JP2010177479A - Charged particle beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charged particle beam device which performs visual field alignment for measurement with a high precision regardless of frictional heat generated from a stage mechanism even in the case that a cumulative movement distance of a stage is long due to the existence of many measurement points. <P>SOLUTION: In the charged particle beam device including a controller which detects position coordinates of an alignment pattern to execute alignment, a temperature sensor is provided, and the controller executes temperature measurement with the temperature sensor in the case that the amount of deflection of a deflector to an addressing pattern formed on a sample or the number of times of measurement in a plurality of measurement positions on the sample exceeds a prescribed value, and a control temperature at which the alignment should be executed is obtained on the basis of the temperature measurement. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charged particle beam apparatus including a sample stage on which a sample is mounted, and in particular, aligns the visual field with respect to an appropriate measurement point regardless of a change in the position of the sample caused by the influence of frictional heat caused by driving the stage. The present invention relates to a charged particle beam apparatus that can be used.

  A sample surface analyzer that scans the surface with a charged particle beam probe and analyzes the quantity or energy of emitted secondary electrons, ions, electromagnetic waves, and other signals to analyze the surface properties. Scanning electrons that obtain information on the surface by converting the amount of secondary electrons into luminance on the screen using electrons as probes and secondary electrons as emission signals. A microscope (SEM: Scanning Electron Microscope) is widely used in practice.

  A scanning electron microscope, a type of charged particle beam device, is sometimes used as a semiconductor element measurement or inspection device, and measures the dimensions of a pattern from a line profile formed based on detection of secondary electrons, etc. A length-measuring scanning electron microscope, and a defect inspection scanning electron microscope that extracts a defect by comparing a reference image with a sample image are known.

  In these charged particle beam irradiation apparatuses, a mask or wafer to be evaluated is mounted on a sample stage placed in a vacuum, and measurement is performed by moving the sample stage to a predetermined position. Due to the higher precision and pattern complexity associated with higher integration of semiconductor elements in recent years, the demand for the dimensional precision of masks and on-wafer patterns is increasing, and the number of measurement points is also increasing to ensure the precision. For this reason, the moving distance of the sample stage during the measurement of one sample is increased, and the frictional heat generated in the sample stage is also increased. Therefore, the deviation of the position of the sample mounted on the sample stage also increases due to the expansion and contraction of the sample stage and the deformation of the components of the sample stage driving unit. As a result, the sample whose position has changed due to the frictional heat from the start of measurement will eventually be out of the field of view of the charged particle beam, and measurement will not be possible.

  To deal with this problem, for example, in Patent Document 1, the relationship between the temperature of the sample stage and the amount of positional deviation of the specimen is determined in advance, and the positional deviation is corrected by a predetermined amount according to the temperature change.

  In addition, a charged particle beam irradiation apparatus in which the inside of the apparatus is held in a vacuum generally uses a water cooling apparatus, but it is difficult to control a sample stage having a large volume to a constant temperature because of poor response. .

JP 2003-1888075 A

  In recent years, as the accuracy of device patterns on masks and wafers and the complexity of patterns have increased, the demand for dimensional accuracy has increased. In order to ensure dimensional accuracy, the number of measurement or observation points for a single sample is increasing, and evaluation exceeding several thousand points may be performed. The sample stage of a charged particle beam irradiation device mounted in a vacuum is generally a system that slides on a moving part, and the moving distance of the stage drive system increases with the increase in the number of evaluation points, and the amount of heat generated by friction also increases. Become more.

  This frictional heat expands the sample chamber where the interferometer is installed and the sample table on which the stage position measurement mirror is mounted, so the distance between the interferometer and the position measurement mirror is not actually moved. As a result of the change, the phenomenon as if the sample is moving is generated, or the sample position is actually changed by deformation of the components of the sample stage. When these sample position change amounts are small, a characteristic pattern around the measurement point (hereinafter referred to as “registered pattern”) is registered in order to accurately measure the measurement pattern position after the sample stage is driven to the target position coordinates of the measurement pattern. This is called “addressing pattern”, and the pattern detection operation is called “addressing”.) Even if it is not found, the charged particle beam deflector can search for the addressing pattern according to the operation specific to the device, but it can measure the length. There was a problem that time was extended. In addition, if the position change amount is large, the charged particle beam deflector exceeds the area that can be deflected, and there is a problem that the addressing pattern cannot be found and the measurement is not performed. Is sustained.

