Patent Publication Number: US-2023143197-A1

Title: Stage apparatus and charged particle beam apparatus including stage apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stage apparatus and a charged particle beam apparatus including the stage apparatus. 
     2. Description of the Related Art 
     In the field related to semiconductors, a stage apparatus for moving and accurately positioning a sample such as a semiconductor wafer is known. In an apparatus that handles charged particle beams such as electron beams, it is necessary to handle a sample such as a semiconductor wafer in a high vacuum environment, and the stage apparatus is also operated in a high vacuum environment. 
     The structure of the stage apparatus is classified into a guide rail type stage that is limited to movement only in a direction along the guide rail and is mechanically prohibited from moving in the other direction, and a floating type stage that floats from the base portion and moves by control in a non-contact state with the base portion. In order to realize planar movement in the guide rail type stage, the upper stage may be moved in a direction orthogonal to the moving direction of the lower stage as a stage configuration of two upper and lower stages. On the other hand, the floating stage includes a uniaxial operation type having a large movable range only in one direction and having a narrow movable range with respect to the other direction, and a planar operation type capable of moving widely in a planar manner. It is also possible to configure a stage that operates planarly by combining a single-axis operation type floating type stage and a guide rail type stage. Further, as a floating mechanism of the floating stage, there are a magnetic floating type that controls a floating amount using electromagnetic force and an air bearing type that controls a floating amount using pressure of gas. 
     The magnetic floating type stage is classified into a type having an electromagnet that gives buoyancy to the stage and a linear motor that gives thrust in a uniaxial direction, and a type having a shaft motor capable of performing both functions of floating and propulsion as one. In both types, the stage is movable while maintaining a non-contact state. In the non-contact state, a mechanical stabilization mechanism cannot be obtained, but there is a possibility that high positional accuracy of the stage can be realized by advanced control of the floating stage. 
     When the floating stage is placed in a vacuum environment, heat generated by a motor that drives the stage cannot be released by solid heat conduction, so that a heat dissipation means using a refrigerant is required. For example, JP 2005-32817 A discloses a technique of cooling a drive unit inside a fine movement stage that moves a wafer with a refrigerant. JP 2001-61269 A discloses a technique for cooling a coil of a motor with a refrigerant in a stage apparatus that moves a substrate table on which a wafer is placed using a shaft motor. Further, JP 2005-64229 A discloses a technique related to a cooling device that cools a linear motor that moves a wafer stage on which a wafer is placed. 
     SUMMARY OF THE INVENTION 
     In processes such as semiconductor wafer manufacturing, measurement, and inspection, the wafer needs to be accurately positioned. In order to accurately position the semiconductor wafer, it is necessary to accurately grasp the position of the stage on which the wafer is moved. As a technique for accurately measuring the position of the stage, there is a technique using a laser interferometer type distance measuring device in which a mirror bar is installed on the stage, laser beam is applied to a reflecting surface of the mirror bar, and distance measurement is performed using interference between incident light and reflected light. In a recent laser interferometer type distance measuring device, distance measurement can be performed with accuracy on the order of picometers. If the distance measurement can be performed with the accuracy of the order, it seems that sufficient positional accuracy of the wafer can be obtained practically. However, in practice, various error factors that deteriorate the positional accuracy of the wafer are combined in the floating stage, so that it is difficult to ensure sufficient positional accuracy of the wafer. 
     Therefore, the present invention provides a technique for ensuring sufficient positional accuracy of a sample in a floating stage. 
     A stage apparatus according to the present invention includes: a first stage configured to move in a first direction; a second stage configured to float from the first stage and move in a second direction orthogonal to at least the first direction; a first cooling unit configured to cool the table of the first stage with a refrigerant; and a control device configured to control an inclination of the second stage with reference to the table of the first stage cooled by the first cooling unit. 
     According to the present invention, it is possible to ensure sufficient positional accuracy of the sample in the floating stage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating an overall configuration of a stage apparatus of a first embodiment; 
         FIG.  2    is a cross-sectional view of the stage apparatus according to the first embodiment; 
         FIG.  3    is a diagram illustrating a control device of the stage apparatus according to the first embodiment; 
         FIG.  4    is a diagram illustrating an overall configuration of a stage apparatus of a second embodiment; and 
         FIG.  5    is a diagram illustrating an overall configuration of a charged particle beam apparatus of a third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described on the basis of the drawings. In the following embodiments, it is needless to say that the components (including element steps and the like) are not necessarily essential unless otherwise specified and considered to be essential in principle. 
