Hydrostatic gas bearing, hydrostatic gas bearing device for use in vacuum environment, and gas recovering method for the hydrostatic gas bearing device

In a hydrostatic gas bearing for use in a vacuum, in order to provide a hydrostatic gas bearing in which an increase in the quantity of gas being discharged during the movement of a moving body is reduced, the surface of a guide shaft of a fixed body and/or the surface of the moving body is subjected to processing for reducing adhesion of gas molecules, for example, by coating the surface(s) with a material having a low adhesion probability of gas molecules, by which the quantity of gas being discharged is decreased.

CROSS REFERENCE TO RELATED APPLICATION

This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP01/00582 which has an International filing date of Jan. 29, 2001, which designated the United States of America.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a hydrostatic gas bearing for use in a vacuum, a hydrostatic gas bearing device incorporating the hydrostatic gas bearing, and a gas recovering method for the hydrostatic gas bearing device.

2. Background Art

Conventionally, in a hydrostatic gas bearing for use in a vacuum, as a shape accuracy required for a moving body and a fixed body surface opposed to the moving body, only flatness to an extent of not affecting the size of a floating gap and a labyrinth seal gap has been required, and pores in the surface have especially not been considered. Also, in selecting the material of a guide shaft of the fixed body and the material of the moving body, only a property that the quantity of gas being discharged when the material is continuously exposed to a vacuum environment for a fixed period of time or more is small has been considered not to exert an influence on the reached degree of vacuum of mounted equipment.

Also, a general hydrostatic gas bearing is configured so that a high-pressure gas is released from an air pad provided on the moving body into a gap between the moving body and the fixed body surface, and the moving body and the fixed body are made in a non-contact state by the hydrostatic pressure of released gas, by which the moving body is moved with frictional resistance being scarcely encountered.

In the hydrostatic gas bearing as described above, in order to maintain the vacuum environment, it is desirable that an atmospheric pressure groove be provided around the air pad, and a mechanism for keeping the gas pressure in the atmospheric pressure groove at the atmospheric pressure provided.

The reason for this is that by providing the atmospheric pressure groove around the air pad, even in the design of hydrostatic gas bearing for vacuum, the load capacity, rigidity, and the like of the air pad can be designed by the same design technique as that for the ordinary hydrostatic gas bearing for use in an atmospheric environment.

Also, when the atmospheric pressure groove is not provided, all gas emitted from the air pad flows into an exhaust pump through a pressure reducing groove, so that the load of the exhaust pump increases undesirably. To prevent this phenomenon, the provision of the atmospheric pressure groove is also effective.

Therefore, as a mechanism for keeping the pressure in the atmospheric pressure groove at the atmospheric pressure, conventionally, an atmospheric pressure pipe has been connected to the atmospheric pressure groove provided around the air pad, and the other end of the atmospheric pressure pipe has simply been opened to the atmosphere on the outside of a vacuum chamber.

For the hydrostatic gas bearing manufactured by using the prior art, even when the quantity of gas discharged from a bearing device is lower than the specified discharge quantity in a stationary state, the quantity of gas discharged from the bearing device increases suddenly at the same time that the moving body starts to move, so that the reached pressure in the vacuum chamber is sometimes deteriorated remarkably. The reason for this is as described below. For example, in the hydrostatic gas bearing provided with the air pad on the moving body side, a portion covered by the moving body of the fixed body surface is exposed to a high-pressure floatation gas in a stationary state, and thus large quantities of gas molecules adhere to that portion. Subsequently, when the moving body moves and the surface thereof is exposed to the vacuum environment, large quantities of gas molecules adhering to the surface of guide shaft are discharged to the outside, which is resultantly detected as a sudden increase in the quantity of gas being discharged.

When the above-mentioned pressure increase occurs in a hydrostatic gas bearing mounted, for example, in an EB exposure system, a sudden increase in pressure degrades the accuracy of exposure pattern, and sometimes damages the electron beam source.

