TWI458564B - Coating machine and fixing method of a substrate - Google Patents

Description

Coating device and substrate holding method thereof

The present invention relates to a coating machine for applying a coating liquid onto a substrate and a method for holding the substrate.

In a flat panel display such as a liquid crystal display or a plasma display, a photoresist is applied to a glass substrate (referred to as a coating). Cloth substrate). The coated substrate is formed by a coating device that uniformly coats the photoresist.

The coating device has a stage on which a substrate is carried, a coating unit that discharges a photoresist, and the coating unit is moved while discharging the photoresist from the coating unit. A photoresist film having a uniform thickness is formed on the substrate.

In such a coating apparatus, a means for holding a substrate on a stage is generally known to have a negative pressure generated in the adsorption hole by forming an adsorption hole in the platform, so that the substrate is adsorbed and held on the platform (for example, refer to Patent Document 1). Specifically, the suction pressure is connected to the negative pressure generating device, and the negative pressure generating device is set at a low pressure (high vacuum side) to generate a negative pressure in the adsorption hole. Further, when the substrate is supplied to the stage, the negative pressure generating means performs high-speed exhausting, and the negative pressure is rapidly generated in the adsorption hole, so that the adsorption time required for adsorbing the substrate on the stage is shortened, and the cycle time of the coating device is sought. (cycle time) improvement.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-281091

However, in the above coating apparatus, high-pressure exhaust is performed by the negative pressure generating means, and a large negative pressure (high vacuum side pressure) is generated in the adsorption holes. When the coating is performed in such a state in which a large attraction force occurs, there is a problem in that coating unevenness occurs in the substrate portion corresponding to the adsorption hole.

Therefore, when the negative pressure generated in the adsorption hole is set to be set (at the atmospheric pressure side), high-speed exhaustion cannot be performed in the negative pressure generating device, and the set pressure is generated in the adsorption hole for a long time. That is, the time required for the substrate to be adsorbed to the stage becomes long, and as a result, there is a problem that the cycle time of the coating device is prolonged.

The present invention has been made in view of the above problems, and an object thereof is to provide a coating apparatus and a substrate holding method thereof, which can suppress coating even if the suction force of the adsorption substrate is set so that coating unevenness does not occur. The cycle time of the cloth device is long-term.

In order to solve the above problems, the coating apparatus of the present invention includes: a stage on which a substrate is supported; a substrate holding means for causing an attraction force to be formed in a suction hole formed on a surface of the stage, and adsorbing and holding the substrate on a surface of the stage; A coating unit that ejects a coating liquid while being held by a substrate held on a surface of the platform, wherein the substrate holding means has a pressure adjusting portion that adjusts an attractive force to the substrate, and the pressure adjusting portion is adjustable The initial pressure of the substrate immediately after being adsorbed on the surface of the platform, and the table in which the substrate is held on the platform after the substrate is adsorbed by the initial pressure In the state of the surface, the holding pressure is set to be smaller than the initial pressure, and the substrate holding means includes an attraction force generating means for generating an attraction force in the suction hole, and is connected to the suction force generating means and the aforementioned Each of the pressure adjusting portions includes a piping path that is adjusted to the initial pressure and a piping path that is adjusted to the holding pressure.

According to the coating apparatus, a negative pressure (a pressure smaller than atmospheric pressure) is generated in the suction hole and rapidly adsorbed while adsorbing the substrate carried on the stage, and the pressure is adjusted by the pressure after the initial pressure is reached. The portion is adjusted to a holding pressure smaller than the initial pressure to maintain the adsorbed substrate on the platform. Therefore, when the coating liquid is applied onto the substrate by the coating unit, the coating can be carried out on the substrate held by the pressure-holding holding with a smaller initial pressure, so that it is carried by adsorption as in the past. When coating is applied at the initial stage of the substrate of the stage, it is possible to suppress coating unevenness in the portion corresponding to the suction hole. Further, even if the substrate is held on the stage by the holding pressure smaller than the initial pressure, the initial pressure can be generated at a high speed when the substrate is adsorbed, so that the cycle time of the coating device can be released for a long period of time.

According to this configuration, the generation of the initial pressure and the generation of the holding pressure in the suction holes can be easily switched only by switching the piping paths. Therefore, the switching responsiveness of the initial pressure and the holding pressure can be improved.

