Atmosphere exchange method

There is provided a method for exchanging an atmosphere of a vacuum chamber of a processing apparatus configured to process a substrate under a vacuum environment. The method includes the steps of holding the substrate using a holding unit provided in the vacuum chamber, and exchanging the atmosphere of the vacuum chamber through exhaustion or air supply, wherein the exchanging step maintains a pressure of the vacuum chamber in a range between 10 Pa and 10000 Pa for a period between 10 seconds and 600 seconds while controlling a temperature of a dust collection unit provided in the vacuum chamber lower than a temperature of the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an atmosphere exchange method.

2. Description of the Related Art

A conventional load lock chamber imports a substrate from a substrate stocker that is placed in the atmosphere environment, into a processing chamber that processes the substrate in the vacuum atmosphere, or exports a processed substrate from the processing chamber to the substrate stocker. The processing chamber, as used herein, means a EUV (extreme ultraviolet) exposure apparatus and a plasma processing apparatus.

The load lock chamber serves to exchange an atmosphere in the internal space between the atmosphere environment and the vacuum environment. More specifically, the load lock chamber exchanges the atmosphere from the atmosphere environment to the vacuum environment in importing the substrate into the processing chamber (in the exhaust process), and exchanges the atmosphere from the vacuum environment to the atmosphere environment in exporting the substrate to the substrate stocker (in the air-supply process). The load lock chamber is connected to the processing chamber via a gate valve, and includes a substrate transport mechanism.

However, particles swirl from the gate valve and the substrate transport mechanism in the air-supply and exhaust time, and a means is necessary to reduce or prevent their adhesions to the substrate. One proposed method reduces particles' adhesions to the substrate utilizing the thermophoretic force. As disclosed in Japanese Patent No. 2,886,521, this method heats the holder of the substrate up to a temperature higher than the peripheral temperature, and collects particles via a low-temperature particle collector maintained at a temperature lower than the peripheral temperature.

According to the principle of the thermophoretic force, with a temperature gradient in the gas around the particles, the particles are given the kinetic energy from the gas molecules at the high temperature side higher than that of the gas molecules at the low temperature side, and move from the object at the high temperature side to the low temperature side. Thermophoretic force Fx is given by the following equation by the thermophoresis coefficient equation described in Kikuo Okuyama, Hiroaki Masuda, and Seiji Morooka, “New System Chemical Engineering, Fine Particles Engineering,” pp. 106-107, May of 1992, Ohmsha Publishing.

Equation 1 assumes that the particle is spherical and the fluid is the ideal gas. Dp is a particle diameter. T is a gas temperature. μ is a viscosity coefficient. ρ is a gas density. Kn is a Knudsen number and 2λ/Dp. λ is a mean free path and η/{0.499 P(8M/πRT)1/2}. M is a molecular weight. R is a gas constant. K is k/kP. k is a thermal conductivity of the gas only caused by the parallel movement energy. kp is the thermal conductivity of the particle. Cs is 1.17. Ct is 2.18. Cm is 1.14. ΔT/Δx is a temperature gradient.

The dimension of the load lock chamber is restricted by the gate opening size (W360 mm×H80 mm) determined by the uniform standard in the semiconductor field, and cannot be made as small as the substrate's external shape. Therefore, the thermophoretic force near the substrate holder inevitably depends upon a shape of the load lock chamber, and thus cannot be maximized.

SUMMARY OF THE INVENTION

The present invention is directed to an atmosphere exchange method that reduces adhesions of particles to the substrate in a vacuum chamber. The “vacuum chamber,” as used in the following embodiments, means an apparatus that needs a reduced pressure state in principle like an exposure chamber in a EUV exposure apparatus, and an apparatus that temporarily holds the reduced pressure state like a load lock chamber of a substrate transport mechanism.

