JP2005201810A - Dimension measuring instrument, dimension measuring method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically move a position for focusing a charged beam on a sample from a measuring position, in dimension measurement for a pattern using the charged beam. <P>SOLUTION: A pattern P4 similar to the measuring objective pattern is detected within a two-dimensional image IE2, using a reference image IR2, a pattern P2 similar to a pattern for alignment is detected from the second area Rm excepting the first area Fm2 irradiated with an electron beam EB, in the measurement within an observation visual field, edge information of the pattern P2 is evaluated, and the focusing position for the electron beam EB is selected from the second area Rm, based on an evaluation result therein, and is determined. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a dimension measuring apparatus, a dimension measuring method, and a program, and for example, targets automatic dimension measurement of a semiconductor pattern using an electron microscope.

  Conventionally, various methods for automatically measuring a dimension of a semiconductor pattern using an electron microscope are known. As a specific example, the method described in Patent Document 1 will be described.

  First, a reference image, which is an image including a pattern that serves as a clue for finding a measurement location, is recorded in advance in a measurement condition file, and information such as coordinates of measurement points and offsets to be described later is described. The reference image is an image including a part of a circuit pattern created on a sample, a positioning pattern, and the like. For example, in the example shown in FIG. 11, the image IR100 including the cross mark P100 corresponds to the reference image.

  Next, the XY stage is driven to perform rough positioning, and then a pattern or mark included in the reference image is searched for in the observation field by a pattern recognition method. The position where the line width should be measured is detected using the searched pattern or mark position as a clue. In the example shown in FIG. 11, a predetermined portion of the reference image IR100, for example, a portion matching one corner is specified in the observation field of view, and this portion is set as a reference position Ps100. The line width of the pattern P120 is measured. The vector Vos100 drawn from the reference position Ps100 to the position MP100 where the line width is to be measured is called an offset.

By such a procedure, the method described in Patent Document 1 is intended to automatically and accurately measure the dimensions of a semiconductor pattern.
Japanese Patent No. 3333669

  However, along with the miniaturization of semiconductor patterns, changes in measured values of semiconductor patterns cannot be ignored due to damage to the sample surface caused by electron beam irradiation or deposition of hydrocarbons or the like from vacuum. There is a problem that the product yield decreases.

  For example, in the dimension measurement method disclosed in Patent Document 1 described above, when the distance between the position on the sample where the objective lens is focused and the pattern to be measured is short, the focusing process and the image of the observation field are captured. The irradiation region of the electron beam may partially overlap with the process, and the wafer may be greatly damaged. Considering such a problem, it is necessary to carefully determine the setting of the reference image for pattern recognition and the amount of movement to the measurement point in the measurement condition file of the method described in Patent Document 1. Conventionally, however, this point has been determined by skilled operators.

  The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a dimension measuring apparatus, a dimension measuring method, and a program capable of automatically moving a focusing position from a measuring position. It is in.

  For automatic focusing, a pattern needs to exist in the observation field at the time of focusing. Accordingly, another object of the present invention is to provide a dimension measuring apparatus, a dimension measuring method, and a program for automatically setting an optimum position for automatic focusing based on design data and an observation field of view of an electron microscope. There is.

  The present invention aims to solve the above problems by the following means.

That is, according to the present invention,
A charged particle source for generating a charged particle beam;
A deflector that deflects the trajectory of the charged particle beam and scans the sample on which the measurement target pattern and the alignment pattern are formed; and
Signal processing means for detecting at least one of secondary electrons, reflected electrons, and backscattered electrons emitted from the sample by irradiation with the charged particle beam, and outputting data of a two-dimensional image representing the surface state of the sample When,
Using a reference image prepared in advance, a first pattern similar to the measurement target pattern is detected in the two-dimensional image, and the charged particle beam is irradiated when measuring the first pattern in the observation field of view. Pattern recognition means for detecting a second pattern similar to the alignment pattern from a second area excluding the first area to be
Focus position determination for evaluating edge information of the second pattern and selecting and determining a focus position that is a position for focusing the charged particle beam from the second region based on the evaluation result Means,
Focusing means for performing focusing of the charged particle beam;
An irradiation position moving means for moving the irradiation position of the charged particle beam;
Measuring means for measuring the dimension of the first pattern;
A dimension measuring device is provided.