  In addition, the effect of frictional heat not only moves the sample in parallel but also moves it in the rotational direction, so that the amount of change and the direction of change vary depending on the position in the sample. Therefore, even if the addressing pattern in a small area can detect the addressing pattern with respect to the change in the sample position, if the measurement location in the sample changes greatly, the addressing will exceed the deflection area of the charged particle beam deflector. There was a possibility. In particular, when the rotation of the sample occurs around the center, the pattern moves in the opposite direction on both sides of the center. For this reason, it is not appropriate to obtain the amount of change in the sample position as a value for the entire area within the sample from the result of addressing the measurement point, and it is difficult to obtain the center of rotation when the change in the measurement position is small. On the other hand, the method of obtaining the position correction amount for the temperature change of the sample stage in advance is that the influence of frictional heat on the sample stage is not constant when the measurement position in the sample and the number of measurement points differ depending on the measurement (especially mask measurement). Since it is not, it is not suitable.

  The purpose of the following is to adjust the visual field for measurement with high accuracy, regardless of the frictional heat generated from the stage mechanism, even when there are many measurement points and the cumulative moving distance of the stage becomes large. A charged particle beam apparatus will be described.

  As one aspect for achieving the above object, in a charged particle beam apparatus equipped with a control device for performing alignment by detecting the position coordinates of an alignment pattern provided on a sample, a sample chamber or a sample stage A temperature sensor for measuring temperature is provided, and the control device detects when the amount of deflection by the deflector to the addressing pattern formed on the sample or the number of measurements for a plurality of measurement positions on the sample exceeds a predetermined value. A charged particle beam apparatus is proposed, in which temperature measurement is performed by the temperature sensor, and a control temperature for performing the alignment is obtained based on the temperature measurement.

  Further, as another aspect for achieving the above object, in the charged particle beam apparatus including the control device that performs alignment by detecting the position coordinates of the alignment pattern provided on the sample, the control device includes: Detecting the cumulative movement distance of the sample stage when the deflection amount by the deflector to the addressing pattern formed on the sample or the number of measurements at a plurality of measurement positions on the sample exceeds a predetermined value, and the cumulative movement Proposed is a charged particle beam device characterized in that an accumulated moving distance for performing alignment is obtained based on the distance.

  According to the above configuration, even when there are a large number of measurement points and the accumulated movement distance of the stage is large, it is possible to perform alignment at an appropriate timing, so that appropriate measurement is performed regardless of the temperature change of the stage mechanism. It is possible to adjust the field of view for.

FIG. 1 is a schematic configuration diagram of a charged particle beam apparatus (Example 1). FIG. 3 is a diagram for explaining an example of an alignment control device (Example 1). FIG. 3 is a diagram for explaining a sample position shift caused by heat generated by a stage mechanism (Example 1). The flowchart (front stage) explaining the procedure which detects the implementation condition of alignment control based on the temperature change of a stage, and performs alignment based on the said implementation condition. The flowchart (following stage) explaining the procedure which detects the implementation condition of alignment control based on the temperature change of a stage, and performs alignment based on the said implementation condition. FIG. 2 is a schematic configuration diagram of a charged particle beam apparatus (Example 2). FIG. 6 is a diagram for explaining an example of an alignment control device (Example 2). The flowchart (front stage) explaining the procedure which detects the implementation condition of alignment control based on the cumulative movement distance of a stage, and performs alignment based on the implementation condition. The flowchart explaining the procedure which detects the implementation condition of alignment control based on the cumulative movement distance of a stage, and performs alignment based on the implementation condition (after stage).

