JP4957152B2 - Measuring method - Google Patents

Description

The present invention relates to a long process measurement you measure the size of the fine workpiece, length measuring method for that particular application of electron microscopy.

  In recent years, higher density and higher performance of semiconductor devices (LSIs) have been promoted, and accordingly, further miniaturization of electronic devices such as transistors constituting the semiconductor devices is required. When an electronic device is miniaturized, the characteristics of the electronic device may change greatly due to slight changes in shape and size. Therefore, it is required to accurately grasp the size of the electronic device (total size or partial size: the same applies hereinafter) on the order of nanometers (nm).

  Conventionally, a scanning electron microscope (hereinafter referred to as “SEM”) has been used for measurement (measurement) of the size of a minute measurement object. However, since the SEM has a limited spatial resolution, it has become impossible to cope with the recent miniaturization of electronic devices. Therefore, in recent years, the size of electronic devices has been measured using a transmission electron microscope (hereinafter referred to as “TEM”), which has a higher spatial resolution than SEM.

  However, in the TEM, a scale error of about ± 5% occurs due to changes in the conditions and magnification of the electron lens. Further, in the measurement at a high magnification of TEM, it is necessary to calibrate the image scale by measuring the lattice spacing in real space using a crystal image of a single crystal whose crystal lattice spacing is known. Even in the process of calibrating the scale, an error occurs in the magnification and aspect ratio depending on the lens conditions and the operator. For this reason, it is difficult to measure in nanometer order with TEM.

  Therefore, in recent years, a scanning transmission electron microscope (hereinafter referred to as “STEM”) has come to be used for measuring an electronic device. STEM has an advantage that the scale of the image does not depend on the conditions of the electron lens because the image of the sample is acquired by scanning the converged electron beam.

  In order to measure the size of a minute measurement object using the STEM, it is necessary to calibrate the scale using a single crystal sample whose crystal lattice spacing is known as in the case of the TEM.

  Hereinafter, a conventional length measurement method using STEM will be described in detail with reference to FIGS. 1 (a) and 1 (b).

  First, a crystal lattice image of a single crystal sample with a known crystal structure is photographed, and the lattice spacing is measured in real space. The resolution (number of pixels) of the lattice image is, for example, 1024 pixels × 1024 pixels. In this resolution, although it depends on the crystal structure of the single crystal, it is necessary to set the size of one pixel to 0.025 nm or less in order to identify the lattice spacing of 0.2 nm. That is, it is necessary to set the magnification to a high magnification of 400,000 or more.

  FIG. 1A is a diagram showing a crystal lattice image of a single crystal sample (silicon single crystal) photographed by STEM. The scale is calibrated by measuring the distance between the atomic images (bright spots) of the lattice image. In this case, since the error increases only by measuring the lattice spacing at one location, generally the lattice spacing is measured at 10 locations or more, and the average value is calculated. For example, as shown in FIG. 1A, lines are drawn in the vertical direction, the horizontal direction, and the diagonal direction, respectively, and the vertical lattice spacing, the horizontal lattice spacing, and the diagonal lattice spacing are measured. And the average value of a lattice space | interval is calculated based on those measurement results.

  After the scale is calibrated in this way, an image of the measurement object is acquired by STEM as shown in FIG. 1B, and the distance of a desired portion (for example, a portion indicated by an arrow in the figure) is measured.

In addition, there exists what was described in patent document 1 as a prior art considered to be related to this invention. This Patent Document 1 describes a microscope observation method for optimizing a defocus amount and erasing a virtual image by calculation in a STEM.
JP 2003-249186 A

  As described above, in the length measurement method using the conventional STEM, a single crystal sample with a known crystal lattice spacing is used for scale calibration at a high magnification. However, the above-described method has a problem that a measurement error of the lattice spacing occurs because the center position of the atomic image (bright spot) and the angle for drawing the line are slightly different for each operator. In addition, the operator needs to draw a line on the lattice image and measure a total of 10 or more lattice intervals in the vertical direction, the horizontal direction, and the oblique direction, which is complicated.

  Furthermore, in general, in the length measurement method using STEM, the object to be measured is observed with a bright field STEM image as shown in FIG. 1B, so that the edge of the object to be measured becomes unclear depending on the diffraction conditions. It becomes difficult to accurately determine the position of the edge. For this reason, there is also a problem that the measurement value varies depending on the operator.