     First Embodiment 
       FIG.  1    is a diagram illustrating an overall configuration of a stage apparatus according to a first embodiment.  FIG.  2    is a cross-sectional view of the stage apparatus according to the first embodiment. A stage apparatus  100  of the first embodiment is an apparatus that moves a placed sample (for example, a semiconductor wafer) in the X-axis direction and the Y-axis direction. The stage apparatus  100  includes an upper stage  10  that moves in the X-axis direction, a lower stage  20  that moves in the Y-axis direction, a cooling water pipe  30  that supplies cooling water for cooling the upper stage  10  and the lower stage  20 , and a control device  50  (see  FIG.  3   ). The upper stage  10  floats from the lower stage  20  by magnetic force with the lower stage  20 , and moves at least in the X-axis direction orthogonal to the Y-axis direction. 
     (Upper Stage  10 ) 
     The upper stage  10  is configured around an X table  1 . The upper stage  10  floats from a Y table  2  of the lower stage  20  and moves in the X-axis direction relative to the lower stage  20 . The upper stage  10  mainly moves in the X-axis direction, and the moving direction includes a deviation of about an error with respect to the X-axis direction. The upper stage  10  may move not only in the X-axis direction but also in a planar manner. Various mechanisms such as a mechanism for floating the upper stage  10  from the Y table  2 , a mechanism for moving the upper stage  10  in the X-axis direction, and a mechanism for moving the upper stage  10  in the Y-axis direction are attached to the upper stage  10 . These various mechanisms are provided inside the X table  1 . These various mechanisms serve as heat sources and conduct heat to the X table  1 . 
     An X mirror  3  which is a mirror bar for measuring an X coordinate and a Y mirror  4  which is a mirror bar for measuring a Y coordinate are fixed on the X table  1 . The X mirror  3  has a reflecting surface perpendicular to the X axis, and reflects a laser beam emitted from a laser interferometer type distance measuring device (not illustrated). The Y mirror  4  has a reflecting surface perpendicular to the Y axis, and reflects a laser beam emitted from a laser interferometer type distance measuring device (not illustrated). This makes it possible to measure the X coordinate of the reflecting surface of the X mirror  3  and the Y coordinate of the reflecting surface of the Y mirror  4 . By measuring the X coordinate and the Y coordinate of the reflecting surface, the XY coordinates of the X table  1  to which the X mirror  3  and the Y mirror  4  are fixed and the XY coordinates of the sample placed on the X table  1  are calculated. 
     (Lower Stage  20 ) 
     The lower stage  20  is configured around the Y table  2 . The lower stage  20  moves in the Y-axis direction. The lower stage  20  mainly moves in the Y-axis direction, but its moving direction includes a deviation of about an error with respect to the Y-axis direction. The lower stage  20  may move not only in the Y-axis direction but also in a planar manner. The lower stage  20  moves in the Y-axis direction on two guide rails  5  arranged along the Y-axis direction. The lower stage  20  is restrained by the two guide rails  5  so as not to be movable in a direction other than the Y-axis direction. The lower stage  20  of the first embodiment is a guide rail type, but may be a floating type stage. The lower stage  20  has various mechanisms such as a mechanism for floating the upper stage  10  from the Y table  2  and a mechanism for moving the lower stage  20  in the Y-axis direction. These various mechanisms are provided inside the Y table  2 . These various mechanisms serve as heat sources and conduct heat to the Y table  2 . 
     (Cooling Water Pipe  30 ) 
     The stage apparatus  100  may be used in a sample chamber in which a sample such as a semiconductor wafer is manufactured, measured, or inspected. In an apparatus that handles charged particle beams such as electron beams, it is necessary to handle a sample such as a semiconductor wafer in a high vacuum environment, and the stage apparatus  100  also operates in the high vacuum environment. It is necessary to cool the upper stage  10  and the lower stage  20  in order to suppress malfunction, thermal expansion, and the like due to heat generation of the mechanism that moves the upper stage  10  and the lower stage  20 . In the first embodiment, the stage apparatus  100  includes the cooling water pipe  30  that supplies a refrigerant to the upper stage  10  and the lower stage  20  in order to cool the upper stage  10  and the lower stage  20 . In the first embodiment, cooling water is used as the refrigerant. As a method of cooling the stage apparatus  100 , water cooling, air cooling, gas cooling, or the like can be adopted. 
     The cooling water supplied from a thermostatic water bath (not illustrated) is supplied to both the upper stage  10  and the lower stage  20  via the cooling water pipe  30 . The cooling water pipe  30  includes a joint  31 , an outgoing pipe  32 , a transition pipe  33 , a return pipe  34 , and a joint  35 . The thermostatic water bath supplies cooling water to the outgoing pipe  32  connected to the joint  31 . The outgoing pipe  32  is connected to a heat exchanger  17  (see  FIG.  2   ) provided inside the X table  1  of the upper stage  10 . The outgoing pipe  32  is disposed along the Y-axis direction from the joint  31 , turns in a U shape, and then disposed along the Y-axis direction. The outgoing pipe  32  disposed along the Y-axis direction is supported by a support  21  provided in the lower stage  20 . As described above, by turning the outgoing pipe  32  in the U shape, the portion turned in the U shape is displaced following the movement of the lower stage  20  in the Y-axis direction. Therefore, a material that can be flexibly bent, such as a resin tube, is used for the cooling water pipe  30 . 
