JP5520491B2 - Sample stage device - Google Patents

Description

  The present invention relates to a sample stage for holding a sample, and more particularly to a sample stage device that enables reduction in stage movement after completion of positioning in a sample stage device including an XY table.

  In precision processing equipment and inspection equipment, a sample stage for holding a sample is used. In such a sample stage, high-speed positioning is required simultaneously with high-speed movement, and the stage position is required to be maintained after the positioning is completed. An example of an apparatus using such a sample stage is an electron microscope.

  The stage described in Patent Document 1 includes a drive mechanism using a stepping motor and a feed screw, and a guide mechanism that guides the trajectory of the stage movement, and achieves high-speed and high-precision position determination by open loop control. . In this drive mechanism, the factors that cause the stage to move after completion of positioning are (1) stage movement due to thermal expansion of the feed screw (hereinafter referred to as thermal drift), and (2) reaction force that pushes back the stage inside the guide mechanism. (Hereinafter referred to as residual reaction force), there is stage movement (hereinafter referred to as guide residual reaction force drift) after the stage stops due to this residual reaction force.

  In the stage described in Patent Document 1, in order to avoid the thermal drift of (1), a gap is provided at the joint between the stage table and the feed screw. As a result, the feed screw and the table are mechanically coupled and separated, and thermal drift can be prevented since the feed screw does not contact the stage after the positioning is completed. In order to avoid the guide residual reaction force drift of (2), when moving to the target position, after overtaking the target position once in the high speed movement, the guide drift is performed by performing the low speed positioning movement in the return direction. We are trying to reduce it. By performing low-speed positioning movement in the return direction, sliding resistance is generated in the opposite direction to the residual reaction force of the guide generated after the high-speed movement, thereby reducing the residual reaction force.

JP 2004-134155 A

  However, in the stage positioning control described in Patent Document 1, it is possible to reduce the residual reaction force inside the guide mechanism after the stage positioning is completed, but the residual reaction force is always set to zero because it changes depending on the movement condition. It ’s difficult.

  A stage apparatus for reducing the residual reaction force regardless of the stage moving condition will be described below. In addition, a stage apparatus that aims to reduce stage drift caused by the guide mechanism by increasing the straightness of the guide mechanism will be described.

  As one aspect for achieving the above object, a sample stage device is proposed that controls the overtaking amount in accordance with the speed of the stage that determines the residual reaction force. As an example, the overtaking amount is set so as to increase as the moving speed of the stage increases. According to such a configuration, it is possible to reduce the residual reaction force that changes depending on the moving speed of the stage and the like. In addition, it is a pressing mechanism that presses the guide mechanism from the side, and is rotatably fixed to a support member that supports the guide mechanism. The rotation presses the guide mechanism and is different from the rotation center of the rotation. A sample stage device having a circular pressing portion having a center position is proposed. According to such a configuration, the pressing force can be controlled by torque management of the pressing mechanism.

  According to the above configuration, the stage can be stopped appropriately in accordance with the residual reaction force regardless of changes in the stage moving speed or the like. In addition, it is possible to reduce stage drift by improving the linearity of the guide mechanism.

The schematic block diagram of a sample stage apparatus. The figure explaining an example of the positioning control mechanism of a sample stage apparatus. The figure explaining the structure of an eccentric pin and an X guide mechanism. The flowchart explaining the positioning process of a sample stage apparatus. The figure explaining the relationship between the drive speed of a sample stage, and the sliding resistance concerning a sample stage. The figure explaining the relationship between another drive speed of a sample stage apparatus, and the sliding resistance concerning a sample stage. The flowchart explaining another positioning process by a sample stage apparatus.

  Hereinafter, the stage configuration for reducing the residual reaction force of the stage and the drift due to the nonlinearity of the guide mechanism (guide mechanism) will be described. In general, a stage using a guide mechanism includes a drift due to guide distortion (hereinafter referred to as guide distortion drift) in addition to a guide residual reaction force drift. The cause of this guide strain drift is the presence of strain that occurs when machining the guide rail and strain that occurs when the guide is assembled to the stage. Since the stopped stage receives a force from the guide distortion, if the guide strain drift moves in a direction beyond the distortion peak, the stage moves in the direction before the stop and stops in front of the distortion peak. The stage moves in the direction opposite to the direction of movement before stopping.