Moreover, according to the present invention,
A procedure for generating a charged particle beam;
A procedure for deflecting the charged particle beam and scanning a sample having a measurement target pattern and an alignment pattern formed on the surface;
A procedure of detecting at least one of secondary electrons, reflected electrons and backscattered electrons emitted from the sample by irradiation of the charged particle beam, and obtaining a two-dimensional image representing the state of the surface of the sample;
Using a reference image prepared in advance, a first pattern similar to the measurement target pattern is detected in the two-dimensional image, and the charged particle beam is irradiated when measuring the first pattern in the observation field of view. Detecting a second pattern similar to the alignment pattern from a second area excluding the first area to be
A procedure for evaluating edge information of the second pattern and selecting and determining a focusing position that is a position for focusing the charged particle beam from the second region based on the evaluation result;
A procedure for performing focusing of the charged particle beam;
A procedure for moving the irradiation position of the charged particle beam;
Measuring the dimensions of the first pattern;
A dimension measuring method is provided.

  Furthermore, according to the present invention, there is provided a program that causes a computer to execute the dimension measuring method.

  The present invention has the following effects.

  That is, according to the present invention, since the optimum position for focusing is automatically set, the focus position is automatically determined with high accuracy without depending on the skill level of the operator in the dimension measurement. be able to.

  Further, according to the present invention, the scanning origin of the charged particle beam is moved from the measurement position to the optimally set focusing position, so that the measurement is performed by damaging the sample surface due to the irradiation of the charged particle beam or depositing hydrocarbon or the like. The influence on the value is suppressed to the minimum, and dimension measurement with high accuracy becomes possible.

  Hereinafter, some embodiments of the present invention will be described with reference to the drawings. In the following, the case where an electron beam is used as the charged particle beam will be described. However, the present invention is not limited to this, and can be applied to the case where an ion beam is used, for example.

(1) One Embodiment of Dimension Measuring Device FIG. 1 is a block diagram showing a schematic configuration of one embodiment of a dimensional measuring device according to the present invention. The dimension measuring apparatus 1 shown in the figure is a scanning electron microscope that measures the dimensions of a semiconductor pattern by scanning a focused electron beam EB.

  The dimension measuring apparatus 1 includes an electron beam column 10, various control circuits 32, 34, 36, and 38, an XY stage 22 that supports a wafer W as a sample, a motor 24, a stage control circuit 44, Detector 26, image memory 46, pattern recognition device 42, monitor 48, control computer 20, communication circuit 52, simulation computer 40, and various storage media built in or removable from the device in advance. MR2, MR4, MR6.

  The control computer 20 controls the entire apparatus via various control circuits 32, 34, 36, 38, a stage control circuit 44, a simulation computer 40, a pattern recognition device 42, and the like.

  The storage media MR2 and MR4 store a recipe file describing a series of procedures of a dimension measuring method to be described later and a measurement condition file. These files are stored in advance in these storage media, and are taken in from each external storage medium or other device via the communication circuit 52 connected to a dedicated line or public line and stored in these storage media. You can also

  The storage medium MR6 stores design data related to the pattern to be measured.

  The simulation computer 40 retrieves design data from the storage medium MR6 as necessary, processes the pattern data, and supplies it to the control computer 20.

  The electron beam column 10 includes an electron gun 12, a condenser lens 14, a scanning lens 16, and an objective lens 18. The electron gun 12 receives a control signal from the electron gun control circuit 32, generates an electron beam EB, and irradiates the wafer W. The condenser lens 14 receives a control signal from the condenser lens control circuit 34, excites a magnetic field or an electric field, and focuses the electron beam EB so as to have an appropriate beam diameter. The objective lens 18 excites a magnetic field or an electric field by a control signal from the objective lens control circuit 38 and refocuses the electron beam so that the electron beam EB is irradiated onto the wafer W with just focus. The scanning lens 16 receives a control signal from the scanning lens control circuit 36, excites an electric field or magnetic field for deflecting the electron beam EB, and thereby scans the wafer W two-dimensionally with the electron beam EB. The motor 24 operates in response to a control signal from the stage control circuit 44, and moves the XY stage 22 in the XY plane.

  The detector 26 detects secondary electrons, reflected electrons, and backscattered electrons generated from the wafer W by irradiation with the electron beam EB. The output signal of the detector 26 constitutes a two-dimensional image representing the state of the surface of the wafer W, and data of this two-dimensional image is stored in the image memory 46.

  The data of the two-dimensional image is output from the image memory 46 to the monitor 48, and the two-dimensional image is displayed for observation of the wafer surface and also output to the pattern recognition device 42.