A hydrostatic gas bearing constructed so that the air pad is provided on the fixed body side also presents the same problem at the time of movement because gas molecules adhere to the surface of the moving body.

The inventor started research and development of a hydrostatic gas bearing capable of being used in an environment of higher vacuum (about 10−5Pa). As the result, it was verified that there occurs, on rare occasions, a phenomenon that the gas pressure in the vacuum chamber increases due to the movement of the moving body even from a cause other than the gas supplied to the air pad.

Thus, in order to determine the cause and to provide a higher-performance hydrostatic gas bearing, the inventor further conducted research and development earnestly.

For example, in the case of a semiconductor exposure system, the vacuum chamber in which a hydrostatic gas bearing is mounted is usually placed in a clean room whose temperature and humidity are controlled.

In the hydrostatic gas bearing in which the atmospheric pressure groove in the bearing is simply opened to the atmosphere on the outside of vacuum chamber via the atmospheric pressure pipe, gas usually flows out from the bearing side to the atmosphere side. However, it was found that gas may sometimes flow in inversely from the atmosphere side to the bearing side depending on the pressure balance of the atmospheric pressure groove fluctuated by the bearing gap etc.

When gas flows inversely from the atmosphere side to the bearing side as described above, the atmosphere having a specific humidity flows in to the bearing side via the atmospheric pressure groove, and thus large amounts of water molecules undesirably adsorb on the surface of the guide shaft. If the moving body of the bearing starts to move in this state and the guide shaft surface on which water molecules have adsorbed is exposed to a vacuum, the adsorbing water molecules are released into the vacuum environment, which results in an increase in gas pressure in the vacuum chamber.

Even if the quantity of adsorbing water molecules is minute, when the pressure in the vacuum chamber is a high vacuum of about 10−5Pa, a remarkable increase in pressure is observed. If such an increase in pressure occurs in the bearing, for example, in an electron beam exposure system, the above-mentioned phenomenon may cause a failure of light source and degradation of exposure accuracy.

In the hydrostatic gas bearing for use in an environment of an especially high vacuum, it is necessary to carry out control so that the causes for the increase in gas pressure in the vacuum chamber are obviated.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention has been made to solve the above problems, and accordingly a first object thereof is to provide a hydrostatic gas bearing in which an increase in the quantity of gas being discharged during the movement of a moving body is reduced.

To achieve the above first object, the present invention provides a hydrostatic gas bearing for use in a vacuum, which is formed of a moving body and a fixed body opposed to the moving body, characterized in that the surface of a guide shaft of the fixed body and/or the surface of the moving body are subjected to processing for reducing adhesion of gas molecules. Since surface treatment for decreasing the quantity of adhering gas is done on the surface of the guide shaft of the fixed body, the increase in the quantity of gas being discharged during the movement of the moving body is reduced.

The degree of vacuum in a vacuum chamber is required to be 10−3to 104Pa or lower depending on the service conditions. Further, movement in a vacuum environment of about 10−5Pa or lower is also expected in the future.

In this description, to decrease the quantity of adhering gas molecules means to decrease the quantity of adhering gas molecule so that gas molecules do not adhere to the guide shaft etc. to an extent that the pressure is not increased to an extent that even if adhering gas molecules are released in a vacuum, they do not hinder the use of device in the above-mentioned vacuum environment.

For example, conventionally, on the surface of the guide shaft newly exposed by the movement of moving body, gas molecules of about 10−6mole per 1 m2adhere at the moment of exposure. These gas molecules are released in the vacuum, exerting an adverse influence on the use of hydrostatic gas bearing in a vacuum environment.

On the other hand, in the hydrostatic gas bearing in accordance with the present invention, the quantity of adhering gas molecules can be decreased to about 10−8mole per 1 m2, so that the use of hydrostatic gas bearing in a vacuum environment is not hindered.

In the present invention, the subjects to be subjected to the above-mentioned surface treatment are not limited to the surface of the fixed body. The effect of surface treatment can be achieved by subjecting a member exposed to the vacuum environment by the movement, of the bearing constituting members, to treatment immediately after the member is exposed to a high-pressure floatation gas.

