JP5588759B2 - Sample stage and measurement, inspection and observation equipment with sample stage - Google Patents

Description

  The present invention relates to a sample stage mounted on an apparatus used for measuring, inspecting, or observing a sample, and more particularly to a sample stage capable of positioning the sample stage at high speed and with high accuracy.

  With the recent miniaturization of semiconductor elements, not only manufacturing apparatuses but also semiconductor device measurement, inspection, and evaluation apparatuses are required to have high precision commensurate with miniaturization. As an example of the measurement and inspection apparatus, there is a scanning electron microscope (hereinafter referred to as a length measurement SEM) having a length measurement function for measuring the dimension of a pattern formed on a semiconductor wafer.

  In the length measurement SEM, the wafer is irradiated with an electron beam, the obtained secondary electron signal is subjected to image processing, and the edge of the pattern is discriminated from the change in brightness (see Patent Document 1).

  Therefore, in order to correspond to the design rule of the 35 nm node, it is an important issue to obtain a secondary electron image with less noise at an observation magnification of 300,000 times or more. Further, in order to improve the contrast by overlaying a number of images, the stage on which the wafer is mounted and held needs to suppress vibration and drift of the order of nm.

  In the length measurement SEM, since the evaluated wafer is returned to the production line, the wafer cannot be divided into small pieces. Therefore, in order to evaluate the entire wafer surface, a wafer stage having a stroke to cover it is necessary.

  At present, the wafer size is mainly 300 mm, and the stage for that is considerably large. At the same time, a high output drive mechanism for increasing the speed of the stage is required from the viewpoint of improving the throughput, and the temperature rises due to the heat generated by the motor and the drive shaft.

  As means for avoiding the drift of the table due to the thermal expansion and contraction, a technique (Patent Document 2) has been devised in which a gap of 20 μm to 100 μm is provided between the moving table and the drive shaft, and the drive shaft is separated when stopped. Yes. Furthermore, a technique (Patent Document 3) is devised that stops driving the table while monitoring the deviation between the measured value by the position detector and the preset target value during fine movement, which is not good due to the dead zone caused by the gap. ing. With these techniques, control by an open loop using a pulse motor is possible.

JP-A-9-166428 JP 2004-134155 A JP 2007-80660 A (corresponding US Pat. No. 7,435,974)

  However, according to the technique disclosed in Patent Document 3, since a structure having a gap in the drive unit is adopted, a table generated depending on the initial state of the gap and the speed / acceleration change in the high-speed movement to the temporary target position. Due to this vibration, the stop position at the temporary target position tends to vary. Furthermore, due to slippage of the table when stopped, the drive shaft and the table are not joined (separated) at the temporary target position. Since the stop position at the temporary target position varies or is separated, a long distance movement or a pulse output for eliminating the gap is required in the subsequent low-speed movement to the original target position. It will be. For this reason, it takes more time to reach the target position, the throughput is lowered, and at the same time, there is a possibility that the characteristics change due to a slight change of the mechanism.

  In the following, we propose a sample stage that aims to perform high-speed and stable positioning regardless of the presence of a dead zone or the like, and a measurement, inspection, and observation apparatus including the sample stage.

  As one aspect for achieving the above object, in a sample stage including a table for placing a sample and a driving mechanism for driving the table, the coupling between the table and the driving mechanism is mechanically coupled. A control unit that controls the connection unit to be separated before the stop of movement of the table by the drive mechanism, and a position detector that detects the position of the table. Performs coarse feedback control based on the position information of the table by the position detector during coarse movement of the table, and performs sequence control to open-control the drive mechanism using a preset velocity displacement pattern during fine movement. A sample stage is proposed.

  According to the above configuration, the sample stage can be moved to the target position at high speed and with high stability.

It is a figure which shows the whole structure of an electron microscope apparatus. 3 is a flowchart showing an execution procedure of a positioning control method executed by a control device 100. It is a block diagram which shows the internal structure of a positioning control apparatus (control apparatus 100). FIG. 3 is a graph showing an example of a motor rotation speed and a time course of relative position displacement from an initial position of a sample stage when the flowchart shown in FIG. 2 is executed by the control device 100.

  Hereinafter, a sample stage capable of realizing high-speed and highly stable movement to a target position and a measurement, inspection, and observation apparatus including the sample stage will be described with reference to the drawings. In this embodiment, a sample stage that can perform high-speed and stable positioning with a stage function whose characteristics change due to the dead zone, and can suppress noise due to thermal drift and vibration when the stage is stopped is mounted. An electron microscope apparatus and a sample stage that enables a sample stage positioning control method in the apparatus will be described.