  The pattern recognition device 42 compares the design data extracted from the storage medium MR6 by the control computer 20 or the pattern data processed by the simulation computer 40 with the two-dimensional image data supplied from the image memory 46, The deviation amount of the actual pattern from the design pattern is calculated, and the obtained value is supplied to the control computer 20. The control computer 20 supplies the command signal to at least one of the scanning lens control circuit 36 and the stage control circuit 44, thereby correcting the deviation amount using at least one of the scanning lens 16 and the XY stage 22.

  The operation of the dimension measuring apparatus shown in FIG. 1 will be described below as an embodiment of the dimension measuring method according to the present invention.

(2) First Embodiment of Dimension Measurement Method FIG. 2 is a flowchart showing a schematic procedure of the first embodiment of the dimension measurement method according to the present invention.

  First, a measurement condition file is read from the storage media MR2 and MR4, and measurement conditions such as position coordinates of measurement points 1 to n (n is a natural number), a threshold value such as a gradation value used for pattern recognition, a reference image, and an offset. Is read (step S1). Next, a count n of a counter (not shown) built in the control computer 20 is set to 1 (step S2), and the XY stage 22 is driven based on the read position information of the first measurement point. The wafer W is moved so that the first measurement point is located at the center of the observation field (step S3). An electron beam is irradiated at that position, and the obtained two-dimensional image is taken into the image memory 46 (step S4).

  In general, it is difficult to precisely specify the measurement point and the position of automatic focusing only by operating the XY stage 22 in step S3. Therefore, the measurement position is searched by comparing the image of the observation field with the reference image, and the pattern is in a known positional relationship (offset) with respect to the searched measurement position in the region outside the observation field at the measurement position measurement. After moving the electron beam irradiation position to a certain position, the excitation current of the objective lens 18 is controlled to perform focusing, and the movement to the measurement position is performed again to measure the line width of the pattern.

  Specifically, the pattern recognition device 21 reads a reference image supplied to the control computer 20 directly from the storage medium MR6 or after being processed by the simulation computer 40 (step S5) and previously stored in the image memory 46. A part that matches the reference image in the image of the observation field is searched (step S6). Next, it is determined whether or not there is a portion that matches the reference image in the observation visual field, that is, whether or not the pattern has been recognized (step S7). If the pattern is recognized, the automatic focusing position and the measurement position are determined (step S8), a vector (offset) subtracted from the measurement position to the automatic focusing position is calculated (step S9), and the XY stage is calculated. 22 or the scanning lens 16 is used to change the scanning origin of the electron beam EB, and the electron beam EB onto the pattern to be automatically focused at a position away from the measurement position in a predetermined direction by a predetermined distance according to the offset. Is moved (step S11), and automatic focusing is performed by controlling the magnetic field or electric field of the objective lens 18 (step S12).

  Next, the electron beam EB is moved onto the pattern to be measured at a position away from the position where the automatic focusing is performed by a distance determined by the offset in a direction opposite to the direction determined by the offset (step S13). Further, the line width of the pattern is measured at that position (step S14). Thereafter, it is determined whether or not the measurement has been completed for all the measurement points (step S15). If there are still points to be measured, the counter (not shown) is incremented by 1 (step S16). Returning to S2, the same operation is repeated. Further, if a portion that matches the reference image cannot be found in the observation field in step S7, that is, if pattern recognition fails, error processing is performed in step S10, and then the process proceeds to step S15.

  A method of determining the automatic focusing position and the measurement position using the reference image will be described with reference to FIG. In FIG. 3, (a) shows an example of a reference image, and (b) shows an example of a two-dimensional image of an actual pattern at the time of pattern recognition. 2C shows a two-dimensional electronic image at the time of automatic focusing on the actual pattern shown in FIG. 2B, and FIG. 3D shows a two-dimensional electronic image when the actual pattern shown in FIG. Indicates.

