JP5357083B2 - Thin film forming apparatus and thin film forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply raw material gas of new type capable of preventing degradation of the quality of a thin film deposited on a substrate like the conventional apparatus when depositing a film by ALD (atomic layer deposition). <P>SOLUTION: A thin film forming apparatus includes an evacuation vessel forming an evacuated film deposition space, and a raw material gas supply unit for supplying raw material gas to the film deposition space. The raw material gas supply unit includes a raw material gas pipe, a purge gas pipe, and a gas supply pipe for supplying raw material gas and purge gas to the film deposition space while the purge gas pipe, the raw material gas pipe and the purge gas pipe are connected to one another. First and second control valves are provided on the raw material gas pipe in the order closer from the connection part of the raw material gas pipe and the purge gas pipe. The raw material gas supply unit opens the second control valve, introduces raw material gas into the raw material gas pipe in an evacuated state between the first and second control valves, and supplies raw material gas into the film deposition space by performing the control to open the first control valve. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a thin film forming apparatus and a thin film forming method for forming a thin film on a substrate.

  Recently, an atomic layer growth method (hereinafter abbreviated as ALD (Atomic Layer Deposition) method) in which a thin film is formed on a substrate in units of atomic layers has attracted attention as a thin film forming method. In the ALD method, two types of gas mainly composed of elements constituting a film to be formed are alternately supplied onto a film formation target substrate, and a thin film is formed on the substrate in units of atomic layers repeatedly several times. This is a thin film forming technique for forming a film having a desired thickness. For example, when an Al2O3 film is formed on a substrate, a source gas made of TMA (Tri-Methyl Aluminum) and an oxidizing gas containing O are used. Further, when a nitride film is formed on the substrate, a nitriding gas is used instead of the oxidizing gas.

  In the ALD method, only one layer or several layers of source gas components are adsorbed on the substrate surface while the source gas is supplied, and the excess source gas does not contribute to the growth. ).

  The ALD method has high step coverage and film thickness controllability compared to the general CVD (Chemical Vapor Deposition) method, and is suitable for the formation of capacitors for memory elements and insulating films called “high-k gates”. Practical use is expected. In addition, since an insulating film can be formed at a low temperature of about 300 ° C., application to formation of a gate insulating film of a thin film transistor of a display device using a glass substrate such as a liquid crystal display is expected.

In this ALD method, for example, when oxidizing the component of the source gas adsorbed on the substrate, plasma is generated using the oxidizing gas. At this time, oxygen radicals are generated by the plasma, and the component of the source gas adsorbed on the substrate is oxidized using the oxygen radicals.
For example, Patent Document 1 below describes a thin film forming apparatus using an ALD method.

JP 2009-209434 A

Such an ALD method makes it possible to embed a thin film with high step coverage even in a minute recess.
However, in this apparatus, for example, when a thin film of aluminum oxide is formed on a substrate using TMA and an oxidizing gas as a raw material gas, a film or powdery particles adhere to the raw material gas supply pipe, and are deposited in some cases. In some cases, the film or powdery particles are peeled off and enter the film forming container, and foreign matter or the like is mixed into the thin film formed on the substrate to deteriorate the quality of the thin film.

FIG. 3 is a diagram for explaining mainly a raw material gas supply pipe of a conventional thin film forming apparatus.
The apparatus 100 in FIG. 3 includes a decompression vessel 102, a source gas supply pipe 104, an exhaust pipe 106, and a substrate stage 110 on which a substrate 108 on which a thin film is formed is placed.
A TMA gas supply pipe 112 and a purge gas supply pipe 114 are connected to the source gas supply pipe 104, a TMA valve valve 116 is provided in the TMA gas supply pipe 112, and a purge gas valve valve 118 is provided in the purge gas supply pipe 114. . By opening the TMA valve valve 116, the source gas supply pipe 104 supplies gaseous TMA to the decompression vessel 102. As a result, the TMA component is adsorbed on the substrate 108 in atomic units. Thereafter, N 2 gas flowing from the purge gas supply pipe 114 is supplied into the decompression vessel 102 as a purge gas. The purge gas functions to efficiently supply gaseous TMA from the source gas supply pipe 104 into the decompression vessel 102 and to efficiently diffuse TMA in the film formation space.
After the TMA gas is exhausted from the decompression vessel 102, an oxidizing gas is supplied into the decompression vessel 102 from a reaction gas supply pipe (not shown), and the components of TMA adsorbed on the substrate 108 are oxidized. At this time, the oxidizing gas is activated using plasma or heat.