  In this embodiment, a gap is provided in the coupling portion between the table and a driving unit such as a ball screw that drives the table, and the speed measured by the position detector follows the preset time displacement of the table position in real time. Provided with feedback control means for controlling and sequence control means for open-controlling the motor with a preset velocity displacement pattern, these are dynamically measured within a series of positioning control based on the measured value by the position detector or the amount of displacement. By switching, feedback control is performed during coarse movement (coarse movement), and sequence control is performed during fine movement or movement in the dead zone (fine movement).

  According to the configuration described above, the movement to the temporary target position can be performed at a high speed by controlling the speed so that the measured value by the position detector follows the time displacement of the table position set in advance for the coarse movement. Highly stable. As a result, the low-speed fine movement distance / time is minimized, and positioning in a short time becomes possible. In the initial driving operation and separation operation, which are operations in the dead zone where the measurement value by the position detector does not change, feedback is performed by switching to sequence control that performs a predetermined operation regardless of the measurement value by the position detector. Servo vibration problems that tend to occur in control can be avoided. This makes it possible to perform high-speed and stable positioning with a sample stage mechanism whose characteristics change due to the dead zone, and to mount an electronic sample stage that can suppress noise due to thermal drift and vibration when the stage is stopped. A microscope apparatus and a sample stage positioning control method in the microscope apparatus can be provided.

  Hereinafter, an electron microscope apparatus and a sample stage positioning control method in the apparatus will be described in detail with reference to the drawings. In the following description, a length measurement SEM for a semiconductor device will be described as an example. However, the sample stage as described above is not limited to the length measurement SEM, and an SEM for inspecting defects or a focused ion beam is used as a sample. The present invention can be applied to an inspection apparatus or an observation apparatus that includes other charged particle beam apparatuses such as an apparatus that irradiates a laser beam. Although it can be applied to measurement, inspection, and observation devices equipped with an optical microscope, the sample stage as described later is generally applied to a scanning electron microscope or the like having a higher resolution than an optical microscope. By doing so, higher effect is demonstrated.

  FIG. 1 is a diagram illustrating an overall configuration of an electron beam microscope apparatus. Here, a length measurement SEM equipped with a sample stage is illustrated.

  In FIG. 1, a sample stage 3 is mounted inside a sample chamber 2 that can be evacuated by a vacuum pump 1. The sample stage 3 includes a base 4, a center table 5, a top table 6, and the like. The center table 5 is restrained by an X sliding guide member 7 as a guide mechanism on the base 4 and can move in one direction (X direction (left and right direction in FIG. 1)). The center table 5 is also pushed and pulled by the X rod 9 that performs linear motion by the rotation of the X ball screw 8 as a driving mechanism, but the pin 10 at the tip of the X rod 9 and the guide 11 of the center table 5 have a gap 12 of 50 μm. Is vacant. The X ball screw 8 is coupled to a shaft 13 that is vacuum sealed and can be rotated by a pulse motor (PM) 14.

  On the center table 5, a Y-sliding guide member 15 that intersects the X-sliding guide member 7 at a right angle is similarly configured, and the top table 6 is arranged in one direction (Y direction (FIG. 1) along the Y-sliding guide member 15. Move to the back and front side)). As for the connection between the top table 6 and the Y rod, a gap is provided between the pin at the tip of the Y rod and the guide portion as in the case of the center table 5. Note that all of the Y rods, pins, guides, and gaps listed here are not shown.

  On the other hand, a sample holder 16 is mounted on the top table 6, and a wafer 17 is fixed on the sample holder 16. Further, a bar mirror 18 is mounted on the top table 6 for stage position control, and position measurement is performed using a position detector such as a laser interferometer (abbreviated as “interferometer” in FIG. 1) 19 or the like. .

  The control apparatus 100 controls the PM 14 based on the position of the sample stage 3 measured by the laser interferometer 19 to perform stage position control in the X direction and the Y direction.

  On the other hand, in the upper part of the sample chamber 2, an electron gun 20 serving as an electron beam source, a deflector 22 that changes the trajectory of the electron beam 21, an electron lens 23 that converges the electron beam 21, and secondary electrons 24 emitted from the wafer 17. A lens barrel 26 in which a secondary electron detector 25 and the like for taking in are incorporated. The signal from the secondary electron detector 25 is signal-processed by the control unit 27 and sent to a CRT (Cathode Ray Tube) 28 for observation.