  The reference image shown in FIG. 3A is an image of patterns P2 and P4 that are part of the semiconductor circuit pattern formed on the wafer W. The reference image IR2 is obtained by extracting design data from a database stored in the storage medium MR6, performing a lithography simulation by the simulation computer 40, and further simulating a secondary electron image of the scanning electron microscope based on the obtained data. A part of the obtained image data is extracted. The lithography simulation data is a simulation of a pattern shape when transferred onto the wafer W based on semiconductor design data (CAD data in the present embodiment) and parameters of an exposure machine used for semiconductor manufacturing. However, since the simulation calculation takes time, an image obtained by omitting the simulation of the two-dimensional image of the scanning electron microscope may be used as the reference image. Also, a simple lithography simulation such as rounding the corner of the design data pattern or the design data itself may be used. In the example shown in FIG. 3, the reference image IR2 in (a) is created using design data, and the center of the reference image, that is, the matching point is made to coincide with the measurement position MP2 (indicated by a cross line in the figure). The measurement position MP2 is searched for in the observation visual field IE2 of FIG. 3B by a pattern recognition technique, and the position Pf2 to be automatically focused is found by using the position as a clue. At this time, the reason why the measurement position MP2 does not coincide with the visual field center Cf2 is the positioning accuracy (+/− 3 μm) of the XY stage 22 in step S3. Here, when the image is stored in the image memory 46, the electron beam EB is also irradiated to the region in the observation visual field Fm2 at the time of measurement. The amount of irradiation of the surrounding electrons is sufficiently low, and damage to the sample surface due to irradiation with the electron beam EB, or dimensional change of the semiconductor pattern due to deposition of hydrocarbon or the like from vacuum can be ignored. In this embodiment, since the magnification at the time of pattern recognition is 15,000 times and the magnification at the time of measurement is 150,000 times, the irradiation amount per unit area at the time of pattern recognition is 1/100 of that at the time of measurement. A vector Vos2 obtained by subtracting the automatic focusing position Pf2 from the measurement position MP2 represented by the reference image in FIG. 3A as the starting point is an offset in the present embodiment. The offset on the reference image IR2 is known and is described in advance in the measurement condition file.

  Next, the scanning origin of the electron beam EB is moved to the automatic focusing position Pf2 (step S11), and the objective lens 18 is controlled to execute automatic focusing as shown in FIG. 3C (step S12). Then, the electron beam EB is moved so that the measurement position MP2 becomes the center of the field of view (see FIG. 3D) (step S13), and the dimension measurement of the measurement target pattern P4 is executed (step S14). In FIG. 3B, reference numeral Faf2 indicates an observation visual field at the time of automatic focusing.

  Next, a method for determining an automatic focusing position and a method for calculating an offset will be described more specifically with reference to FIGS. 4 and 5. FIG. 4 is a flowchart showing a more specific schematic procedure of the method for determining the autofocus position, and FIG. 5 is a diagram for explaining a method for searching for the autofocus position.

  First, a measurement position and a measurement magnification are set on CAD data (step S21). Next, a magnification for performing automatic focusing is set, and a visual field at the time of automatic focusing is calculated (step S22). Subsequently, using CAD data, as shown in FIG. 5, the observation within the range Rm in which the field of view can be moved by image shift with an electron microscope and excluding the observation field Fm at the time of measurement is automatically observed. Scanning is performed in the visual field Faf2, a position where the sum of the edge lengths of the patterns included in the observation visual field Faf2 is maximized is searched, and the searched position is determined as an automatic focusing position (step S23). At this time, the observation visual field Faf2 at the time of automatic focusing must not go out of the range Rm in which the visual field can be moved by image shift with an electron microscope or overlap the observation visual field Fm at the time of measurement. In FIG. 5, the scanning allowable range of the observation visual field Faf2 is indicated by a hatched area. Here, when there are a plurality of positions where the sum of the pattern edge lengths in the visual field Faf2 at the time of automatic focusing is maximized, the distance from the observation visual field Fm at the time of measurement is the farthest in consideration of the effect of charge-up. Select the position.

  In the automatic focusing, the visual field in the automatic focusing does not overlap with the observation visual field at the dimension measurement position, and many pattern edges need to exist. In this embodiment, the range in which the field of view can be moved by image shift with an electron microscope is 10 μm, the measurement magnification is 150,000 times, and the autofocus magnification is 150,000 times. Since the field of view at 150,000 times is 0.96 μm square, an area of 9.04 μm square and an area of 1.92 μm square centering on the measurement point are provided so that the observation fields during autofocusing do not overlap. The autofocus position was searched in the excluded area.

  As described above, according to the present embodiment, based on CAD data, the center of the observation field where there are more pattern edges does not overlap with the observation field at the time of dimension measurement and is automatically set as the optimum focus position. Therefore, in the dimension measurement, it is possible to minimize the influence on the measurement value due to the damage of the sample surface due to the irradiation of the electron beam EB or the deposition of hydrocarbon or the like from the vacuum due to the irradiation of the electron beam EB. In addition, since the focus position is automatically determined based on the operator's intuition and experience, the measurement accuracy does not depend on the operator's experience and skill level.