An atmosphere exchange method according to one aspect of the present invention is a method for exchanging an atmosphere of a vacuum chamber of a processing apparatus configured to process a substrate under a vacuum environment. The method includes the steps of holding the substrate using a holding unit provided in the vacuum chamber, and exchanging the atmosphere of the vacuum chamber through exhaustion or air supply, wherein the exchanging step maintains a pressure of the vacuum chamber in a range between 10 Pa and 10000 Pa for a period between 10 seconds and 600 seconds while controlling a temperature of a dust collection unit provided in the vacuum chamber lower than a temperature of the substrate.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the accompanying drawings, a description will be given of a processing apparatus according to the embodiment of the present invention. This embodiment uses an EUV exposure apparatus as a processing apparatus that processes a substrate under a vacuum environment, but the present invention is not limited to the processing apparatus.

First Embodiment

FIG. 1is a schematic sectional view of an exposure apparatus according to the first embodiment. InFIG. 1,1denotes an excitation laser, and uses a YAG solid laser, etc. The excitation laser1irradiates a laser beam to an emission point of a light source, and emits the light for plasma excitation of the light source material atoms. The point is made by gasifying, liquefying, or spraying a light source material.2denotes a light source emission part in the exposure light source which maintains vacuum in its inside.2A denotes an emission point of the exposure light source.2B denotes a light source mirror arranged as a semispherical mirror around the emission point2A so as to deflect, condense and reflect the overall spherical light from the emission point2A towards the emission direction. A nozzle (not shown) is used to emit liquefied Xe, liquefied Xe spray, or Xe gas as an emission atom to the emission point2A, and the light from the excitation laser1is irradiated to the emission point2A.

3denotes an exposure chamber (processing chamber) connected to the light source emission part2. The exposure chamber3is maintained under a vacuum environment or at a reduced pressure by an exhausting unit (vacuum pump)4A. The exposure chamber3is a vacuum chamber that can maintain the vacuum pressure suitable for the EUV exposure.5denotes an illumination optical system that introduces and shapes the exposure light from the light source emission part2, includes mirrors5A to5D, and homogenizes and shapes the exposure light.6denotes a reticle stage, and a reticle (original)6A is electrostatically held as a reflective original having an exposure pattern, on a movable part of the reticle stage6.

7denotes a projection optical system that projects a reduced image of an exposure pattern reflected from the reticle6A, onto a wafer8A at a preset reduction ratio via mirrors7A to7E sequentially in this order to reflect an exposure pattern reflected by the reticle6A.8denotes a wafer stage that positions to an exposure position a wafer8A as a Si substrate, to which the reticle pattern is exposed, so as to control the position of the wafer stage in six axes directions including XYZ axes directions, tilting directions around the X-axis and Y-axis, and a rotational direction around the Z-axis.

9denotes a support member that supports the reticle stage6on the floor.10denotes a support member that supports the projection optical system7on the floor.11denotes a support member that supports the wafer stage8on the floor. A control unit (not shown) measures and continuously maintains a relative position between the reticle stage6and the projection optical system7and a relative position between the projection optical system7and the wafer stage8. The support members9to11each have a mount (not shown) that isolates the vibration from the floor.

16denotes a wafer stocker that temporarily stores a wafer8A inside the apparatus, which has been carried by a wafer carrier unit17A at the atmospheric air side. The wafer stocker16stores plural wafers. The wafer8A to be exposed is sorted from the wafer stocker16, and transported to the holding unit18that is installed in the vacuum chamber or the load lock chamber26.19denotes a shield (dust collection unit), which encloses the periphery of the wafer.20D is a gate valve that connects the space of the wafer stocker16to the load lock chamber26, and opens and closes when the load lock chamber26is in the atmosphere pressure state.20E is also a gate valve that connects the load lock chamber26to the exposure chamber3, and opens and closes when the load lock chamber26is in the vacuum state. The wafer carrier unit17B that can transport a wafer in the vacuum state carries the wafer from the holding unit18to a wafer mechanical pre-alignment temperature controller (not shown) that is placed in the exposure chamber (processing chamber). The wafer mechanical pre-alignment temperature controller provides rough feeding adjustments in the wafer's rotating direction as well as controlling the wafer temperature to the reference temperature of the exposure apparatus. The wafer carrier unit17B feeds to the wafer stage8the wafer8A aligned and temperature-controlled by the wafer mechanical pre-alignment temperature controller.

