JP2002206532A - Air bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air bearing device capable of preventing the reduction in its rigidity and a leakage of gas even when used in high degree vacuum. SOLUTION: A voltage is applied to piezoelectric elements 5 connected as shown in the drawing to make faces on which an air pad in a fixing part 1 exists act as actuators inside the fixing part 1 to deform the faces on which the air pad in the fixing part 1 exists as shown in the drawing. That is, a voltage is applied to the piezoelectric elements 5 positioned in the vicinity of the center of a movable part 2 to elongate the piezoelectric elements so that they copy the deformation of the movable part 2 by forming the corresponding air pad face of the fixing part 1 into a projecting shape. Consequently, an air gap becomes substantially constant, the rigidity of an air bearing is not deteriorated, and gas does not leak into a vacuum vessel from between the fixing part 1 and the movable part 2 to avoid a problem of worsening a vacuum degree.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air bearing device, and more particularly to an air bearing device suitable for use in a high vacuum atmosphere. In this specification, what is referred to as an air bearing is a concept that includes not only those that provide a bearing effect by using air but also those that have the same function by using other gases.

[0002]

2. Description of the Related Art A charged particle beam exposure apparatus for exposing and transferring a pattern formed on a reticle to a wafer or the like by using a charged particle beam can reduce the line width of the pattern to be exposed and transferred, thereby integrating semiconductor devices and the like. Because it can be increased, it is being developed as a next-generation stepper.

[0003] Among such charged particle beam exposure apparatuses, the most advanced one uses a division exposure system. In the division exposure method, the area to be exposed and transferred is 1
A reticle is created by dividing into a plurality of parts (called subfields) of about mm square, batch exposure transfer is performed for one subfield, and different subfields are sequentially transferred while moving the reticle and the wafer together. Exposure transfer to one wafer is performed as a whole.

In such a charged particle beam exposure apparatus, the reticle is mounted on a reticle stage and the wafer is mounted on a stage called a wafer stage, and the reticle and wafer are moved by driving each stage. An air bearing is used to smoothly drive the reticle stage and the wafer stage.

The principle of the air bearing will be described with reference to FIG. As shown in FIG. 5A, the ring 1 of the stage
When a hole is made in the center of the tube 2 and compressed air is blown from the hole through the air supply space 13, the ring 12 floats by the pressure of the air. This is the principle of the air bearing. However, when it is desired to drive a heavy object with high precision using an air bearing, it is not preferable that the gap between the ring 12 and the shaft 11 be large.

The reason is that when the gap becomes large, the spring constant of the air bearing becomes small, and low-frequency resonance appears in the ring 12. Therefore, usually, a pressure is applied to the bearing to press the ring 12 tightly against the shaft 11 before use. The pressurization is generated as shown in FIG. That is, a groove 14 is provided around the air outlet, and air is exhausted from the groove 14 through an exhaust pipe 15 by a vacuum pump. The exhaust allows the pressure in the groove to be lower than one atmosphere, and the ring can be pressed against the shaft by the atmospheric pressure.

[0007]

Since the electron beam cannot be used in the atmosphere because of its high absorption, it is used in a vacuum. Therefore, the inside of the electron beam exposure apparatus needs to be evacuated.
In such a high vacuum, an air bearing stage for driving a wafer or a reticle cannot be used in a form used in the atmosphere. This is because a large amount of air leaks into the vacuum chamber.

Therefore, an air bearing used in a high vacuum has a structure as shown in FIG. The basic structure is the same as that shown in FIG. 5B, and the same components as those in FIG. 6 are denoted by the same reference numerals and description thereof is omitted.
A groove 14 is dug at a closed line that separates the air blowing portion from the vacuum portion, and the air blown by a vacuum pump through an exhaust pipe 15 is collected therefrom. As a result, the amount of air leaking into the vacuum chamber can be reduced. Unlike the air bearing in the atmosphere, this vacuum air bearing cannot apply a pressure due to the atmospheric pressure.

As a countermeasure, as shown in FIG. 6 (a), the moving part 12 is held by the same vacuum air bearing by sandwiching the shaft 11 from both sides.
Prevent from rising from one. However, since the generating force of a normal air pad is as large as about 100 kg weight, the ring 12 and the shaft 11 are each deformed, and FIG.
As shown in (b), a problem occurs in that the gap between the ring 12 and the shaft 11 widens. This gap fluctuation reduces the rigidity of the air bearing,
There is a problem that the amount of air flowing into the vacuum chamber increases rapidly.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air bearing device whose rigidity is reduced and gas leaks less even when used in a high vacuum. Make it an issue.