  Furthermore, since the observation conditions are different between STEM observation at high magnification and STEM observation at medium or low magnification, even if the scale is calibrated at high magnification, the result cannot be reflected at medium magnification or low magnification. . Conventionally, generally, in STEM observation at a high magnification, the scale is calibrated using a single crystal sample as described above, and in STEM observation at a low magnification, the scale is calibrated using a commercially available standard sample. Yes. However, there is no standard sample with high reliability in STEM observation at medium magnification.

An object of the present invention is to be applied to the determination of the size of the fine workpiece, does not occur variations in measurement values by the operator to provide a long process measuring measurement accuracy is not high.

According to one aspect of the present invention, in a length measurement method using an electron microscope, a step of obtaining a lattice image of a single crystal using a sample having a single crystal with a known crystal lattice interval, and Fourier transform of the lattice image are performed. Obtaining a diffraction spot image, correcting the diffraction spot image so that the position of the diffraction spot of the diffraction spot image matches the theoretical position of the diffraction spot, and inverse Fourier transforming the corrected diffraction spot image. A length measuring method comprising converting and calibrating the scale.

  In the present invention, after obtaining a lattice image of a single crystal with an electron microscope, the lattice image is Fourier-transformed to obtain a diffraction spot image, and the position of the diffraction spot in the diffraction spot image is the position of the theoretical diffraction spot. The diffraction spot image is corrected so as to coincide with. Since the real space and the reciprocal lattice space in which the diffraction spot appears have an inverse relationship, an image of the real space is obtained by performing inverse Fourier transform on the corrected diffraction spot image. At this time, by converting the scale into an inverse, it becomes a real space scale. By using the scale calibrated in this way, the size of the measurement object can be measured with high accuracy.

  According to still another aspect of the present invention, in a length measurement method using an electron microscope, a step of photographing a measurement object by a dark field method to obtain an electron microscope image, and a step of obtaining a line profile of the electron microscope And a step of measuring a distance between peaks of the differential line of the line profile.

  An electron microscope image of a measurement object by an electron microscope is often taken by a bright field method. However, when measuring the size of the measurement object, it is difficult for the operator to accurately determine the edge of the measurement object in the electron microscope image taken by the bright field method, which causes variations in the measurement value. .

  In the present invention, the measurement object is photographed by the dark field method, and the line profile of the measurement location is obtained from the photographed electron microscope image. Then, the line profile is differentiated to obtain a differential line. Differentiating the line profile shows the change in intensity (luminance), so the edge of the measurement object can be easily determined. As a result, variations in measurement values among workers are avoided, and highly accurate length measurement is possible.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Length measuring device)
FIG. 2 is a schematic diagram showing a configuration of a length measuring device (STEM) according to the embodiment of the present invention.

  The length measuring apparatus according to this embodiment includes a control unit 10, an electron gun 11, converging lenses 12a and 12b, a converging lens diaphragm 13, a scanning coil 14, an objective lens 15, a sample mounting unit 16, and a STEM. It comprises a detector (electron beam detector) 17 and an image analysis unit 18.

  The electron gun 11 accelerates electrons with an acceleration voltage corresponding to a signal from the control unit 10 and outputs the electrons as an electron beam. A plurality of stages (two stages in FIG. 2) of converging lenses 12a and 12b are arranged below the electron gun 11. These converging lenses 12 a and 12 b form an electron beam probe having a desired size and a desired current from an electron beam emitted from the electron gun 11 in accordance with a signal from the control unit 10.

  A converging lens diaphragm 13 is disposed below the converging lenses 12a and 12b. Since the electron beam probe formed by the converging lenses 12a and 12b has an unnecessary widened portion, the unnecessary widened portion is cut by the converging lens stop 13.

  The sample 20 is mounted on the sample mounting unit 16. A scanning coil 14 and an objective lens 15 are disposed between the sample mounting portion 16 and the converging lens stop 13. The scanning coil 14 scans the electron beam in a two-dimensional direction in accordance with a signal from the control unit 10. The objective lens 15 refracts the electron beam according to a signal from the control unit 10 so as to be focused on the surface of the sample 20 or in the vicinity thereof.

