JP2007042514A - Stage and correction method of stage stop position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stage which controls a position of a testpiece of an object of which an image is created by scanning a charged particle beam loaded by a servo control and provide a correction method of a stage stop position, in which a fine movement is detected precisely when a servo control of a stage stops and a position where a charged particle irradiates on the testpiece is rectified in real time and a stop position of the stage is rectified in a short time of reaction, without mechanical vibrations and shifts and moreover with a high precision. <P>SOLUTION: A stage is provided with a detecting unit which detects precisely a shift of a position of a stage when a servo control stops and a rectifying means which rectifies a position of charged particle beam irradiating a testpiece based on an extent of shifting of a position detected by the detecting unit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stage and a stage stop position correction method for controlling the position of a sample to be scanned by a charged particle beam beam and generating an image.

  In the semiconductor field, a large mask (for example, 8-inch size) is mounted on a SEM (scanning electron microscope) stage for drawing, measuring, and inspecting patterns such as LSI masks, and has a wide range in the X and Y directions. In addition, there are those that can move with high precision.

  At this time, when observing the SEM image (for example, secondary electron image) of the mask mounted on the stage with the SEM described above, positioning feedback of the servo control system and heat generated by the servo control system are conducted even when the stage is stopped. Since the stage may perform a minute operation, servo control is stopped during SEM image observation in order to avoid the operation.

  However, even if the operation of the servo control system that drives the stage is stopped, the stop position may drift slightly due to thermal expansion due to the thermal change of the ball screw that constitutes the stage, or contact surface friction change of the ultrasonic motor. There was a problem that.

  In addition, after detecting the amount of slight drift of the stop position due to the thermal expansion due to the thermal change of the ball screw mentioned above or the frictional change of the contact surface of the ultrasonic motor, the servo control system mentioned above is operated and corrected each time. If stopped, there is a problem that the stage cannot be stopped with high accuracy because the stage is slightly moved by the heat from the servo control system.

  In order to solve these problems, the present invention detects minute movement with high accuracy when the servo control of the stage is stopped, corrects the position where the charged particles irradiate the sample on the stage in real time, and stops the stage on the image. The purpose is to correct the position with a short response time, no mechanical vibration or displacement, etc., and with high accuracy.

  The present invention detects a minute movement of a stage used in a charged particle microscope with high accuracy when servo control of the stage is stopped, and corrects the position where the charged particle irradiates the sample on the stage in real time, It is possible to correct the stop position with high accuracy by shortening the response time by electronic control and without mechanical vibration or displacement.

  The present invention detects a minute movement of a stage used for a charged particle microscope with high accuracy when the servo control of the stage is stopped, corrects a position where the charged particle irradiates a sample on the stage in real time, and stops the stage. With electronic control, the response time was shortened, and there was no mechanical vibration or displacement.

  FIG. 1 shows a block diagram of an embodiment of the present invention. Hereinafter, an SEM (scanning electron microscope) using an electron beam as a charged particle microscope will be described in detail. As the charged particle beam microscope, there is an ion scanning microscope that uses an ion beam in addition to an electron beam.

FIG. 1A shows an overall configuration diagram.
In FIG. 1A, a SEM 1 is a scanning electron microscope having the configuration shown in the figure.

  The electron gun 2 generates an electron beam (for example, a tip of a tungsten wire is formed to have a sharp and predetermined surface, and a high voltage is applied to extract the electron beam).

  The alignment coil 3 is for deflecting and aligning the electron beam emitted from the electron gun 2.

The condenser lens 4 focuses the electron beam emitted from the electron gun 2.
The deflection scanning coil 5 is for scanning an electron beam narrowly focused on the mask 10 as a sample by the objective lens 7 in the X direction and the Y direction.

  The shift coil 6 shifts (X, Y) the position on the mask 10 irradiated by the electron beam (corrects the minute movement amount of the stop position of the stage 11 when the servo control system described later stops). Is). Instead of providing the shift coil 6 independently, a signal may be added to the deflection scanning coil 5 to similarly shift (X, Y) the position on the mask 10 irradiated with the electron beam. .

The objective lens 7 narrows the electron beam on the mask 10.
The backscattered electron detector 8 detects the backscattered electrons reflected when the mask 10 is irradiated and scanned and amplifies the backscattered electrons to generate a backscattered electron image. The backscattered electron detector 8 is usually a disk-shaped hole in which an electron beam passes, and the entire circumference is, for example, a fan shape that is divided into four parts. Each reflected image is displayed by using a known technique, such as displaying a reflected electron image having a dependent gray level, highlighting the unevenness of the shape by the difference between the two left and right signals, and so on.

