JP2002239441A - Vacuum drying method and coating film forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high throughput in a vacuum drying apparatus for a substrate provided in a coating film forming apparatus. SOLUTION: A closed vessel and a vacuum pump for making a space, where the substrate is placed, into a closed atmosphere are connected to each other through a exhausting pipe, one end of a gas supply passage is connected to the middle of the exhausting pipe and a gas supply means is provided at another end side. A three-way valve for communicating either one of the closed vessel or a gas supply means to the vacuum pump is interposed at the connecting position between the exhausting pipe and the gas supply passage, and the vacuum drying of the substrate is carried out by sealing the gas supply passage side. In the vacuum drying, when a control part recognizes that a prescribed number of sheets of the substrates are treated, the vacuum drying is interrupted and the three way valve is switched to seal the closed vessel. Gaseous nitrogen from the gas supply means is supplied and sucked to the vacuum pump side to wash away the solvent stuck to the exhausting pipe by the gaseous nitrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a method and an apparatus for forming a coating film by applying, for example, a coating liquid for a protective film of a device to a substrate to be processed such as a CD substrate (glass substrate for a liquid crystal display).

[0002]

2. Description of the Related Art As one of semiconductor manufacturing processes, there is a process of applying polyimide on a substrate such as a semiconductor wafer in order to form a protective film and an interlayer insulating film of a semiconductor device. As one method of this coating treatment, a chemical solution obtained by dissolving polyimide in a solvent is further diluted with a solvent before coating, and, for example, the wafer W is rotated as shown in FIG. A method has been studied in which the application liquid is discharged onto the surface of the wafer W while being gradually moved in the direction, and the application liquid is spirally applied in a one-stroke manner.

As the solvent for dissolving the polyimide, a solvent having low volatility is used, and the solvent is quickly removed from the wafer surface to ensure the uniformity of the thickness of the coating film. It is considered that it is preferable to apply the coating solution on the wafer and immediately carry it into the reduced-pressure drying unit to perform the reduced-pressure drying. FIG. 10 is a diagram showing a conventional vacuum drying unit. 1 in the figure
Reference numeral 2 denotes an airtight container composed of a lid 13 and a mounting portion 14, and an opening 13a is formed in the ceiling of the lid 13. The opening 13 a communicates with a vacuum pump 16 provided outside the coating film forming apparatus via an exhaust pipe 15 so that the pressure inside the closed container 12 can be reduced. In such an apparatus, the wafer W is placed on the mounting table 14.
The wafer W is heated by a heating means (not shown), and the vacuum pump 16 is operated to reduce the pressure in the closed vessel 12, so that a solvent such as NMP remaining on the surface of the wafer W is volatilized (dried). Then, the volatilized solvent is sucked toward the vacuum pump 16 and the polyimide component in the coating solution remains on the surface of the wafer W.

[0004]

However, the vacuum pump 16 used in the vacuum drying apparatus is provided on the clean room side outside the coating film forming apparatus. The solvent to be formed condenses in the middle of the exhaust pipe 15 under the influence of the clean room side atmosphere maintained at, for example, about 23 ° C.

[0005] Although the solvent condensed in this way volatilizes again from the adhering portion, the amount of dew condensation newly generated is larger than the volatilization amount of the condensed solvent. Will gradually increase. On the other hand, the exhaust flow rate in the vacuum pump 16 is kept constant, and the rate of dew condensation in the entire volatile solvent sucked by the vacuum pump 16 gradually increases.
Therefore, the time required to reduce the pressure in the closed container 12 to the pressure p1 required for drying the coating liquid is t1 in the first processing as shown by the solid line in FIG. This time gradually increases with the increase of the time, for example, when processing the n-th sheet, it takes t1 + α as shown by the dotted line, and sufficient drying cannot be performed within a predetermined time, thereby lowering the throughput.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique capable of obtaining high throughput in, for example, an apparatus for drying a substrate under reduced pressure provided in a coating film forming apparatus. is there.