Further, the pressure gauge may be attached to a pipe connected to the vicinity of the suction hole, and the pressure may be adjusted to the holding pressure when the pressure gauge reaches the initial pressure.

According to this configuration, since the pressure gauge is disposed in the vicinity of the suction hole of the pipe, the pressure loss can be suppressed as compared with the case of being attached to another pipe portion. The pressure in the suction hole is measured and accurately measured.

In order to solve the above problems, a substrate holding method of a coating apparatus according to the present invention is a substrate holding method including a coating device of a member: a stage on which a substrate is supported; a substrate that holds an attractive force on a surface of the stage and adsorbs and holds the substrate And a coating unit that discharges the coating liquid while relatively moving the substrate held on the surface of the platform, wherein the substrate holding means has a pressure adjustment to the substrate by adjusting a pressure applied to the substrate In the pressure-adjusting portion of the attraction, after the pressure of the substrate adsorbed on the surface of the stage reaches a predetermined initial pressure by the pressure adjusting unit, the substrate is adjusted to a holding pressure smaller than the initial pressure, and the substrate is held. The holding means includes: a suction force generating device that generates an attraction force in the suction hole, and a pipe that connects and connects the suction force generating device and the suction hole, and each of the pressure adjusting portions includes a pipe path that is adjusted to the initial pressure And the piping path adjusted to the aforementioned holding pressure.

According to the substrate holding method of the coating apparatus, when the substrate supported on the stage is adsorbed, the negative pressure is generated in the suction hole and rapidly adsorbed, and after the pressure reaches the initial pressure, the pressure adjusting portion is adjusted by the pressure adjusting portion. The holding pressure is smaller than the initial pressure, and it is possible to suppress the occurrence of coating unevenness in the portion corresponding to the suction hole as compared with the case where the coating is applied at the initial stage of adsorbing the substrate placed on the stage as in the prior art. Further, even if the substrate is held on the stage by the holding pressure smaller than the initial pressure, the initial pressure can be generated at a high speed when the substrate is adsorbed, so that the cycle time of the coating device can be released for a long period of time.

According to the coating apparatus and the substrate holding method of the present invention, even if the suction force of the adsorption substrate is set so that the coating unevenness does not occur, the cycle time of the coating device can be suppressed from becoming long.

The form of the embodiment related to the present invention will be described using the drawings.

Fig. 1 is a perspective view schematically showing a coating apparatus according to an embodiment of the present invention, Fig. 2 is a view showing a vicinity of a leg portion of the coating unit, and Fig. 3 is a view showing a piping system of the coating device.

As shown in FIG. 1 to FIG. 3, the coating device is formed by forming a coating film of a liquid material (hereinafter referred to as a coating liquid) such as a chemical liquid or a photoresist liquid on the substrate 10, and includes a base 2; The substrate 21 carrying the substrate 10; and the coating unit 30 configured to move the platform 21 in a specific direction.

In the following description, the direction in which the coating unit 30 moves is the X-axis direction, the direction orthogonal to the X-axis direction on the horizontal plane is the Y-axis direction, and the two directions orthogonal to the X-axis and the Y-axis direction. The direction is described in the Z-axis direction.

A platform 21 is disposed in the center portion of the base 2 described above. The platform 21 is a substrate 10 on which the loading is carried. Further, a substrate holding means 40 is disposed on the stage 21, and the substrate holding means 40 holds the substrate 10. Specifically, the substrate 10 can be adsorbed and held on the surface of the stage 21 by causing the attraction force to be generated in the plurality of suction holes 21a formed on the surface of the stage 21.

That is, the substrate holding means 40 has a vacuum pump (vacuum) (pump) 81 (the suction force generating device of the present invention) and the pipe 50 that communicates with and connects the vacuum pump 81 (see FIG. 3) and the suction hole 21a, and operates the vacuum pump 81 to make the negative pressure (less than atmospheric pressure) via the pipe 50. The pressure is generated in the suction hole 21a to hold the substrate 10.

Further, the substrate holding means 40 has the pressure adjusting portion 41, and in the present embodiment, the pressure adjusting portion 41 can be adjusted to the initial pressure and the holding pressure. Here, the initial pressure is a pressure at which the substrate 10 immediately after being placed on the surface of the stage 21 is adsorbed on the surface of the stage 21, and the vacuum pump 81 performs high-speed exhaust, and the negative pressure is rapidly generated in the suction hole 21a. The pressure for the substrate 10 is adsorbed. Further, the holding pressure refers to a pressure for maintaining the state in which the substrate 10 is held on the surface of the stage 21 after the substrate 10 is initially pressure-adsorbed, and is smaller than the initial pressure, and the substrate 10 adsorbed on the stage 21 does not generate. Offset pressure.