  For the above reasons, the guide used for the stage has a guide residual reaction force drift that generates a drift in the direction opposite to the movement direction before the stage is stopped, and a guide strain drift in which the drift direction changes depending on the stage stop position. Therefore, the force that generates stage drift is not constant. Therefore, after the stage has been positioned, the brake for holding the stage position requires a braking force having a holding force with respect to the maximum value of the force that generates the guide residual reaction force drift and the guide distortion drift.

  Increasing the braking force increases the force that holds the stage position and reduces stage drift, but the following adverse effects occur depending on the type of brake mounted on the stage.

  In a stage equipped with a passive brake, the brake and the brake rail always rub, so the frictional heat increases as the braking force increases. Therefore, the amount of thermal deformation of the brake rail that generates frictional heat increases, and the amount of stage drift accompanying thermal deformation also increases. Also, in a stage equipped with an active brake equipped with an actuator, a position shift occurs because the posture of the stage changes due to the pressure of the brake immediately after the brake is turned on. This positional deviation increases as the braking force increases, and the positioning accuracy decreases.

  Below, after the stage positioning is completed, the residual reaction force that causes the guide drift is always set to a value close to zero, and the stage device that reduces the residual reaction force drift of the guide and the distortion of the guide are reduced mechanically. A stage device that reduces the stage drift caused by the guide without increasing the braking force by reducing the guide distortion drift will be described.

  Hereinafter, as a configuration for achieving the above-described object, when the stage moves to the target position, after the target position is once overtaken, low-speed positioning movement is performed. A stage apparatus that reduces the residual reaction force generated in the guide by calculating the optimum overtaking amount according to the stage moving speed condition at that time will be described. According to such a configuration, the residual reaction force of the guide can always be a value close to 0 regardless of the stage moving condition. As a result, the stage drift due to the guide can be reduced without increasing the braking force.

  In addition, a stage device is described in which stress is applied by an eccentric pin attached to the side surface of the guide and the straightness of the guide is improved. According to the said structure, it becomes possible by pushing the side surface of a guide to improve the straightness of a guide and to reduce a guide distortion drift.

  Hereinafter, the drift reduction technology of the sample stage apparatus will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a sample stage apparatus. The sample stage 101 of this example has an XY table by a linear motor drive method. The sample stage 101 includes a base 102, an X table 103, and a Y table 104. The X table 103 can be moved in the X direction by the X direction guide mechanism 105, and the Y table 104 can be moved in the Y direction by the Y direction guide mechanism 106. The X table 103 and the Y table 104 move independently of each other.

  The side surfaces of the X direction guide mechanism 105 and the Y direction guide mechanism 106 are pressed by an eccentric pin 107.

  An X linear motor 108 is provided as a drive mechanism for the X table 103. Similarly, a Y linear motor 109 is provided as a drive mechanism for the Y table 104. The linear motor controls the stage position, stage speed, and stage acceleration by servo control. After the positioning is completed, the servo control is turned off to prevent the vibration of the linear motor from being transmitted to the stage.

  An active brake 110 is attached to each of the X table 103 and the Y table 104. The active brake 110 incorporates a piezoelectric element, and the braking force can be adjusted by adjusting the voltage applied to the piezoelectric element. There is no problem even if the brake is always a friction brake, that is, a passive brake.

  Here, only the active brake 110 attached to the X table 103 is shown, and the active brake 110 attached to the Y table 104 is not shown.

  An electrostatic chuck 111 is mounted on the Y table 104, and a sample 112 is fixed to the electrostatic chuck 111. In this example, the sample 112 is a semiconductor wafer. The sample stage device described in this embodiment can be used for an electron microscope, but can be used for precision instruments other than the electron microscope.