[0007]

According to the present invention, there is provided a method for drying under reduced pressure, comprising the steps of: placing a substrate coated with a coating solution obtained by mixing components of a coating film and a solvent in a closed container; The inside is evacuated by an evacuation means through an evacuation path to a reduced-pressure atmosphere, and a reduced-pressure drying step of volatilizing the solvent of the coating solution applied to the substrate, and drying the solvent volatilized from the substrate and condensed in the evacuation path Solvent removal step of flowing a gas for drying to an exhaust path with the closed container closed to remove
It is characterized by including.

According to such a method, the solvent condensed in the exhaust path of the reduced-pressure drying apparatus can be periodically removed, so that the amount of the condensed solvent during the reduced-pressure drying of the substrate is reduced, and the drying is performed. Processing can be performed quickly. In this reduced-pressure drying method, the reduced-pressure drying step is preferably performed by heating the substrate, and the timing of performing the solvent removing step is, for example, grasping in advance the relationship between how many substrates are dried and a delay of a certain time or more in the processing time. In this case, the time when the number of sheets subjected to the drying processing reaches the set value can be set.

[0009] As a specific example of the solvent removing step, a gas supply path connected in the middle of the exhaust path and a vacuum exhaust means are connected through an exhaust path, and an exhaust path between the sealed container and the gas supply path is connected. After closing, there is a method in which an inert gas such as nitrogen gas is supplied from the gas supply path into the exhaust path, and the inert gas is sucked toward the vacuum exhaust means.

The coating film forming apparatus according to the present invention comprises a coating unit for coating a substrate with a coating liquid obtained by mixing components of a coating film and a solvent, and a mounting portion for mounting the substrate. An airtight container provided therein, a conveying means for conveying the substrate between the coating unit and the airtight container, and connected to the airtight container through an exhaust path, and the inside of the airtight container is brought into a reduced pressure atmosphere, and Vacuum evacuation means for volatilizing the solvent from the coating liquid, and connected to the closed vessel or the middle of the exhaust path, supplying a drying gas to the exhaust path to remove the solvent condensed in the exhaust path. A gas supply path, a flow path opening / closing section for opening / closing between the gas supply path and the vacuum evacuation means, and a flow path when it is determined that the amount of solvent condensed in the exhaust path has increased. Controls the opening / closing section to supply gas and exhaust The communicated, and a control unit for flow through the drying gas in the exhaust passage, characterized by comprising a.

[0011] Further, the gas supply path is connected in the middle of the exhaust path,
The flow path opening / closing portion communicates between the gas supply path and the vacuum evacuation means and closes the space between the closed vessel and the gas supply path, and closes the space between the gas supply path and the exhaust path and seals It may be constituted by a valve for selecting one of a state in which the container is in communication with the evacuation means. As a specific example of this valve, a three-way valve can be given, and by providing this at the connection portion between the exhaust path and the gas supply path, the direction communicating with the above-mentioned two states can be switched.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A coating film forming apparatus for carrying out a coating film forming method according to the present invention will be described below.
First, the overall configuration of this device will be briefly described with reference to FIGS. In the figure, reference numeral 21 denotes a cassette station, for example, a cassette C containing 25 wafers W.
And a transfer arm 23 for transferring the wafer W between the cassette mounting portion 22 for mounting the wafer W and the mounted cassette C. This transfer arm 23
A processing unit S1 surrounded by a housing 24 is connected to the rear side of the processing unit S1. A main transport unit 25 is provided at the center of the processing unit S1, and a plurality of coating units 31 are provided on the right side of the processing unit S1 to surround the processing unit S1, and a heating / cooling system is provided on the left side, the near side, and the back side. Of units and the like are stacked in multiple stages.

