the electrode every time the film is formed, and the reaction product obtains some energy during the discharge and peels off. (2) Those generated in the gas phase and not contributing to the formation of a thin film. It is mainly composed. In any case, the fine particles are a reaction product of a raw material gas used for film formation.

[0005] These fine particles adhere to the film to be formed, and cause a significant deterioration in film quality.

In order to solve this problem, it is effective to increase the number of cleanings in the chamber.

[0007] However, even if cleaning is performed every single film formation, the fundamental solution cannot be solved simply by reducing the number of fine particles generated due to the above (1).

In addition, increasing the number of times of cleaning the chamber lowers productivity and complicates the operation, which is not industrially preferable.

[0009]

SUMMARY OF THE INVENTION The invention disclosed in this specification provides a technique for suppressing the presence of fine particles generated during film formation by a plasma CVD method from adversely affecting the quality of a formed thin film. The task is to

[Process leading to the invention] As a result of eagerly pursuing when the fine particles made of the reaction product as described above adhere to the film to be formed, the fine particles adhere to the film before and after the film formation is completed. However, it was found that the film quality was adversely affected.

The process of obtaining the above knowledge will be described below. Generally, the plasma CVD method has a parallel plate type structure as shown in FIG. 1, in which a sample (substrate) 11 is arranged on one electrode 12 maintained at a ground potential, and a high-frequency It has a structure to which a power supply 16 is connected.

FIG. 7 shows a timing relationship between supply of a source gas and high-frequency discharge (RF discharge) when a general film formation is performed.

Generally, in a state where plasma is generated by high frequency discharge, a bias voltage as shown in FIG. 8 is applied between the electrodes.

The bias voltage becomes a large negative voltage on the power supply electrode 15 side and a relatively small negative voltage on the ground electrode 12 side.

Generally, the fine particles floating in the chamber 11 are negatively charged. Therefore, during discharge, the electrode 1
The particles are repelled from 2 and the particles hardly adhere to the substrate placed on the electrode 12.

That is, during the film formation shown in FIG. 7, it is rare that the fine particles adhere to the film.

However, when the discharge is completed, the applied state of the self-bias as shown in FIG. 8 disappears, and accordingly, the fine particles fly down on the substrate and adhere to the surface to be formed. In addition, fine particles adhere to the surface of the substrate (the surface of the formation surface) due to static electricity.

[0018]

According to the invention disclosed in the present specification, the self-bias applied to the electrode on which the substrate is placed at the end of the above-described discharge disappears, and as a result, the fine particles Pays attention to the phenomenon that the particles adhere.

Therefore, in the invention disclosed in this specification, a state is set in which the discharge continues even after the film formation is completed.

By stopping the discharge after all the fine particles present in the atmosphere have been exhausted,
It suppresses the attachment of fine particles to the surface of the film.

That is, the state in which the self-bias is formed as shown in FIG. 8 is maintained until the fine particles are exhausted after the film formation is completed.

In the invention disclosed in this specification for realizing the above state, the atmosphere is switched from the film forming gas to the discharge gas while the high frequency discharge is maintained.

By doing so, the supply of the film forming gas is completed, and the discharge is continued even after the film forming is completed, and the bias state shown in FIG. 8 can be maintained during that time.

By maintaining this state for a while, negatively charged fine particles in the atmosphere are exhausted to the outside in a state where they cannot adhere to the substrate.

Then, the high-frequency discharge is stopped in a state in which the fine particles are exhausted to the outside, that is, in a state in which the atmosphere is replaced, and the supply of the discharge gas is stopped.

By doing so, it is possible to prevent fine particles from adhering to the surface of the film to be formed.

The film forming gas is a gas containing a component of a film to be formed and a component forming fine particles.

Examples of the type of film forming gas include silane and disilane for forming a silicon film, and methane for forming a hard carbon film.

The discharge gas is a gas that does not contribute to film formation or formation of fine particles by itself, but merely discharges and contributes to the formation of plasma. Examples of the discharge gas include hydrogen gas and helium gas.

The type of film to be formed is not particularly limited, and examples thereof include a general semiconductor film and an insulating film. The film to be formed may be a compound film.