  The secondary electron detector 9 is for focusing and detecting secondary electrons emitted when the mask 10 is irradiated with the electron beam beam and scanning, and amplifies the secondary electrons to generate a secondary electron image. .

The mask 10 is an example of a sample mounted (fixed) on the stage 11.
The stage 11 is mounted with a mask 10 and accurately moves to an arbitrary coordinate position, and is driven by a motor (or ultrasonic motor) 12.

  The motor 12 drives the stage 11 (X direction, Y direction), and is a servo motor or an ultrasonic motor.

  The laser length measurement system 13 is a known system that measures the position (positional coordinates) of the stage 11 with ultra-high accuracy by emitting a laser beam, reflecting it with a reflecting mirror attached to the stage 11 and capturing it.

  (B) of FIG. 1 shows a principal part block diagram. Here, the shift coil 6, the mask 10, the stage 11, the motor (ultrasonic motor) 12, and the laser length measurement system 13 are the same as those having the same numbers in FIG.

  In FIG. 1B, the movement command 20 is the position of the stage 11 (position coordinates (X, Y coordinates)) when the switching circuit 24 is switched to the servo control side (solid line in the figure). Is a movement command to a position commanded from an application program (not shown) or to a position commanded by an operator.

  The servo controller 22 controls the driving of the ultrasonic motor 12 according to the movement command 20 based on the values (coordinates (X, Y)) measured by the laser length measurement system 13 (known servo control). To do.

  The beam shift control device 23 is a value obtained by measuring the position of the stage 11 with the laser length measurement system 13 in a state where the switching circuit 24 is switched to a state where servo control is stopped (dotted line in the figure) (a state where servo control is stopped). Based on the coordinates (X, Y)), the shift coil 6 is controlled to correct the position where the electron beam irradiates the mask 10 (while the servo control is stopped, a minute amount due to the drift of the stage 11 or the like). The movement is measured by the laser length measurement system 13, and the position where the electron beam irradiates the mask 10 is corrected electrically (electromagnetically or electrostatically) based on the measured value. This cancels the influence of movement and eliminates minute movement of the image to be measured).

  The switching circuit 24 switches to a solid line during servo control and performs servo control in accordance with the movement command 20 by the servo controller 22, while switching to a dotted line and stops on the electron beam beam mask 10 by the beam shift controller 23 while the servo control is stopped. The position of the stage 11 during the servo control stop is corrected electrically (electromagnetically or electrostatically).

Next, the operation of the configuration of FIG. 1 will be described in detail according to the order of the flowchart of FIG.
FIG. 2 shows a flowchart for explaining the operation of the present invention.

  In FIG. 2, S <b> 1 starts measurement of the position (X, Y) of the stage 11 by the laser length measurement system 13. The measured signal (A / B phase pulse) is sent to the servo controller 22 and sent to the beam shift control device 23 that performs the processing from S2 to S6.

  In S2, the signal (A / B phase pulse) sent in S1 is input to the up / down counting circuit.

In S3, when the stage is stopped (servo control stop is started), the signal (A / B phase pulse) input in S2 is started to be counted by the up / down counter. For example, as described on the right
-8bits (± 1024 resolution), for example 6328cm / 1024 = 0.6nm
With the up / down counter, the count of minute movements (drift, etc.) of the stage 11 from the stage stop (at the start of servo control stop) is started with the up / down counter.

  S4 stores the image and position. In S3, an image (image) when the stage is stopped (servo control stop is started) and its position (position (X, Y) measured by the laser length measurement system 13) are stored.

  S5 performs D / A conversion. This is a digital minute movement amount at every predetermined time (for example, every frame of an image, every time a set of signals (A / B phase pulses) or a plurality of predetermined notifications is received from the laser measurement system 13). (Amount of minute movement counted based on when servo control is stopped) is converted to an analog signal.

  In S6, the beam is shifted. This is because, based on the analog signal converted in S 5, a predetermined current is passed through the shift coil 6, and the minute position of the electron beam beam moved on the mask 10 is measured by the laser length measurement system 13. Only by turning back (turning back to the original position when the servo control is stopped), as a result, the minute movement of the image (secondary electron image) obtained by scanning the electron beam is eliminated.