The shelf units U1, U2 and U3 are constructed by variously combining units for performing pre-processing and post-processing of the coating unit 31, and the combination is, for example, as shown in FIG. The wafer W coated with the coating liquid on the surface thereof at 31 is dried under reduced pressure atmosphere, and the reduced pressure drying unit 32 for volatilizing the solvent contained in the coating liquid, the heating unit 33 for heating (baking) the wafer W, the wafer A cooling unit 34 for cooling W is included. Note that the shelf unit U3 also incorporates a transfer unit 35 having a transfer table for transferring the wafer W. In addition, the above-described main transporting means 25 is configured to be movable up and down and back and forth, and rotatable around a vertical axis, for example, and the coating unit 31 and the shelf unit U1,
It is possible to transfer the wafer W between the units constituting U2 and U3.

Next, the coating unit 31 will be described with reference to FIGS. Here, the casing that forms the exterior body of the coating unit 31 is omitted, but inside the casing (not shown),
For example, an opening (not shown) for loading / unloading the wafer W on the side.
A hollow case body 41 is formed in which a wafer holding portion 42 for horizontally holding the wafer W by vacuum suction from the rear surface side, and supporting the wafer holding portion 42 from below, A rotation mechanism 43 for rotating the wafer holding unit 42 about a vertical axis during processing is provided. A slit 44 extending in the X direction is formed in the ceiling of the case body 41, and above the slit 44,
Nozzle 45 for supplying a polyimide liquid as a coating liquid
However, the drive unit 46 is configured to be able to move in the X direction with the discharge hole 45a at the lower end protruding into the case body 41 through the slit 44.

Next, the configuration of the reduced-pressure drying unit 32 will be described with reference to FIG. In the figure, reference numeral 51 denotes a wafer W
And a lid 52 is provided on an upper portion thereof. The lid 52 can be moved up and down by the operation of an elevating mechanism 53 including a holding arm 53a and a driving unit 53b. To form a closed container 5 in which the atmosphere in which the wafer W is placed is a closed atmosphere.

In the mounting portion 51, three lift pins 54 are provided so as to be able to transfer a wafer W to and from a wafer transfer arm (not shown). For example, it can be moved up and down by an elevating unit 56 such as an air cylinder. The atmosphere in which the wafer W is placed is the through hole 5 of the lift pin 53.
In order to prevent communication with the atmosphere side via 4a,
A bellows 56 a is provided between the peripheral portion of the mounting member 5 and the mounting portion 51.

In the vicinity of the surface of the mounting portion 51, a heater 57 for heating the wafer W at the time of drying under reduced pressure, which is constituted by, for example, a resistance heater, is embedded. On the other hand, the lid 5
An opening 58 is formed in the ceiling portion 52a of the second container 52 so that the atmosphere in the closed container 5 can be sucked, and a wafer mounted on the mounting portion 51 is provided in a space facing the wafer W in the lid 52. A baffle plate 59, which is a plate-shaped rectifying member, is provided so as to be opposed to W and to have a gap with any of the ceiling portion 52a and the side wall 52b of the lid 52. A uniform exhaust flow is formed along the wall surface.

The opening 58 is connected to an exhaust pipe 6 forming an exhaust passage made of, for example, stainless steel.
The other end of the exhaust pipe 6 passes through a casing (not shown) of the reduced-pressure drying unit 32 and the casing 24 of the processing section S1, and through a valve V1 to, for example, a vacuum pump 61 which is a vacuum exhaust means provided in a clean room. Connected. The exhaust pipe 6 rises vertically from the lid 52 and is further bent horizontally, and a gas supply path 6a for supplying a drying gas into the exhaust pipe 6 is connected at the bent portion. The other end of the gas supply path 6a is connected to a gas supply means 62 via a valve V2.