An export procedure of the wafer8A from the exposure chamber3is opposite to the loading procedure.

27denotes an SMIF pod as a miniature environment used to transport a reticle cassette in the device factory.31denotes a reticle cassette held in the SMIF pod. As soon as an SMIF indexer34opens and closes the SMIF pod, the reticle cassette31is introduced into the exposure apparatus so that the reticle carrier unit14A is ready to carry the reticle cassette31.24denotes a load lock chamber used to exchange an atmosphere for the reticle cassette31from the air atmosphere to the vacuum atmosphere, and includes a cassette holding unit28.

20A denotes a gate valve that connects the space of the reticle cassette31to the load lock chamber24, and opens and closes when the load lock chamber24is in the atmosphere pressure state. It is a gate opening/closing mechanism that imports the reticle6A into the holding unit of the load lock chamber24from the SMIF indexer34.20B denotes also a gate valve that opens and closes when the load lock chamber24is in the vacuum state.20C denotes also a gate valve that opens and closes in importing the reticle6A into the exposure chamber3.

12denotes a reticle stocker that temporarily stores the reticle6A carried from the outside of the apparatus to the inside of the apparatus while the reticle6A is housed in the reticle cassette31. The reticle stocker12stores the reticles6A having different patterns and different exposure conditions at multiple stages.

14A denotes a reticle carrier unit that carries the reticle cassette31to the reticle stocker12from the load lock chamber24. The reticle carrier unit14B is arranged in a reticle carrier chamber13, selects a target reticle from the reticle stocker12, and transports the reticle cassette31to a lid opening mechanism13A that divides it into a cassette's upper lid and a cassette's lower plate. The reticle carrier unit14B transports the cassette's lower plate that has been separated by the lid opening mechanism13A, to a reticle alignment scope15that is provided at the end of the reticle stage6. Thereby, it minutely moves for alignments in the XYZ-axes rotational direction on the reticle6A relative to the alignment mark15A on the housing of the projection optical system7.

The aligned reticle6A is chucked on the reticle stage6directly from the cassette's lower plate. At least one of ascending of the cassette support member or descending of the reticle stage is performed so as to reduce a distance between a cassette support member of an alignment part and the reticle stage6. At the same time, an inclination is adjusted between the reticle6A and the reticle stage6. A vacant cassette's lower plate is returned to the lid opening mechanism13A by the reticle carrier unit14B after the reticle6A is handed to the reticle stage6, and it is stored in the reticle stocker12after the lid is closed.

FIG. 2is a schematic sectional view of the load lock chamber26, in which a driving unit21moves the shield19as a dust collection unit in the lower direction, and the shield19covers the surface of the wafer8A. The driving unit21serves to move one of the holding unit18and the shield19close to the other after the temperature control units22A and22B control the temperature of the surface of the shield19opposite to the wafer8A.

Since a narrow space having a distance of 0.5 cm or smaller can be made between the wafer surface and the shield19by moving the shield19, the temperature gradient of the space can be made larger near the wafer surface than that of the conventional vacuum chamber.

The load lock chamber26is partitioned from the exposure chamber3by the gate valve20E, and the pressure detection unit32detects that the inside of the load lock chamber becomes vacuum. The gate valve20E is opened, and the wafer8A is imported into or exported from the exposure chamber3. The exhausting unit4B exhausts or decompresses the internal space of the load lock chamber26, and the air supply unit29supplies the air to or compresses the internal space. Thus, the load lock chamber26exchanges the atmosphere of the internal space between the vacuum environment and the atmospheric environment.

A flow variable valve33A is provided to adjust the exhaust flow and the air supply flow to a pipe23between the exhausting unit4B and an exhaust opening of the load lock chamber26. The pipe23between the air supply unit29and an air supply opening of the load lock chamber26is provided with a flow variable valve33B to adjust the exhaust flow and the air supply flow. A pressure detection unit32and the control unit30that controls the exhaust/air-supply unit can arbitrarily adjust the gas flow in the pipe23.