  The STEM detector 17 is disposed below the sample mounting unit 16. The STEM detector 17 detects an electron beam that has passed through the sample 20 and outputs an electrical signal corresponding to the detection result to the image analysis unit 18. The image analysis unit 18 is controlled by the control unit 10, generates a STEM image from the electrical signal output from the STEM detector 17, performs image processing described later on the STEM image, and calibrates the scale. A circular detector is used as the STEM detector 17 when a bright field STEM image is taken, and an annular detector is used as the STEM detector 17 when a dark field STEM image is taken.

  The basic configuration of the length measuring apparatus according to the present embodiment is the same as that of a normal STEM, but an image analysis unit 18 that performs image processing on the STEM image acquired via the STEM detector 17 to calibrate the scale. This is different from ordinary STEM.

  Hereinafter, a method for calibrating the image scale of the length measuring apparatus described above will be described. In the embodiment of the present invention, calibration of the scale of an image acquired by a length measuring device (STEM) is performed at a high magnification of 400,000 or more, a medium magnification of 100,000 or more and less than 400,000, and a magnification of less than 100,000. This is divided into three stages of low magnification.

(Scale calibration at high magnification)
FIGS. 3A and 3B are diagrams showing a scale calibration method at a high magnification of 400,000 or more. First, a crystal lattice image of a single crystal sample with a known crystal lattice interval is taken by a length measuring device (STEM). FIG. 3A is a lattice image of a single crystal sample (silicon single crystal) imaged by a length measuring device. Here, the resolution (number of pixels) of the lattice image is 1024 pixels × 1024 pixels. The grid image may be captured by either the bright field method or the dark field method, but it is preferable to capture the grid image by the dark field method with little change in the grid image depending on the focus condition.

  When this lattice image is subjected to Fourier transformation (FFT), a diffraction spot image as shown in FIG. 3B is obtained. The position of the diffraction spot (bright spot) in the diffraction spot image is compared with the position of the diffraction spot (theoretical position of the diffraction spot) obtained by calculation, and the magnification, aspect ratio, and image distortion of the image are corrected.

  FIG. 4A is a diagram showing the position of the bright spot of the diffraction spot image obtained by Fourier transform of the grating image taken by the length measuring device, and the position of the diffraction spot obtained by calculation. In FIG. 4 (a), the unmarked white spot indicates the position (correction target position) of the diffraction spot obtained by calculation, and the white spot to which x is added is the position of the diffraction spot obtained by Fourier transform of the lattice image. (Measurement position) is shown, and the arrow indicates the direction of correction. As shown in FIG. 4A, the magnification, aspect ratio, and distortion of the image are corrected so that the position of the diffraction spot obtained by Fourier transform overlaps the correction target position.

  FIG. 4B is a diagram showing a diffraction spot image after correcting the magnification, aspect ratio, and distortion. As shown in FIG. 4B, the magnification, aspect ratio, and distortion are corrected so that the position of the diffraction spot coincides with the correction target position, and then the image scale is converted to a real space scale. Since the real space and the reciprocal space where the diffraction spots appear are in the reciprocal relationship, the corrected diffraction spot image is subjected to inverse Fourier transform (inverse FFT) to return to the real space image, and then the scale is converted to the reciprocal. The real space scale. In this way, calibration of the scale at a high magnification is completed, and it becomes possible to measure the measurement object with high accuracy in the observation with an electron microscope at a high magnification.

(Scale calibration at medium magnification)
In calibration of a scale at a medium magnification of 100,000 times or more and less than 400,000 times, a reference crystal is formed by patterning a single crystal with a known crystal lattice spacing by photolithography. This reference pattern is composed of, for example, a comb-like pattern or a plurality of quadrangles arranged in a two-dimensional direction.

  FIG. 5A shows an example of a reference pattern formed by patterning a silicon single crystal. In this example, a square pattern 31 having a side of 50 nm (however, a design value) arranged in a two-dimensional direction at regular intervals is used as a reference pattern. The square pattern 31 is made of silicon single crystal, and the space between the square patterns 31 is made of silicon oxide.

  When this reference pattern is observed at a magnification of, for example, 400,000 times, a crystal lattice image is obtained. When this lattice image is Fourier transformed, a diffraction spot image is obtained. FIG. 5B shows a diffraction spot image obtained by Fourier transform of the lattice image. In FIG. 5B, diffraction spots appear at the center of the image and the tip of each arrow. The magnification, aspect ratio, and distortion of the image are corrected by comparing the position of the diffraction spot in the diffraction spot image with the theoretical position of the diffraction spot.

