JP2003317654A - Electron microscopy method, electron microscope and biological sample inspection method and biological inspection apparatus using the same - Google Patents

Abstract

(57) [Summary] [Problem] The performance of a system for obtaining a correction value based on a positional shift of an image pair, such as a focus correction system using parallax, largely depends on a positional shift analysis method. However, the conventionally employed displacement analysis method has problems that the analysis accuracy does not become less than one pixel, there is no function for verifying the reliability of the analysis result, and it is susceptible to a background change. SOLUTION: An image pair S1 (n,
m) and the phase difference image P ′ (k, l) between the Fourier transform images of S2 (n, m)
Is calculated, and is obtained from the position of the center of gravity of a δ-like peak appearing on the inverse Fourier transform image of the image. [Effect] Since the displacement analysis accuracy is less than one pixel, the focus analysis accuracy is improved. Alternatively, the number of pixels required to obtain the same analysis accuracy can be reduced. The reliability of the analysis result can be evaluated based on the δ-like peak intensity. Since the phase component is used, it is hardly affected by the background change. With the above performance improvement, unskilled persons can make the same correction as skilled persons.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for automatically correcting a focus and a movement amount by using an image of an electron beam microscope.

[0002]

2. Description of the Related Art The applicant of the present invention uses an image of an electron microscope to determine whether or not to automatically correct the focal point and the amount of movement, and an apparatus for correcting the amount of deviation in a continuously moving sample stage. Regarding the amendment, as a result of conducting a prior art search, three items that are likely to be related were extracted. The first is the proceedings of the 51st Scientific Lecture Meeting of the Electron Microscope Society of Japan by Norihiko Ichise and others (1
(May 995) There is a drift correction for automatic adjustment of the transmission electron microscope by the phase spectrum method described on page 161, and if the influence of image drift is analyzed and corrected in the phase spectrum method that analyzes the focus, astigmatism, and axis shift. There is disclosure.
However, there is no disclosure regarding improvement of analysis accuracy by calculation of peak center of gravity, determination using a correlation value, and correction of focus and drift during continuous movement of the sample stage. The second case is Japanese Laid-Open Patent Publication No. 10-187993, which discloses an apparatus for analyzing the positional deviation between the images based on the phase difference between the Fourier transform images of the two images taken under different conditions. However, it is only the disclosure that the posture and distance of the object are measured from the mark attached to the object, and there is no disclosure about returning to the electron beam device including the technical idea. The third case is Japanese Unexamined Patent Publication No. 09-148932, which discloses that the amount of positional deviation due to the parallax of an electron microscope image is detected by image processing and the result is returned to the electron beam apparatus. More specifically, when the sample is located on the focal plane, there is no movement between the images before and after the change of the electron beam incident angle, but if the sample is out of the focal plane, the image is changed before and after the change of the electron beam incident angle. There is a movement between them. where α is the swing angle of the incident electron beam, M is the magnification, and Cs is the spherical aberration coefficient, D = Mα for the position shift D and the focus shift F.
There is a relationship of (F + Csα ² ), and if the positional shift D due to parallax can be measured, the focal shift F can be obtained. There is a description of an apparatus for recording the image pair before and after the change of the incident angle in a memory, analyzing the positional deviation D by using the cross-correlation method or the least squares method to obtain the focal deviation F, and correcting the focus of the objective lens. However, there is no disclosure about the positional shift analysis method using the phase difference of the Fourier transform image. In the device that automatically corrects the focus and movement amount using the image of the electron microscope,
The performance is determined by the setting of the image analysis method and the analysis result feedback method, but the optimization has not been performed in accordance with the correction purpose, the correction accuracy, and the correction time.

[0003]

The performance of the apparatus for automatically correcting the electron microscope from the positional deviation D between the electron microscope images, such as focus analysis using parallax, largely depends on the method of analyzing the positional deviation D. The accuracy of the positional shift analysis methods that have been used for electron microscope image analysis such as the cross-correlation method and the least square method has been limited by the size of one pixel of the electron beam detector. The length of one side of one pixel of the CCD camera used for the current electron microscope image capturing is about 25 μm. The defocus F corresponding to one pixel depends on the incident electron beam angle and magnification, but the incident angle change α is at most large because it is limited by the hole diameter of the objective diaphragm.
It is about 0.5 °, and the magnification must be the actual observation magnification. For example, when the magnification is 5,000 and the incident angle change is 0.5 °, the focal length corresponding to the positional deviation D of one pixel is about 0.6 μm. This is lower than the focus correction accuracy by a trained operator. It is not practical to improve the device performance such as making the image used for the position shift analysis finer in order to improve the accuracy in the focus analysis, because the analysis time and the device cost increase extremely.

