Abstract:
The present invention provides a stage apparatus capable of reducing a positioning time without increasing a positional deviation. A positioning control method of a sample stage apparatus includes: a high-speed movement step of moving a table to a high-speed movement target position at a first movement speed; a positional deviation correcting step of moving the table to a low-speed positioning step start position at a second movement speed that is lower than the first movement speed; a low-speed positioning step of moving the table to a target position at a third movement speed that is lower than the second movement speed. After the low-speed positioning step is completed, a rod connected to a motor returns to its original position to separate a pin of the rod side from a concave portion of the table side.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a sample stage that holds a sample, and more particularly, to a positioning technique of a sample stage apparatus including X and Y tables. 
         [0003]    2. Description of the Related Art 
         [0004]    Precision machines and test apparatuses use sample stages that hold samples. The sample stage requires high-speed movement and high-accuracy positioning. An example of an apparatus using the sample stage is an electron microscope. 
         [0005]    Japanese Patent Application Laid-Open (JP-A) No. 2007-80660 (corresponding to U.S. Pat. No. 7,435,974) discloses a stage that has a driving mechanism including a stepping motor and a feed screw and performs open-loop control to achieve high-speed and high-accuracy positioning. In the driving mechanism, a gap is provided in a connection portion between a table of the stage and the feed screw in order to prevent the movement of the stage due to the thermal expansion of the feed screw. In this way, the feed screw and the table are mechanically connected to or separated from each other. 
         [0006]    As a positioning control method of correcting a positional deviation, the following method has been proposed: a method of dividing the movement of a table into two steps and performs two processes, that is, a high-speed movement process and a low-speed movement process. The low-speed movement process stops the driving of the table at a designated position while monitoring the position of the stage using a position detector. In this way, it is possible to correct the positional deviation and achieve high-accuracy positioning. 
         [0007]    However, in the stage positioning control disclosed in JP-A No. 2007-80660, after the high-speed movement process is performed, the table is moved by inertial force due to the gap formed in the stage connection portion, and a positional deviation occurs. The positional deviation occurring after the high-speed movement process is affected by the movement conditions of the table(for example, the inertia, the movement distance, and the movement speed of the table) or brake force. Therefore, in the case of an apparatus including a plurality of tables with different axes, the positional deviations of the tables are different from each other, and a difference in positional deviation occurs whenever the tables are moved. 
         [0008]    That is, during the low-speed movement process performed after the high-speed movement process, a movement distance varies all the time. Therefore, the following two problems arise. (1) In the case of a stage apparatus including a plurality of tables with different axes, although the positioning of one of the tables is completed, the positioning of the other table is not completed yet, which results in a waste time for positioning. (2) A plurality of tables with different axes are not completely positioned at the same time. Therefore, when one of the tables is moved and the positioning of the other table is completed, a positional deviation occurs in the other table that has been completely positioned due to the inertia of the one table being moved. 
         [0009]    The waste time for positioning and the positional deviation may further increase due to an increase in the speed of the table and an increase in inertia as growing the size of the table. 
       SUMMARY OF THE INVENTION 
       [0010]    An object of the present invention is to provide a stage apparatus capable of reducing a waste time for positioning, which occurs when a positional deviation increase, and performing high-accuracy positioning. 
         [0011]    According to the present invention, a positioning control method of a sample stage apparatus includes: a high-speed movement process of moving a table to a high-speed movement target position at a first movement speed; a positional deviation correcting process of moving the table to a low-speed positioning step start position at a second movement speed that is lower than the first movement speed; a low-speed positioning step of moving the table to a target position at a third movement speed that is lower than the second movement speed. After the low-speed positioning process is completed, a rod connected to a motor returns to its original position to separate a pin of the rod from a concave portion of the table side. 