     The outgoing pipe  32  that has passed the support  21  is disposed along the X-axis direction, turns in a U shape, and then disposed along the X-axis direction. The outgoing pipe  32  disposed along the X-axis direction is supported by a support  11  provided on the upper stage  10 . As described above, by turning the outgoing pipe  32  in the U shape, the portion turned in the U shape is displaced following the movement of the upper stage  10  in the X-axis direction. The outgoing pipe  32  that has passed the support  11  is connected to a joint  12  fixed to the X table  1 . As a result, the cooling water supplied from the thermostatic water bath is supplied to the heat exchanger  17  of the X table  1  via the joint  31 , the outgoing pipe  32 , and the joint  12 . As a result, the X table  1  in contact with the surface of the heat exchanger  17  through which the cooling water passes is cooled. 
     The cooling water used for cooling the X table  1  is supplied from a joint  13  fixed to the X table  1  to a heat exchanger  27  of the Y table  2  via the transition pipe  33 . The transition pipe  33  is supported by the support  11 . The transition pipe  33  supported by the support  11  is disposed along the X-axis direction, turns into a U shape, and then disposed along the X-axis direction. The transition pipe  33  is connected to a joint  22  fixed to the Y table  2 . As a result, the cooling water cooled in the X table  1  is supplied to the heat exchanger  27  of the Y table  2  via the joint  13 , the transition pipe  33 , and the joint  22 . As a result, the Y table  2  in contact with the surface of the heat exchanger  27  through which the cooling water passes is cooled. 
     The cooling water used for cooling the Y table  2  returns from a joint  23  fixed to the Y table  2  to the thermostatic water bath through the return pipe  34 . The return pipe  34  is supported by the support  21 . The return pipe  34  supported by the support  21  is disposed along the Y-axis direction, turns in a U shape, and then disposed along the Y-axis direction. The return pipe  34  is connected to the joint  35  of the thermostatic water bath. The cooling water cooled in the thermostatic water bath is supplied to the joint  31  again. 
     The outgoing pipe  32  and the transition pipe  33  are connected to a surface  16  perpendicular to the Y-axis direction of the upper stage  10 . The transition pipe  33  and the return pipe  34  are connected to a surface  28  perpendicular to the Y-axis direction of the lower stage  20 . The vertical surface  16  of the upper stage  10  to which the outgoing pipe  32  and the transition pipe  33  are connected and the vertical surface  28  of the lower stage  20  to which the transition pipe  33  and the return pipe  34  are connected are surfaces on the same side. The vertical surface  16  of the upper stage  10  to which the outgoing pipe  32  and the transition pipe  33  are connected and the vertical surface  28  of the lower stage  20  to which the transition pipe  33  and the return pipe  34  are connected may be surfaces on different sides. For example, the outgoing pipe  32  and the transition pipe  33  may be connected to a surface  18  perpendicular to the X-axis direction of the upper stage  10 , and the transition pipe  33  and the return pipe  34  may be connected to the surface  28  perpendicular to the Y-axis direction of the lower stage  20 . 
     (Inclination Angle of Upper Stage  10 ) 
     The control device  50  measures the inclination angle of the upper stage  10  and controls the upper stage  10  to be horizontal. The Y table  2  has a vertical surface  24  perpendicular to the Y-axis direction, and a linear scale  25  (see  FIG.  3   ) is attached to the vertical surface  24 . The X table  1  has a vertical surface  14  perpendicular to the Y-axis direction, and a sensor  15  (see  FIG.  3   ) that reads the linear scale  25  is attached to the vertical surface  14 . When the linear scale  25  is read by the sensor  15  facing the vertical surface  24  and the vertical surface  14 , the height of the X table  1  with respect to the Y table  2  can be measured (Z displacement measurement). The linear scale  25  has, for example, a plate shape in which a pattern for reflecting laser beam is formed by a fine lattice, and is used in combination with the sensor  15  that emits laser beam and reads reflected light. If the reflection pattern formed on the linear scale  25  is two-dimensional, not only the amount of displacement of the relative position between the linear scale  25  and the sensor  15  in the Z-axis direction but also the amount of displacement in the X-axis direction can be measured. Further, when height measurement is performed on one linear scale by two sensors, the inclination angle of the X table  1  can be obtained from the difference between the heights of the two points. That is, it is possible to measure the pitching angle of the X table  1  moving in the X-axis direction. Using this principle, when the number of sets of the linear scale  25  and the sensor  15  is further increased by 2, it is possible to measure the yawing angle and the rolling angle. This makes it possible to perform highly accurate inclination angle measurement with a simple configuration. 