  As described above, when the servo control is stopped by switching the switching circuit 24 from the solid line to the dotted line in FIG. 1B when the servo control is stopped (when the start signal is notified when the stage is stopped in S3), the servo control is performed. The stopped stage 11 is left as it is (mechanically as it is), and the position of the electron beam applied to the mask 10 mounted on the stage 11 is slightly moved in the direction for correcting the minute movement of the stage 11 (electrical The electron beam beam is moved slightly so as to correct the irradiation position of the electron beam beam on the mask 10 (with a magnetic field or an electric field), and as a result, the mask 10 on the stage 11 is irradiated (planar scanning irradiation). It is possible to completely eliminate the influence of the minute movement of the stage 11 on the image (secondary electron image, reflected electron image).

  When the servo control is stopped, the power generated by the ultrasonic motor 12 or the like that affects the minute movement of the stage is turned off, or the stage is heated by controlling the heat generation amount to be as small as possible. Minimize 11 minute movements.

  Next, S7 resumes. Since the movement command 20 is notified, the servo control is resumed (the switching circuit 24 in FIG. 1B is switched from the dotted line to the solid line).

  In step S8, the image is compared with an image added with shift. This compares the initial image (image position) when the servo control is stopped with the image (image position) after the shift is repeated in S6.

  In S9, it is determined whether the error is within a certain range. This is to determine whether the error between the image (image position) when the servo control is stopped and the image (image position) after taking into account the shifted minute movement amount is within a certain range compared in S8. In the case of YES, since it has been found that there is no need to correct the movement error of the image while the servo control is stopped within a certain range, OK is made in S10 and the servo control is resumed. On the other hand, in the case of NO, since it has been found that the movement error of the image during servo control stop is not within a certain value and correction is necessary, the error is corrected in S11, and the servo control is performed based on the corrected image position. To resume. When restarting, instead of comparing the position of the image when the servo control is stopped and the position of the image when the servo control is started, the mask reference position (the predetermined position of the reference pattern, the predetermined position of the mask alignment pattern) ) Compare the servo control stop time and servo control start time to calculate the movement error.

FIG. 3 is an explanatory diagram of the drift of the stage.
FIG. 3A schematically shows the state of current (or voltage) to the motor 12. In the section described as stage movement in the figure, the servo controller 22 in FIG. 1B supplies a predetermined current to the motor 12 in accordance with the movement command 20 (in the case of the ultrasonic motor 12, the phase is 90 ° different. A voltage pulse having a predetermined frequency is supplied to each piezoelectric element) to perform known servo control.

  FIG. 3B schematically shows an example of the drift amount of the stage 11. The drift of the stage 11 is very small in a certain direction due to thermal expansion and expansion / contraction of the stage 11 and the mechanism part holding the stage 11 due to heat generated by supplying current / voltage to the motor (ultrasonic motor) 12. This is shown schematically because of the nature of movement.

  FIG. 3C schematically shows an example of the distance from the target coordinates. In the stage movement section of FIG. 3A, the servo controller 22 of FIG. 1B performs known servo control in accordance with the movement command 20, so that there is almost no distance from the target coordinates. However, in the sections other than the stage moving section, the servo control by the servo controller 22 moves minutely due to the drift of the stage 11 in FIG. The amount is measured and, for example, servo-controlled so as to correct the error every 0.125 sec shown. As described above, if the servo control is continuously performed in the stage moving section and the stop section outside the stage moving section, heat is generated even when the motor (ultrasonic motor) 12 that performs servo control is stopped. The conducted heat is transferred to the stage 11 and the mechanism part connected thereto, and expands and contracts to generate a large drift as shown in the figure, and the amount of minute movement at the position when the servo control is stopped becomes very large. There is a problem that it cannot be reduced (thermal influence + large amount of stage fine movement).

  In the present invention, as shown in FIG. 4 described later, the servo control is stopped except for the stage moving section, and the power supply to the motor (ultrasonic motor) 12 and other heat generating components is turned off (or the heat generation amount is reduced as much as possible). ) To minimize the amount of drift of the stage, measure the minimum amount of drift (amount of minute movement) with the laser length measurement system 13, and return the electron beam so that only the amount of minute movement measured is returned. The irradiation position of the mask 10 is corrected electrically (magnetically or electrostatically). This will be described below.

FIG. 4 is an explanatory diagram of stage stop position correction according to the present invention.
FIG. 4A schematically shows a state of current (or voltage) to the motor. In the section described as stage movement in the figure, the servo controller 22 in FIG. 1B supplies a predetermined current to the motor 12 in accordance with the movement command 20 (in the case of the ultrasonic motor 12, the phase is 90 ° different. A voltage pulse having a predetermined frequency is supplied to each piezoelectric element) to perform known servo control. Then, in the section described as stage stop, the servo control system is powered off (or controlled to keep the heat generation amount as small as possible) to minimize the drift amount of the stage 11 when the stage is stopped.