Further, the conventional displacement analysis method does not have a function of numerically confirming whether or not the analysis is correctly executed, and the observer visually confirms it. Alternatively, focus correction was performed based on the obtained analysis results, and there was no choice but to confirm that the correction was correct. Since there is no guarantee that all the analyzes will be executed correctly in the automatic correction device, a function for stopping the correction is necessary when the reliability of the analysis results is poor.

Further, the conventional displacement analysis method cannot be analyzed when the background changes greatly or when the shadow of the objective aperture enters the image. The above phenomenon is a phenomenon that occurs on a daily basis in TEM observation, and it becomes a practical problem that it becomes inoperable.

[0006]

In the present invention, the following analysis method is adopted for the analysis of displacement between electron microscope images.

An image pair having a positional deviation is obtained by using an angle deflecting means for changing the incident angle of the first electron beam on the sample, Fourier transform is applied to each image, and the phase difference image is calculated. To do. In the analysis image obtained by performing the inverse Fourier transform or the Fourier transform on the phase difference image, a δ-like peak occurs at a position corresponding to the position shift. Since it can be assumed that only δ-like peaks are present in the analysis image, the delta-like peaks can be regarded as noise components. Therefore, if the barycentric position of the δ-like peak is calculated, the δ-like peak position can be correctly obtained even if it includes a decimal point. Further, the intensity of the δ-like peak calculated after normalizing the intensity of the analysis image can be used as the correlation value indicating the degree of coincidence of the images.

[0008]

Embodiment 1 FIG. 19 is a basic configuration diagram of a transmission electron microscope (hereinafter abbreviated as TEM) used in an embodiment of the present invention. Electron gun 11 and its control circuit 11 ', irradiation lens 12 and its control circuit 1
2 ', irradiation system electronic deflection coil 13 and its control circuit 13',
Objective lens 14 and its control circuit 14 ', projection lens 15 and its control circuit 15', imaging system electron deflection coil 16 and its control circuit 16 ', electron beam detector 17 and its control circuit 17', sample stage 18 and It is composed of the control circuit 18 ', a computer 19 equipped with control software and image processing software. Each control circuit receives the control command sent from the control software of the computer 19, and when the control ends, sends a return value to the computer. The electron beam detector 17 is an electron beam detector composed of a large number of pixels such as a CCD camera, and the obtained image signal is based on the recording device of the computer 19 or the phase analysis of the Fourier transform image with a cable for image transmission. It is transmitted at high speed to the arithmetic unit 20 for position shift analysis. The calculator 19 is connected to a calculator 20 for positional deviation analysis based on phase analysis of Fourier transform images.

FIG. 3 shows a flowchart of TEM image photography. First, an irradiation system electron beam deflection coil as an angle deflection means for applying an acceleration voltage to an electron beam which is a first charged particle beam generated by the electron gun 11 and deflecting the angle so that the electron beam passes on the optical axis. Make an adjustment using 13 and confirm that the electron beam reaches the electron beam detector 17. The direction parallel to the optical axis is the z direction, and the plane orthogonal to the optical axis is the xy plane. Irradiation system lens 1
After adjusting 2, TEM of Sample 21 is inserted at low magnification by inserting Sample 21.
Check the statue. An objective aperture is inserted in the optical axis to increase the TEM image contrast. The observation field of view is selected while increasing the magnification of the projection lens 15, focus correction is performed, and an image by the electron beam that has passed through the sample that is the second charged particle beam is captured by the electron beam detector 17.

A focus analysis method utilizing parallax is applied to the focus analysis in this focus correction. A first TEM image taken by injecting an electron beam from a first angle substantially parallel to the optical axis and a second TEM image taken by entering an electron beam at a second angle inclined by an angle α from the optical axis. To use. As shown in FIG. 4, when the focal point is deviated, a positional deviation occurs between the first TEM image and the second TEM image. D = M for defocus F and displacement D due to parallax
There is a relationship of α (F + Csα ² ). The operator sets the magnification M and the swing angle α. Since the spherical aberration coefficient Cs is unique to the apparatus, if the positional deviation D between image pairs can be measured, the defocus F can be specified. The present invention is characterized in that an analysis method based on a phase difference analysis of a Fourier transform image is applied to the analysis of the positional deviation D. As shown in FIG. 1, an electron beam detector 17 is used to obtain the first and second TEM images obtained by changing the incident angle of the electron beam to the sample by using the electron deflection coil 13 provided above the objective lens 14. To shoot. The photographed first and second TEM images are arithmetic units for position shift analysis based on phase difference analysis of Fourier transform images.
It is sent to 20, and the positional deviation D as the analysis result is sent to the computer 19. The calculator 19 calculates the focus shift F from the position shift D, finds the objective current I _obj necessary to set the target focus, and corrects the focus of the objective lens 14 based on it.