Whenever the pretreatment or post-treatment wafer8A is fed in and out of the load lock chamber26, the air supply and the exhaust are repeated. Thereby, particles, such as fine fluorine particles generated from the gate valve in the load lock chamber26or fine silverplating particles generated from the wafer transport mechanism, are likely to swirl in the exhaust or air supply process, and adhere to the wafer8A. It is thus important to reduce particles that would adhere to the wafer8A in the exhaust or air supply process of the load lock chamber26.

The holding unit18that holds the wafer8A controls the temperatures of all members that includes a support pin18A to a first temperature (23° C.) through a first temperature control unit22A. This temperature is as high as the temperature of the wafer8A transported by the holding unit18. This embodiment circulates the heat medium in the holding unit18, and uniformly controls the temperature of the entire surface of the holding unit18. The temperature of the surface opposite to the wafer surface of the shield19used to protect the wafer surface from the particles is controlled to the second temperature (13° C.) by a second temperature control unit22B. The second temperature of the surface of the shield19is lower than the first temperature by 10° C. Thus, the temperature control units22A and22B can control the temperature of the surface of the shield19opposite to the wafer8A to the temperature lower than that of the wafer8A. Thereby, the shield19operates as a dust collection unit that has a dust collection part.

FIG. 3is a graph between the gravity and the thermophoretic force affecting the fine fluorine particles when the temperature gradient is 10 [K/cm]. The ordinate axis denotes a force [m/s2], and an abscissa axis denotes a pressure [Pa] of the load lock chamber26. The thermophoretic force curve is calculated by weighing Equation 1, and a difference between the gas temperature and the solid temperature. It is understood fromFIG. 3that the force affecting the fine particles becomes maximum under a pressure range between 10 Pa and 10,000 Pa. The pressure of the load lock chamber26is controlled within the pressure range.

This embodiment controls the temperature and the position of the shield19so that the temperature gradient of the space can be 10 [K/cm], and further controls the pressure of the load lock chamber26.

FIG. 4is a graph showing the velocity of the fine fluorine particles having diameters between 0.1 to 1.5 μm that float near the wafer8A in the load lock chamber26. The ordinate axis denotes the velocity [m/s] of the fine particle, and the abscissa axis denotes the pressure [Pa] of the load lock chamber26. The velocity is positive in the gravity direction. Velocity V1of the fine particle floating near the wafer's front surface is illustrated by a solid line. Velocity V2of the fine particle floating near the wafer's back surface is illustrated by an alternate long and short dash line. The velocity of the fine particle floating near the surface is given as follows:
V1=(average deposition velocity)+(thermophoretic velocity)
V2=(average deposition velocity)−(thermophoretic velocity)   EQUATION 2

The thermophoretic velocity is given as follows:
Vth=−KthνΔT/TEQUATION 3

The thermophoretic velocity coefficient Kthis given as follows:

ν is a kinematic viscosity. α is a specific-heat ratio, and given as a heat conduction ratio of a gas divided by a heat conduction ratio of a particle. The average deposition velocity to the wafer8A in the laminar flow field is given as follows.
vn=0.739(D/L)(u0L/ν)1/2Sc1/3+Vg

D is a diffusion coefficient and given by CckT/(3πμDp). L is a wafer diameter. u0is an average flow rate of the airflow sufficiently distant from the wafer8A. Scis a Schmidt number and is given by ν/D. k is a Boltzmann's factor. vgis a gravity deposition velocity of Dp2ρpgCc/(18μ). ρpis a density of a fine particle. g is gravity acceleration. Ccis a Cunnningham's correction coefficient, and given by 1+Kn[1.25+0.4 exp(−1.1/Kn)].

EQUATIONS 2 to 4 are disclosed in Takeshi Hattori edition, Realize Science & Engineering Center Publisher, “New Edition Cleaning Technology of Silicon Wafer Surface,” May of 2000, pp. 72-74.