  One of the main purposes of the embodiments described below is to correct the position change of the sample due to the frictional heat of the sample stage to the charged particle beam deflection system, and to manage the amount of temperature change and movement of the sample stage for each measurement. By controlling the operation, high-efficiency and highly reliable length measurement is realized.

  A charged particle beam apparatus having means for determining the amount of change in the position of the sample and controlling the deflector of the charged particle beam and means for managing the amount of change in the temperature of the sample stage and performing alignment control will be described below.

  Also, a means for determining the amount of change in the position of the sample to control the deflector of the charged particle beam and a means for controlling the amount of movement of the sample stage and controlling the alignment will be described.

  In a charged particle beam device, it is difficult to measure the exact pattern position only by driving the sample stage, so the addressing pattern registered in advance after moving to the target coordinate where the measurement pattern exists once on the sample stage Is detected by a charged particle beam deflector to obtain an accurate measurement pattern position. This is because the positional accuracy of the charged particle beam deflector is superior to that of the sample stage. When the sample stage repeatedly moves for measurement and thermal expansion occurs, the position of the sample mounted on the sample stage changes, so the measurement point coordinates determined by the alignment before the measurement starts and the addressing pattern that is actually detected The distance will change. Therefore, by adding the amount of change to the charged particle beam deflection system in advance every time the pattern is measured, there is no need to change the scanning area of the charged particle beam when detecting the addressing pattern, and the heat of the sample stage When the influence of expansion is small, efficient measurement is possible.

  However, if the measurement position in the sample changes significantly, the correction direction may be reversed by the rotation of the sample, so check the distance between the previous measurement point and the target coordinate before addressing, If this distance exceeds a predetermined value set in advance, the amount of change added to the charged particle beam deflection system should be reset. Moreover, since the deflection range of the charged particle beam deflector is limited, it is necessary to consider the case where the change in the position of the sample exceeds this amount. Alignment generally detects the pattern position near the outer periphery of the sample and obtains the center position and rotation amount of the sample, so that the tendency of the sample misalignment is known, and it is preferable to use this.

  Allowable from the coordinates of each alignment point in the alignment before the start of measurement and the maximum position change calculated from the coordinates of each point in the alignment performed in advance, the temperature change between them and the deflection range of the charged particle beam A control temperature at which alignment is performed during measurement is determined using the amount of positional deviation that can be made.

  In charged particle beam irradiation equipment, the temperature change of the sample stage is caused by frictional heat due to the movement of the sample stage. Therefore, a method of managing the amount of movement of the sample stage instead of changing the temperature of the sample stage and performing alignment is also suitable. is there. From the coordinates of each alignment point in the alignment before the start of measurement and the maximum position change amount calculated from the coordinates of each point in the alignment performed in advance, from the amount of movement of the sample stage between them and the deflection range of the charged particle beam A management movement amount of the sample stage for performing alignment during measurement is determined using an allowable positional deviation amount.

  According to the above-described configuration, the sample position change caused by the expansion of the sample stage component due to the heat generated by the sliding of the sample stage drive system is wasted searching for the pattern by the correction operation to the charged particle beam deflection system. Measurement failures can be prevented by eliminating the operation and performing alignment control by managing the temperature change amount and movement amount of the sample stage.

  In this embodiment, the control of the change in the sample position caused by the frictional heat generated by driving the sample stage is realized by the method of performing the alignment operation by the deflection operation of the charged particle beam and the temperature management and movement amount management of the sample stage.

  FIG. 1 is a diagram illustrating the configuration of an SEM that is an example of a charged particle beam apparatus. In the embodiment described below, an example in which the SEM measurement and inspection target is a mask used in the exposure process of a semiconductor device will be described. However, the present invention is not limited to this. For example, a semiconductor wafer is measured, It is also possible to make it an inspection object.