One of the inventions disclosed in this specification is a first step in which a high-frequency discharge is performed in a state where a film forming gas is supplied to form a plasma to form a film, And performing a high-frequency discharge and subsequently forming a plasma that does not follow the film formation.

In the above structure, it is important to keep the pressure in the atmosphere constant between the first stage and the second stage.
This is to keep the conditions under which the plasma is formed from changing.

For example, when the pressure of the atmosphere changes suddenly, a sudden discharge such as an arc discharge occurs, and the quality of the film to be formed may be greatly impaired. In order to prevent such a situation, the pressure in the atmosphere is kept constant between the first stage and the second stage as described above.

According to another aspect of the present invention, a high-frequency discharge is performed in a state where a film-forming gas is supplied to form a plasma to form a film, and the film-forming gas is switched to a discharge gas. A film forming apparatus having a function of performing a high-frequency discharge and a second step of forming a plasma that does not follow the film formation.

In this configuration, it is important to have a function of keeping the pressure in the atmosphere constant between the first stage and the second stage.

Another aspect of the invention is a method of forming a film by a plasma gas phase reaction by causing a high-frequency discharge between parallel plate electrodes, and forming the film with a self-bias applied to the surface on which the film is formed. A gas phase reaction method in which the supply of gas for film is stopped and the gas for discharge is supplied at the same time, so that a self-bias is applied to the surface on which the film is formed even after the film formation is completed. There is a feature.

Another aspect of the present invention is an apparatus for forming a film by a plasma gas phase reaction by causing a high-frequency discharge between parallel-plate electrodes, wherein the apparatus is formed with a self-bias applied to the surface on which the film is formed. The film formation is characterized in that the supply of the gas for the film is stopped and the gas for the discharge is supplied at the same time, so that the self-bias is applied to the surface on which the film is formed even after the film formation is completed. The device is characterized in that:

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In forming an amorphous silicon film by plasma CVD using silane as a film forming gas, silane gas and hydrogen gas are exchanged at the end of film formation. On this occasion,
The high frequency discharge is maintained.

Thus, the state where the negative self-bias is applied to the surface on which the film is formed can be maintained even after the film formation is completed. Then, the discharge by the hydrogen gas is continued for a while until the negatively charged reaction product fine particles are exhausted out of the atmosphere, whereby the fine particles can be prevented from adhering to the surface on which the particles are to be formed.

[0040]

【Example】

Embodiment 1 (Description of Film Forming Apparatus) First, an outline of a film forming apparatus used in this embodiment will be described. FIG. 1 schematically shows a plasma CVD apparatus for forming an amorphous silicon film.

This apparatus includes a pair of parallel plate electrodes 12 and 15 inside a reduced pressure chamber 10 made of stainless steel.
Is provided.

One electrode 12 connected to the ground potential
A substrate (sample) 11 is disposed on the upper side. A high frequency power supply 16 is connected to the other electrode 15. Also,
Although omitted in the figure, a matching circuit is arranged between the electrode 15 and the high frequency power supply 16.

The high-frequency power supply has a function of outputting required high-frequency power. 13.56 MHz is generally used as the frequency of the high frequency power. Of course, other frequencies may be used. However, the frequency must be such that a self-bias is formed as shown in FIG.

In the decompression chamber 10, gas supply systems 17 and 18 for supplying gas to the inside thereof are arranged.

Here, 17 is a gas line for supplying silane gas, and 18 is a gas line for supplying hydrogen gas.

The decompression chamber 10 is provided with an evacuation system 13 having an evacuation pump 14 for setting the inside to a required decompression state.

Although not shown, the decompression chamber 10
Is provided with a door for carrying a substrate into the apparatus from the outside.

In this embodiment, rectangular electrodes having an area of 490 cm ² are arranged as electrodes. In addition, the high frequency power supply 16
Then, high-frequency power having a frequency of 13.56 MHz and an output of 20 W is supplied to the electrode 15 via a matching circuit (not shown).

(Method of Forming Amorphous Silicon Film) Here, an example in which an amorphous silicon film is formed using the method disclosed in this specification will be described.