  In order to grow the thin film formed in the atomic unit thus formed, the TMA valve valve 116 is opened and TMA gas is supplied again into the decompression vessel 102. In this way, the formation of the atomic thin film is repeatedly performed. However, at this time, a film or powder particles adheres to the inner surface of the portion R in the drawing of the source gas supply pipe 104 immediately after the merge of the TMA gas supply pipe 112 and the purge gas supply pipe 114. Since this portion of the tube is fixed to the decompression vessel 102 and cannot be replaced, as the ALD is repeated, the film thickness and the accumulation of powdery particles also progress. In some cases, some of the particles may peel off and enter the vacuum container 102. For this reason, there exists a possibility of leading to the quality degradation of the thin film formed.

  Therefore, the present invention provides a new system in which when forming a thin film, the film forming space is not contaminated and the quality of the thin film formed on the substrate is not deteriorated, unlike the conventional thin film forming apparatus. An object of the present invention is to provide a thin film forming apparatus and a thin film forming method for realizing the supply of the raw material gas.

  The film or powder particles formed and deposited on the inner surface of the source gas supply pipe 104 described in the above-mentioned conventional problems are reaction products formed by the reaction of moisture mixed in the N2 gas with the source gas. The present inventors have found that this is the case. Based on this knowledge, the present invention has been reached.

One embodiment of the present invention is a thin film forming apparatus for forming a thin film over a substrate.
The device is
A decompression container that forms a decompressed film formation space;
A source gas pipe for flowing a source gas toward the film formation space, a purge gas pipe for flowing a purge gas toward the film formation space, and the source gas pipe and the purge gas pipe are connected to generate the source gas and the purge gas. A gas supply pipe that supplies the membrane space, and a raw material gas supply unit in which the first control valve and the second control valve are provided in the raw material gas pipe in order from the connection portion of the raw material gas pipe and the purge gas pipe, Have
At that time, in the source gas supply unit, the pressure in the source gas pipe between the first control valve and the second control valve just before the source gas is supplied to the film formation space is the source gas flow. Lower than the pressure upstream of the second control valve.

It is preferable that the inside of the source gas pipe between the first control valve and the second control valve immediately before supplying the source gas to the film formation space is in a reduced pressure state equivalent to the reduced pressure state of the reduced pressure vessel.
When the source gas supply unit finishes supplying the source gas to the film formation space, the timing for closing the first control valve is set to be slower than the timing for closing the second control valve. It is preferable to control.

  The source gas supply unit opens the second control valve to introduce a source gas into a source gas pipe in a reduced pressure state between the first control valve and the second control valve, and the first control valve It is preferable that the first control valve is closed when the source gas is supplied to the film formation space by opening and the purge gas is supplied to the film formation space.

Alternatively, the raw material gas pipe is provided with a plurality of pores extending in parallel to the passage in a passage of the raw material gas between the first control valve and the second control valve. It is preferable to have an inner surface increasing portion with an increased inner surface area. More preferably, the inner surface area increasing portion has a replaceable configuration.
The source gas supply unit intermittently supplies source gas to the film formation space, for example.

Another embodiment of the present invention is a thin film forming method for forming a thin film on a substrate in a film forming space.
The method is
Of the two control valves provided in series with the source gas pipe extending from the source gas source, by opening the second control valve away from the film formation space and the first control valve close to the film formation space, the source gas is supplied. Supplying a source gas component from the source gas pipe through the gas supply pipe to the film formation space to adsorb a component of the source gas on the substrate;
After the first control valve is closed, a third control valve provided in a purge gas pipe is opened to supply purge gas to the film formation space, and the purge gas pipe enters the film formation space through the gas supply pipe. A second step of supplying a purge gas;
A third step of forming a thin film on the substrate by reacting the component of the reactive gas with the component of the source gas adsorbed on the substrate by supplying the reactive gas to the film formation space.
The pressure in the source gas pipe between the first control valve and the second control valve immediately before supplying the source gas to the film formation space is set to a pressure upstream of the second control valve in the source gas flow. Low compared.

In the second step, it is preferable that the first control valve is closed when the purge gas is supplied to the film formation space.
It is preferable that the thin film is grown by repeating the first step, the second step, and the third step.