[0011]

A first means for solving the above-mentioned problems comprises a shaft and a ring fitted to the shaft, and an inner surface of the ring is provided with an air pad on an opposing surface. An air bearing device according to claim 1, wherein said air bearing device has a function of adjusting a variation in an air gap by deforming at least one of said shaft and said ring with an actuator.

In the present invention, the fluctuation of the air gap between the shaft and the ring of the air bearing, which occurs when gas is supplied to the air bearing, is compensated by deforming at least one of the shaft and the ring by the actuator. ing. Therefore, since the fluctuation of the air gap is reduced, it is possible to provide an air bearing device in which the rigidity is reduced and the gas is less likely to leak.
The “ring” does not necessarily mean a circular one, but may be a polygonal one.

[0013] A second means for solving the above-mentioned problems is as follows.
The first means, wherein the inside of the shaft is hollow, an inner wall surface of the shaft facing the air pad is connected by an actuator provided inside the shaft, and the shaft is deformed by the actuator. And a function of adjusting the fluctuation of the air gap (claim 2).

As described above, an air bearing used in a high vacuum has a structure in which a ring is fitted to a shaft. The shaft is usually hollow to reduce the weight. In this means, an actuator is installed in the hollow portion, the actuator connects the shaft surfaces facing the air pad of the ring, and deforms the shaft surface by operating the actuator. This alleviates the fluctuation of the air gap, thereby preventing the rigidity of the air bearing device from decreasing and preventing gas from leaking.

A third means for solving the above-mentioned problem is the first means, wherein a beam is provided on an outer peripheral portion of an air pad surface of the ring, and the beam is connected to the outer peripheral surface of the air pad by an actuator. The air pad surface is deformed by the actuator to adjust the fluctuation of the air gap (claim 3).

In this means, the beam provided on the outer peripheral portion of the air pad surface of the ring and the outer peripheral surface of the air pad are connected by an actuator, and the air pad of the ring is deformed by operating the actuator. This alleviates the fluctuation of the air gap, thereby preventing the rigidity of the air bearing device from decreasing and preventing gas from leaking.

A fourth means for solving the above-mentioned problem is:
The first means, wherein an actuator is provided on an air pad surface of the ring, and the actuator has a function of adjusting a variation in an air gap by changing a height of the air pad surface. (Claim 4).

In this means, the height of the air pad surface of the ring is changed by an actuator provided on the ring. This alleviates the fluctuation of the air gap, thereby preventing the rigidity of the air bearing device from decreasing and preventing gas from leaking.

A fifth means for solving the above-mentioned problem is:
The fourth means, wherein the actuator is adjusted in advance so that a stroke of the actuator has a predetermined value according to a position of an air pad surface of a ring. 5).

In most cases, since the pressure and flow rate of the gas supplied to the air bearing are constant, the size of the air gap is a predetermined value according to the location of the ring. Therefore, by adjusting the stroke of the actuator to a predetermined value according to the position of the ring,
The height of the air pad surface is determined at each location according to the amount of the air gap, and the air gap can be kept at a constant value. This is achieved by providing a plurality of actuators with different strokes. Also, as described in the section of the embodiment of the invention,
When using a piezoelectric element as an actuator,
This can be realized by varying the thickness depending on the location.

A sixth means for solving the above-mentioned problem is as follows.
The first means, wherein an actuator is provided on a surface of the shaft facing the air pad, and a function of adjusting a variation in an air gap by changing a height of the surface facing the air pad with the actuator is provided. (Claim 6).

When viewed from the center of the shaft, the air gap at a predetermined position of the shaft changes depending on the position where the ring exists. In this means, since the height of the surface of the shaft facing the air pad surface is changed by the actuator, for example, the position of the ring is detected, and the height of the surface of each portion of the shaft is determined accordingly. By changing it, the air gap can be kept constant. Also in this case, a plurality of actuators are provided,
This can be realized by making the strokes different.

A seventh means for solving the above problem is as follows.
Any one of the first to sixth means, wherein the actuator has a piezoelectric element (claim 7).

When a piezoelectric element is used as a driving means of the actuator, the stroke of the actuator can be adjusted by a simple means of applying a voltage to the piezoelectric element, so that other mechanical and electric actuators can be used. In comparison with this, the configuration is simple, and a minute amount of stroke variation can be accurately controlled.

An eighth means for solving the above-mentioned problems is the first to seventh means, wherein a gap sensor for detecting an air gap between the shaft and the ring is provided, and a signal from the sensor is provided. It has a function of adjusting the gap by feeding back to the actuator (claim 8).

In this means, since the air gap between the shaft and the ring is directly detected and the feedback is applied to the actuator so as to adjust it to a predetermined value, it is possible to accurately control the air gap. it can. As the gap sensor, a known sensor of an optical type or a capacitance type can be used.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of the first embodiment of the present invention. In FIG. 1, 1 is a shaft, 2 is a ring, 3 is an air bearing portion, 4 is an exhaust groove, and 5 is a piezoelectric element.