First, a door (not shown) provided in the decompression chamber is opened, and the substrate 11 is loaded into the chamber 10. The substrate 11 is disposed on the electrode 12 connected to the ground potential.

Next, the door (not shown) is closed, and the decompression chamber 10 is closed. Then, the evacuation pump 14 is operated to bring the inside of the decompression chamber 10 into a decompression state.

Here, in order to eliminate impurities in the chamber, nitrogen gas is supplied from a gas supply system (not shown), the chamber is once filled with nitrogen gas, and then the pressure inside the pressure reducing chamber 10 is reduced. Is preferred.

At this stage, it is preferable to make the inside of the chamber 10 a high vacuum state as much as possible.

Next, an amorphous silicon film is formed on the substrate 11 according to the timing chart shown in FIG.

First, the inside of the decompression chamber 10 is brought into an ultra-high vacuum state (a state in which exhaustion is performed as much as possible). Then, silane gas (SiH ₄ gas) is supplied from the gas supply system 17 at 100 sccm.
Supply at a flow rate of In this embodiment, the pressure in the decompression chamber 10 is 0.5 Torr under these conditions. (The relationship between flow rate and pressure depends on the volume of the chamber and the capacity of the exhaust pump.)

Then, high-frequency power (RF power) (output 20 W) is supplied from the high-frequency power supply 16 in a state where the inside of the chamber 10 is at a predetermined pressure.

The point at which the supply of high-frequency power is started can be regarded as the starting point of film formation.

The film formation is completed by stopping the supply of the silane gas. Here, the supply of hydrogen gas is performed from the gas system 18 at the same time as the supply of silane gas is stopped.

The supply of hydrogen gas is set to 100 sccm. This is to minimize the pressure change in the chamber according to the gas switching.

In this manner, the film formation can be stopped in a state where the discharge is maintained (a state where the plasma is generated).

In this embodiment, the switching timing is set so that the pressure change according to the gas switching is minimized.

Here, the time of the transient state following the stop of syngas and the time of the transient state following the start of the supply of hydrogen gas are set to be the same, and furthermore, both transient states are set to overlap. The time in the transition state is 2 seconds.

When the supply of the silane gas is stopped, the film formation is completed. Then, the discharge by the hydrogen gas is continued for a predetermined time t.

The value of t differs depending on the capacity of the chamber, the gas supply capacity, the capacity of the exhaust system, and the like.

What is important is to make the value of t larger than the time when the gas in the chamber is replaced (this is referred to as t '). That is, t> t ′.

By doing so, it is possible to prevent the presence of fine particles in the atmosphere when the discharge is stopped, and to prevent the fine particles from adhering to the surface of the formed film. it can.

If the relationship of t> t 'is not maintained, the state where the particles are suspended in the atmosphere after the discharge is stopped is realized, and the particles adhere to the surface of the film. In this case, the effects of the invention cannot be obtained.

After stopping the discharge, the supply of hydrogen gas is stopped. Thus, the film forming process is completed.

The film forming method shown in FIG. 2 is characterized in that the timing of stopping the film formation and the timing of stopping the discharge are shifted. That is, the discharge is continued so that the formation of plasma which does not affect the film formation is continued even after the film formation is completed, and the self-bias as shown in FIG. 8 is formed.

By doing so, it is possible to prevent the fine particles from adhering to the film after the completion of the film formation.

[Embodiment 2] In this embodiment, a process of manufacturing a thin film transistor by using the method for forming an amorphous silicon film shown in Embodiment 1 will be described.

FIG. 3 shows a manufacturing process of this embodiment. First, as shown in FIG. 3A, a silicon oxide film 102 is formed as a base film on a glass substrate 101 for 300 nm by a plasma CVD method.
m to form a film.

Next, an amorphous silicon film 103 is formed to a thickness of 50 nm by the method described in the first embodiment. FIG.
The state shown in FIG.

Next, the amorphous silicon film 103 is crystallized by irradiating a laser beam. As a method for crystallizing the amorphous silicon film, a method such as heating, a combination of heating and irradiation with strong light, a combination of heating and irradiation with laser light, or the like can be used.