  When the supply of the source gas to the film formation space is terminated, it is preferable that the timing for closing the first control valve is delayed compared to the timing for closing the second control valve.

  In the above-described thin film forming apparatus and thin film forming method, reaction products such as a film and powdery particles are not deposited on the inner surface of a source gas supply pipe or the like. For this reason, the film formation space is not contaminated, and the quality of the thin film formed on the substrate does not deteriorate.

It is a figure explaining the structure of the ALD apparatus which is one Example of the thin film formation apparatus of this invention. (A)-(d) is a figure explaining the source gas supply system in the ALD apparatus shown in FIG. It is a figure explaining the conventional thin film forming apparatus.

Hereinafter, the thin film forming apparatus and the thin film forming method of the present invention will be described in detail.
FIG. 1 shows a schematic configuration of the ALD apparatus of the present embodiment.
The ALD apparatus 10 shown in FIG. 1 alternately supplies two kinds of film forming gases (raw material gas and oxidizing gas) whose main components are elements constituting a film to be formed onto a substrate 12 to be formed. At that time, an oxide film of a source gas is formed on the substrate 12 in units of atomic layers using plasma in order to increase the reaction activity. A film having a desired thickness is formed by repeating the process for a plurality of cycles with the above process as one cycle. A nitriding gas can be used instead of the oxidizing gas.

  The ALD apparatus 10 includes a high-frequency power source 14, a film forming container 16, a source gas supply unit 18, a reaction gas supply unit 20, and an exhaust unit 22. Hereinafter, a case where an oxide film is formed on the substrate 12 will be described as an example, but the same applies to a nitride film.

A film forming space 24 in the decompression vessel 16 is provided with a substrate stage 26 that also serves as a lower electrode, and a heater (not shown) below the substrate stage 26. The lower electrode is grounded.
The substrate stage 26 is provided below the film formation space 26 together with a heater (not shown). The substrate 12 is placed on the substrate stage 26 while being supported by lift pins 13 a and 13 b that extend from the outside of the decompression container 16 through the substrate stage 26. The lift pins 13 a and 13 b can be moved up and down by an elevating mechanism 13 c for exchanging the substrate 12.
On the upper surface of the film formation space 24, an upper electrode 28 and a heater 30 are provided. The upper electrode 28 is connected to the high-frequency power source 14 provided outside the decompression vessel 16 and receives a high-frequency current having a predetermined frequency. As described above, the ALD apparatus 10 is a so-called parallel plate type plasma generation apparatus that includes the upper electrode and the lower electrode to generate plasma.

  The right side wall of the decompression vessel 16 is provided with an exhaust port for exhausting the source gas, the reaction gas, and the purge gas, and is exhausted through the exhaust pipe 31 and the valve 32. The exhaust pipe 31 is connected to a dry pump or the like (not shown). Thereby, even if source gas, oxidizing gas, or purge gas is supplied as will be described later, the film formation space 24 in the decompression vessel 16 is maintained at a vacuum degree of about 10 (Pa).

The source gas supply unit 18 supplies source gas or purge gas to the film formation space 24 through a gas supply port 34 provided in the decompression vessel 16. Details of the source gas supply unit 18 will be described later.
The reactive gas supply unit 20 supplies an oxidizing gas (reactive gas) from an oxidizing gas source (not shown) to the film formation space 24 via a gas supply port 36 provided in the decompression vessel 16.
When the supply of the source gas and the purge gas to the film formation space 24 is stopped, the upper electrode 28 that is supplied with electric power from the high-frequency power source 14 in the film formation space 24 to which the oxidizing gas is supplied Plasma is generated between the substrate stage 26 as an electrode. A part of the oxidizing gas is activated by this plasma, and a component of the oxidizing gas, for example, radical oxygen reacts with a component of the source gas adsorbed on the substrate 12 to form a thin film such as a metal oxide film in atomic units. Is done.