  Next, the corrected diffraction spot image is subjected to inverse Fourier transform to return it to the real space image, and the scale is converted to the reciprocal to obtain the real space scale. And the magnitude | size, space | interval, pitch, etc. of the square pattern 31 are measured using the scale. A sample having a standard pattern in which the length of the predetermined portion is determined in this manner is used as a standard sample.

  By calibrating the scale using this standard sample, it becomes possible to measure the measurement object with high accuracy in the observation with an electron microscope of medium magnification.

  In FIG. 5 (a), the reference pattern is composed of a plurality of square patterns 31 made of silicon single crystal, but the shape of the reference pattern is not limited to this, and is rectangular, comb-like or other It may be a shape. When the reference pattern is formed by a square or rectangular pattern, the length of one side (design value) is preferably 50 to 100 nm.

(Scale calibration at low magnification)
For calibration of the scale at a low magnification of less than 100,000 times, a standard sample having the reference pattern described in the calibration of the image scale at medium magnification is used.

  FIG. 6 is a diagram illustrating an example of a reference pattern provided on the standard sample 30. This reference pattern is formed by arranging square patterns 31 in a two-dimensional direction at regular intervals. Here, it is assumed that the arrangement pitch of the square patterns 31 is measured by the method described in the scale calibration at the medium magnification and is known. The length of one side of the square pattern 31 is 50 nm.

  An STEM image is obtained by observing such a standard sample 30 at a low magnification. In this case, the acquisition of the STEM image is preferably performed by the dark field method, but may be acquired by the bright field method. Thereafter, the line profiles in the vertical direction, the horizontal direction, and the diagonal direction of the STEM image are measured. That is, as shown in FIG. 7A, lines are drawn in the vertical direction, the horizontal direction, and the diagonal direction of the STEM image, and the relationship between the position and intensity (luminance) is obtained for each line. FIG. 7B is a diagram showing line profiles in the vertical direction, the horizontal direction, and the diagonal direction of FIG. From this line profile, the average value of the pitch of the square pattern 31 is calculated to calibrate the scale.

  In this way, a standard sample for image scale calibration at a low magnification is obtained, and it becomes possible to measure a measurement object with high accuracy in an electron microscope observation at a low magnification.

(Measurement of measured object)
After the scale is calibrated at the high magnification, medium magnification, and low magnification as described above, the measurement object is actually measured (measured) at the desired magnification.

  In order to measure a measurement object, first, an electron microscope image (STEM image) of the measurement object is taken with a length measuring device (STEM). It is preferable to take an electron microscope image by a dark field method capable of grasping the atomic number and density distribution of the material without depending on the diffraction conditions.

In addition, since the length measurement value varies depending on the measurement conditions such as the STEM lens conditions, scan speed, and flyback time, it is preferable that the STEM image photographing conditions are the same as those at the time of scale calibration. Although the image intensity depends on the diffraction condition depending on the capture angle of the detector, an image independent of the diffraction condition can be obtained by setting the capture angle to 50 mrad or more. Therefore, it is preferable that the detector capture angle is 50 mrad or more.

  Next, a line profile of a portion to be measured is extracted from the dark field STEM image. FIG. 8 is a diagram showing a dark field STEM image of a measurement object photographed by a length measuring device (STEM). In FIG. 8, line A indicates a portion from which a line profile is extracted, and line B indicates a line profile at the position of line A. Line C is a differential line obtained by differentiating the line profile once.

  In the present embodiment, the peak interval of the inflection point of the differential line is measured and used as the width of the measurement object. Conventionally, since the position of the edge of the measurement object is not clear, there has been a problem that the measurement value varies depending on the operator or the apparatus. However, in the length measurement method according to the present embodiment, a line profile is extracted by the image analysis unit 18, a differential line is generated by differentiating the line profile, a peak position of an inflection point of the differential line is detected, and an edge is detected. Since the position of is automatically determined, variations in measured values by the operator and the apparatus are avoided, and highly accurate measurement is possible.

  FIG. 9 is a flowchart showing an outline of a length measuring method using the length measuring apparatus of the present embodiment.

  First, in step S11, high-resolution observation conditions for a length measuring device (STEM) are set. Thereafter, in step S12, a single crystal thin film sample 20 having a known crystal lattice spacing is mounted on the sample mounting portion 16 of the length measuring device.