The shaft 1 is hollow for weight reduction. A ring 2 is provided so as to surround the shaft 1. The hatched square portion of the ring 2 is the air bearing 3. Exhaust grooves 4 are provided at both ends inside the ring 2. Here, the piezoelectric element 5 is arranged as shown in the hollow portion inside the shaft 1.

The operation of the piezoelectric element will be described with reference to FIG. In the following drawings, the same reference numerals are given to the components shown in the preceding drawings in the section of the embodiment of the invention, and the description thereof will be omitted. In FIG. 2, 6 is an air supply pipe, 7
Is an exhaust pipe.

FIG. 2 (a) is a schematic diagram showing a cross section cut at the center of the one shown in FIG. Gas such as air is supplied to the air bearing portion of the ring 2 from the air supply pipe 6,
The pressure causes a gap between the shaft 1 and the ring 2 to exert a bearing effect. When this air bearing device is used in a high vacuum, the exhaust gas is exhausted from exhaust grooves 4 provided near both ends of the ring 2 so that the supplied gas does not leak from the gap between the shaft 1 and the ring 2. Gas is sucked through the pipe 7 and exhausted to the outside.

When the air bearing is used in a high vacuum, the ring 2 is deformed outward and the shaft 1 is actually deformed due to the pressure of the supplied gas, as shown in FIG. Deform to. As a result, as described above, the rigidity of the air bearing deteriorates, and gas leaks out from between the shaft 1 and the ring 2 into the vacuum vessel, thereby deteriorating the degree of vacuum.

In the present embodiment, this problem is solved by the method shown in FIG. That is, the surfaces of the shaft 1 where the air pads are present are made to act as actuators by applying a voltage to the piezoelectric elements 5 connected to each other as shown in FIG. Deform as shown. In other words, when a voltage is applied to the piezoelectric element 5 located near the center of the ring 2, the piezoelectric element is expanded, and the air pad surface of the corresponding shaft 1 is made convex to imitate the deformation of the ring 2. As a result, the air gap becomes substantially constant, thereby avoiding the problem that the rigidity of the air bearing is deteriorated and that the gas leaks from the space between the shaft 1 and the ring 2 into the vacuum vessel to deteriorate the degree of vacuum.

At this time, a gap sensor may be attached to the ring 2 to measure the air gap between the ring 2 and the shaft 1, and the value may be fed back to the piezoelectric element to keep the air gap constant. As the gap sensor, a known sensor such as an optical sensor or a capacitance sensor can be used. If a capacitive sensor is used, the shaft surface must be coated with metal. Thus, if the gap sensor is used, the air gap can be kept constant even when the pressure of the compressed air fluctuates. In the above description, a plurality of piezoelectric elements are arranged in the longitudinal direction of the shaft 1. However, if a plurality of similar piezoelectric elements are provided in the lateral direction of the shaft 1 as necessary, the gap in the lateral direction can be increased. Fluctuations can also be corrected.

FIGS. 3A and 3B are schematic views showing an example of the second embodiment of the present invention. FIG. 3A is a perspective view, and FIG. 3B is a view for explaining the operation (a cross section cut at the center). Figure).
In FIG. 3, reference numeral 8 denotes a beam. In the first embodiment shown in FIG. 1, the piezoelectric element 5 is provided on the shaft 1 side.
In the second embodiment, it is provided on the ring 2 side.

That is, the two-sided beams 8 above and below the ring 2
Is provided, and the piezoelectric element 5 is provided between the beam 8 and the ring 2 main body. In (b), when gas is supplied from the air supply pipe 6 and a voltage is applied to the piezoelectric element 5 to expand the piezoelectric element 5, the air pad surface of the ring 2 is deformed as shown in the figure. Therefore, the deformation of the ring 2 can be made to follow the deformation of the shaft 1, and a desired amount of air gap can be secured. As a result, the air gap becomes substantially constant, so that the problems of deterioration of the rigidity of the air bearing and leakage of gas from between the shaft 1 and the ring 2 into the vacuum container to deteriorate the degree of vacuum are avoided. In this case, the deformation of the ring may be measured in advance, and a voltage sufficient to cancel the deformation may be applied. However, as described above, the air gap sensor is provided and applied to the piezoelectric element 5 so that the air gap becomes constant. The voltage may be adjusted.

FIG. 4 shows another example of the embodiment, and is a sectional view taken at the center. In FIG. 4, 9
Reference numerals a and 9b denote electrodes, and reference numeral 10 denotes an insulator. In these drawings, a gas supply path and a gas discharge path are omitted for simplification.