  With reference to FIG. 2, the example of the positioning control structure of the X table 103 in the stage apparatus of a present Example is demonstrated. According to this example, the positioning control configuration includes a bar mirror 201, a laser beam transmitter 202, a laser interferometer 203, a laser beam receiver 204, and a control device 205. The laser interferometer 203 irradiates the bar mirror 201 with the laser light and sends the reflected light from the bar mirror 201 to the laser light receiver 204. The control device 205 measures the position of the stage with the laser light taken from the laser light receiver. Based on the position measurement, the X linear motor 108 is controlled. The control of the linear motor is feedback control of the stage position, stage speed, and stage acceleration. The control device 303 controls the active brake 114 based on the stage position, and controls the position of the X table 103. In order to control the braking force of the active brake 114, the voltage applied to the piezoelectric element incorporated in the active brake 114 may be adjusted.

  Although the position control of the X table 103 has been described here, the position control of the Y table 104 is the same. In this example, the position of the X table 103 is measured using the bar mirror 201, the laser beam transmitter 202, the laser interferometer 203, and the laser beam receiver 204, but other position measurement devices may be used.

  Next, the eccentric pin of the present embodiment will be described with reference to FIG. FIG. 3 is a diagram illustrating the configuration of the X-direction guide mechanism 105, the eccentric pin 107, and the base 102 (support member). An X guide mechanism attachment guide surface 301 for attaching the X direction guide mechanism 105 is processed on the base 102, and the X direction guide mechanism 105 is pressed against the X guide mechanism attachment guide surface 301 by the eccentric pin 107. When the eccentric pin 107 is pressed, a groove is formed in the head portion of the eccentric pin, and a minus screwdriver or a dedicated tool is inserted into the groove and rotated. At this time, by performing torque management, the pressure from the eccentric pin to the X-direction guide mechanism is kept constant (or within a predetermined range), and the straightness of the guide mechanism in each direction is improved.

  The X-direction guide mechanism 105 is pressed by an eccentric pin 107 from a direction perpendicular to the guide direction of the stage. The eccentric pin 107 is configured to have a circular pressing portion (the upper end of the eccentric pin 107) having a center position at a position different from the rotational axis center of the eccentric pin 107. That is, when the eccentric portion 107 rotates, the pressing portion presses the side of the guide mechanism or rotates in the opposite direction, so that the pressing portion is separated from the guide mechanism.

  In the stage mechanism of this embodiment, in order to prevent the X-direction guide mechanism 105 from being deformed, the eccentric pin is idled when excessive torque is applied. The distance between the mounting hole center of the X direction guide mechanism 105 and the mounting hole center of the eccentric pin 107 is D, the distance L between the mounting hole center of the X direction guide mechanism 105 and the guide surface, and the maximum eccentric radius Rmax of the eccentric pin 107. The stage described in the patent is designed so that (L + Rmax) −D = 0.1 mm to 0.15 mm. The gap between the eccentric pin 107 and the eccentric pin insertion hole 302 is about 30 μm. Furthermore, the base 102 is made of a material with low rigidity (for example, aluminum), and the rail portion of the X-direction guide mechanism and the eccentric pin are made of a material with high rigidity (for example, stainless steel), thereby making the eccentric pin 2Nm. When rotating with the above torque, the eccentric pin insertion hole formed in the base is deformed, and the eccentric pin is idle. When the torque is about 2 Nm, the X-direction guide mechanism made of SUS is not deformed and the linearity is maintained.

  Next, a sample stage positioning control method according to this embodiment will be described with reference to FIGS. The positioning of the sample stage includes a high-speed movement process (first movement process) that moves to a temporary target position (hereinafter referred to as a temporary target position) obtained by adding an overtaking amount to the target position, and a low-speed positioning process (second process). The table is positioned in two steps (moving step).

  According to the flowchart shown in FIG. 4, steps S401 to S405 are high-speed movement processes. First, in step S401, a target position for positioning the sample stage is set. The target position is the coordinates of the position that the stage should finally reach. The target position may be registered in advance, but may be set by manual input by an operator, designation by a cursor, or the like.

  Next, in step S <b> 402, the control device 205 detects the current position of the sample stage 101 by the laser light taken into the laser light receiver 204 from the laser interferometer 203. At this time, the maximum speed of the stage is calculated from the deviation between the current position and the target position, the amount overtaking the target position is calculated according to the calculated maximum speed, and the temporary target position is set.