Next, the obtained crystalline silicon film is patterned to obtain a pattern indicated by 104 in FIG.

Further, a silicon oxide film 105 functioning as a gate insulating film is formed to a thickness of 100 nm by a plasma CVD method.

Further, a film made of aluminum is
A film is formed by a sputtering method to a thickness of Then, this aluminum film is patterned using the resist mask 107. Thus, the pattern shown by 106 is obtained. This pattern 106 becomes a base for forming a gate electrode later.

Thus, the state shown in FIG. 3B is obtained. Next, anodic oxidation is performed using the aluminum pattern 106 as an anode while the resist mask 107 remains. Here, an aqueous solution containing 3% by volume of oxalic acid is used as an electrolytic solution, and anodic oxidation is performed using the pattern 106 as an anode and platinum as a cathode.

In this step, an anodic oxide film 108 is formed on the side surface of aluminum pattern 106 in a state as shown in FIG.

The thickness of this anodic oxide film 108 is 400 nm.
And The anodic oxide film 108 formed in this step is obtained as having a porous shape (porous shape).

After obtaining the state shown in FIG. 3C, the resist mask 107 is removed. Then, anodic oxidation is performed again. Here, as the electrolytic solution, a solution obtained by neutralizing an ethylene glycol solution containing tartaric acid at 3% by volume with aqueous ammonia is used.

In this step, an anodic oxide film is formed as shown by 109 in FIG. 3D because the electrolytic solution enters the inside of the porous anodic oxide film 108. The thickness of the anodic oxide film 109 is 70 nm. Where 110
The pattern shown by becomes a gate electrode.

The anodic oxide film 109 formed in this step has a dense film quality.

Thus, the state shown in FIG. 3D is obtained. Next, doping with an impurity element is performed in a state illustrated in FIG. Here, phosphorus is doped by a plasma doping method in order to manufacture an N-channel TFT.

Here, a plasma doping method is used in which phosphorus ions are extracted from a plasma containing phosphorus ions with an electric field, and further accelerated electrically to perform doping. However, an ion implantation method in which phosphorus ions are electrically accelerated and implanted after mass separation may be used as the doping means.

This doping is performed under the conditions for forming ordinary source and drain regions. Thus, FIG.
As shown in (A), the regions 111 and 115 are doped with phosphorus in a self-aligned manner. Here, 111 is a source region and 115 is a drain region.

Next, the porous anodic oxide film 108 is removed to obtain the state shown in FIG. Then, doping of phosphorus is performed again by the plasma doping method.

This doping is performed under the condition of light doping as compared with the doping performed in the state of FIG.

In this step, low concentration impurity concentration regions 112 and 114 are formed in a self-aligned manner. Also 113
Region is defined as a channel forming region. (FIG. 4
(B))

Here, the low impurity concentration means that the concentration of the dopant (phosphorus in this case) is lower than that of the source region 111 and the drain region 115.

When the doping is completed, the crystallinity of the doped region is improved and the doping is activated by irradiating a laser beam.

Here, an example in which laser light irradiation is performed is shown, but a method using strong light irradiation may be used.

Next, as shown in FIG.
16 is formed to a thickness of 150 nm by a plasma CVD method, and a silicon oxide film 117 is formed to a thickness of 400 nm by a plasma CVD method.

Further, an acrylic resin is applied, and a resin film 11 is formed.
8 is formed. If a resin film is used, its surface can be made flat. In addition to the acrylic resin, resin materials such as polyimide, polyimide amide, polyamide, and epoxy can be used.

Next, a contact hole is formed, and a source electrode 119 and a drain electrode 120 are formed. Thus, the TFT is completed.

In this embodiment, an example in which a glass substrate is used as the substrate has been described. However, a quartz substrate, a semiconductor substrate on which an insulating film is formed, or a metal substrate may be used. (These are collectively called substrates with insulating surfaces.)

Further, in this embodiment, an example in which the semiconductor film constituting the active layer of the TFT is a crystalline silicon film has been described, but the active layer may be constituted by an amorphous silicon film. Is also good.