(2) Second Embodiment of Dimension Measurement Method In the procedure for determining the autofocus position and the measurement position in the first embodiment described above, the optimum autofocus position is searched on the CAD data. The feature of this embodiment is that the automatic focusing position is also searched in parallel with the search of the measurement position using the pattern recognition technique in the observation field at low magnification. Therefore, it is not necessary to set information on the autofocus position and offset amount in the measurement condition file. In this embodiment, other procedures are substantially the same as those in the first embodiment described above.

  A method for determining an automatic focusing position and a method for calculating an offset in the present embodiment will be described with reference to FIGS.

  FIG. 6 is a flowchart showing an automatic focusing position determination procedure and an offset calculation procedure in the second embodiment of the dimension measuring method according to the present invention, and FIG. 7 is an automatic focusing position in the present embodiment. It is a figure explaining the search method of this concretely.

  First, as shown in FIG. 6, a low-magnification image Im4 near the measurement position is acquired (step S31). Next, as shown in FIG. 7, the measurement position MP4 is searched by the pattern recognition method using the reference image registered in advance in the measurement condition file (step S32). Next, a pattern edge is extracted by differentiating the obtained low-magnification image Im4 (step S33). Subsequently, in an area in the low-magnification image Im4 subjected to the edge extraction process and excluding the observation visual field Fm4 at the time of measurement (a portion indicated by hatching in FIG. 7), an observation visual field at the time of automatic focusing A position where the sum of the pixels in the pattern edge portion is maximized is searched for in Faf4 and determined as an automatic focusing position (step S34). At this time, the observation visual field Faf4 at the time of automatic focusing should not go out of the low-magnification image Im4 or overlap the observation visual field Fm4 at the time of dimension measurement. In this embodiment, differentiation processing is used for edge extraction, but line element extraction processing such as binarization, a sobel filter, and a Laplacian filter can also be used.

(3) Third Embodiment of Dimension Measurement Method A feature of this embodiment is that autofocus is executed using line scanning. In this embodiment, other procedures are substantially the same as those in the first embodiment described above.

  Automatic focusing using line scanning in this embodiment will be described with reference to FIGS. FIG. 8 is a flowchart showing a procedure for determining an automatic focusing position and a procedure for calculating an offset in the present embodiment, and FIG. 9 is a diagram for explaining a method for searching for an automatic focusing position.

  As shown in FIG. 8, first, the measurement position MP6 (see FIG. 9) and the measurement magnification are set on the CAD data (step S41). Next, a magnification for performing automatic focusing is set, and a region Faf6 for line scanning at the time of automatic focusing is calculated (step S42). As shown by the cross line SL6 in FIG. 9, in the present embodiment, two intersecting line scanning methods are employed. Next, using CAD data, line scanning at the time of automatic focusing is the largest in a range Rm6 in which the field of view can be moved by image shift with an electron microscope and excluding the observation field of view Fm6 at the time of measurement. A position that crosses the edge is searched (step S44). At this time, the line scan at the time of automatic focusing should not go out of the range Rm6 in which the field of view can be moved by image shift with the electron microscope or overlap the observation field of view Fm6 at the time of measurement.

  In the present embodiment, the cross-shaped line scan method is used. However, the present invention is not limited to this. For example, as shown in the explanatory diagram of FIG. 10, one line set along the direction across the range Rm6 in which visual field movement is possible. It is also possible to scan using the line SL8.

(4) Program The series of steps of the dimension measurement method described above is stored in a storage medium such as a floppy disk or CD-ROM as a program to be executed by a computer, for example, in the form of the recipe file described above, and is read by the computer and executed. May be. Thereby, the dimension measuring method according to the present invention can be realized using a general-purpose computer capable of image processing. The recording medium is not limited to a portable medium such as a magnetic disk or an optical disk, but may be a fixed storage medium such as a hard disk device or a memory. Further, a program incorporating a series of procedures of the dimension measuring method described above may be distributed via a communication line (including wireless communication) such as the Internet. Furthermore, the program incorporating the above-described series of dimension measurement methods is encrypted, modulated, or compressed, and stored in a recording medium via a wired or wireless line such as the Internet. You may distribute it.

(5) Manufacturing method of semiconductor device If any of the above-described dimension measuring methods according to the present invention is executed in the manufacturing process of the semiconductor device, the optimum position for focusing does not depend on the skill level of the operator. It is automatically set, and the influence on the measurement value due to the damage of the sample surface due to the irradiation of the charged particle beam and the deposition of hydrocarbon or the like is suppressed to the minimum. As a result, it is possible to measure the dimensions with high accuracy, so that the semiconductor device can be manufactured with a high yield.