The source gas supply unit 18 includes a source gas source 18a, control valves 18b and 18c, a source gas pipe 18d, a gas supply pipe 18e, a purge gas source 18f, a control valve 18g, a purge gas pipe 18h, and a controller 18i.
The source gas source 18a is a buffer gas source that stores a source gas such as TMA at a pressure of several kPa. A source gas pipe 18d extends from the source gas source 18a, and a control valve (second control valve) 18b and a control valve (first control valve) 18c are provided in series on the way. A source gas pipe 18d extending from the control valve 18c toward the film formation space 24 is connected to a purge gas pipe 18h and connected to a gas supply pipe 18e.
The purge gas source 18f is a gas source that stores a purge gas such as N2 gas at a pressure of several kPa. The purge gas functions to push the source gas from the gas supply pipe 18 e into the film formation space 24, and functions so that the source gas is diffused in the film formation space 24. A purge gas pipe 18h extends from the purge gas source 18f, and a control valve (third control valve) 18g is provided in the middle thereof. A purge gas pipe 18h extending from the control valve 18g toward the film forming space 24 is connected to the source gas pipe 18d and connected to the gas supply pipe 18e.

  In each of the control valves 18b, 18c and the control valve 18g, the open / close state of the valves is controlled by a signal from the control unit 18i. Control operations of the control valves 18b and 18c and the control valve 18g will be described later.

The pressure of the portion of the source gas pipe 18d between the control valve 18b and the control valve 18c is higher than the pressure on the upstream side of the control valve 18b, that is, on the source gas source 18a immediately before the source gas is supplied. For example, it is equivalent to the reduced pressure state of the film formation space 24.
In addition, a portion between the control valve 18b and the control valve 18c, that is, a raw material gas passage between the control valve 18b and the control valve 18c, is provided with a plurality of pores extending in parallel to the passage. A honeycomb structure 18j is provided. Moreover, the honeycomb structure 18j is replaceable with the material gas pipe 18d being detachable. The honeycomb structure 18j serves as an inner surface increasing portion in which the inner surface area of the source gas pipe 18d is increased in this portion.

  As will be described later, due to the operation of the control valve 18b and the control valve 18c, the portion between the control valve 18b and the control valve 18c has a reduced pressure atmosphere in the film formation space 24 when the source gas is not supplied to the film formation space 24. The pressure is reduced to a few Pa. For this reason, when the control valve 18b changes from the closed state to the open state, and the raw material gas stored in the raw material gas source 18a in a pressure state of 2 kPa moves to the above-mentioned portion in a reduced pressure state of several Pa, the raw material gas expands A part of the gas is condensed, and the component of the source gas adheres to the inner surface of the source gas pipe 18d. For this reason, in order to adsorb | suck the component which the source gas condensed to the wall surface efficiently, the internal surface area of the channel | path is increased using the honeycomb structure 18j. Moreover, the honeycomb structure 18j to which the component of the raw material gas is attached can be replaced with a new one.

2A to 2D illustrate the supply of the source gas to the film formation space 24 and the supply of the purge gas to the film formation space 24 and the open / closed states of the control valves 18b, 18c, and 18g.
First, as shown in FIG. 2A, the control valves 18b and 18c are controlled to be closed and the control valve 18g is controlled to be opened. In this state, the source gas supply unit 18 supplies the purge gas from the purge gas source 18f to the film formation space 24 through the purge gas pipe 18h and the gas supply pipe 18e. At this time, the pressure in the portion between the control valve 18b and the control valve 18c is lower than the pressure on the upstream side of the control valve 18b, that is, on the source gas source 18a side, and is in a reduced pressure state equivalent to the film formation space 24. It has become.

  Next, as shown in FIG. 2B, the control valve 18g is controlled to be in a closed state, and the control valves 18b and 18c are controlled to be in an open state at substantially the same time. Thereby, the source gas supply unit 18 flows the source gas into the gas supply pipe 18e, and supplies the source gas to the film formation space 24 from the gas supply pipe 18e. Since the inside of the source gas pipe 18d between the control valve 18b and the control valve 18c is in a reduced pressure state equivalent to that of the film formation space 24 immediately before the source gas flows, a part of the source gas passes through this part. Condenses. However, since the honeycomb structure 18j is provided at this portion, the component of the source gas condensed (liquid component) adheres to the surface of the honeycomb structure 18j. Therefore, the raw material gas that has passed through the control valve 18c passes through the gas supply pipe 18e without being condensed in the passages thereafter.

  Next, after the raw material gas is supplied for a certain period of time, as shown in FIG. 2C, the control valve 18b is controlled from the open state to the closed state. Thereby, supply of source gas from source gas source 18a stops. Therefore, the portion of the source gas pipe 18d between the control valve 18b and the control valve 18c is in a decompressed state equivalent to the film formation space 24.