The pressure adjusting unit 41 is configured such that a pipe (main pipe 51) adjusted to an initial pressure and a pipe (sub pipe 52) adjusted to maintain a pressure are constituted by respective pipe paths. Specifically, as shown in FIG. 3, a main valve 51a is disposed in the main pipe 51 adjusted to the initial pressure, and the vacuum pump 81 and the suction hole 21a can be communicated or shielded by the main valve 51a. Therefore, the vacuum pump 81 is operated in a state where the main valve 51a is fully opened, and an initial pressure is generated in the suction hole 21a. According to this, the initial pressure can be applied to the substrate 10 carried on the surface of the stage 21 and adsorbed.

Further, the sub-pipe 52 adjusted to maintain the pressure is provided with a sub valve 52a and a sub regulator 52b. The sub-valve 52a is the same as the main valve 51a, and is permeable to the sub-pipe by switching the sub-valve 52a. 52 connects or shields the vacuum pump 81 from the suction hole 21a. Further, the sub-regulator 52b sets the 俾 pipe to a predetermined pressure, and in the present embodiment, the set pressure of the 俾 sub-regulator 52b is set to the holding pressure. Therefore, since the vacuum pump 81 is operated in a state where the sub valve 52a is fully opened, the pressure is controlled by the sub-regulator 52b, so that a holding pressure is generated in the suction hole 21a. When the vacuum pump 81 is operated in a state where the main valve 51a and the sub-valve 52a are fully opened, the initial pressure is generated in the suction hole 21a by being sucked through the main pipe 51.

Further, a pressure gauge 53 is disposed in the pipe 50. The pressure gauge 53 is a pressure in the measurement pipe 50, and in the present embodiment, is a portion of the pipe 50 disposed in the vicinity of the suction hole 21a directly below the stage 21. According to this, it is possible to suppress the influence of pressure loss or the like, and it is possible to accurately measure the pressure state of the suction hole 21a.

Further, a substrate elevating mechanism for elevating and lowering the substrate 10 is disposed on the stage 21. Specifically, a plurality of pin holes are formed on the surface of the stage 21, and a lift pin (not shown) that can be lifted and lowered in the Z-axis direction is embedded in the pin hole. That is, when the substrate 10 is carried in a state where the ejector pin is protruded from the surface of the stage 21, the tip end portion of the ejector pin abuts against the substrate 10 and can hold the substrate 10, so that the ejector pin is lowered and It is housed in the pin hole, and the substrate 10 can be carried on the surface of the platform 21.

Further, by raising the ejector pin in a state where the substrate 10 is carried on the surface of the stage 21, the tip end portion of the ejector pin abuts against the substrate 10, and the substrate 10 can be held at a predetermined height by the tip end portions of the plurality of ejector pins. position. According to this, it is possible to suppress the contact portion with the substrate 10 as much as possible, and it is possible to smoothly replace the substrate 10 without damaging the substrate 10.

Further, the coating unit 30 is coated with a coating liquid on the substrate 10. The coating As shown in FIGS. 1 and 2, the unit 30 has a leg portion 31 coupled to the base 2 and a slit nozzle portion 34 extending in the Y-axis direction across the base 2 in the Y-axis direction. The state can be moved in the X-axis direction and installed. Specifically, rails 22 extending in the X-axis direction are respectively provided at both end portions of the base 2 in the Y-axis direction, and the leg portions 31 are slidably attached to the rails 22. Further, a linear motor 33 is attached to the leg portion 31, and the linear motor 33 is driven to move the coating unit 30 in the X-axis direction, and can be stopped at an arbitrary position.

A slit nozzle portion 34 to which a coating liquid is applied is attached to the leg portion 31 of the coating unit 30 as shown in Fig. 2 . Specifically, the leg portion 31 is provided with a rail 37 extending in the Z-axis direction and a slider 35 sliding along the rail 37, and the slider 35 and the slit nozzle portion 34 are connected. . Further, a ball screw mechanism driven by a servo motor 36 (refer to FIG. 4) is attached to the slider 35, and the servo motor 36 is driven to move the slider 35 in the Z-axis direction, and can be arbitrarily The position stops. That is, the slit nozzle portion 34 is supported by attaching and detaching the substrate 10 held by the stage 21.