Here, a method for setting a temporary target position according to the maximum speed of the stage in the high-speed movement process will be described with reference to FIG. The upper diagram of FIG. 5 shows a stage drive pattern during high-speed movement. The horizontal axis is time (sec), and the vertical axis is stage speed (mm / s). The drive pattern of the sample stage described in the present embodiment performs trapezoidal drive control with a maximum speed of 200 mm / s and an acceleration of 1000 mm / s ² . For example, according to the upper diagram of FIG. 5, when the sample stage moves 300 mm, the sample stage is accelerated simultaneously with the start of movement, reaches 200 mm / s after a lapse of 0.2 sec, and moves at a constant speed. After 1.5 seconds have elapsed, deceleration is started, and after 1.7 seconds have elapsed, the 300 mm movement is completed.

  The lower diagram of FIG. 5 shows the time change of the stage sliding resistance corresponding to the upper diagram. The horizontal axis represents time (sec), and the vertical axis represents sliding resistance (N). The sliding resistance is positive in the direction of pushing back the stage. In the lower diagram of FIG. 5, the sliding resistance is 0 (zero) N at the start of the movement of the sample stage, and reaches the maximum sliding resistance of 30 N after 0.2 sec. After 1.5 seconds, a decrease in sliding resistance is observed, and a residual reaction force of 8 N is generated at 1.7 seconds when the stage stops. Since the stage described in this embodiment is equipped with an active brake, the stage sliding resistance is only the sliding resistance of the guide. The reason why the sliding resistance of the sample stage shows a tendency similar to the stage drive pattern is that the main factor of the sliding resistance of the guide is the oil circulating in the guide, and the oil is proportional to the moving speed of the sample stage. This is to generate sliding resistance. The sliding resistance remaining after the stage is stopped becomes the residual reaction force.

  This residual reaction force changes depending on the maximum speed of the stage. When the change in sliding resistance is compared for each moving amount, the residual reaction force decreases as the maximum speed decreases. In other words, for the residual reaction force 8N generated during 300mm movement, the maximum speed reaches 200mm / s at 40mm movement or more, such as 8N for 100mm movement, 8N for 40mm movement, 4N for 20mm movement, and so on. Although the reaction force is constant at 8N, the maximum reaction speed is reduced at a stage movement amount of less than 40 mm, and the residual reaction force is also reduced. To reduce the generated residual reaction force, if the stage is moved in the opposite direction, sliding resistance in the opposite direction to the residual reaction force is generated, so the stage must be moved in the opposite direction by the amount of movement that makes the residual reaction force zero. That's fine. In the stage described in this patent, a position obtained by adding an overtaking amount of 60 μm for 40 mm to 300 mm, 30 μm for 20 mm movement and 15 μm for 10 mm movement to the target position is set as the temporary target position, and the movement amount in the reverse direction is set. ing.

  What influences the overtaking amount is the residual reaction force and the speed during the low-speed positioning process. As the value of the residual reaction force increases, the overtaking amount for making the residual reaction force zero becomes longer. Further, since the sliding resistance generated when the stage speed increases during the low-speed positioning process, the amount of movement can be short. In the stage described in this patent, the overtaking amount is necessary when the low-speed positioning movement is performed at a constant speed of 2.5 mm / s. Further, when a different guide is used for the sample stage, the value of the residual reaction force changes, so the overtaking amount and the stage speed change.

  Therefore, the optimum overtaking amount for reducing the residual reaction force to zero depends on the guide mechanism attached to the stage and the stage speed at the time of the low-speed positioning process. Therefore, it is necessary to evaluate the overtaking amount for each stage. For evaluation of the overtaking amount, a measuring instrument such as a load cell is attached to the guide mechanism used for the stage, and the guide mechanism is moved at high speed under the same movement conditions as the stage drive pattern. Then, the residual reaction force generated when the guide stops is measured, and then the same drive pattern as that in the low-speed positioning movement process is performed to measure the distance and the stage speed conditions at which the residual reaction force becomes zero. For example, in the stage control described in this patent, the overtaking amount is measured every 10 mm. The control device prepares a table for setting the overtaking amount every 10 mm movement, and the operator inputs the overtaking amount obtained by the evaluation. For example, if the stage movement ≦ 10 mm, the overtaking amount is set to 15 μm, 10 mm ≦ stage movement ≦ 20 mm, 30 μm,... In addition to table input, it is also possible to represent the temporary target position as a function in a 10 mm to 40 mm movement where the temporary target position changes, and to calculate the temporary target position from the deviation between the current position and the target position. In the case of the stage described in the present embodiment, provisional target position = target position + overtaking amount, overtaking amount [μm] = 1.5 [μm] × deviation [mm].