         [0012]    According to the present invention, it is possible to reduce a waste time for positioning, which occurs when a positional deviation increases, and perform high-accuracy positioning. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a diagram illustrating an example of the structure of a sample stage apparatus according to the present invention; 
           [0014]      FIG. 1B  is a diagram illustrating the structure of a connection portion between an X rod and an X table in the sample stage apparatus according to the present invention; 
           [0015]      FIGS. 2A ,  2 B, and  2 C are diagrams illustrating the operation of the X rod moving the X table in the sample stage apparatus according to the present invention; 
           [0016]      FIG. 3  is a diagram illustrating an example of a positioning control mechanism of the sample stage apparatus according to the present invention; 
           [0017]      FIG. 4  is a flowchart illustrating an example of a positioning control method of the sample stage apparatus according to the present invention; and 
           [0018]      FIG. 5  is a diagram illustrating the relationship between brake force and the deviation between a target position and a current position in the positioning control method of the sample stage apparatus according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Hereinafter, a positioning control technique of a sample stage apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 
         [0020]      FIG. 1A  is a diagram illustrating an example of the sample stage apparatus according to the present invention. A sample stage apparatus  101  includes X and Y tables that are driven by stepping motors. The sample stage apparatus  101  includes a base  102 , an X table  103 , and a Y table  104 . The X table  103  can be moved in an X direction by an X-direction guide mechanism  105 , and the Y table  104  can be moved in a Y direction by a Y-direction guide mechanism  106 . The X table  103  and the Y table  104  are independently moved. 
         [0021]    A driving mechanism of the X table  103  includes an X ball screw  107 , an X rod  108 , and a stepping motor  113 . When the X ball screw  107  is rotated by the stepping motor  113 , the X rod  108  is moved in a straight line to press the X table  103  in the X direction. Similarly, a driving mechanism of the Y table  104  includes a Y ball screw  109 , a Y rod  110 , and a stepping motor  113 . When the Y ball screw  109  is rotated by the stepping motor  113 , the Y rod  110  is moved in a straight line to press the Y table  104  in the Y direction. 
         [0022]    Active brakes  114  are attached to the X table  103  and the Y table  104  respectively. A piezoelectric element is provided in each of the active brakes  114 . It is possible to control brake force by adjusting a voltage applied to the piezoelectric element. 
         [0023]    When the table is moved at a relatively high speed, the inertial force thereof is relatively large. Therefore, even when the stepping motor  113  stops and the active brake  114  is turned on, the table does not stop immediately, but stops after it is moved a predetermined distance. On the other hand, when the table is moved at a relatively low speed, the inertial force thereof is relatively small. Therefore, immediately after the stepping motor  113  stops and the active brake  114  is turned on, the table stops. 
         [0024]    In this embodiment, only the active brake  114  attached to the X table  103  is shown, but the active brake  114  attached to the Y table  104  is not shown. 
         [0025]    A sample holder  115  is mounted on the Y table  104 , and a sample  116  is fixed to the sample holder  115 . In this embodiment, the sample  116  is a semiconductor wafer. The sample stage apparatus according to the present invention can be used for an electron microscope. However, the sample stage apparatus may be used for precision machines other than the electron microscope. 
         [0026]    The structure of a connection portion  120  between the X rod  108  and the X table  103  will be described with reference to  FIG. 1B . A pin  111  is attached to the leading end of the X rod  108 . A concave portion  121  is provided in the X table  103 . The pin  111  of the X rod  108  is inserted into the concave portion  121  of the X table  103 . The outside diameter of the pin  111  is referred to as d, and the inside diameter of the concave portion  121  is referred to as D. In this embodiment, the following relationship is established: D−d=50 μm. Therefore, the distance between the outer surface of the pin  111  and the inner surface of the concave portion  121 , that is, a gap therebetween is 25 μm. 
         [0027]    The operation of the X rod  108  moving the X table  103  will be described with reference to  FIGS. 2A ,  2 B, and  2 C. As shown in  FIG. 2A , both the X rod  108  and the X table  103  are moved in a direction that is represented by an arrow. In this case, the pin  111  comes into contact with a front inner surface  121 A of the concave portion  121  of the X table  103 . It is assumed that the stepping motor  113  stops, and the X rod  108  stops in the state shown in  FIG. 2A . When the table is moved at a relatively high speed, the inertial force thereof is relatively large. Therefore, even when the X rod  108  stops and the active brake  114  is turned on, the table does not stop immediately. As shown in  FIG. 2B , the X table  103  stops after it is moved a predetermined distance. Therefore, the pin  111  is separated from the front inner surface  121 A of the concave portion  121  of the X table  103 . 