The electron beam 106 is emitted from the electron source 101, converged by the electron lens 102, and deflector 103 for scanning the charged particle beam and deflection for correcting the scanning center position used for correcting addressing and stage position errors. A desired position on the sample 109 is scanned by a scanner 104 (hereinafter referred to as “image shift”). Secondary electrons generated by the scanning of the charged particle beam are detected by the detector 105 and enter the image processing device 111, converted into an image signal, and displayed on the image display device 113 as a sample image. The sample 109 transported from the outside of the apparatus into the sample chamber 107 maintained at a high vacuum of about 1 × 10 ⁻⁴ Pa by the vacuum evacuation device 110 is mounted on the sample table 108 and moves in the sample chamber along with the measurement. This movement control is performed by a stage control device 119, which monitors the position of the sample table with a stage interferometer 116 installed in the sample chamber 107 and a measurement mirror 117 mounted on the sample table 108, and a drive motor 118. The sample table is moved to a desired position. The sample chamber 107 is provided with a temperature sensor 114 for measuring the temperature. The SEM control device 112 performs overall control such as scanning of these charged particle beams, image information processing, dimension measurement, and stage movement. The alignment control device 115 in the SEM control device 112 is used in the sample chamber 107. The alignment operation is controlled using the temperature change. The place where the temperature is measured may be the sample table 108.

  FIG. 2 illustrates the alignment control device 115 in detail. The image shift management device 201 includes an image shift amount calculation unit and an image shift amount storage unit, and the temperature change management device 202 includes a temperature change amount calculation unit and a temperature storage. The alignment amount management device 203 includes an alignment change amount calculation unit and an alignment amount storage unit.

  FIG. 3 is a diagram for explaining a change in the position of the mask mounted on the sample stage. A mask 301 shows a state immediately after the start of measurement, and shows a state in which the movement of the X-axis and Y-axis of the length measurement system is parallel to the mask by performing alignment at four alignment points 303. On the other hand, the mask 302 shows a state after the measurement in the mask is repeatedly performed. When the sample stage is thermally expanded due to the influence of frictional heat, the change is caused by the distribution of heat or the heat of the sliding portion of the sample stage. The sample chamber, sample stage, and sample stage sliding portion are affected, and the mask position is considered to move not only in parallel but also in the rotational direction. The amount of movement due to the rotation of the mask differs depending on the location in the mask. In the example of FIG. 3, the amount of movement at the upper right measurement point 305 is larger than the measurement point 304 at the lower left that is near the center of rotation. Therefore, for example, when the vicinity of the measurement point 304 at the lower left is measured, the amount of change in position is small, so even if measurement is possible, the amount of change in position of the measurement point when the measurement point moves to the measurement point 305 at the upper right. If the addressing pattern is not found in the field of view, it is necessary to search for the addressing pattern and the measurement time increases. Further, when the amount of change in position is large, the deflectable area of the image shift 104 is exceeded, and the addressing pattern cannot be found and measurement is not performed.

  4 and 5 are flowcharts for performing alignment control during measurement using the temperature change of the sample stage by the apparatus of FIG. In step 401 of FIG. 4, measurement is started by a command from the SEM control device 112. In step 402, the temperature sensor 114 measures the temperature of the sample chamber 107 and stores it in the temperature change management device 202. In step 403, alignment is performed by detecting a pattern position in the vicinity of the outer periphery on the mask, and the absolute coordinate of the stage of each pattern used is stored in the alignment amount management device 203. In step 404, the address shift pattern calculated in the previous measurement is read from the image shift storage unit of the image shift management apparatus 201 and set as the initial value of the image shift amount. Therefore, it is not necessary to search the pattern by changing the position of the visual field, and efficient addressing can be realized in step 405.

  However, when the measurement position coordinates greatly change from the previous measurement point, the correction direction may be different due to the rotation of the mask. Therefore, in step 404, the information in the image shift amount storage unit of the image shift management device 201 is reset, and the image Addressing is performed in a state where the correction amount is not included in the shift amount. In step 406, the image shift amount when the addressing pattern is detected, the information about the distance between the image center acquired from the image acquired at the time of addressing and the addressing pattern, and the difference between the design value from the measurement point to the addressing pattern Is calculated by the image shift amount calculation unit of the image shift management device 201 and stored in the image shift amount storage unit as the positional shift amount of the addressing pattern, and this is read out as the initial value of the image shift amount in step 404 of the next measurement point. It will be.