The slit nozzle portion 34 is a coating liquid applied to form a coating film on the substrate 10. The slit nozzle portion 34 is a columnar member having a shape extending in a unidirectional direction, and is disposed substantially perpendicular to the running direction of the coating unit 30. In the slit nozzle portion 34, a slit nozzle 34a extending in the longitudinal direction is formed, and the coating liquid supplied to the slit nozzle portion 34 is discharged by the slit nozzle 34a in the same length direction. Therefore, the coating unit 30 is moved in a state where the coating liquid is discharged by the slit nozzle 34a. In the X-axis direction, a coating film having a certain thickness is formed on the substrate 10 throughout the longitudinal direction of the slit nozzle 34a.

Next, the configuration of the control system of the above coating apparatus will be described using a block diagram shown in FIG. 4.

4 is a block diagram showing a control system of a control device 90 disposed in the coating device. As shown in Fig. 4, the coating device is provided with a control device 90 for controlling the driving of the various units described above. The control device 90 includes a control main unit 91, a drive control unit 92, a pressure control unit 93, an input/output device control unit 94, and an external device control unit 95.

The control main unit 91 includes a CPU that performs a logical operation, a ROM (Read-Only Memory) that stores various programs such as the CPU in advance, and a memory of various types of data during the operation of the device ( Data) RAM (Random Access Memory); HDD (Hard Disk) that stores various programs such as programs or OSs (Operating System) and memorizes production programs. Further, the control main unit 91 includes a main control unit 91a, a determination unit 91b, and a storage unit 91c.

The main control unit 91a is a drive device that drives and controls the servo motor 36, the linear motor 33, and the like of each unit through the drive control unit 92 in order to execute a series of coating operations in accordance with a program stored in advance.

The determination unit 91b determines whether or not the pressure state of the suction force is appropriate in the case where the holding substrate 10 is adsorbed and held. That is, it is determined whether or not the pressure detected by the pressure gauge 53 reaches the initial pressure. Specifically, the memory unit 91c, which will be described later, stores predetermined initial pressure data, and determines whether or not the detected pressure is the initial pressure. Under the assumption that the initial pressure is reached, the pressure control described later is transmitted. The portion 93 controls the cymbal main valve 51a to be in a closed state. As a result, the pipe 50 that communicates with the vacuum pump 81 through the suction hole 21a is switched only to the sub-pipe 52, and the pressure generated in the suction hole 21a is adjusted to the holding pressure set by the sub-regulator 52b. Further, when the pressure gauge 53 does not reach the initial pressure, the state of the main valve 51a and the sub-valve 52a is maintained in a state of being intact.

The memory unit 91c is for storing various materials, and stores calculation results and the like at one time. Specifically, the memory has information such as initial pressure and holding pressure.

The drive control unit 92 drives and controls the linear motor 33, the servo motor 36, and the like in accordance with a control signal from the control main unit 91. Specifically, the linear motor 33 and the servo motor 36 are controlled to drive and control the movement of the coating unit 30 and the lifting operation of the slit nozzle portion 34.

The pressure control unit 93 detects the pressure in the pipe 50, and controls the pressure generated in the suction hole 21a based on a control signal from the control body unit 91. Specifically, the pressure in the pipe 50 in the vicinity of the suction hole 21a is detected by a signal from the pressure gauge 53. When the initial pressure is transmitted through the pressure gauge 53, and the control body portion 91 transmits a signal for switching to the holding pressure, the main valve 51a is changed from the open state to the closed state by controlling the driving of the main valve 51a. The inside of the control pipe 50 (correctly in the vicinity of the suction hole 21a) becomes a holding pressure.

The input/output device control unit 94 is a control input/output device such as a keyboard 83, a touch panel 82, and the like. Specifically, the keyboard 83 and the touch panel 82 can be used to set the conditions of the coating operation, etc., and the initial pressure, the holding pressure, and the like can be appropriately set. Further, when the initial pressure is adjusted to the holding pressure, it should be adjusted in the pipe 50 but does not become the holding pressure. In the case of a warning display on the touch panel and urge the operator to warn.