FIG. 3A is a diagram in which a plate-like piezoelectric element 5 is provided on the back surface of the air pad surface of the ring 2. By applying a voltage between the electrodes 9a and 9b provided on the front and back surfaces, the piezoelectric element 5 is extended and the surface of the electrode 9b is made to follow the shaft 1. Also in this case, a feedback control may be performed by providing a gap sensor. At this time, the electrode 9b
It is necessary that the shaft 1 and the shaft 1 have the same electric potential such as a ground electric potential so that an electric short circuit does not occur even when they contact each other.
At this time, as shown in (b), if the thickness of the piezoelectric element 5 in a portion where deformation is large is increased, a more uniform gap can be realized over the entire air pad.

(C) shows the entire area near the surface of the shaft 1
This is an embodiment in which a plate-shaped piezoelectric element 5 is provided. As shown in (a), if a configuration is adopted in which a voltage is applied to the plate-shaped piezoelectric element 5 by one common electrode to change the entire thickness uniformly, air is supplied to the piezoelectric element at the same time. By applying a voltage and increasing the thickness of the entire shaft, gap fluctuation can be suppressed to a small value.

However, when the gap management is performed more finely, the thickness of each electrode portion can be changed by patterning the electrodes of the piezoelectric element. In (c), the electrode 9b is patterned and divided, and the voltage applied to each part of the piezoelectric element 5 is changed in synchronization with the driving of the ring 2 so as to match the size of the gap between the shaft 1 and the ring 2. The extension amount of the piezoelectric element 5 is controlled, and as a result, the gap amount can be set to a constant value. Also in this case, a feedback control may be performed by providing a gap sensor.

The above description has been made on the assumption that the air bearing is used in a high vacuum. Of course, the present invention is most effective in such an air bearing, but can also be applied to an air bearing used in the atmosphere. In that case, a vacuum evacuation system for applying pressurization becomes unnecessary, and the system can be simplified.

[0041]

When the present invention is used for an air bearing in a vacuum, the gap fluctuation due to the deformation of the ring due to the pressure of the air pad can be reduced. As a result, the rigidity of the air bearing can be kept high, and the outflow of air into the vacuum chamber can be reduced. On the other hand, when the present invention is applied to an air bearing used in the atmosphere, a vacuum system for applying pressurization becomes unnecessary, and the system can be simplified.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating the adoption of a piezoelectric element in the present invention in comparison with a conventional example.

FIG. 3 is a schematic diagram illustrating an example of a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing an example of another embodiment of the present invention.

FIG. 5 is a schematic view showing the principle of an air bearing.

6A and 6B are a schematic diagram of an air bearing used in a vacuum and a diagram for explaining its problems.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Shaft 2 ... Ring 3 ... Air bearing part 4 ... Exhaust groove 5 ... Piezoelectric element 6 ... Air supply pipe 7 ... Exhaust pipe 8 ... Beam part 9a, 9b ... Electrode 10 ... Insulator

Claims (8)

[Claims] 1. An air bearing device comprising a shaft and a ring fitted to the shaft, wherein an inner surface of the ring is provided with an air pad on an opposing surface, wherein at least one of the shaft and the ring is actuated by an actuator. An air bearing device having a function of adjusting a change in an air gap by deforming one of them. 2. The air bearing device according to claim 1, wherein the inside of the shaft is hollow, and an inner wall surface of the shaft facing the air pad is connected by an actuator provided inside the shaft. An air bearing device having a function of adjusting a fluctuation of an air gap by deforming the shaft. 3. The air bearing device according to claim 1, wherein a beam is provided on an outer peripheral portion of the air pad surface of the ring, and the beam and the outer peripheral surface of the air pad are connected by an actuator, and the actuator uses the beam. An air bearing device having a function of adjusting a change in an air gap by deforming an air pad surface. 4. The air bearing device according to claim 1, wherein an actuator is provided on an air pad surface of the ring, and the height of the air pad surface is changed by the actuator to adjust a change in an air gap. An air bearing device having a function. 5. The air bearing device according to claim 4, wherein the actuator is adjusted in advance so that a stroke of the actuator has a predetermined value according to a position of an air pad surface of a ring. An air bearing device, characterized in that: 6. The air bearing device according to claim 1, wherein an actuator is provided on a surface of the shaft facing the air pad, and the height of the surface facing the air pad is changed by the actuator. An air bearing device having a function of adjusting a fluctuation of an air gap. 7. One of claims 1 to 6
Item 7. The air bearing device according to Item 1, wherein the actuator has a piezoelectric element. 8. The air bearing device according to claim 1, further comprising a gap sensor for detecting an air gap between the shaft and the ring, and adjusting a gap by feeding back a signal from the sensor to an actuator. An air bearing device having a function to perform.