Also, as the surface treatment for decreasing the quantity of adhering gas, the surface of the guide shaft of fixed body and/or the surface of the moving body is coated with a material having a lower adhesion probability of gas. By this method, the adhesion probability of gas on the bearing surface is decreased. Also, pores in a ceramics surface are filled with the coating and thus a smooth surface is formed, so that the quantity of adhering gas molecules is further decreased. For example, by coating an Al2O3surface with TiC by CVD, the quantity of adhering H2O, which especially poses a problem of adhesion of gas molecules, can be kept about two orders of magnitude smaller.

Also, since the film of TiC has electric conductivity, for the hydrostatic gas bearing mounted in an EB exposure system, an antistatic effect due to electron can be expected.

As a preferred mode of the present invention, the guide shaft of fixed body and/or the moving body formed of high-density ceramics having few pores in the surface thereof is manufactured, by which an increase in the quantity of gas being discharged caused by the influence of the above-mentioned pores is reduced.

Usually, since an infinite number of pores exist in the surface of ceramics, when the surface is exposed to a high-pressure gas, the pores are filled with the gas. Therefore, when the moving body moves and the surface thereof is exposed to a vacuum, the gas filled in the pores is slowly released into the vacuum chamber, so that the reached degree of vacuum of the vacuum chamber is deteriorated. Also, when the ceramics are machined, dirt such as a grinding fluid is liable to remain in the pores, and much gas adheres to the dirt, so that the dirt sometimes becomes a serious gas release source.

Ceramics having few pores can be obtained by a method in which ceramics are manufactured using fine-grain raw material powder having an average grain size of 1 μm or smaller, a method in which ceramics are subjected to hot press processing before firing to density them, a method in which the ordinary alumina ceramics are subjected to HIP processing, or the like method. It is desirable that the theoretical density of pore area in the ceramics surface be 1% or lower.

Also, as a floatation gas for hydrostatic gas bearing suitable to the present invention, an inert gas such as argon, which has less interaction with a solid and less adhesion to the surface, is used to decrease the quantity of gas being discharged at the time of movement. When argon is used, since the gas molecular weight is higher than that of the ordinary gas (N2and O2), the conductance of a labyrinth seal becomes low, which achieves an effect of obtaining high sealing performance.

Also, a second object of the present invention is to provide a hydrostatic gas bearing device for use in a vacuum environment, in which in a device incorporating a hydrostatic gas bearing for use in a vacuum environment, the pressure in an atmospheric pressure groove within the bearing in a vacuum environment is kept fixed, and the inflow of impurities such as water content of gas caused by the backward flow of outside gas into the atmospheric pressure groove through a pipe for atmospheric pressure groove is prevented, by which a decrease in the degree of vacuum in the vacuum environment can be prevented, and a gas recovering method for the hydrostatic gas bearing device.

To achieve the second object, the present invention provides a hydrostatic gas bearing device for use in a vacuum environment, in which a guide shaft and a moving body moving along the guide shaft are provided in a vacuum chamber; the moving body is formed with an air pad for releasing gas fed from the outside into a gap between the moving body and the guide shaft; an atmospheric pressure groove, which recovers the gas released into the gap and discharges the recovered gas to the outside through a pipe, is provided around the air pad; and a pressure reducing groove, which recovers the gas having not been recovered by the atmospheric pressure groove and discharges the recovered gas to the outside through a pipe, is provided around the atmospheric pressure groove, characterized in that in a pipe for discharging the gas recovered through the atmospheric pressure groove to the outside, there is provided a pressure buffering chamber, in which the internal gas pressure thereof is a fixed pressure higher than the atmospheric pressure so that gas does not flow backward from the outside to the atmospheric pressure groove through the pipe.

Thereby, the inflow of impurities such as water content of gas caused by the backward flow of outside gas into the atmospheric pressure groove within the bearing through the pipe is inhibited, by which a decrease in the degree of vacuum in the vacuum environment can be prevented.