FIG. 5 shows an explanatory diagram of the positional deviation analysis method using the phase component of the Fourier transform. S1 (n, m) = S2 (n + dx, m + dy) is assumed for image pair (S1, S2) with misregistration D = (dx, dy), and S1 (n, m), S2 Let S be the two-dimensional discrete Fourier transform of (n, m).
Let 1 '(k, l) and S2' (k, l).

For the Fourier transform, F {S (n + dx, m + dy)} = F {S (n,
m)} exp (idxk + idyl), so S1 '(k, l) = S2'
It can be transformed into (k, l) exp (idxk + idyl). So S1 '(k, l)
The positional deviation of S2 '(k, l) is the phase difference exp (idxk + idyl) = P' (k,
Expressed as l). P '(k, l) is also a wave with a period of (dx, dy), so an image obtained by inverse Fourier transform of the phase difference image P' (k, l)
In P (n, m), a δ-like peak occurs at the position of (dx, dy).
If (dx, dy) has a decimal point, for example (dx, dy) = (2.5,2.5)
Then, the intensity of δ-like peak is equally distributed to (2,2), (2,3), (3,2), (3,3). Since it can be assumed that only the δ-like peak exists in the image P (n, m), if the center of gravity of the four pixel intensities is calculated, even if the δ-like peak position includes a decimal point, it can be correctly obtained. In the cross-correlation method, which is a conventional analysis method, | S1 '|| S2' | is used as an analysis image, and the displacement is analyzed from the position having the maximum value in the analysis image. Since the analysis image contains the image intensity, that is, the amplitude information together with the positional deviation information, the positional deviation analysis accuracy is not improved even if the center of gravity calculation is performed. Note that instead of removing all amplitude information, S1 '(k, l) ・ S2' (k, l) ^* = | S1 '|| S2' | exp (idxk + idyl)
An image in which the amplitude component is suppressed by performing log or √ processing on the amplitude component of is calculated, and a δ-like peak occurs at the position (dx, dy) of the displacement vector even if the image is subjected to inverse Fourier transform. Therefore, the displacement analysis may be performed on the image.
Even if the phase difference image P '(k, l) is Fourier transformed, (-dx, -dy)
Since a δ-like peak occurs in the position difference analysis, the position shift analysis may be performed on the Fourier transform image of the phase difference image P ′ (k, l). Further, instead of the Fourier transform, another orthogonal transform may be used to calculate an image having a peak corresponding to the positional deviation.

It should be noted that even if the difference between S1 (n, m) and S2 (n, m) includes not only the positional shift but also the noise component and the change in the background, the image is slightly deformed due to the change in the incident electron beam angle. Even if it includes, misregistration analysis is possible if there is sufficient common part in S1 (n, m) and S2 (n, m). In this case δ
The peaks other than the specific peak are regarded as noise components. When the intensities of δ-like peaks are calculated after normalizing the intensities of the entire image P (n, m), the peak intensities become weaker as the number of non-coincident portions between image pairs, that is, noise components, increases. If there are many matching parts, the peak intensity will be strong, and if there are few matching parts, the peak intensity will be weak.Therefore, if this peak intensity is indicated as a correlation value indicating the matching degree of the image pair, the operator can calculate the noise component ratio, that is, The reliability can be identified. If the lower limit value of the correlation value is set and the calculated correlation value is less than or equal to the lower limit value, the objective lens is not adjusted so that malfunction can be prevented.

Further, since the above-mentioned positional shift analysis method is an analysis method utilizing the phase component of the image, it is also less susceptible to the influence of background changes. The conventional misalignment analysis method cannot be analyzed if there is a background difference due to the distribution of the irradiation current density between image pairs, but it can be analyzed by the misalignment analysis method used in the present invention. Further, in the conventional misalignment analysis method, if the shadow of the objective aperture is mixed in the image, the analysis becomes impossible. However, in the misalignment analysis method used in the present invention, even if some shadow of the objective aperture is mixed, the image pair is common. If enough parts exist, it can be analyzed. Since the automatic correction device may be used by a person who is unfamiliar with TEM operation, it is important to be able to operate even if the TEM adjustment is somewhat inadequate.