Further, in this embodiment, an example in which aluminum is used for the gate electrode has been described. However, another silicon material or silicide material, or an appropriate metal material may be used.

In this embodiment, the example of the top gate type TFT in which the gate electrode is located above the active layer is shown. However, the bottom gate type TFT in which the gate electrode is located below the active layer (substrate side). It may be.

[Embodiment 3] This embodiment is an example in which the configuration shown in Embodiment 1 is further improved.

In this embodiment, the film is formed according to the timing chart shown in FIG. What is important in the timing chart of FIG. 5 is that the discharge power is gradually reduced in the discharge after the film formation is completed (that is, after the supply of the silane gas is stopped).

By doing so, it is possible to prevent the fine particles attached to the inner wall of the chamber from being released into the atmosphere. In addition, it is possible to suppress plasma damage to the formed film.

Here, an example is shown in which the discharge power of 20 W is reduced to 5 W after the film formation is completed (after the supply of silane gas is stopped).

The manner of changing the discharge power may be further stepwise. It may be changed continuously. Also, a combination of a stepwise change and a continuous change may be used.

[Embodiment 4] This embodiment relates to the configuration shown in Embodiment 1 in which the start of discharge is considered.

In the case where the film is formed at the timing shown in FIG. 2 shown in Example 1, the start of the discharge coincides with the start of the film formation. That is, in this case, the film formation is started by starting the discharge. In other words, film formation is started simultaneously with the start of plasma generation.

However, depending on the structure of the electrodes and the like,
At the start of discharge, a period during which the discharge state is not stable may last for several seconds.

In this embodiment, in order to suppress this problem,
First, the atmosphere is used as a discharge gas, and discharge is performed in that state. Next, the gas is switched to a gas for film formation, and film formation is performed while the discharge is maintained.

When an amorphous silicon film is formed, hydrogen is used as a discharge gas, and silane is used as a film formation gas.

FIG. 6 is a timing chart in the case of performing the film formation of this embodiment. Also in this embodiment, it is preferable that the pressure change of the atmosphere according to the gas switching be as small as possible.

By performing the film formation at the timing shown in FIG. 6, it is possible to prevent the instability of the discharge during the period indicated by t at the start of the discharge from affecting the film formation.

As shown in FIG. 6, in this embodiment, immediately before the start of the film formation and immediately after the start of the film formation, the hydrogen gas as the discharge gas is used only for performing the discharge (only for generating the plasma). Make an introduction.

In this way, it is possible to prevent the instability at the start of the discharge from affecting the film formation and to prevent the fine particles after the film formation from adhering to the surface of the film.

[Embodiment 5] This embodiment is an example in which a hard carbon film such as a DLC film (diamond-like carbon film) is formed.

There are various types of hard carbon films other than the DLC film, and there is no fixed classification method or evaluation. Therefore, a carbon film used as a protective film or a film having wear resistance is collectively referred to as a hard carbon film.

When a hard carbon film is formed, a method is used in which a strong self-bias is used to strike carbon ions on the surface to be formed.

In such a film forming method, the surface to be formed is arranged on the side of the electrode 15 connected to the high frequency power supply 16 of the plasma CVD apparatus as shown in FIG.

That is, the substrate 11 (or a substrate instead thereof) is disposed on the electrode 15 side.

The invention disclosed in this specification is useful in such a configuration. That is, by forming the film according to the timing chart shown in FIG. 2, it is possible to prevent the fine particles from adhering to the surface of the formed film.

In this case as well, after the film formation is completed, a self-bias according to the formation of plasma is applied to the surface on which the plasma is to be formed, and further, the discharge is stopped in a state where the atmosphere in the chamber is replaced, so that the particles are covered. It can be prevented from adhering to the formation surface.

[Embodiment 6] This embodiment is an example in which the invention disclosed in this specification is used for performing continuous film formation.

In a multi-chamber film forming apparatus in which a number of film forming chambers are connected in series or in parallel,
In the case where different films are stacked in multiple layers, the presence of fine particles remaining on the underlying film is particularly problematic.

Therefore, for example, a method as shown in Embodiment 1 is executed for each film formation. By doing so, the above problem can be solved.