  Next, in step S13, the specimen incidence direction of the electron beam is adjusted. In step S14, the magnification is adjusted, and in step S15, the image size is set.

  Next, in step S16, the electron gun 11 is driven to generate an electron beam. Thereby, the electron beam which permeate | transmitted the sample 20 is detected by the STEM detector 17, and a crystal lattice image is obtained. Next, in step S <b> 17, the grating image is Fourier transformed by the image analysis unit 18 to generate a diffraction spot image. Thereafter, the process proceeds to step S18, where the image analysis unit 18 compares the diffraction spot position of the diffraction spot image with the theoretical diffraction spot position, and corrects the magnification, aspect ratio, and distortion of the image. Steps S16, 17, and 18 are performed until the error between the position of the diffraction spot in the diffraction spot image and the position of the theoretical diffraction spot disappears, that is, the position of the diffraction spot in the diffraction spot image and the position of the theoretical diffraction spot. Repeat until they match.

  After calibrating the scale in this way, an electron microscope image of the measurement object is acquired in step S19. Thereafter, in step S20, a line profile is acquired from an electron microscope image of the measurement object. In step S21, the line profile is fitted to the scale after calibration, and the distance is measured in step S22.

  Hereinafter, the results of measuring the lattice constant of a silicon single crystal using three apparatuses (STEM) using the method of this embodiment will be described.

  Using three devices (devices A, B, and C), the lattice spacings of the 111, 002, and 022 surfaces of the silicon single crystal were measured at a magnification of 400,000 times. The results are shown in Table 1 below. In Table 1, the Si lattice constant is the theoretical lattice spacing on each lattice plane, and the calibration value is the lattice spacing actually measured by each device.

  As shown in Table 1, in the length measurement method of the present embodiment, the error of the three apparatuses is within ± 0.006 nm, and it was confirmed that the length measurement value does not depend on the apparatus.

  Moreover, the length (length in the vertical direction and length in the horizontal direction) of the measurement object shown in FIG. 8 was measured using these three devices. The results are shown in Table 2 below. In Table 2, the measurement error is indicated by the difference between the measured value by the device A and the measured value by the device B or C, based on the measured value by the device A.

  As can be seen from Table 2, the measurement error between the devices was within ± 0.3%.

  As described above, according to the present invention, in measurement at high magnification, medium magnification, and low magnification, there is no variation in measured values by the apparatus, and highly accurate measurement is possible. In particular, since there is no standard sample with high reliability in the measurement of medium magnification, the reliability of the measurement value was not sufficient, but according to the present invention, the reliability of the measurement value at medium magnification is remarkably high. improves.

  In addition, according to the present invention, an image is taken using a dark field method that does not depend on diffraction conditions or sample conditions, and the edge of the measurement object is determined based on the line profile of the image. There is no variation in value.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1) an electron gun that generates an electron beam;
A converging lens for converging the electron beam emitted from the electron beam;
A scanning coil for scanning an electron beam converged by the convergent lens;
An objective lens for focusing the electron beam scanned by the scanning coil on or near the surface of the sample;
An electron beam detector for detecting an electron beam transmitted through the sample;
A length measuring apparatus comprising: an image analysis unit that inputs a signal output from the electron beam detector, draws an electron microscope image, and Fourier transforms the electron microscope image.

(Additional remark 2) The said image analysis part acquires the grating | lattice image of a single crystal sample as said electron microscope image, Fourier-transforms the grating | lattice image, acquires a diffraction spot image, The position of the diffraction spot of the said diffraction spot image is The length measuring apparatus according to appendix 1, wherein the image is corrected so as to coincide with a theoretical position of the diffraction spot.

  (Supplementary note 3) The length measuring apparatus according to supplementary note 2, wherein the image analysis unit calibrates the scale by performing inverse Fourier transform on the corrected image.

  (Additional remark 4) The said image analysis part has a function which acquires the line profile of the said electron microscope image, and measures the distance between the peaks of the differential line of the said line profile, The length measurement of Additional remark 1 characterized by the above-mentioned. apparatus.

(Appendix 5) In a length measuring method using an electron microscope,
Obtaining a lattice image of a single crystal using a sample having a single crystal with a known crystal lattice spacing;
Obtaining a diffraction spot image by Fourier transforming the grating image;
Correcting the diffraction spot image so that the position of the diffraction spot of the diffraction spot image matches the theoretical position of the diffraction spot;
And a step of calibrating the scale by performing inverse Fourier transform on the corrected diffraction spot image.