  In step 407, measurement is performed. In step 408, it is confirmed that the measurement of all points has not been completed. In step 409, the image shift management apparatus 201 confirms that the image shift amount updated in step 406 is less than or equal to a threshold value. Since image shift is a deflector, the deflection area is limited, and a threshold value must be set in advance so as not to exceed the deflection area.

  If the image shift amount exceeds the threshold value, the process proceeds to FIG. 5. If it does not exceed the threshold value, the process proceeds to step 410 to check whether the measurement exceeds the specified number of times. Go to step 5. If not, return to step 404 to measure the next pattern. This specified number of times is a guideline for the number of times that the target pattern enters the field of view during addressing, but the number of times varies depending on the addressing magnification, the measurement position in the mask, the temperature of the sample stage, the pattern, etc. Keep it.

  In step 501 of FIG. 5, the temperature sensor 114 measures the temperature of the sample chamber 107 when the image shift amount exceeds the specified value in step 409 or when the measurement exceeds the specified number of times in step 410, and the temperature change management device 202. The temperature change amount calculation unit calculates the temperature change amount from the initial temperature and simultaneously stores it as the reference temperature. In step 502, alignment is performed again at the same point as in step 403, so that the coordinates of each pattern used for the alignment at this time and the coordinates before the start of measurement stored in the alignment amount management device 203 in step 403 are obtained. In comparison, the alignment amount change amount calculation unit calculates the maximum amount of the absolute value of the position change. In step 503, the maximum value of the position change amount per 1 ° C. can be calculated from the temperature change amount dT calculated in step 501 and the position change maximum amount dL in step 502, and this value and the threshold value D of the image shift amount in step 406. The temperature change amount T at which the alignment is performed is calculated from the following equation.

T = (D * dT) / dL
By storing this as the alignment control temperature in the alignment control temperature storage unit of the temperature change management device 202, a temperature change amount for controlling the alignment in the subsequent flow is obtained. In step 504, the temperature of the sample chamber 107 is measured before measurement of each point, and a temperature change amount is calculated from comparison with the reference temperature stored in the temperature change management device 202 in step 505. Until this change amount exceeds the alignment control temperature stored in the temperature change management device 202, the measurement is performed in steps 506 to 510 as in steps 404 to 408, and in the case where the alignment control temperature is exceeded, in step 511. The alignment is performed, the reference temperature stored in the temperature change management device 203 is reset, and the temperature of the sample stage measured in the next step 504 is stored in the temperature change management device 202 as a new reference temperature.

  FIG. 6 shows the configuration of an SEM that is an example of a charged particle beam apparatus, which is different from the first embodiment in that a temperature sensor for measuring the temperature of the sample chamber 107 is not installed.

  FIG. 7 illustrates the alignment control device 115 in detail. The image shift management device 701 includes an image shift amount calculation unit and an image shift amount storage unit, and the stage movement distance management device 702 includes a stage movement amount calculation unit and a stage. The alignment amount management device 703 includes an alignment change amount calculation unit and an alignment amount storage unit.

  8 and 9 are flowcharts for performing alignment control during measurement using the movement amount change of the sample stage by the apparatus of FIG. In step 401 of FIG. 8, measurement is started by a command from the SEM control device 112. In step 801, the value of the stage movement amount storage unit of the stage movement distance management device 702 is initialized. Thereafter, the movement amount of the sample stage in all operations is added. The stage target coordinates issued from the SEM control device 112 to the stage control device 119 when the sample stage is moved and the stage coordinates before the movement are acquired from the stage control device 119, and the movement amount is calculated by the stage movement amount calculation unit of the stage movement distance management device 702. Is calculated and cumulatively added to the stage movement amount storage unit. Thereafter, the processing from step 404 to 410 is repeated.