     (Heat Exchanger) 
       FIG.  2    is a cross-sectional view taken along line S 1 -S 2  in  FIG.  1   . A structure for cooling the X table  1  and the Y table  2  will be specifically described with reference to  FIG.  2   . The X table  1  is made of aluminum alloy. The X table  1  includes the heat exchanger  17  formed of a stainless pipe therein, and the heat exchanger  17  is a cooling unit that cools the X table  1  with a refrigerant. The heat exchanger  17  built in the X table  1  cools the X table  1  by bringing the surface of a pipe through which a refrigerant (for example, cooling water) passes into contact with the X table  1 . The pipe constituting the heat exchanger  17  is formed by bending one pipe, and one pipe has an inlet and an outlet for cooling water. A mechanism for floating the upper stage  10  from the Y table  2 , a mechanism for moving the upper stage  10  in the X-axis direction, a mechanism for moving the upper stage  10  in the Y-axis direction, and the like are attached to the X table  1 . These mechanisms serve as heat sources and conduct heat to the X table  1 . Since the X table  1  is formed of an aluminum alloy, a temperature gradient accompanying thermal conduction is reduced, and a temperature rise and temperature unevenness can be reduced. 
     Similarly, the Y table  2  is also formed of an aluminum alloy. The Y table  2  also has the heat exchanger  27  formed of a stainless pipe therein. The heat exchanger  27  is a cooling unit that cools the Y table  2  with a refrigerant. The heat exchanger  27  incorporated in the Y table  2  cools the Y table  2  by bringing the surface of a pipe through which the refrigerant passes into contact with the Y table  2 . The pipe constituting the heat exchanger  27  is also formed by bending one pipe, and one pipe has an inlet and an outlet for cooling water. A mechanism for floating the upper stage  10  from the Y table  2 , a mechanism for moving the lower stage  20  in the Y-axis direction, and the like are attached to the Y table  2 . The mechanism serves as a heat source and conducts heat to the Y table  2 . Since the Y table  2  is also formed of an aluminum alloy, a temperature gradient associated with thermal conduction is reduced, and a temperature rise and temperature unevenness can be reduced. 
     (Guide Rail  5  and Slide Unit  26 ) 
     The lower stage  20  centered on the Y table  2  is restrained by the two guide rails  5  so as not to be movable in a direction other than the Y-axis direction. The guide rail  5  is fixed to a sample chamber  40 . The lower stage  20  includes slide units  26  arranged at four corners of the lower stage  20 , and the slide units  26  come into contact with the guide rails  5 . A rolling element is disposed inside the slide unit  26 , and this rolling element makes contact with the guide rail  5  into rolling contact. As a result, the slide unit  26  and the guide rail  5  form a contact structure with low friction and no play. 
     When the temperature of the Y table  2  rises, the movement of the Y table  2  in the Y-axis direction is not restricted, so that the Y table  2  freely expands in the Y-axis direction. On the other hand, since the movement in the direction other than the Y-axis direction is restricted by the guide rail.  5 , the Y table  2  cannot expand in the direction other than the Y-axis direction. Therefore, the expansion due to the temperature rise is absorbed by the Y table  2  being curved in a mountain shape. That is, when the Y table  2  is curved in a mountain shape, the Y table  2  is lowered to the right on the right side of  FIG.  2   , and the Y table  2  is lowered to the left on the left side of  FIG.  2   . On the other hand, the X table  1  moves to the positive side or the negative side of the X coordinate. When the X table  1  moves, the inclination angle of the X table  1  is measured with reference to the Y table  2  at the position of the movement destination. 
     (Control Device  50 ) 
     The control device  50  controls a stage drive mechanism  60  to move the lower stage  20  in the Y-axis direction, move the upper stage  10  in the Y-axis direction and the X-axis direction, and change the inclination of the upper stage  10 . The stage drive mechanism  60  includes a mechanism for floating the upper stage  10  from the Y table  2 , a mechanism for moving the upper stage  10  in the X-axis direction, a mechanism for moving the upper stage  10  in the Y-axis direction, and a mechanism for moving the lower stage  20  in the Y-axis direction. The control device  50  of the first embodiment measures the inclination angle of the X table  1 , and controls the inclination of the X table  1  so that the X table  1  becomes horizontal based on the measured inclination angle. 
     The control device  50  controls the inclination of the upper stage  10  with reference to the Y table  2  of the lower stage  20  cooled by the heat exchanger  27 . Specifically, the control device  50  measures the position of the upper stage  10  at a plurality of places with reference to the vertical surface  24  provided on the Y table  2 , and controls the inclination of the upper stage  10  on the basis of the measurement result. 
     The control device  50  measures the XY coordinates of the X table  1  of the upper stage  10  based on the laser beam reflected by the X mirror  3  and the Y mirror  4 . Then, the control device  50  controls the movement of the upper stage  10  and the lower stage  20  based on the XY coordinates of the X table  1  to move the sample placed on the upper stage  10  to a desired position. 