  FIG. 4B schematically shows an example of the drift amount of the stage 11. The drift of the stage 11 is very small in a certain direction due to thermal expansion and expansion / contraction of the stage 11 and the mechanism part holding the stage 11 due to heat generated by supplying current / voltage to the motor (ultrasonic motor) 12. This is shown schematically because of the nature of movement. In the stage stop period, as described above, the amount of heat generation is reduced by turning off the power of the motor (ultrasonic motor) 12, so that the drift amount is small.

FIGS. 4C to 4E illustrate the operation of the present invention.
FIG. 4C schematically shows the state of current (or voltage) to the motor 12. In the section described as stage movement in the figure, the servo controller 22 in FIG. 1B supplies a predetermined current to the motor 12 in accordance with the movement command 20 (in the case of the ultrasonic motor 12, the phase is 90 ° different. A voltage pulse having a predetermined frequency is supplied to each piezoelectric element) to perform known servo control. In the stage stop section other than the stage movement section, the power supply of the servo control system is turned off (or controlled to keep the heat generation amount as small as possible).

  FIG. 4D schematically shows an example of the drift amount of the stage 11. The drift of the stage 11 is very small in a certain direction due to thermal expansion and expansion / contraction of the stage 11 and the mechanism part holding the stage 11 due to heat generated by supplying current / voltage to the motor (ultrasonic motor) 12. This is shown schematically because of the nature of movement. In the stage stop section other than the stage movement section, the servo control system is powered off (or controlled to keep the heat generation as small as possible), and the drift amount of the stage 11 when the stage is stopped is shown in the figure. To minimize.

  FIG. 4E schematically shows an example of the distance from the target coordinates. In the stage movement section of FIG. 4C, since the servo controller 22 of FIG. 1B performs known servo control in accordance with the movement command 20, there is almost no distance from the target coordinates. When the servo control is stopped, the servo control system is turned off to minimize the amount of drift of the stage 11, and in the present invention, a correction current is supplied to the shift coil 6 in S6 of FIG. An image (secondary electron image, reflection) obtained by scanning the electron beam is used to correct the mask 10 mounted on the stage 11 so that the mask 10 mounted on the stage 11 is turned back to irradiate the original position where the servo control is stopped. On the electronic image), it is always constant while the servo control is stopped, and even if the stage 11 moves slightly (minute drift), the image can be electrically corrected so that the image does not move at all.

  The present invention relates to a stage for use in a charged particle microscope, a stage for detecting a minute movement with high accuracy when servo control of the stage is stopped, and correcting a position where the charged particles irradiate a sample on the stage in real time and a stage stop position The present invention relates to a correction method.

It is a system configuration diagram of the present invention. It is an operation | movement explanatory flowchart of this invention. It is stage drift explanatory drawing. It is explanatory drawing of the stage stop position correction | amendment of this invention.

Explanation of symbols

1: SEM (scanning electron microscope)
2: electron gun 3: alignment coil 4: condenser lens 5: deflection scanning coil 6: shift coil 7: objective lens 8: backscattered electron detector 9: secondary electron detector 10: mask 11: stage 12: motor (ultrasonic wave) motor)
13: Laser length measurement system 20: Movement command 22: Servo controller 23: Beam shift control device 24: Switching circuit

Claims (4)

In a stage that controls the position of the target sample to be scanned by a charged particle beam beam and generated by servo control,
A detection device that detects the movement of the position of the stage with high accuracy when the servo control is stopped;
A stage comprising correction means for correcting a position of a charged particle beam irradiated to the sample based on a movement amount of a position detected by the detection device.   2. The stage according to claim 1, wherein the position of the charged particle beam irradiating the sample is deflected and corrected by an electromagnetic deflector or an electrostatic deflector based on the amount of movement.   3. The stage according to claim 1, wherein a correction amount corrected by the correction unit when the servo control is resumed is corrected for the stop position when the servo control is stopped. In a stage stop position correction method for controlling the position of a target sample to be scanned by a charged particle beam beam and generating an image mounted by servo control,
Provided with a detection device that detects the movement of the stage position with high accuracy when the servo control is stopped,
A stage stop position correction method, comprising: correcting a position of a charged particle beam irradiated to the sample based on a movement amount of a position detected by the detection device.

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