In particular, in the hydrostatic gas bearing for use in a high vacuum environment, the present invention achieves great effects.

Also, it is preferable that the pressure buffering chamber be provided with a gas recovery port connected with a pipe for recovering gas from the atmospheric pressure groove; a gas feed port connected with a pipe for feeding gas by controlling the quantity of gas being fed so that the gas pressure in the pressure buffering chamber is a fixed pressure higher than the atmospheric pressure; and a gas leak port connected with a pipe for always discharging the gas in the pressure buffering chamber to the outside.

Thereby, since gas is always discharged to the outside through the gas leak port of the pressure buffering chamber, the inflow of impurities from the outside into the pressure buffering chamber can be prevented.

That is to say, impurities coming from the outside can be prevented from flowing into the atmospheric pressure groove, so that a decrease in the degree of vacuum of the vacuum environment can be prevented.

Also, as a gas fed into the pressure buffering chamber, high-purity nitrogen or dry air is preferable.

Thus, even if gas flows into the atmospheric pressure groove through the pressure buffering chamber, gas in the air containing much water does not flow in, and high-purity nitrogen flows into the pressure buffering chamber, so that there is no fear of degraded vacuum environment.

Also, in a gas recovering method for the hydrostatic gas bearing device, the gas pressure in a pressure buffering chamber provided on the outside of the hydrostatic gas bearing device is controlled so as to be a fixed pressure higher than the atmospheric pressure to always discharge gas from the pressure buffering chamber to the outside, and the gas recovered through the atmospheric pressure groove is also discharged to the outside through the pressure buffering chamber.

Thereby, since gas is always discharged to the outside through the gas leak port of the pressure buffering chamber, the inflow of impurities from the outside to the pressure buffering chamber can be prevented, and the gas released from the air pad can be recovered through the atmospheric pressure groove in the bearing.

That is to say, when the gas released from the air pad is recovered through the atmospheric pressure groove in the bearing, impurities coming from the outside can be prevented from flowing into the atmospheric pressure groove, so that a decrease in the degree of vacuum of the vacuum environment can be prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment according to this embodiment will be described below.

FIG. 1is a perspective view showing one embodiment of a hydrostatic bearing mechanism for achieving the first object of the present invention. A moving body1is installed to a guide shaft2awith a minute gap G provided therebetween so as to be capable of being moved transversely without friction by the supply of a floatation gas. At each end, right and left, of the guide shaft2ais provided a support2bwhich is fixed to a surface plate, not shown. The supports2bare not necessarily be fixed to the surface plate, but each of the supports2bof hydrostatic bearing in accordance with the present invention located horizontally may be fixed to a moving body of another hydrostatic bearing (not shown) arranged in parallel in the direction perpendicular to the guide shaft2a. In this case, the moving body of hydrostatic bearing located horizontally can be moved two-dimensionally. When being fixed to another moving body, the guide shaft ends may be fixed directly to the moving body without the supports2b.

FIG. 2is a sectional view showing one embodiment of a hydrostatic bearing in accordance with the present invention, which view shows an example in which a coating3is applied to the surface of the guide shaft2a. The coating3was applied to the outer periphery of the guide shaft2ausing a material having a low gas adhesion probability.

Hereunder, the improvement in performance achieved by the present invention will be described.

A conventional hydrostatic gas bearing was placed in a vacuum chamber of about 4×10−4Pa, and a change in the degree of vacuum in the vacuum chamber at the time when air is used as the floatation gas was shown inFIG. 3.

The ordinates represent the pressures in the vacuum chamber.

The abscissas represent times. First, recording was started in a state in which the bearing moving body stands still. After two seconds have elapsed, the movement of moving body was started (speed: 55 m/s), and then the moving body was stopped after the movement has been continued for about four seconds. The recording was finished 20 seconds after the measurement start (about 14 seconds after the stopping of moving body).

As shown inFIG. 3, when the conventional hydrostatic gas bearing was used, the chamber pressure began to increase simultaneously with the movement start and reached about 1×10−3Pa. The chamber pressure did not return to the original pressure even 20 seconds after the measurement start.