  Here, the principle of operation of the electron microscope illustrated in FIG. 1 will be described. Usually, a user evaluates the pattern shape of a wafer by (1) where the desired pattern is located in the chip, and (2) which chip pattern is arranged on one wafer. Each of these is registered in advance using coordinates.

  At the time of evaluation, the control apparatus 100 automatically moves the sample stage to the coordinate position based on the registered contents, and then irradiates the electron beam 21 onto the wafer 17 and scans it with the deflector 22 to tens of thousands of times. A secondary electron image of several hundred thousand times is acquired from the image and displayed on the CRT 28. Then, the shape of the pattern is discriminated from the change in brightness of the secondary electron image, and the dimension value of the designated shape (pattern line width, pitch, etc.) is calculated. Thereafter, the CPU moves to the coordinate position of the next registered chip and repeats image acquisition in the same manner.

  Next, the sample stage positioning control apparatus and positioning control method according to the present embodiment will be described with reference to FIGS.

  FIG. 2 is a flowchart showing an execution procedure of the positioning control method executed by the control device 100. FIG. 3 is a block diagram showing an internal configuration of the positioning control device (control device 100) according to the present embodiment. FIG. 4 is a graph showing an example of the motor rotation speed and the time course of the relative position displacement from the initial position of the sample stage when the flowchart shown in FIG.

  The control device 100 includes a control CPU 200 that reads a program recorded in a built-in memory and sequentially executes a procedure according to the flowchart of FIG. In addition, a sequence controller for controlling the pulse amount and frequency of the drive pulse 202 to the PM 14 in accordance with a motor rotation sequence instruction 201 comprising a combination of parameters that directly specify the rotation operation of the motor, such as the rotation speed, acceleration, and rotation amount of the pulse motor 203, feedback for controlling the rotational speed of the PM 14 so that the deviation between the time displacement pattern 204 of the position of the sample stage 3 determined in advance and the position information 208 of the sample stage 3 provided from the laser interferometer 19 is zero as much as possible. And a control unit 205, and further includes a selector 207 that switches the drive pulse path to the PM 14 to the output of the sequence control unit 203 or to the feedback control unit 205 by the control switching instruction 206 of the control CPU 200.

  According to the flowchart shown in FIG. 2, the target position 400 is first set in step S100. The target position 400 is determined by stage coordinates registered in advance, manual input by the apparatus operator, or coordinate designation by a cursor. In step S110, the current coordinates of the stage are acquired from the laser interferometer 19. Up to this point, the current coordinates and the required amount of movement to the target position are clarified. Although not shown here, when the required movement amount is short, it is also effective to shorten the positioning time without performing high-speed movement by feedback control described later and performing only low-speed movement by sequence control.

  Subsequently, in step S <b> 120, the control CPU 200 switches the control unit to the sequence control unit 203 in accordance with a control switching instruction 206. At the start of the movement, the pin 10 and the guide 11 are in a non-contact state by a separation operation described later, and even if the PM 14 rotates until the PM 14 rotates and the pin 10 and the guide 11 come into contact with each other, the laser interferometer 19 This is a dead zone operation 401 in which the position information 208 does not change. In the dead zone, the feedback control that controls the PM 14 based on the position information 208 from the laser interferometer 19 is not effective because it may cause excessive motor rotation. It is important to remove the dead zone region in order to effectively operate high-speed movement by feedback control. In the dead zone region, control is performed without any fear of excessive motor rotation if the sequence operation controls the rotation of the motor by the predetermined motor rotation sequence instruction 201 without depending on the position information 208 from the laser interferometer 19. it can.

  Further, the gap amount is a predetermined amount (50 μm in this embodiment), and by setting the upper limit of the rotation amount in advance by the sequence operation, for example, from the laser interferometer 19 even if the rotation amount reaches the upper limit. When the position information 208 hardly changes, it can be used for error determination such as cable disconnection between the control device 100 and the PM 14. In step S130, a motor rotation sequence instruction 201 is set. Based on the instruction, a gap removal operation 402 is performed by sequence control in step S140.