         [0028]    On the other hand, when the table is moved at a relatively low speed, the inertial force thereof is relatively small. Therefore, immediately after the X rod  108  stops and the active brake  114  is turned on, the table stops. As shown in  FIG. 2A , the pin  111  comes into contact with the front inner surface  121 A of the concave portion  121  of the X table  103 . Then, the X rod  108  is moved in the opposite direction. As shown in  FIG. 2C , the pin  111  is separated from the front inner surface  121 A of the concave portion  121  of the X table  103 . Since the X rod  108  and the X table  103  are separated from each other, the thermal deformation and vibration of the screw  107  are not transmitted from the X rod  108  to the X table  103 . 
         [0029]    According to the present invention, the position of the table is determined by three processes, that is, a high-speed movement process, a positional deviation correcting process, and a low-speed positioning process. During the final low-speed positioning process, the movement speed of the table is sufficiently low, and the inertial force thereof is sufficiently small. When the stepping motor  113  stops, the table stops immediately by the operation of the active brake  114 . Therefore, as shown in  FIG. 2A , when the table stops, the pin  111  comes into contact with the front inner surface  121 A of the concave portion  121  of the X table  103 . Then, the X rod  108  is moved in the opposite direction. In this way, as shown in  FIG. 2C , the pin  111  is separated from the front inner surface  121 A of the concave portion  121  of the X table  103 . In this case, the gap between the pin  111  and each of the inner surfaces  121 A and  121 B of the concave portion  121  is 25 μm. 
         [0030]    In this embodiment, the connection portion between the X rod  108  and the X table  103  has been described above. A connection portion between the Y rod  110  and the Y table  104  has the same structure as the connection portion. 
         [0031]    An example of the positioning control mechanism of the sample stage apparatus according to the present invention will be described with reference to  FIG. 3 . The sample stage apparatus  101  includes the base  102 , the X table  103 , and the Y table  104 . The X rod  108  is connected to the X table  103  through the connection portion  120 . The X rod  108  is driven by the stepping motor  113 . 
         [0032]    According to this embodiment of the present invention, the positioning control mechanism includes a bar mirror  201 , a laser interferometer  202 , and a control device  203 . The laser interferometer  202  radiates laser light to the bar mirror  201  and detects light reflected from the bar mirror  201  to measure a distance. The control device  203  controls the stepping motor  113  and the active brake  114  on the basis of the distance obtained by the laser interferometer  202 , that is, the current position, to control the position of the X table  103 . A voltage that is applied to the piezoelectric element provided in the active brake  114  may be adjusted in order to control the brake force of the active brake  114 . 
         [0033]    In this embodiment, the position control of the X table  103  has been described. The position control of the Y table  104  is the same as that of the X table. In this embodiment, the bar mirror  201  and the laser interferometer  202  are used to measure the position of the X table  103 . However, other position measuring devices may be used. 
         [0034]    An example of a method of controlling the position of the table in the sample stage apparatus according to the present invention will be described with reference to  FIG. 4 . According to the present invention, three processes, that is, the high-speed movement process, the positional deviation correcting process, and the low-speed positioning process are performed to position the table. In Step S 301 , a target position, a high-speed movement target position, and a low-speed positioning process start position are set. The target position means the coordinates of the final position of the table. The target position may be registered in advance, or an operator may manually input the target position by designating the target position with a cursor. 
         [0035]    The high-speed movement target position means the position of the table by the high-speed movement process, and is disposed a predetermined offset from the target position. The offset of the high-speed movement target position is equal to or greater than the difference between the inside diameter D of the concave portion  121  and the outside diameter d of the pin  111 , that is, D−d=50 μm. In this embodiment, the offset of the high-speed movement target position is set to 100 μm in order to prevent the table from being moved by inertial force to reach the target position when the high-speed movement process is completed and the stepping motor  113  stops. 