The reason for this is that gas molecules adhere to the guide shaft, and the guide shaft is exposed in the vacuum chamber by the movement of moving body, so that the adhering gas molecules are released into the vacuum.

When the movement speed is further increased, the pressure in the vacuum chamber increases in proportion to the speed.

Next, a result of measurement made by using a hydrostatic gas bearing was shown inFIG. 4. The surface of fixed body was coated with TiC, and measurement was made under the same conditions as those ofFIG. 3. As the result, the increase in chamber pressure caused by movement reduced to an extent of not being detected.

The coating material is not limited to TiC. SiC may be used, or a metal such as aluminum may be deposited.

Contrarily, a result of measurement made by using a hydrostatic gas bearing was shown inFIG. 5. As a material for fixed body, HIP processed alumina ceramics having a limited number of pores were used, and measurement was made under the same conditions as those ofFIG. 3. As the result, the increase in chamber pressure reduced to about one-tenth of the conventional bearing (FIG. 3).

In this embodiment, since an air pad is provided on the moving body side, the surface treatment is done only on the surface of guide shaft2a. However, in the hydrostatic gas bearing having a construction in which the air pad is provided on the fixed body side, surface treatment on the surface of moving body1is effective. Further, the surface treatment is not limited to either one of the guide shaft2aand the moving body1, and can be done on both of the guide shaft2aand the moving body1. As a concrete method for coating the ceramics surface with TiC, for example, a technique called plasma CVD, in which in a state in which ceramics are heated to

900° C., a mixture gas of TiCl4and CH4is made in a plasma state around the ceramics, by which TiC film is formed on the ceramics surface, can be used.

Also, as a concrete method for manufacturing ceramics having few pores by HIP, for example, a method in which fired alumina ceramics are held for 10 hours in argon gas having a high temperature of 1650° C. and a high pressure of 100 MPa is used.

Next, a hydrostatic gas bearing device A for achieving the second object of the present invention is shown inFIGS. 6 to 9.

As can be seen inFIG. 6, the hydrostatic gas bearing device A has a surface plate B and a hydrostatic gas bearing D provided in a vacuum chamber C. The pressure of vacuum environment in the vacuum chamber C in which the hydrostatic gas bearing D moves is required to be 10−3to 10−4Pa or lower. Further, movement in a vacuum environment of about 10−5Pa or lower is also expected in the future.

The hydrostatic gas bearing D is formed of a moving body1and a guide shaft2a(fixed body). As shown inFIGS. 7 to 9, the moving body1is formed with air pads7for releasing a gas supplied from the outside into a gap between the moving body1and the guide shaft2. The moving body1includes upper plate1aand lower plate6. Further, around the air pad7, there is provided an atmospheric pressure groove8for recovering the gas released into the gap and discharging it to the outside via a pipe15bfor atmospheric pressure groove.

Also, around the atmospheric pressure grooves8, there is provided pressure reducing groove9for recovering the gas having not been recovered by the atmospheric pressure groove8and discharging it to the outside via a pipe.

Although the atmospheric pressure groove8and the pressure reducing groove9are provided in the moving body1, the pipe for pressure reducing groove is also provided on the guide shaft2aside.

FIGS. 8(A)and (B), respectively, show an inside surface and a section view of an upper plate member1aof the moving body1. Bolt holes21indicate where an upper plate1ais clamped to a side plate of the moving body1. As shown inFIGS. 8(A)and (B), exhaust connecting groove9acommunicating with the pressure reducing groove9is formed in the vertical direction in the figure.

As can be seen inFIG. 9(A), the guide shaft2ais formed with an exhaust hole22is formed in guide shaft2afor recovering gas through the pressure reducing groove9(including the exhaust connecting groove9a) at a position opposed to the vertical exhaust connecting groove9a(shown inFIG. 7). Therefore, even if the moving body1moves in the range from a position shown inFIG. 9(B)to a position shown inFIG. 9(C), the exhaust hole22communicates with the exhaust connecting groove9a, so that gas in the pressure reducing groove9(including the exhaust connecting groove9a) can be exhausted through the exhaust hole22.