FIG. 5is a flowchart of a wafer process according to a first embodiment.FIG. 6Ais a graph showing an exhaust step of the load lock chamber26according to the first embodiment. The ordinate axis denotes the pressure [Pa] of the load lock chamber26, and the abscissa axis denotes an exhaust time period [second].FIG. 6Bis a graph showing an air supply step of the load lock chamber26according to the first embodiment. The ordinate axis denotes the pressure [Pa] of the load lock chamber26, and the abscissa axis denotes an air supply time period [second]. InFIGS. 6A and 6B, E±XX denotes x10±XX.

The first embodiment is suitable for example for fine fluorine particles having diameters of 1.0 μm. As shown inFIG. 4, the moving velocity of a fine fluorine particle having a diameter of 1.0 μm that floats in the load lock chamber26in a direction opposite to the wafer8A becomes maximum at a pressure range between 3.0E+04 Pa and 5.0E+04 Pa. A time period necessary to move a distance of 0.05 mm from the wafer8A to the shield19is 27 seconds. Therefore, by maintaining the pressure between 3.0E+04 and 5.0E+04 Pa for 27 seconds or greater, the fine fluorine particles having diameters of 1.0 μm which float between the wafer surface and the shield19collide with the shield19at least once. The collision is likely to induce the fine particle to adhere to the shield19, and thus reduce a fine particle's adhesion to the wafer surface. This embodiment sets the pressure range between 3.0E−04 Pa and 5.0E−04 Pa to a first pressure, and reduces the adhesions of the fine particles to the wafer8A utilizing the thermophoretic force that is generated in this pressure range. This embodiment discusses the fine fluorine particles having specific gravity of 2,130 kg/m3in an example, but this embodiment is applicable to other fine particles having different specific gravity.

InFIG. 5, S100is a resist application step that feeds the wafer8A that has undergone the application step, to the exposure apparatus. S101is a step that loads the wafer8A to the wafer stocker in the exposure apparatus.

S102is a step that controls the temperature of the holding unit18to the temperature (24° C.) lower by about 1° C. than that of the wafer8A imported from the wafer stocker16, and controls the temperature of the shield19to 4° C. This step effectively prevents adhesions of the fine particles to the wafer8A by utilizing the thermophoretic force by holding the temperature of the shield19lower than that of the wafer8A. S103detects or checks completions of the temperature controls over the holding unit18and the shield19utilizing a temperature sensor (not shown). Upon completions of the temperature controls, the procedure proceeds to the next step. When the temperature controls have not yet been completed, the procedure returns to the previous step S102.

S104is a step that opens the gate valve20D, carries the wafer8A to the holding unit18, and holds there, before the load lock chamber26is exhausted or in the atmosphere pressure. After the wafer8A is carried, the gate valve20D closes. When the load lock chamber26is at the atmosphere pressure, the fine particles having diameters of 1.0 μm or smaller do not fall due to the gravity, but float due to the airflow and the Brownian motions. The fine particles having diameters greater than 1.0 μm move in the gravity direction, and would adhere to the wafer8A. However, the shield19encloses the wafer8A in the load lock chamber26, and thus the adhesion probability to the wafer8A reduces.

When the density of the fine particles that float in the space between the shield19and the wafer8A is equal to that of the fine particles that float in another space, the effect increases as a ratio between the volume near the wafer8A inside the shield and the volume outside the shield increases. In this embodiment, the volume ratio is about 0.003. Therefore, if 1,000 fine particles move in the gravity direction in the load lock chamber, only three fine particles of them adhere to the wafer8A and the adhesion number of fine particles reduces.

S105is a step of moving the shield19towards the holding unit18, and of bringing the shield19close to the wafer8A so as to enclose the wafer8A. The wafer8A is wholly enclosed with a small space having a distance of 0.5 cm between the shield19and the surface of the wafer8A. This embodiment provides the shield19with an aperture that has a conductance that can be exhausted and air-supplied simultaneous with the load lock chamber26. Therefore, the inside of the shield19can be exhausted and air-supplied simultaneous with the load lock chamber26. This embodiment controls the temperature and the position of the shield19so that the space between the shield19and the wafer8A has a temperature gradient of 40 [K/cm].