  Since the stage mechanism of this embodiment is controlled so that the table moving speed increases when the moving amount is large, the temporary target position is set based on the moving amount of the stage. As a reference, the temporary target position may be set, or the temporary target position may be set based on other parameters for evaluating the residual reaction force.

  Actually, it is very difficult to always set the residual reaction force to zero accurately, so a brake is necessary. The stage described in this patent is equipped with an active brake with 4N braking force, and a temporary target. When the residual reaction force at the position is 2N or less (in the stage described in this patent, when the movement is 10 mm or less), the sample stage is set so that the overtaking amount is zero, that is, the temporary target position = target position. This is because even if the low-speed positioning step is omitted, the residual reaction force is small and no drift occurs, so that the low-speed positioning step that takes time is avoided and the stage moving time is shortened.

  Based on the overtaking amount setting method described above, the temporary target position can be calculated according to the movement distance between the target position of the stage and the current position.

  Next, in step S403, the sample stage moves at a high speed toward the calculated temporary target position. At this time, the stage is moved based on the driving pattern by performing feedback control on the position, velocity, and acceleration by the control device 205.

  Next, in step S404, high-speed movement is performed until the current position of the sample stage reaches the temporary target position.

  Next, in step S405, after confirming that the sample stage has reached the temporary target position, based on the overtaking amount calculated in step S402, when the overtaking amount is zero, the temporary target position becomes the target position, and thereafter Since the low-speed positioning process becomes unnecessary, the process proceeds to step S408, where the active brake is activated to stop the sample stage. If the overtaking amount is not zero, a low-speed positioning process is required, and the process proceeds to step S406.

  Steps S406 to S408 are low-speed positioning processes. In step S406, positioning is performed while monitoring the stage position and stage speed by feedback control.

  Next, in step S407, a constant speed movement is performed until the sample stage reaches the target position.

  Next, in step S408, after the sample stage reaches the target position, the linear motor 113 is turned off to complete the positioning of the sample stage.

  According to the above flowchart, stage drift can be reduced by performing stage positioning. Next, a stage drift reduction control method for positioning using a thrust value generated in the linear motor will be described with reference to FIGS.

  The upper diagram in FIG. 6 shows a stage control drive pattern in the case where the residual reaction force is directly measured using the thrust value of the linear motor to reduce the stage drift. The drive pattern differs from the drive pattern shown in the upper diagram of FIG. 5 in that the stage stop position after the high-speed movement process is always the target position, and after reaching the target position, a small low-speed movement process (hereinafter referred to as the high-speed movement process) Is called a minute low-speed movement step), and after the minute low-speed movement step, a low-speed positioning step is performed toward the target position.

  The movement distance in the minute movement process will be described with reference to the lower diagram of FIG. The lower diagram of FIG. 6 shows the time change of the sliding resistance of the stage in the drive pattern of the upper diagram of FIG. If the stage moving speed is low, the sliding resistance of the stage in the minute low-speed moving process is characterized by a constant value from the start of the minute low-speed moving process to the stage stop, that is, the residual reaction force. In the stage described in this patent, the stage speed during the minute low-speed movement process is 2.5 mm / s, similar to the speed during the low-speed positioning movement, so that the thrust of the linear motor during the minute low-speed movement process = sliding Resistance = residual reaction force. Since the linear motor performs feedback control of position, speed, and acceleration, the controller 205 sends a thrust generation signal to the linear motor to obtain a thrust of 2.5 mm / s during the minute low-speed movement process. Yes. If the residual reaction force is obtained from this thrust generation signal, it is possible to derive a movement amount at which the residual reaction force during the low-speed positioning movement process becomes zero, as in the above-described calculation of the overtaking amount. In the overtaking amount calculation method described above, the guide alone is moved, but after moving the stage at high speed, the low-speed positioning movement is performed in the reverse direction while monitoring the thrust generation signal, and the residual reaction force becomes zero. It is also possible to set the amount of movement in which the corresponding thrust generation signal is generated as the overtaking amount. For example, when the movement amount of the sample stage is 100 mm, after the high-speed movement of 100 mm is performed, the low-speed positioning movement is moved in the reverse direction at the same speed. The thrust generation signal at that time is monitored, and the position where the residual reaction force is zero and the deviation of 100 mm are the movement amount. For this measurement, for example, it is possible to create a table in which the amount of movement during the minute positioning movement process is set for each amount of movement of the sample stage. The advantage of monitoring the thrust generation signal and calculating the amount of movement in the low-speed positioning process is that the stage is actually moved compared to the case where the residual reaction force is evaluated with the guide alone using the load cell. Since the true residual reaction force is measured because the amount is calculated, the residual reaction force after the low-speed positioning step approaches zero, and the stage drift can be reduced. The stage control method using the thrust generation signal in the linear motor has been described above. However, when a ball screw is used instead of the linear motor, the same amount of movement can be calculated by attaching a torque measuring machine and monitoring the torque. It becomes possible.