     Next, a hardware configuration of the control device  50  will be described with reference to  FIG.  3   . The control device  50  includes a processor  51 , a communication interface  52  (Hereinafter, the interface is abbreviated as an I/F), a main storage device  53 , an auxiliary storage device  54 , an input/output I/F  55 , and a bus  56  that communicably connects the above-described modules. 
     The processor  51  is a central processing unit that controls the operation of each unit of the stage apparatus  100 . The processor  51  is, for example, a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), or the like. The processor  51  develops the program stored in the auxiliary storage device  54  in a work area of the main storage device  53  in an executable manner. The main storage device  53  stores a program executed by the processor  51 , data processed by the processor, and the like. The main storage device  53  is a flash memory random access memory (RAM), a read only memory (ROM), or the like. The auxiliary storage device  54  stores various programs and various data. The auxiliary storage device  54  stores, for example, an operating system (OS), various programs, various tables, and the like. The auxiliary storage device  54  is a silicon disk including a nonvolatile semiconductor memory (flash memory, EPROM (Erasable Programmable ROM)), a solid state drive device, a hard disk (HDD, Hard Disk Drive) device, or the like. 
     The communication I/F  52  is an interface for communicably connecting the stage apparatus  100  to the outside via a network. The measurement result of the sensor  15  connected to the input/output I/F  55  and the measurement result of a distance measuring device  70  are input to the input/output I/F  55 . The distance measuring device  70  is a laser interferometer type distance measuring device, and irradiates the reflecting surfaces of the X mirror  3  and the Y mirror  4  with laser beam. The processor  51  calculates the inclination angle of the X table  1  based on the measurement result of the sensor  15 , and controls the stage drive mechanism  60  so that the X table  1  becomes horizontal based on the calculated inclination angle of the X table  1 . The processor  51  measures the XY coordinates of the X table  1  and the XY coordinates of the sample placed on the X table  1  based on the measurement result of the distance measuring device  70 . The input/output I/F  55  outputs a drive instruction to the stage drive mechanism  60  connected to the input/output I/F  55 . The stage drive mechanism  60  moves the lower stage  20  in the Y-axis direction, moves the upper stage  10  in the Y-axis direction and the X-axis direction, and changes the inclination angle of the upper stage  10  in accordance with a drive instruction from the control device  50 . 
     Effects of First Embodiment 
     The control device  50  can accurately level the upper stage  10  by controlling the inclination of the upper stage  10  with reference to the Y table  2  cooled by the heat exchanger  27 . In the first embodiment, since the movement of the Y table  2  in a direction other than the Y-axis direction is restricted by the guide rail.  5 , the Y table  2  is thermally expanded and curved in a mountain shape unless the Y table  2  is cooled. Even if the X table  1  is controlled to be horizontal with reference to the Y table  2  due to the curvature of the Y table  2  serving as a reference for calculating the inclination angle of the X table  1 , the X table  1  does not actually become horizontal. Therefore, in the first embodiment, by cooling the Y table  2 , the curvature of the Y table  2  as a reference can be suppressed, and the X table  1  can be controlled to be horizontal with high accuracy. As a result, it is possible to accurately maintain the XY plane, which is the XY coordinate of the sample, and the horizontal of the upper stage  10  in parallel. In a case where the height of the plane for measuring the position coordinates of the upper stage  10  and the height of the plane of the position coordinates of the sample coincide with each other, even if there is a slight angular deviation between both heights, an error in the coordinates can be reduced. However, if there is a difference between the heights, a coordinate error occurs by an amount proportional to a product of the height difference and the angular difference. In the first embodiment, by accurately leveling the upper stage  10 , the angular deviation is reduced, the above-described coordinate error is reduced, and the positioning accuracy of the sample is improved. 
     In the first embodiment, the cooling water used for cooling the X table  1  of the upper stage  10  is used for cooling the Y table  2  of the lower stage  20 , so that the two tables can be cooled with the common cooling water. 
     In the first embodiment, by floating the upper stage  10  from the lower stage  20  by magnetic force, it is possible to prevent the influence of the thermal expansion of the lower stage  20  from being directly transmitted to the upper stage  10 . 
     In the first embodiment, the inclination of the upper stage  10  can be calculated with a simple configuration by measuring the position of the upper stage  10  at a plurality of places with reference to the vertical surface  24  provided on the Y table  2  of the lower stage  20 . In the first embodiment, the inclination of the upper stage  10  can be calculated with a simple configuration by attaching the linear scale  25  to the vertical surface  24  and attaching the sensor  15  that reads the linear scale  25  to the vertical surface  14 . 