In the above description, variations have been described based on the first embodiment. However, the embodiments can be combined as needed.

[0125]

By utilizing the invention disclosed in this specification, it is possible to prevent the presence of fine particles, which are reaction products generated during film formation in a plasma CVD method, from adversely affecting the quality of the formed thin film. can do.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a plasma CVD apparatus.

FIG. 2 is a diagram showing timings of gas supply and high-frequency power (RF) supply.

FIG. 3 illustrates a manufacturing process of a thin film transistor.

FIG. 4 illustrates a manufacturing process of a thin film transistor.

FIG. 5 is a diagram showing timings of gas supply and high-frequency power (RF) supply.

FIG. 6 is a diagram showing timings of supply of gas and supply of high frequency power (RF).

FIG. 7 shows a conventional gas supply and high-frequency power (R
The figure which shows the timing with supply of F).

FIG. 8 is a diagram showing a state of self-bias during high-frequency discharge.

[Explanation of symbols]

 Reference Signs List 10 chamber 11 substrate (sample) 12 electrode 13 evacuation system 14 evacuation pump 15 electrode 16 high frequency power supply 17 silane gas supply system 18 hydrogen gas supply system 101 glass substrate 102 base film (silicon oxide film) 103 amorphous silicon film 104 active layer ( (Crystalline silicon film) 105 gate insulating film 106 aluminum pattern 107 resist mask 108 porous anodic oxide film 109 anodic oxide film having dense film quality 110 gate electrode 111 source region 115 drain region 112 low concentration impurity region 114 low concentration impurity Region 113 Channel formation region 116 Silicon nitride film 117 Silicon oxide film 118 Acrylic resin film 119 Source electrode 120 Drain electrode

Claims (12)

[Claims] A high-frequency discharge is performed in a state where a film-forming gas is supplied to form a plasma to form a film, and a high-frequency discharge is performed by switching from the film-forming gas to a discharge gas. A second step of performing plasma formation that does not obey film formation by using the method. 2. The film forming method according to claim 1, wherein the pressure in the atmosphere is kept constant between the first stage and the second stage. 3. The film forming method according to claim 1, wherein silane is used as a film forming gas and hydrogen is used as a discharge gas. 4. The film forming method according to claim 1, wherein the high-frequency discharge is performed between the electrodes of the parallel plate type, and the surface to be formed is disposed on the electrode side maintained at the ground potential. 5. The film forming method according to claim 1, wherein the time for maintaining the second stage is longer than the time for changing the atmosphere. 6. A first step in which high-frequency discharge is performed in a state where a film-forming gas is supplied to form a plasma by forming a plasma, and a high-frequency discharge is performed by switching from the film-forming gas to a discharge gas. A second step of forming a plasma that does not obey film formation by using the same. 7. The film forming apparatus according to claim 6, wherein the film forming apparatus has a function of keeping the pressure in the atmosphere constant between the first stage and the second stage. 8. The film forming apparatus according to claim 6, wherein silane is supplied as a film forming gas and hydrogen is supplied as a discharge gas. 9. A film forming apparatus according to claim 6, wherein the electrode has a parallel plate type electrode structure, and a surface on which the electrode is formed is disposed on the side of the electrode which is held at a ground potential. 10. A method for forming a film by a plasma gas phase reaction by causing high-frequency discharge between parallel plate type electrodes, wherein a gas for forming a film is supplied while a self-bias is applied to a surface on which the film is formed. A film formation method, comprising: stopping and supplying a discharge gas at the same time to maintain a state where a self-bias is applied to a formation surface even after completion of film formation. 11. The film forming method according to claim 10, wherein a time during which the self-bias is applied to the surface on which the film is formed after the film formation is completed is longer than a time when the atmosphere is replaced. 12. An apparatus for forming a film by a plasma gas phase reaction by generating a high-frequency discharge between parallel plate type electrodes, and supplying a film forming gas while a self-bias is applied to a surface on which the film is formed. A film formation apparatus having a function of stopping and supplying a discharge gas at the same time to maintain a state where a self-bias is applied to a formation surface even after completion of film formation.