In order to perform the above displacement analysis, TEM
The image is captured by an electron beam detector 17 such as a CCD camera. The signal detected by the electron beam detector 17 is amplified by an amplifier, quantized, and then sent to a computer 19 or a position shift analysis calculator 20 based on a phase difference analysis of a Fourier transform image.
If the gain and offset settings of the amplifier are inappropriate, many image features will be removed during quantization. The electron beam detector 17 is provided with a function of calculating the image intensity average value and the variance and automatically adjusting them by using the gain and offset of the detector amplifier so as to be designated values. In addition, the gain and offset may not reach the specified average value and variance, so if the contrast adjustment is insufficient, a function is added to alert the operator to change the field of view and make a decision such as readjustment of the TEM body. Has been done.

FIG. 6 shows a basic configuration diagram of the electron beam detector 17 used in the TEM. It is composed of a scintillator 71, a connecting portion 72, and a CCD camera 73. The electrons emitted to the scintillator 71 generate photons. The generated photons pass through a coupling part 72 in which a large number of optical fibers are bundled, and are transmitted to a CCD camera 73 while retaining positional information. The CCD camera 73 is composed of a large number of pixels arranged two-dimensionally. CCD camera 7
The electric charge generated by the photons reaching 3 is accumulated in each pixel. The accumulated charge is read as an output signal of each pixel. The gain of each pixel, that is, the output signal intensity by one incident electron is determined by the luminous efficiency of the scintillator 71, the coupling portion.
It is determined by the transmission efficiency of 72 and the quantum efficiency of CCD camera 73. Since the respective constants vary from pixel to pixel, a fixed pattern is formed on the electron beam detector 17.

The image captured by the electron beam detector 17 having the fixed pattern has the first contrast reflecting the sample structure and the second contrast reflecting the fixed pattern of the electron beam detector 17.
The contrast of is recorded. When the above displacement analysis is applied to the image recorded by the electron beam detector 17 having a fixed pattern, the first contrast reflecting the sample structure is the image pair S1 (n, m) and S2 (n, m). However, since the second contrast reflecting the fixed pattern of the electron beam detector 17 does not move, the first peak due to the sample structure corresponds to the positional deviation in the analysis image P (n, m). A second peak due to a fixed pattern is generated at the origin at the origin. TE
In an image such as M image in which the contrast of the sample structure is very low, the second peak intensity due to the fixed pattern is often larger than the first peak intensity due to the sample structure. The above-mentioned displacement analysis method has been applied so far to images with high sharpness and contrast captured by an optical device, and since there was almost no effect of the fixed pattern,
It was determined that the peak with the highest intensity in the analysis image P (n, m) was the analysis result. However, the influence of the fixed pattern cannot be ignored in the TEM image, and the conventional peak determination method that uses the peak with the highest intensity as the analysis result determines that the second peak due to the fixed pattern is the analysis result and that there is no misalignment. Is often issued.

CCD camera control software may be provided with preprocessing such as gain normalization for dividing an image by a fixed pattern photographed in advance to reduce the influence of the fixed pattern. However, since the fixed pattern changes over time, it needs to be updated regularly. In order to reduce the influence of the fixed pattern, it is always necessary to perform maintenance. Even if maintenance is performed, it is inevitable that the fixed pattern will change due to differences in individual imaging conditions such as the electron beam irradiation amount. Although the gain normalization alone can reduce the effect of the fixed pattern, it is difficult to remove it. In images with low contrast of sample structure such as electron microscope images, even if image processing such as gain normalization is applied to image pair S1 (n, m) and S2 (n, m), May also increase the intensity of the second peak due to the fixed pattern.

In the position shift analysis of the TEM image, it is necessary to add a step of automatically determining the first peak due to the sample structure from the analysis image having the second peak due to the fixed pattern together with the first peak due to the sample structure. There is. There are the following two algorithms for automatic peak determination. Both utilize the feature that the second peak due to the fixed pattern always occurs at the origin.