         [0036]    The low-speed positioning process starts at the low-speed positioning process start position. The low-speed positioning process start position is set between the target position and the high-speed movement target position. In this embodiment, the low-speed positioning process start position is set a predetermined offset from the target position. The offset of the low-speed positioning process start position is 30 μm. In the table positioning control according to this embodiment, even when the table is moved along only one axis, the high-speed movement target position and the low-speed positioning process start position are set. Therefore, it is necessary to move both the X table  103  and the Y table  104  all the time. 
         [0037]    Steps S 302  to S 305  correspond to the high-speed movement process. In Step S 302 , the control device  203  controls the laser interferometer  202  to detect the current position of the sample stage apparatus  101 . Then, the control device calculates the distance from the current position to the high-speed movement target position. Then, the control device calculates a movement amount in the high-speed movement process on the basis of the calculated distance. Then, the control device transmits the number of pulses corresponding to the movement amount to the stepping motor  113 . In this way, the X table  103  is moved at a high speed. The movement speed of the X table  103  during the high-speed movement process is 250 mm/s. 
         [0038]    Then, in Step S 303 , the stepping motor  113  stops. During the high-speed movement process, the movement speeds of the X and Y tables are relatively high. Therefore, even when the stepping motor  113  stops, the X and Y tables do not stop immediately. As shown in  FIG. 2B , the X and Y tables are moved in the range of the gap between the pin  111  and the concave portion  121 . The active brake is turned on at the same time as the stepping motor  113  stops. In this case, the brake force is about  15  N and is constant. In this embodiment, the brake force does not reach its maximum value immediately even after the active brake is turned on. The reasons are as two follows: (1) it is necessary to prevent the deformation of the stage when the brake force is rapidly generated; and (2) it is necessary to prevent an increase in the abrasion of a brake part when a load is suddenly applied to the brake part. Therefore, in this embodiment of the present invention, immediately after the high-speed movement process is completed, the active brake is turned on to generate a brake force of 15 N. During the positional deviation correcting process (Steps S 306  to S 309 ), the brake force is gradually increased. During the low-speed positioning process, the maximum brake force (30 N) is generated. 
         [0039]    Then, in Step S 304 , the control device  203  controls the laser interferometer  202  to detect the current position of the X table  103 . In addition, the control device calculates the deviation between the target position and the current position of the X table  103 . Then, the control device determines whether the deviation is equal to or greater than 30 μm. That is, the control device determines whether the X table  103  reaches the low-speed positioning process start position. When the deviation is 30 μm or more, that is, when the X table does not reach the low-speed positioning process start position, the control device ends the high-speed movement process of the X table  103 . When the deviation is less than 30 μm, that is, when the X table  103  passes the low-speed positioning process start position, the control device returns the X table  103  to its original position, and performs the high-speed movement process again. When the X table  103  is too close to the target position, it is difficult to perform the next positional deviation correcting process. 
         [0040]    Then, in Step S 305 , the control device determines whether the high-speed movement process is completely performed on the X table  103  and the Y table  104 . When it is determined that the high-speed movement process is completely performed on the X table  103  and the Y table  104 , the control device proceeds to the positional deviation correcting process. 
         [0041]    Steps S 306  to S 309  correspond to the positional deviation correcting process. In Step S 306 , the control device  203  moves the X table. During the positional deviation correcting process, the movement speed of the X table is 10 mm/s. During the positional deviation correcting process, the movement speeds of the X and Y tables are relatively low. Therefore, immediately after the stepping motors  113  stop, the X and Y tables stop. In this embodiment, the control device  203  starts to control the laser interferometer  202  to monitor the current position of the X table  103  at the same time as starting to move the X table. 
         [0042]    The control device  203  increases the voltage applied to the active brake  114  at the same time as starting to move the X table. That is, the control device increases the brake force. The control device  203  calculates the deviation between the target position and the current position of the X table, and adjusts the voltage applied to the active brake  114  on the basis of the calculated deviation. When the X table reaches the low-speed positioning process start position, the control device increases the brake force to a maximum value. The maximum value of the brake force is 30 N. 