  Next, as shown in FIG. 2D, the control valve 18c is controlled from the open state to the closed state. Thereby, the portion of the source gas pipe 18d between the control valve 18b and the control valve 18c is in a reduced pressure state close to the film formation space 24 and forms a closed space. Thereafter, as shown in FIG. 2A, the control valve 18 g is controlled from the closed state to the open state, and the source gas supply unit 18 supplies the purge gas to the film formation space 24. As described above, the control valve 18g for controlling the supply of the purge gas to the film formation space is opened after the control valve 18c and the control valve 18b are closed.

The following thin film formation is performed according to the operation of the source gas supply unit 18 described above.
By controlling the control valves 18b and 18c in the reduced-pressure film formation space 24 in which the heated substrate 12 is disposed, the source gas supply unit 18 generates source gas as shown in FIG. It supplies to the film | membrane space 24, and the component of source gas is made to adsorb | suck to the board | substrate 12 per atom.

After the component of the source gas is adsorbed on the substrate 12 in atomic units, the control valve 18b is first closed as shown in FIG. Thereafter, as shown in FIG. 2D, the control valve 18c is closed. That is, the timing at which the control valve 18c is closed is later than the timing at which the control valve 18b is closed. As a result, the portion of the source gas pipe 18d between the control valve 18b and the control valve 18c becomes a closed space in a reduced pressure state equivalent to the film formation space 24.
On the other hand, in the state shown in FIG. 2D, an oxidizing gas is supplied from the reaction gas supply unit 20 to the film formation space 24 as a reaction gas. During this supply, high frequency power is supplied from the high frequency power source 14 to the upper electrode 28, and plasma is generated in the film formation space 24. After a part of the oxidizing gas is ionized by the generated plasma, radical oxygen is produced, and this radical oxygen reacts with the component of the source gas adsorbed on the substrate 12 to cause the substrate 12 to have atomic units. The metal oxide film is formed.
Thereafter, as shown in FIG. 2A, the control valve 18g is controlled to be in the open state, and the source gas supply unit 18 supplies the purge gas to the film formation space 24 to purge the oxidizing gas. Thereafter, the state returns to the state of FIG.
In this way, by repeating the respective states of FIGS. 2A to 2D, the adsorption of the component of the source gas to the substrate, the supply of the purge gas, the reaction of the component of the reactive gas and the component of the source gas are performed. repeat. As a result, the ALD apparatus 10 forms a thin film having a desired thickness.

  Thus, when the raw material supply unit 18 supplies the raw material gas to the film formation space 24, the raw material gas is introduced into the raw material gas pipe 18d in a reduced pressure state between the control valve 18b and the control valve 18c, and the control is performed. Since the opening and closing of the control valves 18b and 18c is controlled so as to open the valve 18c, the condensation of the raw material gas occurs in the raw material gas pipe 18d between the control valve 18b and the control valve 18c, and the downstream side thereafter. Condensation does not occur in the passage. For this reason, the water | moisture content etc. in source gas and purge gas do not react. Furthermore, when the purge gas is supplied to the film formation space 24, the source gas pipe 18d is shut off by the control valve 18c, and the purge gas does not move into the source gas pipe 18d. For this reason, there is no opportunity for the raw material gas and the moisture in the purge gas to react. Therefore, unlike the conventional case, a reaction product such as a film thickness and powdery particles is not generated and deposited on the raw material gas pipe 18d and the gas supply pipe 18e. Part of the film peels off and does not enter the decompression vessel 24.

The ALD apparatus 10 of the present embodiment is a plasma generation apparatus using two parallel plate type electrodes as a plasma generation element, but is not limited to a parallel plate type plasma generation element, and a known plasma generation element is used. Can do. A plurality of monopole antennas that alternately protrude from the opposing wall surfaces of the film formation container into a rod shape and generate uniform plasma with a large area can also be used as the plasma generation element. Such a plasma generating element is described in detail in WO2007 / 114155, for example.
Further, the ALD apparatus 10 is not limited to a thin film forming apparatus using plasma. A thermal ALD method in which a reactive gas is heated to several hundred degrees to form a thin film can also be used.

  As described above, the thin film forming apparatus and the thin film forming method of the present invention have been described in detail. However, the thin film forming apparatus and the thin film forming method of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Of course, improvements and changes may be made.