By the above-described configuration, by using the atmospheric pressure grooves8surrounding the air pads7of the hydrostatic gas bearing D, and further by using a labyrinth exhaust mechanism surrounding the atmospheric pressure grooves8, the quantity of gas flowing out into the vacuum chamber C is kept small to an extent of having no influence on the degree of vacuum of the vacuum chamber C. A plurality of pressure reducing grooves9may be provided according to the required degree of vacuum of operation environment to improve the recovery rate of gas.

Also, although the case where the exhaust hole22for pressure reducing groove is provided within the guide shaft2ahas been shown, the pipe15bcan be provided in the moving body1. For example, in order that the moving body1is made smaller in size and the pipe15bis not restricted by the movement distance of the moving body1, the pipe15bis preferably provided in the moving body1if the pumping performance is sacrificed to some extent. In this case, the above-mentioned vertical pressure reducing groove9is unnecessary.

However, since gas is recovered by an evacuator, the diameter of the exhaust hole22for pressure reducing groove9is, in general, considerably larger than the diameter of the pipe15bconnected to the air pad7or the atmospheric pressure groove8. In this case, if the exhaust hole22for pressure reducing groove9is connected to the moving body1, the exhaust hole22works as a source of resistance and vibration, which may exert an adverse influence on the high movement accuracy required by the moving body1. Therefore, the exhaust hole11for pressure reducing groove9should usually be provided on the guide shaft2aside. (See FIGS.9(A)–(C).)

In effect, it should be determined whether the exhaust hole22for pressure reducing groove9is provided in the moving body1or in the guide shaft2aconsidering the size and movement distance of the moving body1, the influence exerted on the moving body1as resistance by the exhaust hole22in the case where the exhaust hole22is connected to the moving body1, and other factors.

InFIG. 6, a pipe and a feed pump for feeding gas to the air pad7, the pipe for pressure reducing groove, and the evacuator are omitted.

As shown inFIG. 6, for this hydrostatic bearing device, a pressure buffering4chamber10on the outside of the vacuum chamber C is connected to a pipe15bfor atmospheric pressure groove8for discharging the gas recovered through the atmospheric pressure groove8to the outside to prevent gas from flowing backward from the outside to the atmospheric pressure groove8through the pipe15bfor atmospheric pressure groove8.

The pressure buffering chamber10is provided with a gas recovery port11, a gas feed port12, and a gas leak port13.

The gas recovery port11is connected with the pipe15bfor atmospheric pressure groove8for recovering gas from the atmospheric pressure groove8through an introduction port14in the vacuum chamber C.

Also, the gas feed port12is connected with a gas feed pipe15afor feeding gas by controlling the quantity of gas being fed so that the gas pressure in the pressure buffering chamber10is a fixed pressure higher than the atmospheric pressure. A pressure gage16is provided to measure the internal pressure of the pressure buffering chamber10, and also a mass-flow controller17is connected in the gas feed pipe15a. A signal is sent from the pressure gage16to the mass-flow controller17via a signal cable20so that the pressure in the pressure buffering chamber10is about 10% higher than the atmospheric pressure to control the flow rate of gas being fed. Thereby, the flow rate of nitrogen flowing from a nitrogen cylinder18into the pressure buffering chamber10through the gas feed pipe15ais controlled.

Also, the gas leak port13is connected with a pipe for always discharging the gas in the pressure buffering chamber10to the outside. It is preferable that a leak valve19provided in the pressure buffering chamber10be throttled properly to regulate the flow rate of nitrogen flowing out from the leak valve19to the outside so as to be about 5 to 10 liters/minute. Thereby, the quantity of nitrogen being consumed can be kept small while the air is prevented from flowing from the leak valve19into the pressure buffering chamber10.