     In the first embodiment, the outgoing pipe  32  is disposed along the Y-axis direction, turned around, and then disposed along the Y-axis direction. By displacing the U-turned portion with the movement of the Y table  2  in the Y-axis direction, the refrigerant can be supplied to the Y table  2  even if the lower stage  20  moves. Similarly, the outgoing pipe  32  is disposed along the X-axis direction, turned around, and then disposed along the X-axis direction, and the U-turned portion is displaced along with the movement of the X table  1  in the X-axis direction, whereby the refrigerant can be supplied to the X table  1  even if the upper stage  10  moves. 
     In the first embodiment, the outgoing pipe  32  and the transition pipe  33  are connected to the surface  16  of the X table  1  perpendicular to the Y-axis direction, and the pipe  33  and the return pipe  34  are connected to the surface  28  of the Y table  2  perpendicular to the Y-axis direction. As described above, since the pipes can be connected to the vertical surfaces on the same side of the X table  1  and the Y table  2 , the pipes can be easily connected. The connection surface of the pipe may be appropriately selected in consideration of preventing vibration associated with circulation of the cooling water. 
     In the first embodiment, the heat exchanger  17  obtained by bending one pipe is provided inside the X table  1 , and the heat exchanger  27  obtained by bending one pipe is provided inside the Y table  2 , whereby the X table  1  and the Y table  2  can be efficiently cooled. 
     In the first embodiment, the lower stage  20  is a guide rail type, but may be a floating type stage. In a case where the lower stage  20  is a floating stage, there is no restriction of movement by the guide rail  5 , and thermal deformation associated therewith does not occur. However, thermal deformation may occur due to mixing of components of various materials in the configuration of the stage apparatus  100 . When materials having different linear expansion coefficients are connected, a curve is generated such that a part having a larger elongation due to a temperature rise is located outside a curvature radius and a part having a smaller elongation is located inside the curvature radius. Therefore, even if the lower stage  20  is a floating stage, it is possible to accurately level the X table  1  by suppressing the thermal expansion of the Y table  2  as a reference. 
     In the first embodiment, the single-stroke cooling water pipe  30  is configured to cool both the X table  1  and the Y table  2 , but each of the X table  1  and the Y table  2  may be cooled by branching the cooling water pipe  30 . The cooling water that has branched and cooled each table is returned to the joint pipe. In a portion where the pipes merge, flow vibration is likely to occur. The configuration of the single-stroke cooling water pipe  30  of the first embodiment has an effect of preventing vibration due to the flow of cooling water. When the pipe vibrates, the vibration is transmitted to the upper stage  10  and the lower stage  20 , but vibration prevention by eliminating the joint pipe leads to vibration prevention of the X table  1  and the Y table  2 . 
     It is also possible to provide independent cooling water pipes  30  in the upper stage  10  and the lower stage  20 . However, the upper stage  10  moves in the X-axis direction and also moves in the Y-axis direction following the lower stage  20 . Therefore, the cooling water pipe  30  of the upper stage  10  needs a U-shaped turn for following the movement of the lower stage  20  and a U-shaped turn for following the movement of the upper stage  10 . Since the lower stage  20  moves in the Y-axis direction, the cooling water pipe  30  of the lower stage  20  requires a U-shaped turn for following the lower stage  20 . That is, when the independent cooling water pipe  30  is provided in each of the upper stage  10  and the lower stage  20 , the overlapping cooling water pipe  30  is required. Therefore, the single-stroke cooling water pipe  30  has an effect of reducing the pipe amount. 
     In the single-stroke cooling water pipe  30 , when one of the X table  1  and the Y table  2  is cooled with the cooling water, the temperature of the cooling water increases by the amount of heat received therein, and the other cooling effect decreases. Therefore, in the single-stroke cooling water pipe  30 , the cooling effect becomes larger when the cooling water is supplied first. In the first embodiment, by first supplying the cooling water to the upper stage  10 , the X table  1  can be effectively cooled. 
     Second Embodiment 
       FIG.  4    is a cross-sectional view of a stage apparatus according to a second embodiment.  FIG.  4    is a cross-sectional view of the stage apparatus  100  according to the second embodiment taken along a plane perpendicular to the X axis. The same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and the description thereof will be omitted. In the second embodiment, as a configuration for cooling the Y table  2 , the heat exchanger  27  is not embedded inside the Y table  2 , but an external heat sink  128  is attached to the lower stage  20 . The heat sink  128  has a flow path  129  for allowing a refrigerant to flow therein. The heat sink  128  of the second embodiment may be a heat sink that does not allow the refrigerant to flow, or may have a plurality of fins so as to increase the surface area. 
     A stainless pipe may be embedded in the heat sink  128  to form the flow path  129 , or a base material of the heat sink  128  may be grooved and covered to form the flow path  129 . 
     In  FIG.  4   , the configuration of the upper stage  10  is described more specifically than in the first embodiment. The upper stage  10  includes the X table  1 , the X mirror  3  (see  FIG.  1   ) and the Y mirror  4  described in the first embodiment, a top table  6 , a chuck  7 , and a coil  8 . 