S106is a first exhaust step, which uses the exhausting unit4B to reduce the pressure of the load lock chamber26from the atmosphere pressure state down to 5.0E+04 Pa. When the conventional load lock chamber26is decompressed, the fine particles having diameters of 1.0 μm or smaller start moving in the gravity direction. On the other hand, in the load lock chamber26of this embodiment, the fine particles having diameters of 1.0 μm or smaller move towards the shield19rather than in the gravity direction due to the thermophoretic force. In addition, as illustrated by the graph ofFIG. 4, the gravity exceeds the thermophoretic force for the fine particles having diameters of 1.5 μm or greater, and they cannot move towards the shield19.

S107is a second exhaust step, which reduces the pressure of the load lock chamber26at a constant exhaust rate, as shown inFIG. 6A, so that the pressure of the load lock chamber26can fall in a range between 5.0E+04 Pa and 3.0E+04 Pa, and maintains the first pressure for a minimum time period that provides an effect of the thermophoretic force. This embodiment provides control that makes small an aperture degree of the flow variable valve33A when the pressure of the load lock chamber26reaches 5.0E+04 Pa so that the exhaust speed of this embodiment is smaller than that of the first exhaust step. Parts of the fine particles that collide with the shield19adhere to the shield19due to the adhesion force of the van der Waals' force.

This embodiment requires 40 seconds to move the fine fluorine particle of 1.0 μm to the shield19placed distant from the surface of the wafer8A in upper direction by 0.5 cm. In other words, within 40 seconds, the pressure is reduced to a range between 5.0E+04 and 3.0E+04 Pa, and the fine particle is collected. The time period can be adjusted by the specific gravity of the fine particle, which is most concerned in the processing step of the wafer8A.

S108is a third exhaust step, which vacuum-pumps the first pressure that ranges from 5.0E+04 to 3.0E+04 Pa to a second pressure of 1.0E−04 Pa. S109is a step for moving the shield19in a direction opposite to the holding unit18. The shield19retreats to an appropriate position, and enables the wafer8A to be carried by the carrier unit17B.

In general, it is sufficient that the second exhaust step controls the temperature of the shield19installed in the load lock chamber to the temperature lower than that of the substrate while maintaining the pressure range between 10 Pa and 10000 Pa for a time period from 10 seconds to 600 seconds. The “pressure range between 10 Pa and 10,000 Pa” is a range of 98% of a maximum or maximum value of the thermophoretic force obtained fromFIG. 3. A time period of 10 seconds is a minimum time period necessary for the fine fluorine particle having a diameter of 1.0 μm to move to the shield19, where a distance between the wafer8A and the shield19is 0.2 cm, and a temperature gradient of a space between the shield19and the wafer8A is 100 [K/cm]. A time period of 600 seconds is a maximum time period necessary for the fine fluorine particle having a diameter of 1.0 μm to move to the shield19, where a distance between the wafer8A and the shield19is 1.0 cm, and a temperature gradient of a space between the shield19and the wafer8A is 10 [K/cm]. Although the exhaust speed monotonously decreases in the second exhaust step inFIG. 6A, its gradient is not limited. Although the gradient of the second exhaust step inFIG. 6Ais different from gradients of the first exhaust step and the third exhaust step, the exhaust speeds of the first to third exhaust steps may monotonously decrease. This is true of second and third embodiments which will be described with reference toFIGS. 7 and 8.

S110is a carrying step under vacuum, which carries the wafer8A to the exposure chamber3utilizing the carrier unit17B after opening the gate valve20E while maintaining the second pressure by vacuum-pumping the load lock chamber26. After the transport, the gate valve20E closes. Few fine particles float in the load lock chamber26in this step, and the transport is less likely to cause their adhesions to the wafer8A.

S111is an exposure process. S112is the same as S102, and thus a description thereof will be omitted. S113is a step that controls the temperature of the holder18to the temperature of 22° C. lower by 1° C. than that of the wafer to be carried from the exposure chamber3, and controls the temperature of the shield19to 12° C. S114is a carrying step under vacuum, which carries the wafer8A to the holding unit18in the load lock chamber26by the carrier unit17B after opening the gate valve20E while the load lock chamber26is in the second pressure state, and holds the wafer there. After the transport, the gate valve20E closes.