If the exhaust passage extending from the bent portion to the closed container 5 is designated by reference numeral 6b, one of the gas supply passage 6a and the exhaust passage 6b is sealed in the bent portion while the other is sealed. A three-way valve 63 serving as a flow path opening / closing part to be opened is interposed. By closing the gas supply path 6a side, the sealed container 5 and the vacuum pump 61 communicate with each other, and the exhaust path 6b side is sealed. The gas supply means 62 and the vacuum pump 61 communicate with each other. Incidentally, the position where the three-way valve 63 is provided in the exhaust pipe 6 is preferably upstream of a portion where the solvent in the coating liquid volatilized by the drying under reduced pressure is condensed under the influence of the clean room atmosphere. Since the gas accumulates at the horizontal portion of the exhaust pipe 6, the three-way valve 63 is arranged at the bent portion so that the drying gas can be supplied into the exhaust pipe 6. Further, the flow direction (gas supply path 6a, exhaust path 6b) of the exhaust pipe 6 sealed by the three-way valve 63 can be switched based on a control signal from the control unit 7. .

Next, the operation of the above embodiment will be described. First, when the cassette C is carried into the cassette station 21, the wafer W is taken out by the transfer arm 23. Then, the wafer W is transferred from the transfer arm 23 to the main transfer unit 25 via the transfer unit 35 in the shelf unit U2, and is loaded into the coating unit 31. The wafer W carried into the coating unit 31 is sucked on the back side by the wafer holding unit 42 and is held substantially horizontally. After the nozzle 45 is positioned above the center of the wafer W, the discharge of the polyimide liquid is started, and the nozzle 45 is gradually moved from the center of the rotating wafer W toward the outer edge side,
Draw a spiral pattern.

Next, the wafer W on which the resist solution has been applied is transferred to the reduced-pressure drying unit 32 by the main transfer means 25. When the wafer W is loaded into the reduced-pressure drying unit 32, first, an arm (not shown) of the main transfer means 25 enters a position above the mounting portion 51 with the lid 52 raised, and lifts the lift pins 54 from the arm. After receiving the wafer W, the lift pins 54 are lowered to perform the operation.

Thereafter, the lid 52 is lowered to form the closed container 5, and drying under reduced pressure is started. At this time, the three-way valve seals the gas supply path 6a and allows the closed vessel 5 and the vacuum pump 61 to communicate with each other.
The wafer W is heated to a sufficient degree, the valve V1 is opened, and suction in the closed container 5 is started by a vacuum pump.
Is set to a reduced pressure atmosphere of, for example, 13.3 Pa. The polyimide liquid (coating liquid) applied to the surface of the wafer W is obtained by converting a polyimide component which is a component of the coating film into N
Although dissolved in a solvent such as MP (N-methylpyrrolidone), the solvent volatilizes violently when placed in a reduced-pressure atmosphere, and is sucked into the exhaust pipe 6 through the opening 58 and the exhaust path 6b. Is done. At this time, since the exhaust flow in the closed container 5 is formed so as to bypass the baffle plate 59 as described above, the solvent vapor volatilized from the wafer W does not pass through the baffle plate 59.
Then, the air flow is changed to the outer side, and spreads uniformly in the radial direction with the exhaust flow toward the opening 58.

In this manner, the surface of the wafer W is dried in a short time, and after completion of the drying process, the inside of the closed container 5 is purged with, for example, dried air or nitrogen gas through a gas supply source (not shown), and the inside of the closed container 5 is enlarged. Return to atmospheric pressure. And the lid 52
Is raised, and the wafer W is carried out by the main carrying means 25 through a process in the reverse order of the time when the wafer W is carried into the reduced-pressure drying unit 32.

Here, returning to the vacuum drying unit 32 again, the solvent removing operation in the exhaust pipe 6 will be described with reference to FIG. First, shortly after the start of the processing, FIG.
As shown in (2), the evaporated solvent is sucked into the vacuum pump 61, and the drying under reduced pressure is performed within a predetermined time. However, since the horizontal portion is affected by the temperature on the clean room side maintained at, for example, about 23 ° C., a very small amount of the volatile solvent is condensed in this portion and adheres to the exhaust pipe 6.