     The coil  8  of the Z motor is attached to the X table  1 . A yoke  9  paired with the Z motor is installed on the Y table  2 . The Z motor applies a force in the Z direction (=floating force) to the upper stage  10 , and includes the coil  8  through which a current flows and the yoke  9  made of a magnetic material. Since the Z motor may have a small movable range, the yoke  9  may be configured using a permanent magnet or a magnetic body such as iron that is not magnetic. When a permanent magnet is used, an attractive force and a repulsive force can be generated between the coil  8  and the yoke  9  of the magnet. However, when the yoke  9  made of a magnetic material not having magnetism is used, only attractive force is generated. Therefore, when the yoke  9  made of a magnetic material not having magnetism is used, the yoke  9  is disposed on the upper side and the coil  8  is disposed on the lower side. As a result, the coil.  8  floats to a desired height by controlling the balance between the downward force due to gravity applied to the coil  8  and the upward force due to the attractive force of the magnetic force. 
     The coils  8  are disposed at four corners of the X table  1 . The four coils  8  are independently controlled by the control device  50 . The control device  50  controls the flying height, the pitching angle, and the rolling angle of the upper stage  10 . Since the upper stage  10  moves greatly in the X-axis direction, the yoke  9  that is stationary with respect to the moving coil  8  needs to generate similar electromagnetic force at any position. If the yoke  9  is made of only a magnetic material and has a shape extending in the depth direction of the paper surface of  FIG.  4   , the relationship between the coil  8  and the yoke  9  is the same even if the upper stage  10  moves in the X-axis direction. Therefore, while there are four coils  8 , there are two yokes  9 . That is, two coils  8  correspond to one yoke  9 . The X table  1  includes a linear motor that applies thrust in the X-axis direction and a mechanism for following the movement of the lower stage  20  in the Y-axis direction, but the configuration thereof is omitted in  FIG.  4   . 
     In the second embodiment, the X mirror  3 , the Y mirror  4 , and the chuck  7  are installed on the top table  6 . The chuck  7  is for mounting a sample  80  such as a semiconductor wafer. Since it is difficult to directly measure the position of the sample  80  when the sample  80  is used, the positions of the reflecting surfaces of the X mirror  3  and the Y mirror  4  are measured to measure the XY coordinates of the sample  80 . Therefore, it is important to prevent the positional relationship between the X mirror  3  and the Y mirror  4  and the sample  80  from changing. Therefore, the chuck  7  is made of a material that is hardly thermally deformed, or the X mirror  3  and the Y mirror  4  are installed on the top table  6 . The top table  6  has an integral structure with the X table  1 , but has a structure in which columns are placed between the top table  6  and the X table  1  so as to reduce the influence of deformation generated in the X table  1  on the positions and angles of the X mirror  3  and the Y mirror  4 . The configuration of the upper stage  10  of the second embodiment is also applicable to the upper stage  10  of the first embodiment. 
     Effect of Second Embodiment 
     Since various components such as a mechanism for moving the lower stage  20  in the Y-axis direction are attached to the Y table  2 , the lower stage  20  has a complicated shape. By preparing the heat sink  128  separates from the lower stage  20  having such a complicated shape, it is possible to prevent the lower stage  20  from becoming complicated. The lower stage  20  is easily manufactured, and the manufacturing accuracy of the lower stage  20  is improved. 
     Other effects are the same as those of the first embodiment, and thus the description thereof will be omitted. 
     Third Embodiment 
       FIG.  5    is a configuration diagram of a charged particle beam apparatus according to a third embodiment. A charged particle beam apparatus  200  includes a stage apparatus  100  therein. The stage apparatus  100  inside the charged particle beam apparatus  200  is the stage apparatus  100  described in the first embodiment or the second embodiment. The charged particle beam apparatus  200  includes an electron microscope that applies an electron beam to the sample  80  such as a semiconductor wafer to be observed to enlarge an image. The electron microscope includes an electron optical system lens barrel  90 , the stage apparatus  100 , a sample chamber  40 , and a distance measuring device  70 . 