  During the gap removal operation, the position information 208 from the laser interferometer 19 is monitored in step S150, and when the displacement exceeds a predetermined threshold value, the pin 10 and the guide 11 come into contact and the gap is removed. It is determined that it has been completed (Y in step S160), and the process proceeds to the next high-speed movement operation. If the displacement amount is equal to or smaller than the threshold value (N in step S160), the gap removal operation is continued. In the gap removal operation 402 shown in FIG. 4, the motor rotation speed is switched in two stages from high speed to low speed. This is because the position information 208 from the laser interferometer 19 starts to change when the motor rotates and the pin 10 and the guide 11 are in contact with each other and the gap disappears. However, the motor is caused by lost motion due to spring elements such as deformation of the drive system. This is a state in which the movement of the stage does not linearly follow the rotation of. In this case, the sequence control is performed in the same manner as the gap removal operation. However, the load is small in the region where the lost motion immediately after the contact is present compared to the region where the load is small because the pin 10 and the guide 11 are not in contact with each other. Therefore, it is desirable to suppress the rotation speed in order to avoid the occurrence of vibration due to step-out or collision. It also has the effect of avoiding a steep change in speed at the start of the next high speed movement.

  Next, in step S <b> 170, the control CPU 200 switches the control means to the feedback control unit 205 in accordance with the control switching instruction 206 in order to perform the coarse motion feed movement control 403. The control CPU 200 acquires the current position from the position information 208 from the laser interferometer 19 and sets a temporary target position 404. The provisional target position 404 shown in FIG. 4 is set to a certain amount (offset 405) before the target position 400. The offset 405 is desirably as small as possible in consideration of shortening of the positioning time. The target position 400 and the temporary target position 404 may be the same as long as sufficient positioning accuracy and low drift after stopping can be secured by the coarse movement. Absent. It is also possible to set the temporary target position 404 on the far side of the target position so that the fine movement feed is on the opposite side of the coarse movement direction. In this case, an effect of canceling the drift caused by the coarse movement can be expected. In the present embodiment, a case where fine movement feeding is required for the purpose of driving the stop position accuracy and reducing drift after the coarse movement will be described.

  Next, in step S200, a time displacement pattern 204 of an ideal position until the sample stage 3 reaches the provisional target position 404 is calculated, and this is instructed to the feedback control unit 205. The feedback control unit 205 performs the laser interferometer. While monitoring the position information 208 from 19 in real time, the rotational speed of the PM 14 is controlled to move to the temporary target position 404. The time displacement pattern 204 at the ideal position is set so that, in addition to high-speed movement, steep changes in speed and acceleration are suppressed, and the stop position of the sample stage at the temporary target position and the state of the gap at the time of stop are stable. .

  When moving at high speed by sequence control, the stage moves due to the inertial force due to the reaction when stopped, and the state of the gap becomes unstable. However, in addition to removing the dead band by the gap removal operation before the coarse movement, the feedback control performs positioning control while monitoring the position information 208 in real time. Compared to the case of feeding, it is possible to stabilize the stop position and the gap state at the temporary target position 404 without variation. By stabilizing the stop position and the gap state at the temporary target position 404, it is possible to minimize the fine movement feed to be performed next. That is, the positioning time is shortened.

  In addition, since the calculation process of the time displacement pattern 204 at the ideal position requires a certain amount of time, if it is performed after the gap removal operation is completed, there is a control dead time between the gap removal operation 402 and the coarse feed movement control 403. As a result, the stage moves due to an inertial force due to a decrease in throughput or a reaction of stopping the control, which hinders subsequent operations.

  In the control apparatus 100 shown in FIG. 4, the sequence control unit 203 and the feedback control unit 205 are mounted in parallel, and are configured to be capable of parallel processing of both. Since the sequence control unit 203 operates autonomously in accordance with a preset motor rotation sequence instruction 201, the time displacement pattern 204 of the ideal position is calculated during the gap removal operation 402 to prevent the occurrence of dead time. Is possible.

  The control CPU 200 monitors the position information 208 from the laser interferometer 19 in step S220, and if the deviation between the current position and the temporary target position 404 is equal to or less than a predetermined threshold value in step S230 (Y in step S240). In step S240, the control CPU 200 switches the control unit to the sequence control unit 203 in response to the control switching instruction 206 in order to perform fine feed movement control 406.

  In feedback control, positioning is performed while referring to the position information 208 in real time, so that high-speed and high-accuracy positioning is possible. However, because the operation in the dead zone described above is poor and automatic control is performed. It is difficult to perform detailed conditional actions. In addition, it has been found that the low-speed movement in a mechanism with a relatively large gap and lost motion is dominated by the spring characteristics, and the behavior of the stage with respect to the rotation of the motor is significantly different from that during high-speed movement. Therefore, the control from the temporary target position 404 to the target position 400 is switched to the sequence control in which the condition control is easy and the motor rotation is controlled by the predetermined motor rotation sequence instruction 201, and the fine feed movement control 406 is performed. .