The condensed solvent volatilizes again, but on the other hand, new dew condensation occurs, and the amount of newly condensed exceeds the volatilization amount of the once condensed solvent. In the meantime, as shown in FIG.
The amount of the solvent R accumulated inside increases. At this time, the control unit 7 counts the number of wafers W that have been subjected to the reduced pressure drying, and temporarily recognizes that the number of wafers W has reached a certain amount, and temporarily stops the reduced pressure drying processing.

The control unit 7 switches the three-way valve 63 to seal the exhaust path 6b, communicates the gas supply path 6a with the exhaust pipe 6, and controls the valves V1 and V2 to open. Thus, an inert gas such as nitrogen gas is supplied from the gas supply means 62 into the gas supply path 6a, and the nitrogen gas filled in the gas supply path 6a and the exhaust pipe 6 is sucked by the vacuum pump 61. As shown in FIG. 7C, the solvent R attached to the exhaust pipe 6 is sucked toward the vacuum pump 61, and the solvent in the exhaust pipe 6 is removed. The time required for the removal operation is determined based on, for example, the relationship between the number of wafers W processed until the removal operation is known in advance and the time required for solvent removal according to the number.

After the removal operation is performed for a predetermined time in this manner, the supply and the suction (discharge) of the nitrogen gas in the exhaust pipe 6 are stopped by closing the valves V1 and V2, and the three-way valve 63 is removed. Return (switch) to the state before the start. Then, the number of processed wafers counted before the start of the operation is returned to zero, and the reduced-pressure drying process is restarted.

According to the above-described embodiment, since the solvent condensed on the exhaust pipe 6 of the reduced-pressure drying unit 32 can be periodically removed, the amount of the solvent condensed during the reduced-pressure drying of the wafer W is small. Become. Therefore, the solvent can be actively volatilized from the coating film on the wafer W, and the drying process can be performed promptly, so that a high throughput can be obtained.

When a plurality of reduced-pressure drying units 32 are provided in the coating film forming apparatus as in the above-described embodiment, it is preferable that the control unit 7 performs control as follows, for example. That is, for example, when the main transfer unit 25 attempts to transfer the wafer W from the coating unit 31 to one reduced-pressure drying unit 32, the one reduced-pressure drying unit 32
When the solvent removal operation in the exhaust pipe 6 is performed, the main transfer unit 25 transfers the wafer W to another reduced-pressure drying unit 32 other than the reduced-pressure drying unit 32 without waiting for the completion of the solvent removing operation. To do.

The wafer W on which the coating liquid has been applied is transported to the vacuum drying unit 32 in the shortest possible time while maintaining the state of the liquid film on the surface, and the solvent is volatilized uniformly and quickly from the entire surface. is necessary. For this reason, by controlling as described above, the waiting time for the coated wafer W can be reduced, and the in-plane uniformity of the film thickness and film quality can be increased.

The vacuum drying unit 32 is, for example, as shown in FIG.
May be configured as shown in FIG. In the present embodiment, for example, a wafer transfer unit 80 rotatable around a vertical axis, and a standby unit 8 provided below the closed container 5 are provided in a reduced-pressure drying unit 32. Reference numeral 8 denotes a configuration in which, for example, the temperature and humidity are adjusted so as to suppress the volatilization of the solvent in the coating liquid, or the mounting table 82 is provided in a case 81 body further filled with the solvent vapor. 81a is a door.

According to such a configuration, for example, when the solvent is removed from the exhaust pipe 6 in the reduced-pressure drying unit 32, the wafer W is once carried into the standby section 8 by the main transfer means 25. Waiting for the completion of the solvent removing operation while maintaining the state of the liquid film applied to the surface of the wafer W, and after the solvent removing operation is completed, the wafer W is promptly transferred to the closed container 5 by the wafer transfer means 80 and dried under reduced pressure. Can be transferred to.