     The electron optical system lens barrel  90  has a charged particle source, and the sample  80  is irradiated with a beam emitted from the charged particle source. When the beam (electron beam) is applied to the sample  80 , the sample  80  is placed in a vacuum environment in order to avoid scattering due to gas molecules. Therefore, the sample chamber  40  has a function of a vacuum chamber. Although the cooling water pipe  30  is not illustrated in  FIG.  5   , the cooling water pipe  30  illustrated in  FIG.  1    is installed in the sample chamber  40 . The stage apparatus  100  moves the chuck  7  on which the sample  80  is mounted in the X-axis direction and the Y-axis direction.  FIG.  5    is a cross section taken along a plane perpendicular to the X-axis direction, and thus illustrates a cross section of the Y mirror  4 . The Y mirror  4  is a right vertical reflecting surface in the drawing, and the distance measuring device  70  irradiates the reflecting surface with a laser beam  71  to measure the Y coordinate of the Y mirror  4 . The distance measuring device  70  is a laser interferometer type distance measuring device. The distance measuring device  70  is fixed to the sample chamber  40 . Although not illustrated in  FIG.  5   , the X mirror  3  and the distance measuring device  70  that irradiates the reflecting surface of the X mirror  3  with laser beam and measures the X coordinate of the X mirror  3  are provided at a position rotated by 90°. The XY coordinates of the sample  80  placed on the stage apparatus  100  are calculated based on the Y coordinate of the Y mirror  4  and the X coordinate of the X mirror  3 . 
     The electron optical system lens barrel  90  is fixed to the sample chamber  40 . Since observing the sample with the electron microscope is observation at a high magnification, the distance between the electron microscope and the sample  80  cannot be increased. Therefore, the distance between the electron optical system lens barrel  90  and the sample  80  is small. On the other hand, the X mirror  3  and the Y mirror  4  on the upper stage  10  may come directly below the electron optical system lens barrel  90  along with the operation of the upper stage  10 . In order to prevent contact with the X mirror  3  and the Y mirror  4  in the electron optical system lens barrel  90 , the uppermost portions of the X mirror  3  and the Y mirror  4  needs to be lower than the lowermost portion of the electron optical system lens barrel  90 . Therefore, the uppermost portions of the X mirror  3  and the Y mirror  4  cannot be made significantly higher than the sample  80 . The reflecting surfaces of the X mirror  3  and the Y mirror  4  are not usable up to the uppermost part of the vertical surface, and the perpendicularity is secured up to a portion slightly away from the ridge line which forms the corner. For this reason, the laser beam  71  emitted by the distance measuring device  70  of the laser interferometer type has to be positioned lower than the upper surface of the sample  80 . As a result, the height of the plane of the XY coordinates where the position of the upper stage  10  is measured (the height of the laser beam  71 ) becomes lower than the upper surface of the sample  80 . What the stage apparatus  100  wants to position is the position irradiated with the electron beam on the upper surface of the sample  80 , and is the XY coordinates on the upper surface of the sample  80 . 
     One of the principles of distance measurement is the Abbe principle, and when distance measurement is performed on parallel lines, an error increases as compared with distance measurement performed on an extension line of two points to be measured. Measuring the XY coordinates of the upper stage  10  on a plane having a height deviated from the upper surface of the sample  80  is similar to the condition in which the error indicated by the Abbe principle increases. It is explained that the factor of the error expansion indicated by the Abbe principle is that the measurement target and the axis of the actual measurement point are not completely parallel. Therefore, when both are brought close to perfect parallel, the measurement error also decreases. When this principle is used, it is considered that positioning accuracy of the sample is improved if the upper stage  10  can be brought close to perfect horizontal. 
     In order to keep the floating upper stage  10  horizontal, it is necessary to grasp the inclination angle of the upper stage  10  and control the upper stage  10  to be horizontal based on the inclination angle. As the actuator for control, Z motors (coils  8 ) installed at the four corners of the upper stage  10  can be used. Regarding the measurement of the inclination angle of the upper stage  10 , when the method used in the description of the first embodiment is used, simple and accurate measurement can be performed. As a result, when the measurement accuracy of the inclination angle of the upper stage  10  is improved, the accuracy of the control for keeping the upper stage  10  horizontal is improved, and the positioning accuracy of the sample is improved. 
     Effect of Third Embodiment 
     Since the effect of the charged particle beam apparatus  200  of a third embodiment is similar to that of the first embodiment, the description thereof will be omitted. 
     The present invention is not limited to the above embodiments, and various modifications may be contained. The above-described embodiments have been described in detail for clear understating of the present invention, and are not necessarily limited to those having all the described configurations. Some of the configurations of a certain embodiment may be replaced with the configurations of the other embodiments, and the configurations of the other embodiments may also be added to the configurations of the subject embodiment. For some of the configurations of each embodiment, other configurations may be added omitted, or replaced. 
     In the first embodiment, both the X table  1  and the Y table  2  are cooled, but only the Y table  2  may be cooled. In the first embodiment, the cooling is performed in the order of the X table  1  and the Y table  2 , but the cooling may be performed in the order of the Y table  2  and the X table  1 . 
     The floating upper stage  10  of the first to third embodiments may be of a type including an electromagnet that applies buoyancy to the upper stage  10  and a linear motor that applies thrust in a uniaxial direction, or may be of a type including a shaft motor that has both functions of floating and propulsion as one. 
     The upper stage  10  of the first to third embodiments is a magnetic floating type that floats using electromagnetic force, but may be an air bearing type that floats using pressure of gas.