  Next, the positioning control method will be described using the flowchart of FIG. Steps S701 to S705 are high-speed movement processes. First, in step S701, a target position for positioning the sample stage is set.

  Next, in step S <b> 702, the control device 205 detects the current position of the sample stage 101 with the laser light taken into the laser light receiver 204 from the laser interferometer 203, and calculates the amount of movement of the sample stage to the target position.

  Next, in step S703, the position, speed, and acceleration of the sample stage are moved at high speed by feedback control, and it is confirmed in step S704 that the target position has been reached.

  Next, in step S705, the value of the residual reaction force acting on the sample stage that has reached the target position is calculated based on the thrust generation signal generated by the control device 205. If the residual reaction force is smaller than ½ of the braking force, the process proceeds to step S710 to activate the active rake and stop the stage. In the stage described in this patent, the safety factor of the braking force against the residual reaction force is 2, but a low safety factor may be used as long as the stage drift is allowed. In step S711, the linear motor is stopped to complete positioning. If the residual reaction force is greater than ½ of the braking force, the process proceeds to step S706, and a movement amount for performing the minute low-speed movement process is calculated from the value of the residual reaction force.

  Next, in step S707, the sample stage is moved at a low speed by a minute low speed movement amount in the same direction as the high speed movement process, and in step S708, low speed positioning movement is started.

  Next, in step S709, after confirming that the sample stage has reached the target position, in step S710, the active rake is activated to stop the stage. In step S711, the linear motor is stopped to complete positioning.

101 Sample stage 102 Base 103 X table 104 Y table 105 X direction guide mechanism 106 Y direction guide mechanism 107 Eccentric pin 108 X linear motor 109 Y linear motor 110 Brake 111 Electrostatic chuck 112 Sample 201 Bar mirror 202 Laser beam transmitter 203 Laser interference Total 204 Laser beam receiver 205 Control device 301 X guide mechanism mounting guide surface 302 Eccentric pin insertion hole

Claims (5)

In a sample stage device having a multi-axis table, a drive mechanism for driving each of the tables, and a guide mechanism for guiding the table in the moving direction of the table ,
In the stage positioning step, the stage completes positioning through a high-speed movement step and a low-speed positioning movement step,
Movement distance at the slow positioning step, the sample stage device characterized that you change according to the moving speed condition in the high-speed movement process. In claim 1,
The moving distance in the slow positioning step, the sample stage and wherein the Rukoto is calculated according to the thrust signal obtained in controlling the drive mechanism. In claim 1,
The moving distance in the slow positioning step is calculated according to the load signal obtained by the attached measuring instrument to the driving mechanism sample stage apparatus according to claim Rukoto. In any of claims 2 and 3,
A sample stage apparatus characterized by performing a low-speed positioning movement step after performing a low-speed movement by a movement distance obtained from the thrust signal or the load signal after a high-speed movement step . In any of claims 2 and 3 ,
The thrust signal or the moving distance obtained from the load signal, based on a comparison of the retention force of the brake provided in the sample stage, the calculated sample stage device according to claim Rukoto.

Images