In this embodiment, however, the wafer transfer means 80
The transfer of the wafer W from the standby unit 8 to the closed container 5 may be performed by the main transfer unit 25 without providing the wafer transfer unit 25. However, if the wafer transfer unit 80 is used, the burden on the main transfer unit 25 is reduced, and the throughput is reduced. Can be enhanced. The standby unit 8 may be used not only when the solvent removing operation is being performed, but also when the wafer W is on standby, for example, when another reduced-pressure drying unit 32 provided in the coating film forming apparatus is operating. Good.

After drying under reduced pressure, the lid 52
Before the wafer W is taken out, the closed vessel 5 is purged with air or nitrogen gas as described above,
A step of returning to the atmospheric pressure is performed. The gas for purging may be supplied from the gas supply unit 62 or may be supplied through a path different from the gas supply unit 62.

That is, in the former case, the direction of the three-way valve 63, which has communicated the vacuum pump 61 and the sealed container 5 at the time of drying under reduced pressure, is switched so that the gas supply means 62 and the sealed container 5 are communicated. Of the closed container 5
The internal pressure is returned to atmospheric pressure. On the other hand, in the latter case, although not shown here, for example, a gas supply means for purging is provided near the ceiling of the lid 52 in FIG.
After the drying under reduced pressure, purging with, for example, nitrogen gas is performed from the gas supply means until the inside of the closed vessel 5 becomes atmospheric pressure.

In the above description, the timing for removing the solvent in the supply pipe 6 is determined by counting the number of wafers subjected to the drying process by the control unit 7 and making the determination based on this number. The purpose of the method is to prevent the time required for drying under reduced pressure from being longer than a certain amount. For example, a monitoring means such as a CCD camera is provided in order to grasp the amount of the solvent adhering in the exhaust pipe 6, and a certain amount or more is provided. May be determined, or the correlation between the number of processed wafers and the time required for drying is grasped in advance, and the number of wafers to be processed before solvent removal becomes necessary based on the data is determined in advance. You may decide.

In removing the solvent, the gas supplied from the gas supply means 62 is not limited to nitrogen gas.
For example, it may be dry air. The gas used may be heated so that the solvent is easily evaporated.

[0038]

As described above, according to the present invention, a high throughput can be obtained in a reduced-pressure drying apparatus for a substrate provided in a coating film forming apparatus.

[Brief description of the drawings]

FIG. 1 is a plan view showing an overall structure of a coating film forming apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the entire structure in the embodiment.

FIG. 3 is a schematic sectional view showing a configuration of a shelf unit used in the embodiment.

FIG. 4 is a longitudinal sectional view for explaining a coating unit used in the above embodiment.

FIG. 5 is a plan view for explaining the coating unit.

FIG. 6 is a longitudinal sectional view illustrating a reduced-pressure drying unit incorporated in the shelf unit.

FIG. 7 is an explanatory diagram for explaining the operation of the present embodiment.

FIG. 8 is an explanatory diagram for explaining another embodiment according to the present invention.

FIG. 9 is an explanatory diagram illustrating a conventional invention.

FIG. 10 is a schematic cross-sectional view illustrating a reduced-pressure drying device according to a conventional invention.

FIG. 11 is an explanatory diagram for explaining a problem in the conventional invention.

[Explanation of symbols]

 C cassette W wafer S1 processing unit U1, U2, U3 shelf unit 21 cassette station 25 main transport means 31 coating unit 32 reduced-pressure drying unit 41 case body 42 wafer holding unit 43 rotation mechanism 45 nozzle 46 drive unit 5 closed container 51 mounting unit 52 Lid 6 Exhaust pipe 6a Gas supply path 6b Exhaust path 61 Vacuum pump 62 Gas supply means 63 Three-way valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G03F 7/38 501 G03F 7/38 501 H01L 21/31 H01L 21/31 A 21/312 21/312 B ( 72) Inventor Takahiro Kitano 5-3-6 Akasaka, Minato-ku, Tokyo TBS Release Center Inside Tokyo Electron Co., Ltd. (72) Inventor Jun Okura 5-36-6 Akasaka, Minato-ku, Tokyo TBS Release Center Tokyo Electron Co., Ltd. (72) Inventor Hirotoshi Kurishima 5-3, Akasaka, Minato-ku, Tokyo TBS Release Center Tokyo Electron Co., Ltd. F-term (reference) 2H096 AA25 CA12 DA10 JA02 4D075 AC84 BB56Z BB91Z DA06 DB11 DC21 EA05 EA45 EA45 EA60 EB39 4F042 AA02 AA06 CC03 CC07 DF09 DF32 EB09 EB12 EB18 5F045 EB19 EK09 EM10 EN05 5F058 AC02 AF04 AG01 AH02 B A20