  After confirming the current position in step S260, a motor rotation sequence instruction 201 to the target position is set in step S270. Since the stop position of the temporary target position and the state of the gap are stable due to coarse feed by feedback control, and the continuous switching from coarse feed feed control to fine feed feed control, the gap is removed here. No action is required and the distance of fine movement can be minimized. Thereby, the fine feed time can be shortened and the positioning time can be reduced. The position information 208 is monitored in step S280, and if it is determined that the deviation between the current position and the target position is equal to or less than the threshold value (Y in step S290), the motor is stopped in step S300. In fine movement feed movement control 406 shown in FIG. 4, the speed is switched in two stages from high speed to low speed. At a position away from the target position, the rotational speed of the motor is increased to shorten the movement time, and near the target position, the rotational speed is decreased to reduce drift after stopping. By performing fine movement feed by sequence control in this way, conditional control based on the position information 208 is facilitated, and control can be simplified.

  After stopping, the pin 10 and the guide 11 are separated 407 in order to avoid the occurrence of drift due to thermal expansion and contraction of the motor and the drive shaft. The separation operation 407 is control in the dead zone in the same manner as the gap removal operation 402. Therefore, the sequence control used in the fine feed is performed without switching the control means. Since the gap amount is a predetermined amount (50 μm in this embodiment) and the inertia force due to the reaction at the stage stop is small due to the low-speed fine movement feed, the gap position is stable, and a predetermined motor is set in advance. The separation operation 407 can be performed by rotating by a predetermined rotation amount.

DESCRIPTION OF SYMBOLS 1 Vacuum pump 2 Sample chamber 3 Sample stage 4 Base 5 Center table 6 Top table 7 X slide guide member 8 X ball screw 9 X rod 10 Pin 11 Guide 12 Gap 13 Shaft 14 Pulse motor (PM)
15 Y sliding guide member 16 Sample holder 17 Wafer 18 Bar mirror 19 Laser interferometer 20 Electron gun 21 Electron beam 22 Deflector 23 Electron lens 24 Secondary electron 25 Secondary electron detector 26 Lens barrel 27 Control unit 28 CRT
100 control device 200 control CPU
201 Motor rotation sequence instruction 202 Drive pulse 203 Sequence control unit 204 Position temporal displacement pattern 205 Feedback control unit 206 Control switching instruction 207 Selector 208 Position information 400 Target position 401 Dead zone operation 402 Gap removal operation 403 Coarse feed movement control 404 Target position 405 offset 406 fine feed movement control 407 separation operation

Claims (6)

In a sample stage equipped with a table for placing a sample and a drive mechanism for driving the table,
A coupling part capable of mechanically separating the coupling between the table and the driving mechanism; a control device for controlling the coupling part to be separated before the driving mechanism stops moving the table; and a position of the table The control device performs feedback control based on the position information of the table by the position detector during the coarse movement of the table, and uses a preset velocity displacement pattern during the fine movement. In addition to performing sequence control to open-control the drive mechanism, the control device switches from the sequence control to feedback control when the amount of positional displacement detected by the position detector exceeds a predetermined threshold value. A sample stage characterized by performing switching. In a sample stage equipped with a table for placing a sample and a drive mechanism for driving the table,
A coupling part capable of mechanically separating the coupling between the table and the driving mechanism; a control device for controlling the coupling part to be separated before the driving mechanism stops moving the table; and a position of the table The control device performs feedback control based on the position information of the table by the position detector during the coarse movement of the table, and uses a preset velocity displacement pattern during the fine movement. In addition to performing sequence control for open control of the drive mechanism, the control device increases the rotational speed of the drive mechanism from a high speed before the position displacement detected by the position detector exceeds a predetermined threshold value. A sample stage characterized by switching to a low speed. In a sample stage equipped with a table for placing a sample and a drive mechanism for driving the table,
A coupling part capable of mechanically separating the coupling between the table and the driving mechanism; a control device for controlling the coupling part to be separated before the driving mechanism stops moving the table; and a position of the table The control device performs feedback control based on the position information of the table by the position detector during the coarse movement of the table, and uses a preset velocity displacement pattern during the fine movement. In addition to performing sequence control for open control of the drive mechanism, the control device increases the rotational speed of the drive mechanism after the position displacement detected by the position detector has become equal to or less than a predetermined threshold value. Sample stage characterized by switching from low to low speed. In claim 3,
The control device performs switching from the feedback control to the sequence control when a deviation between a current position of the sample stage and a temporary target position becomes a predetermined threshold value or less. Sample stage. A charged particle beam apparatus comprising the sample stage according to claim 1. An optical microscope comprising the sample stage according to any one of claims 1 to 3.

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