DESCRIPTION OF SYMBOLS 10 ALD apparatus 12 Substrate 13a, 13b Lift pin 13c Elevating mechanism 14 High frequency power source 16 Film formation container 18 Raw material gas supply unit 18a Raw material gas source 18b, 18c Control valve 18d Raw material gas pipe 18e Gas supply pipe 18f Purge gas source 18g Control valve 18h Purge gas pipe 18i Control unit 20 Reactive gas supply unit 22 Exhaust unit 24 Deposition space 26 Substrate stage 28 Upper electrode 30 Heater 31 Exhaust pipe 32 Valves 34 and 36 Gas supply port 100 Apparatus 102 Depressurization vessel 104 Source gas supply pipe 106 Exhaust pipe 108 Substrate 110 Substrate stage 112 TMA gas supply pipe 114 Purge gas supply pipe 116 TMA valve valve 118 Purge gas valve valve

Claims (11)

A thin film forming apparatus for forming a thin film on a substrate,
A decompression container that forms a decompressed film formation space;
A source gas pipe for flowing a source gas toward the film formation space, a purge gas pipe for flowing a purge gas toward the film formation space, and the source gas pipe and the purge gas pipe are connected to generate the source gas and the purge gas. A gas supply pipe that supplies the membrane space, and a raw material gas supply unit in which the first control valve and the second control valve are provided in the raw material gas pipe in order from the connection portion of the raw material gas pipe and the purge gas pipe, Have
In the source gas supply unit, the pressure in the source gas pipe between the first control valve and the second control valve immediately before the source gas is supplied to the film formation space is the second control of the source gas flow. A thin film forming apparatus characterized in that the pressure is lower than the pressure upstream of the valve.   The source gas pipe between the first control valve and the second control valve immediately before supplying the source gas to the film formation space is in a reduced pressure state equivalent to the reduced pressure state of the reduced pressure container. Thin film forming equipment.   When the source gas supply unit finishes supplying the source gas to the film formation space, the timing for closing the first control valve is set to be slower than the timing for closing the second control valve. The thin film forming apparatus according to claim 1, wherein the thin film forming apparatus is controlled.   The source gas supply unit opens the second control valve to introduce a source gas into a source gas pipe in a reduced pressure state between the first control valve and the second control valve, and the first control valve The thin film formation according to any one of claims 1 to 3, wherein the first control valve is closed when the raw material gas is supplied to the film formation space by being opened and the purge gas is supplied to the film formation space. apparatus.   The source gas pipe has an inner surface area of the source gas pipe by providing a plurality of pores extending in parallel to the passage in a path of the source gas between the first control valve and the second control valve. The thin film formation apparatus of any one of Claims 1-4 which has an inner surface increase part which increased this.   The thin film forming apparatus according to claim 5, wherein the inner surface area increasing portion has a replaceable configuration.   The thin film forming apparatus according to claim 1, wherein the source gas supply unit intermittently supplies source gas to the film formation space. A thin film forming method for forming a thin film on a substrate in a film formation space,
Of the two control valves provided in series with the source gas pipe extending from the source gas source, by opening the second control valve away from the film formation space and the first control valve close to the film formation space, the source gas is supplied. Supplying a source gas component from the source gas pipe through the gas supply pipe to the film formation space to adsorb a component of the source gas on the substrate;
After the first control valve is closed, a third control valve provided in a purge gas pipe is opened to supply purge gas to the film formation space, and the purge gas pipe enters the film formation space through the gas supply pipe. A second step of supplying a purge gas;
A third step of forming a thin film on the substrate by reacting a component of the reactive gas with a component of the source gas adsorbed on the substrate by supplying a reactive gas to the film formation space;
The pressure in the source gas pipe between the first control valve and the second control valve immediately before supplying the source gas to the film formation space is set to a pressure upstream of the second control valve in the source gas flow. A method for forming a thin film, characterized in that the method is lower than the above.   The thin film forming method according to claim 8, wherein, in the second step, the first control valve is closed when the purge gas is supplied to the film forming space.   The thin film formation method according to claim 8 or 9, wherein the thin film is grown by repeating the first step, the second step, and the third step.   The timing for closing the first control valve is delayed as compared with the timing for closing the second control valve when the supply of the source gas to the film formation space is terminated. A method for forming a thin film according to 1.