  (Additional remark 6) The length measuring method of Additional remark 5 characterized by using a silicon single crystal as said sample.

  (Supplementary note 7) The length measurement method according to supplementary note 5, wherein the lattice image is acquired at a magnification of 400,000 times or more.

(Supplementary Note 8) The sample has a reference pattern formed by patterning a single crystal,
The length measuring method according to claim 5, further comprising a step of measuring the reference pattern using the calibrated scale after the step of calibrating the scale.

(Supplementary note 9) The measurement of the reference pattern
The sample is photographed by a dark field method to obtain an electron microscope image of a reference pattern,
Obtain a line profile of the electron microscope image,
9. The length measuring method according to appendix 8, wherein the distance between peaks of the differential line of the line profile is fitted to a scale after calibration.

  (Supplementary note 10) The length measurement method according to supplementary note 9, wherein the reference pattern is used for length measurement in an electron microscope image of less than 400,000 times.

(Supplementary Note 11) In a length measuring method using an electron microscope,
A step of taking a measurement object by a dark field method and obtaining an electron microscope image;
Obtaining a line profile of the electron microscope;
Measuring the distance between the peaks of the differential line of the line profile.

  (Supplementary note 12) The length measuring method according to supplementary note 11, wherein, in the step of acquiring the electron microscope image, a detector capture angle is set to 50 mrad or more.

FIGS. 1A and 1B are diagrams showing a conventional length measurement method. FIG. 1A is a crystal lattice image of a single crystal sample (silicon single crystal) photographed by STEM, and FIG. It is a STEM image of a measurement object. FIG. 2 is a schematic diagram showing a configuration of a length measuring device (STEM) according to the embodiment of the present invention. 3A and 3B are diagrams showing a scale calibration method at a high magnification. FIG. 3A is a lattice image of a single crystal sample (silicon single crystal) imaged by a length measuring device, and FIG. b) is a diffraction spot image obtained by Fourier transform of the grating image. FIG. 4A shows the position of the bright spot of the diffraction spot image obtained by Fourier transform of the grating image taken by the length measuring device and the position of the diffraction spot obtained by calculation, and FIG. It is a figure which shows the diffraction spot image after correct | amending a magnification, an aspect ratio, and distortion. FIG. 5A is a view showing an example of a reference pattern formed by patterning a silicon single crystal, and FIG. 5B is a view showing a diffraction spot image obtained by Fourier-transforming the lattice image of the reference pattern. is there. FIG. 6 is a diagram illustrating an example of a reference pattern provided in a standard sample. FIG. 7A is a diagram showing a position where a line profile is acquired in the STEM image of the standard sample, and FIG. 7B is a diagram showing the line profile. FIG. 8 is a diagram showing a dark field STEM image of a measurement object photographed by a length measuring device (STEM). FIG. 9 is a flowchart showing an outline of a length measuring method using the length measuring apparatus of the present embodiment.

Explanation of symbols

10 ... control unit,
11 ... electron gun,
12a, 12b ... convergent lens,
13 ... Convergent lens aperture,
14: Scanning coil,
15 ... Objective lens,
16 ... Sample mounting part,
17 ... STEM detector,
18 ... Image analysis unit,
20 ... Sample 30 ... Standard sample,
31 ... Square pattern.

Claims (3)

In the length measurement method using an electron microscope,
Obtaining a lattice image of a single crystal using a sample having a single crystal with a known crystal lattice spacing;
Obtaining a diffraction spot image by Fourier transforming the grating image;
Correcting the diffraction spot image so that the position of the diffraction spot of the diffraction spot image matches the theoretical position of the diffraction spot;
And a step of calibrating the scale by performing inverse Fourier transform on the corrected diffraction spot image. The sample has a reference pattern formed by patterning a single crystal;
The length measuring method according to claim 1, further comprising a step of measuring the reference pattern using the calibrated scale after the step of calibrating the scale. The measurement of the reference pattern is
The sample is photographed by a dark field method to obtain an electron microscope image of a reference pattern,
Obtain a line profile of the electron microscope image,
Fitting the distance between the peaks of the differential line of the line profile to the scale after calibration
The length measuring method according to claim 2, wherein the length measuring method is performed.

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