  In step 901 of FIG. 9, when the image shift amount exceeds the specified value in step 409 or the measurement amount exceeds the specified number of times in step 410, the moving amount of the sample stage is stored in the stage moving amount storage unit of the stage moving distance management device 702. Confirm with. In step 502, alignment is performed again at the same point as in step 403, so that the coordinates of each pattern used for the alignment at this time and the coordinates before the start of measurement stored in the alignment amount management device 203 in step 403 are obtained. The maximum amount of misalignment is calculated by comparison. In step 902, the stage moving distance S for alignment is calculated from the following equation using the movement amount Lt of the sample stage confirmed in step 901, the maximum position change amount dL in step 502 and the threshold value D of the image shift amount in step 406. To do.

S = (D * Lt) / dL
By storing this amount as the alignment control moving distance in the stage moving distance management device 702, the moving amount of the sample stage whose alignment is controlled in the subsequent flow is obtained. In step 903, the moving amount of the sample stage is confirmed by the stage moving distance management device 702, and until this moving amount exceeds the alignment control moving distance, measurement is performed in steps 506 to 510 as in steps 404 to 408, and alignment control is performed. If the movement distance is exceeded, alignment is performed in step 511 and at the same time, the value of the stage movement amount storage unit of the stage movement distance management device 702 is initialized once, and the movement distance is cumulatively added to the subsequent operation of the sample stage. Go.

Reference Signs List 101 electron source 102 electron lens 103 deflector 104 image shift 105 detector 106 electron beam 107 sample chamber 108 sample table 109 sample 110 vacuum exhaust device 111 image processing device 112 SEM control device 113 image display device 114 temperature sensor 115 alignment control device 116 Stage interferometer 117 Measurement mirror 118 Drive motor 119 Stage controller 301 Mask (before measurement)
302 Mask (during measurement)
303 Alignment point 304 Measurement point (lower left)
305 Measuring point (upper right)

Claims (4)

A charged particle beam source;
A deflector for deflecting the scanning position of the charged particle beam emitted from the charged particle beam source;
A sample stage for moving the sample so that the scanning position of the charged particle beam is positioned with respect to a plurality of measurement positions;
In the charged particle beam apparatus including a control device that performs alignment by detecting the position coordinates of the alignment pattern provided on the sample,
A temperature sensor for measuring the temperature of the sample chamber or the sample stage;
The control device includes:
When the deflection amount by the deflector to the addressing pattern formed on the sample or the number of measurements for a plurality of measurement positions on the sample exceeds a predetermined value, the temperature measurement by the temperature sensor is performed, A charged particle beam apparatus characterized in that a control temperature for executing the alignment is obtained based on the temperature measurement. In claim 1,
The charged particle beam device, wherein the control device calculates the control temperature based on the following arithmetic expression.
T = (D × dT) / dL
T: Control temperature D: Threshold value set in deflector that deflects scanning position dT: Temperature change amount measured by temperature sensor dL: Maximum position change amount of alignment pattern A charged particle beam source;
A deflector for deflecting the scanning position of the charged particle beam emitted from the charged particle beam source;
A sample stage for moving the sample so that the scanning position of the charged particle beam is positioned with respect to a plurality of measurement positions;
In the charged particle beam apparatus including a control device that performs alignment by detecting the position coordinates of the alignment pattern provided on the sample,
The control device includes:
Detecting the amount of deflection by the deflector to the addressing pattern formed on the sample, or the cumulative movement distance of the sample stage when the number of measurements for a plurality of measurement positions on the sample exceeds a predetermined value, A charged particle beam apparatus characterized in that an accumulated movement distance for executing the alignment is obtained based on the accumulated movement distance. In claim 3,
The charged particle beam device, wherein the control device calculates a cumulative movement distance for performing the alignment based on the following arithmetic expression.
S = (D × LT) / dL
S: Cumulative movement distance for executing alignment D: Threshold value set in deflector for deflecting scanning position LT: Detected cumulative movement distance dL: Maximum amount of position change of alignment pattern

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