It is a block diagram which shows schematic structure of one Embodiment of the dimension measuring apparatus concerning this invention. It is a flowchart which shows the schematic procedure of 1st Embodiment of the dimension measuring method concerning this invention. It is a figure explaining an example of the method of determining an autofocus position and a measurement position using a reference image. It is a flowchart which shows the specific procedure of the determination method of an automatic focusing position. It is a figure explaining the method of searching for an automatic focusing position. It is a flowchart which shows the determination procedure of an automatic focusing position, and the calculation procedure of offset in 2nd Embodiment of the dimension measuring method concerning this invention. It is a figure explaining concretely the search method of the automatic focus position in 2nd Embodiment of the dimension measuring method concerning this invention. It is a flowchart which shows the determination procedure of the automatic focusing position in the 3rd Embodiment of the dimension measuring method concerning this invention, and the calculation procedure of offset. It is a figure explaining the search method of the automatic focus position in 3rd Embodiment of the dimension measuring method concerning this invention. It is a figure explaining the other search method of the automatic focusing position in 3rd Embodiment of the dimension measuring method concerning this invention. It is a figure which shows an example of a reference image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scanning electron microscope 10 Electron beam column 12 Electron gun 14 Condenser lens 16 Scan lens 18 Objective lens 20 Control computer 22 XY stage 24 Motor 26 Detector 40 Simulation computer 42 Pattern recognition device 44 Stage control circuit 46 Image memory 48 Monitor 52 Communication Circuit EB Electron Beams Faf2, Faf4, Faf6 Observation Field of View Fm2, Fm4, Fm6 at Automatic Focusing Observation Field Im4 at Measurement Low-Magnification Image MP2, MP4 Near Measurement Position Measurement Position MR2, MR4, MR6 Storage Medium P2 Measurement target pattern P4 Positioning pattern Pf2 Automatic focusing position Rm2, Rm6 Range of visual field movement by image shift W

Claims (5)

A charged particle source for generating a charged particle beam;
A deflector that deflects the trajectory of the charged particle beam and scans a sample on which a measurement target pattern and an alignment pattern are formed; and
Signal processing means for detecting at least one of secondary electrons, reflected electrons, and backscattered electrons emitted from the sample by irradiation with the charged particle beam, and outputting data of a two-dimensional image representing the surface state of the sample When,
Using a reference image prepared in advance, a first pattern similar to the measurement target pattern is detected in the two-dimensional image, and the charged particle beam is irradiated during measurement of the first pattern within an observation field Pattern recognition means for detecting a second pattern similar to the alignment pattern from a second area excluding the first area to be
Focus position determination for evaluating edge information of the second pattern and selecting and determining a focus position that is a position for focusing the charged particle beam from the second area based on the evaluation result Means,
Focusing means for performing focusing of the charged particle beam;
An irradiation position moving means for moving the irradiation position of the charged particle beam;
Measuring means for measuring the dimension of the first pattern;
A dimension measuring device comprising:   The dimension measuring apparatus according to claim 1, wherein the edge information of the second pattern is evaluated based on design information of the alignment pattern.   The edge information of the second pattern is evaluated based on a two-dimensional image obtained by irradiating the sample with the charged particle beam at a magnification lower than the magnification at the time of dimension measurement. The dimension measuring apparatus according to 1. A procedure for generating a charged particle beam;
A procedure of deflecting the charged particle beam and scanning a sample on which a measurement target pattern and an alignment pattern are formed;
A procedure for detecting at least one of secondary electrons, reflected electrons and backscattered electrons emitted from the sample by irradiation of the charged particle beam, and obtaining a two-dimensional image representing the state of the surface of the sample;
Using a reference image prepared in advance, a first pattern similar to the measurement target pattern is detected in the two-dimensional image, and the charged particle beam is irradiated during measurement of the first pattern within an observation field Detecting a second pattern similar to the alignment pattern from a second area excluding the first area to be
A step of evaluating edge information of the second pattern, and selecting and determining a focusing position which is a position for focusing the charged particle beam from the second region based on the evaluation result;
A procedure for performing focusing of the charged particle beam;
A procedure for moving the irradiation position of the charged particle beam;
Measuring the dimensions of the first pattern;
A dimension measuring method comprising:   The program which makes a computer perform the dimension measuring method of Claim 4.

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