S115is a step of moving the shield19toward the holding unit18. Since this step is similar to S105, a description thereof will be omitted. S116is a first air supply step, which supplies air so that the pressure in the load lock chamber26becomes 3.0E+0.4 Pa from the second pressure 1E-04 Pa.

S117is a second air supply step, which supplies air until the pressure in the load lock chamber26becomes 5.0E+04 Pa. In the first air supply step, the fine particles that have swirled in the load lock chamber fall, but the thermophoretic force applies near the wafer8A, and moves them to the shield19, reducing their adhesions to the wafer8A. Similar to S107, this embodiment sets a time period to 40 seconds necessary to move the fine fluorine particles of 1.0 μm to the shield19that is placed distant from the surface of the wafer8A in upper direction by 0.5 cm.

S118is a third air supply step, which supplies air until the pressure in the load lock chamber26can be an atmosphere pressure. In this step, the fine particles float, which have swirled in the first and second air supply steps. The shield19encloses the wafer8A, and reduces the adhesions of the fine particles to the wafer8A. S119is a retreating step of the shield19to an appropriate position in which the wafer carrier unit17A can carry the wafer8A. S120is a carrying step of the wafer8A in the load lock chamber26at the atmosphere pressure to the wafer stocker16. S121is a step that unloads the wafer from the wafer stocker in the exposure apparatus to the atmospheric air side.

In general, similar to the second exhaust step, it is sufficient that the second air supply step controls the temperature of the shield19installed in the load lock chamber lower than that of the substrate while maintaining the pressure range between 10 Pa and 10,000 Pa for a time period from 10 seconds to 600 seconds. The “pressure range between 10 Pa and 10000 Pa” and the “time period from 10 seconds to 600 seconds” are required for the same reasons as those for the second exhaust step. Although the air supply speed monotonously decreases in the second air supply step inFIG. 6B, its gradient is not limited. Although the gradient of the second air supply step inFIG. 6Bis different from gradients of the first air supply step and the third air supply step, the air supply speeds of the first to third air supply steps may monotonously increase. This is true of second and third embodiments which will be described with reference toFIGS. 7B and 8B.

From the above description, in the exhaust/air supply steps of the load lock chamber26, the maintenance of the first pressure range between 5.0E+04 Pa and 3.0E+04 Pa for a certain time period maximizes the thermophoretic force, and reduces adhesions of the fine particles to the wafer surface.

Second Embodiment

This embodiment is different from the first embodiment in that this embodiment allows the pressure in the load lock chamber26to fluctuate in a certain pressure range in the second exhaust step S107and the second air supply step S117.FIG. 7Ais a graph showing an exhaust step of the load lock chamber26according to the second embodiment. The ordinate axis denotes the pressure [Pa] of the load lock chamber26, and the abscissa axis denotes an exhaust time period [second].FIG. 7Bis a graph showing an air supply step of the load lock chamber26according to the second embodiment. The ordinate axis denotes the pressure [Pa] of the load lock chamber26, and the abscissa axis denotes an air supply time period [second].

A description will be given of a second exhaust step S107, which reduces the pressure of the load lock chamber26down to a range between 3.0E+04 Pa and 5.0E+04 Pa. When the pressure of the load lock chamber26reaches 100 Pa, the exhaust valve closes and the exhaust temporarily stops. This action reduces the Brownian motion of the gas that affects the fine particles, and can enhance the relative thermophoretic fore. The pressure in the load lock chamber26gradually increases due to emitted and leaked gases, but the thermophoretic force effect is so large in this pressure range that the adhesions of the fine particles can be reduced. In this pressure range, the fine particles inside the shield19do not fall due to the gravity, but move to the shield19due to the thermophoretic force and adhere to the shield19.