         [0043]    Then, in Step S 307 , the control device  203  measures the current position of the X table, and determines whether the X table reaches the low-speed positioning process start position. When the X table reaches the low-speed positioning process start position, the control device proceeds to Step S 308 . When the X table does not reach the low-speed positioning process start position, the control device returns to Step S 306  to continuously move the X table. 
         [0044]    Then, in Step S 308 , the control device stops the stepping motor  113  to stop the movement of the X table. The movement speed of the X table is sufficiently low, and the brake force is the maximum. Therefore, immediately after the stepping motor  113  stops, the X table stops. 
         [0045]    Then, in Step S 309 , the control device determines whether the positional deviation correcting process is completely performed on the X table  103  and the Y table  104 . When the positional deviation correcting process is completely performed on the X table  103  and the Y table  104 , the control device proceeds to the low-speed positioning process. 
         [0046]    Steps S 310  and S 311  correspond to the low-speed positioning process. In Step S 310 , the control device  203  moves the X table  103  and the Y table  104 . The movement speeds of the both tables are  1  mm/s. The control device  203  starts to control the laser interferometer  202  to monitor the current position of the X table  103  at the same time as starting to move the X table. 
         [0047]    According to this embodiment, the movement start time of the X table  103  and the Y table  104  is set such that the X table  103  and the Y table  104  simultaneously reach the target position. The control device  203  measures the current positions of the X table  103  and the Y table  104 , and calculates the deviations between the target position and the current positions. The control device sets the movement start time of the X table  103  and the Y table  104  on the basis of the calculated deviations. 
         [0048]    Then, in Step S 311 , the control device  203  measures the current positions of the X table  103  and the Y table  104 , and determines whether the X table  103  and the Y table  104  reach the target position. When the X table  103  and the Y table  104  reach the target position, the control device stops the stepping motor  113 . When the X table  103  and the Y table  104  do not reach the target position, the control device returns to Step S 310  to continuously move the X table  103  and the Y table  104 . 
         [0049]    During the low-speed positioning process, the movement speeds of the X and Y tables are sufficiently low, and the maximum brake force is obtained. Therefore, immediately after the stepping motors  113  stop, the X and Y tables stop. 
         [0050]    Then, in Step S 312 , the ball screws  107  and  109  arranged in the X and Y directions are moved in the directions that are opposite to the movement directions of the X and Y tables, respectively. Then, as shown in  FIG. 2C , the pins  111  of the X rod  108  and the Y rod  110  are separated from the inner surfaces of the concave portions  121  of the X table  103  and the Y table  104 , respectively. In this way, positioning is completed. 
         [0051]    Next, the brake force generated by the active brake  114  in the method of controlling the position of the table according to the present invention will be described with reference to  FIG. 5 . In a graph shown in  FIG. 5 , the horizontal axis indicates the deviation between the target position and the current position of each table, and the vertical axis indicates the brake force. In the final step of the high-speed movement process, when the stepping motor  113  stops and the active brake is turned on, a brake force of 15 N is obtained. Then, during the positional deviation correcting process, the control device increases the brake force while moving the table. When the positional deviation correcting process starts, the brake force is 15 N. However, when the positional deviation correcting process ends, the brake force is 30 N, that is, the maximum value. During the final low-speed positioning process, the brake force is 30 N. 
         [0052]    Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment. It will be understood by those skilled in the art that various modifications and changes of the present invention can be made without departing from the scope of the present invention described in the appended claims. 
       DESCRIPTION OF THE REFERENCE NUMERALS  
       [0000]    
       
           101 : sample stage apparatus 
           102 : base 
           103 : X table 
           104 : Y table 
           105 : X-direction guide mechanism 
           106 : Y-direction guide mechanism 
           107 : X ball screw 
           108 : X rod 
           109 : Y ball screw 
           110 : Y rod 
           111 : pin 
           112 : gap 
           113 : stepping motor 
           114 : active brake 
           115 : sample holder 
           116 : sample wafer 
           120 : connection portion 
           121 : concave portion 
           201 : bar mirror 
           202 : laser interferometer 
           203 : control device