The nitrogen supplied from the nitrogen cylinder18is preferably of high purity to prevent the degree of vacuum around the bearing from decreasing even if the gas in the pressure buffering chamber10flows backward to the atmospheric pressure groove8. The purity of the high-purity nitrogen is preferably 99.99% or higher. Especially when the hydrostatic gas bearing is used in a high vacuum of about 10−5Pa, the purity of nitrogen is preferably 99.9999% or higher.

Also, the gas fed into the pressure buffering chamber10through the gas feed pipe15amay be dry air. In this case, the dry air preferably has a dew point of −30° C. or lower so that the degree of vacuum does not decrease even if the gas in the pressure buffering chamber10flows backward to the atmospheric pressure groove8.

Next, a gas recovering method for a hydrostatic gas bearing4for use in the above-described vacuum environment will be described in due succession.

First, a high-pressure gas is released from the air pad7provided on the moving body1into the gap between the guide shaft2aand the moving body1. The moving body1and the guide shaft2aare made in a non-contact state by the static force of the released gas, so that the moving body1can move along the guide shaft2awith frictional resistance being scarcely encountered.

Next, the gas released into the above-mentioned gap is recovered through the atmospheric pressure groove8provided around the air pad7.

At this time, the gas pressure in the pressure buffering chamber10provided on the outside of the hydrostatic gas bearing device A is controlled so as to be a fixed pressure higher than the atmospheric pressure (for example, a pressure 10% higher than the atmospheric pressure), by which gas is always discharged from the pressure buffering chamber10to the outside, and also the gas recovered through the atmospheric pressure groove8is also discharged to the outside through the pressure buffering chamber10. Thereby, the outside air is prevented from flowing backward into the atmospheric pressure groove8.

Further, in order to decrease the gas released in the vacuum from the end of the moving body1, the gas that has not been recovered through the atmospheric pressure groove8is recovered through the pressure reducing groove9provided around the atmospheric pressure groove8.

In the above-described process, the atmospheric pressure groove8communicates with the air only through the leak valve19provided in the pressure buffering chamber10. Since nitrogen of about 5 to 10 liters/minute flows out through the leak valve19, the inflow of impurities from the air can be restrained. Thereupon, the gas flowing into the atmospheric pressure groove8is only the gas flowing in through the air pad7or the nitrogen supplied from the nitrogen cylinder18through the pressure buffering chamber10, so that a trouble such as an increase in the quantity of gas being discharged from the bearing caused by the inflow of impurities can be prevented.

INDUSTRIAL APPLICABILITY

As described above, in the present invention, since surface treatment is done on the surface of the guide shaft of fixed body and/or the surface of the moving body to decrease the quantity of adhering gas, there can be provided a hydrostatic gas bearing capable of restraining the increase in the quantity of gas being discharged at the time of movement.

Also, the surface of the guide shaft of fixed body and/or the surface of the moving body is coated with a material having a lower gas adhesion probability, especially, coating is performed on an Al2O3surface by physically depositing TiC having electric conductivity. Therefore, there can be provided a hydrostatic gas bearing capable of keeping the quantity of adhering H2O, which especially poses a problem of adhesion of gas molecules, about two orders of magnitude smaller.

Also, the guide shaft of fixed body and/or the moving body is manufactured of high-density ceramics having few pores in the surface thereof. Therefore, there can be provided a hydrostatic gas bearing capable of reducing the increase in the quantity of gas being discharged caused by the influence of pores.

Also, as a floatation gas of hydrostatic gas bearing, an inert gas such as argon, which has less interaction with a solid and less adhesion to the surface, is used. Therefore, there can be provided a hydrostatic gas bearing capable of decreasing the quantity of gas being discharged at the time of movement.

Further, according to the hydrostatic gas bearing device in accordance with the present invention, the pressure in the atmospheric pressure groove in the bearing in a vacuum environment is kept fixed, and the inflow of impurities such as water content of gas caused by the backward flow of outside gas into the atmospheric pressure groove through the pipe for atmospheric pressure groove is inhibited, by which a decrease in the degree of vacuum in the vacuum environment can be prevented.