A description will be given of the second air supply step S117of the second embodiment. The air is supplied until the pressure in the load lock chamber26reaches 100 Pa. As soon as the pressure in the load lock chamber26reaches 100 Pa, the flow variable valve33B is closed to temporarily stop the air supply. This action reduces the Brownian motion of the gas that affects the fine particles, and can enhance the relative thermophoretic force. Thus, the second embodiment can reduce adhesions of the fine particles to the wafer8A.

Third Embodiment

This embodiment is suitable to reduce the fine fluorine particles having diameters of 1.0 μm. This embodiment is different from the first embodiment in that this embodiment controls the aperture degree of the exhaust valve of the load lock chamber26in the second exhaust step, and controls the exhaust flow, and maintains 4.0E+04 Pa. The first pressure of this embodiment is 4.0E+04 Pa.

As shown inFIG. 4, when the pressure of the load lock chamber26is 4.0E+04 Pa, the speed in the direction opposite to the gravity becomes maximum, where it takes 215 seconds for the fine particle to move a distance from the wafer8A to the shield19. Therefore, the fine particles that float between the wafer surface and the shield19collide with the shield19at least once by maintaining the pressure state of 4.0E+04 Pa for 215 seconds. The collision is likely to induce the fine particle to adhere to the shield19, and thus reduce a fine particle's adhesion to the wafer surface.

It takes 221 seconds for the fine particle to move to the shield at the pressure of 3.0E-04 Pa of the load lock chamber26, and it takes 230 seconds at the pressure of 5.0E-04 Pa, reducing the throughput of the apparatus. Therefore, this embodiment sets the pressure of 4.0E+04 Pa to the first pressure, and utilizes the thermophoretic force generated in this pressure range to reduce the adhesions of the fine particles to the wafer8A. This configuration reduces the fine particles having large diameters and large masses within a minimum time period.

FIG. 8Ais a graph showing an exhaust step of the load lock chamber26according to the third embodiment. The ordinate axis denotes the pressure [Pa] of the load lock chamber26, and the abscissa axis denotes a time period [second].FIG. 8Aspecifies the carrying step at the atmosphere pressure, the first exhaust step, the second exhaust step, and the third exhaust step, and the carrying step under vacuum as well as the carrying step of the wafer8A, and the moving step of the shield19. This embodiment is different from the first embodiment in the second exhaust step.

A description will now be given of the second exhaust step, which switches to the slow exhaust so as to maintain 500 Pa and provides the slow exhaust and the slow air supply, after the pressure of the load lock chamber26reaches 500 Pa. The exhaust flow of the load lock chamber26is controlled by controlling the aperture degree of the flow variable valve33A provided between the exhausting unit4B and the load lock chamber26. The air supply flow of the load lock chamber26is controlled by controlling the aperture degree of the flow variable valve33B provided between the air supply unit29and the load lock chamber26.

FIG. 8Bis a graph showing an air supply step of the load lock chamber26according to this embodiment. The ordinate axis denotes the pressure [Pa] of the load lock chamber26, and the abscissa axis denotes a time period [second].FIG. 8Bspecifies the carrying step under vacuum, the first air supply step, the second air supply step, and the third air supply step, and the carrying step at the atmosphere pressure as well as the carrying step of the wafer8A, and the moving step of the shield19. This embodiment is different from the first embodiment in the second air supply step. Control similar to that of the second air supply step maintains 500 Pa in the load lock chamber26.

The load lock chamber26of the third embodiment can always generate a maximum thermophoretic force, and provide a greater effect of the adhesion reduction of the fine particle than those of the load lock chamber26in the first and second embodiments. Therefore, the third embodiment reduces the adhesions of the fine particles to the wafer8A.

While the above embodiments discuss an application to a semiconductor wafer as a silicon substrate, the substrate to which the present invention is applicable is not limited to the wafer. The vacuum chamber allows the thermophoretic force to apply to the floating particles near the substrate surface, and can reduce the particles' adhesions to the substrate surface. While this embodiment arranges the surface of the substrate perpendicular to the gravity direction, the present invention does not limit the orientation of the substrate.

This application claims a foreign priority benefit based on Japanese Patent Applications Nos. 2007-100301, filed on Apr. 6, 2007, and 2008-075897, filed on Mar. 24, 2008, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.