The external device control unit 95 performs drive control of the external device based on a control signal from the control main unit 91. In the present embodiment, the vacuum pump 81 is connected, and by driving the vacuum pump 81, a negative pressure is generated in the suction hole 21a.

Next, the operation in the coating apparatus will be described with reference to the flowchart shown in FIG. 5.

First, the loading of the substrate 10 is performed in step S1. Specifically, in a state in which a plurality of ejector pins are protruded from the surface of the stage 21, the substrate 10 is placed on the tip end portion of the ejector pin by a robot hand (not shown).

Next, the substrate 10 is carried on the stage 21 in step S2. Specifically, the ejector pin is lowered and the substrate 10 is carried on the surface of the stage 21 by the state in which the substrate 10 is carried at the tip end portion of the ejector pin. At this time, the substrate 10 is positioned at a predetermined position by a positioning means (not shown).

Then, the substrate 10 is held on the stage 21 by steps S3 to S5. First, the substrate adsorption operation is performed by the step S3, and the substrate 10 is adsorbed on the stage 21. Specifically, the vacuum pump 81 is driven and the high-speed exhaust is performed in a state where the main valve 51a and the sub-valve 52a are opened, and the suction force is rapidly generated in the suction hole 21a. In other words, the atmosphere in the through-pipe 50 is rapidly sucked by the main pipe 51 by the vacuum pump 81, and a negative pressure is rapidly generated in the suction hole 21a, and the substrate 10 is instantaneously adsorbed on the stage 21.

Then, it is judged whether or not the pressure in the pipe 50 has reached the initial pressure (step S4). Specifically, whether the pressure gauge 53 reaches the initial pressure is judged, and does not arrive. In the case of the initial pressure, the process proceeds to the NO direction, and the substrate adsorption operation continues.

When the pressure gauge 53 reaches the initial pressure, the process proceeds to the YES direction, and the adsorption holding operation of the substrate is performed (step S5). Specifically, the main valve 51a is switched from the open state to the closed state. In other words, the vacuum pump 81 and the suction hole 21a are blocked, and the piping path of the suction hole 21a and the vacuum pump 81 becomes only the sub-pipe 52, and the pressure in the suction hole 21a is adjusted to the holding pressure set by the sub-regulator 52b. Therefore, the substrate 10 is held on the stage 21 by maintaining pressure adsorption.

Next, the coating operation is performed in step S6. In other words, the coating liquid is discharged while the coating unit 30 is traveling in a specific direction, and the coating film is formed on the surface of the substrate 10.

Next, the take-out of the substrate 10 is performed in step S7. In other words, after the coating film is formed on the surface of the substrate 10 by the coating operation in S6, the vacuum pump 81 is stopped, and the pressure in the suction hole 21a is returned to the atmospheric pressure. Further, by raising the ejector pin, the substrate 10 is held at the tip end portion of the ejector pin, and the delivery of the substrate 10 is performed on a robot (not shown), and the substrate 10 is discharged from the surface of the stage 21.

According to the coating apparatus and the substrate holding method thereof, in the case of adsorbing the substrate 10 carried on the stage 21, the negative pressure is generated in the suction hole 21a and rapidly adsorbed, and the pressure on the adsorption substrate 10 reaches the initial pressure. By the pressure adjusting portion 41 being adjusted to a holding pressure smaller than the initial pressure, the adsorbed substrate 10 can be held on the stage 21. Therefore, in the case where the coating liquid is applied onto the substrate 10 by the coating unit 30, it can be made smaller than the initial pressure. Since the coating is carried out on the substrate 10 which is held by the pressure-sucking, it is possible to suppress the coating of the portion corresponding to the suction hole 21a as compared with the case where the coating is applied to the substrate 10 which is carried by the stage 21 at the initial stage. Uneven cloth. Further, even if the substrate 10 is held on the stage 21 by a holding pressure smaller than the initial pressure, the initial pressure can be generated at a high speed when the substrate 10 is adsorbed, so that the problem of prolonging the cycle time of the coating device can be eliminated.

In the above-described embodiment, the main pipe 51 and the sub-pipe 52 are arranged to switch the piping paths of the main pipe 51 and the sub-pipe 52, and the initial pressure and the holding pressure are switched. It is a configuration in which only one of the main valve 51a and the regulator 50 is provided, and the initial pressure and the holding pressure are switched by controlling the adjustment of the regulator. According to this configuration, in comparison with the above-described embodiment, it takes time to switch the initial pressure and the holding pressure. However, since the piping path becomes one, the space of the entire coating apparatus becomes advantageous.