Claims (11)

[Claims] 1. A step of placing a substrate coated with a coating liquid obtained by mixing a component of a coating film and a solvent in a closed container, and exhausting the closed container through an exhaust path by a vacuum exhaust means. A reduced pressure drying step to evaporate the solvent of the coating liquid applied to the substrate by evaporating the solvent in the depressurized atmosphere.Exhaust with the closed container closed to dry and remove the solvent that evaporates from the substrate and condenses in the exhaust path. A solvent removing step of flowing a drying gas through a path. 2. The reduced pressure drying method according to claim 1, wherein the solvent removing step is performed after the number of substrates subjected to the drying process reaches a predetermined number. 3. The solvent removing step comprises sucking a drying gas from a gas supply path in the middle of an exhaust path or from a gas supply path connected to a sealed container by a vacuum exhaust means to remove the solvent condensed in the exhaust path. 3. The method of drying under reduced pressure according to claim 1, wherein the step is a step of removing to the side. 4. The solvent removing step includes connecting a gas supply path connected in the middle of the exhaust path and a vacuum exhaust means via an exhaust path, and closing an exhaust path between the sealed container and the gas supply path. 4. The method of drying under reduced pressure according to claim 1, wherein the drying is performed. 5. The method according to claim 1, wherein the drying gas used in the solvent removing step is an inert gas. 6. The method according to claim 1, wherein the step of drying under reduced pressure includes a step of heating the substrate. 7. A coating unit for coating a substrate with a coating solution obtained by mixing a component of a coating film and a solvent, a sealed container provided with a mounting portion for mounting the substrate therein, Transport means for transporting the substrate between the coating unit and the closed container; connected to the closed container via an exhaust path to reduce the pressure in the closed container to volatilize the solvent from the coating liquid on the substrate; A gas supply path connected to the closed vessel or the middle of the exhaust path, for supplying a gas for drying to the exhaust path to remove the solvent condensed in the exhaust path, A flow path opening / closing section for opening and closing between a supply path and the vacuum evacuation means, and a gas supply path by controlling the flow path opening / closing section when it is determined that the amount of solvent condensed in the exhaust path has increased. And the vacuum evacuation means, and the gas for drying is Coating film forming apparatus characterized by comprising a control unit for causing flow through the air passage. 8. The method according to claim 7, wherein the point of time when it is determined that the amount of the solvent condensed in the exhaust path has increased is a point in time when the number of substrates subjected to the drying process reaches a preset number. The coating film forming apparatus as described in the above. 9. The gas supply path is connected in the middle of the exhaust path, and the flow path opening / closing portion communicates between the gas supply path and the vacuum exhaust means and closes the space between the sealed container and the gas supply path. And a valve for selecting one of a closed state between the gas supply path and the evacuation means and a state of communication between the closed vessel and the evacuation means. The coating film forming apparatus according to claim 7 or 8, wherein the coating film is formed. 10. The reduced-pressure drying unit includes a standby unit for temporarily placing a substrate on standby, and the control unit supplies a drying gas to an exhaust path to remove a solvent in the exhaust path. The transport means is configured to transport the substrate to the standby unit during the operation.
10. The coating film forming apparatus according to any one of claims 9 to 9. 11. The coating film forming apparatus according to claim 10, wherein the standby section is configured so that the atmosphere in which the substrate is placed is a solvent atmosphere.