2‧‧‧Abutment

10‧‧‧Substrate

21‧‧‧ platform

21a‧‧‧Attraction hole

22, 37‧‧ ‧ rails

30‧‧‧ Coating unit

31‧‧‧ feet

33‧‧‧Linear motor

34‧‧‧Slotted nozzle section

34a‧‧‧Slot nozzle

35‧‧‧ Slider

36‧‧‧Servo motor

40‧‧‧Substrate retention means

41‧‧‧ Pressure Regulatory Department

50‧‧‧Pipe

51‧‧‧Main piping

51a‧‧‧Main valve

52‧‧‧Sub-pipe

52a‧‧‧Separate valve

52b‧‧‧Sub Regulator

53‧‧‧ pressure gauge

81‧‧‧Vacuum pump

82‧‧‧Touch panel

83‧‧‧ keyboard

90‧‧‧Control device

91‧‧‧Control body

91a‧‧‧Main Control Department

91b‧‧‧Decision Department

91c‧‧‧Memory Department

92‧‧‧Drive Control Department

93‧‧‧Pressure Control Department

94‧‧‧Input/output device control unit

95‧‧‧External Device Control

Fig. 1 is a perspective view showing a coating apparatus according to an embodiment of the present invention.

Fig. 2 is a schematic view showing the vicinity of a leg portion of a coating unit.

Fig. 3 is a schematic view showing a vacuum pump and a piping system of the coating device.

Fig. 4 is a block diagram showing a control system of the above coating apparatus.

Fig. 5 is a flow chart showing the operation of the above coating apparatus.

10‧‧‧Substrate

21‧‧‧ platform

21a‧‧‧Attraction hole

40‧‧‧Substrate retention means

41‧‧‧ Pressure Regulatory Department

50‧‧‧Pipe

51‧‧‧Main piping

51a‧‧‧Main valve

52‧‧‧Sub-pipe

52a‧‧‧Separate valve

52b‧‧‧Sub Regulator

53‧‧‧ pressure gauge

81‧‧‧Vacuum pump

Claims (3)

A coating apparatus comprising: a platform for carrying a substrate; a substrate holding means for causing attraction to be formed on a surface of the platform, and holding the substrate on the surface of the platform; and holding the substrate on the platform a coating unit that ejects a coating liquid while moving relative to the surface of the substrate, wherein the substrate holding means has a pressure adjusting portion that can adjust an attractive force to the substrate, and the pressure adjusting portion can be adjusted so that the adsorption is just carried on The initial pressure of the substrate behind the surface of the platform, and the holding pressure in which the substrate is held by the surface of the stage after the substrate is adsorbed by the initial pressure, the holding pressure is set to be smaller than the initial pressure, and the substrate is held. The means includes: a suction force generating device that generates an attraction force in the suction hole, and a pipe that communicates and connects the attraction force generating device and the suction hole, each of the pressure adjustment portions: a pipe path that is adjusted to the initial pressure, And the piping path adjusted to the holding pressure. A coating apparatus according to claim 1, wherein a pipe connected to the suction hole is provided with a pressure gauge, and the pressure gauge is adjusted to the holding pressure when the pressure gauge reaches an initial pressure. A substrate holding method of a coating device is a substrate holding method of a coating device comprising: a platform for carrying a substrate; a substrate holding means for generating an attractive force on a surface of the platform and adsorbing and holding the substrate; and holding the substrate at one side The substrate on the surface of the platform moves relatively and spits out A coating unit for a coating liquid, characterized in that the substrate holding means has a pressure adjusting portion that can adjust an attractive force to the substrate by adjusting a pressure applied to the substrate, and the pair is adsorbed to the platform by the pressure adjusting portion After the pressure of the substrate on the surface reaches a predetermined initial pressure, the substrate is adjusted to have a holding pressure smaller than the initial pressure, and the substrate is held. The substrate holding means has an attraction generating device for causing an attractive force to be generated in the suction hole. And connecting the suction force generating device and the pipe for the suction hole, each of the pressure adjusting portions having a pipe path adjusted to the initial pressure and a pipe path adjusted to the holding pressure.