First, in one method, since the second peak due to the fixed pattern always occurs at the origin, the intensity at the origin is set to 0.
Alternatively, it is a method of applying an origin mask for replacing with another constant value. However, since the first peak may occur at the origin, it is necessary to judge whether to apply the origin mask. Now, assuming a specific example shown in FIG. 7, a flow of peak determination will be described. The position D1 and the intensity I1 of the first peak 31 due to the sample structure, and the position D2 and the intensity I2 of the second peak 32 due to the fixed pattern are assumed. Since D2 = 0, the case assumed is | D1 |> 0 and I1> I2 (Fig. 7 (a)), | D
When 1 |> 0 and I1 <I2 (Fig. 7 (b)), when | D1 | ~ = 0 (Fig. 7)
There is (c)). In each case, the analysis image P (n, m) is standardized and the intensity I of the maximum peak 33 searched and the analysis image P (n, m) is subjected to the origin mask and then standardized and searched. The intensity I ′ of the peak 34 having the highest intensity is compared. Figure 7 (a)
In the case of, if the intensity of the second peak is so small that it can be ignored, the intensity of the peak with the maximum intensity does not change before and after applying the origin mask. If the intensity of the second peak is strong, the origin mask is applied to the second peak 32. Since the cracked intensity moves to the first peak 31 and the noise component 35, I ≦ I ′. In the case of FIG. 7B, the first peak 3 is applied before the origin mask is applied.
The intensities assigned to 1 and the second peak 32 are put together in the first peak 31, so that I <I '. Meanwhile, Fig. 7 (c)
In this case, when the origin mask is applied, the first peak 31 is removed together with the second peak 32, and only the noise component 35 increases, so that I> I ′. As described above, the first peak 31 can be determined by comparing the analysis results before and after applying the origin mask.
FIG. 8 (a) shows the flow of the peak determination process. Intensity before and after applying the origin mask The strength of the maximum peak, that is, the correlation value is compared.If the correlation value decreases by applying the origin mask, the result before applying the origin mask is adopted, and the correlation value increases or changes by applying the origin mask. If not, the result after applying the origin mask is used.

As a second method, it is assumed that there are two peaks in the analysis image P (n, m), and the positions and intensities of the two peaks are set to be output. In addition,
If there are two peaks, the correlation value of each becomes smaller, so it is better to reset the lower limit of the correlation value. FIG. 8 (b) shows the flow of two peak detection steps. 7 (a) and 7 (b)
Since the peaks larger than the lower limit of the correlation value are the first peak 31 and the second peak 32, two peaks are output. | D1 |
Since || D2 | = 0, the first peak is selected when the one having a larger positional deviation amount is selected from the output peaks. In the case of FIG. 7C, since the first peak and the second peak overlap, there is only one peak in P (n, m). If there is only one peak having a correlation value larger than the lower limit, that peak is used as the analysis result.

Next, regarding the setting of the swing angle α, the swing angle α of the electron beam incident on the sample is used when the focus shift F is obtained from the positional shift D due to parallax. Must be set. The swing angle α is measured using a diffraction image of a crystalline sample such as gold or silicon whose lattice constant is known. Since the lattice constant is known, the scattering angle per pixel of the diffraction image can be calculated if the wavelength of the incident electron beam is known. Misalignment D between the first diffraction image taken at the first incident angle and the second diffraction image taken at the second incident angle
_{When α} is analyzed and the product of the positional deviation D _α and the scattering angle per pixel is calculated, the measured value of the swing angle α of the incident electron beam is obtained. The swing angle α of the incident electron beam is almost proportional to the current value I _BT of the irradiation system electron deflection coil 13, but the irradiation system electron deflection coil 13 is provided above the objective lens 14 as shown in FIG. Therefore, the angle of incidence on the sample also changes depending on the electromagnetic field of the objective lens 14. Swing angle α of incident electron beam
It is necessary to introduce a correction term with the exciting current I _obj value of the objective lens 14 as a parameter in the calculation formula of. For example α = A * I _BH
+ B * I _obj * I _BH is used. Here, A and B are device-specific constants.

As for the swing angle α, the swing angle α
Is larger, the defocus F corresponding to the positional deviation D of the image is smaller, and it is expected that the analysis accuracy of the defocus F is improved.
The reduction of the common part in the image pair causes a malfunction. When the common part becomes less than half of the entire image, the correlation value decreases and the reliability of the analysis result extremely decreases. Therefore, the positional deviation D due to parallax needs to be set to less than half the length of one side of the CCD camera. . Even when the magnification is the same, if the assumed defocus range is wide, that is, the swing angle α is set small in the rough adjustment, and if the assumed defocus range is narrow, that is, the swing angle α is set large in the fine adjustment. For example, the assumed defocus range is 20
μm range, one side of electron beam detector is 2 cm, magnification is 5
If it is 0,000, the swing angle α needs to be 0.5 ° or less.

Since the defocus F is larger than expected, the common part of the two images is reduced, which may make analysis impossible. In order to deal with such a situation, a lower limit value of the peak intensity is provided, and when the calculated peak intensity is less than or equal to the lower limit value, the magnification is decreased, and the common part is increased to perform the preliminary correction of the focus. A flow is provided in which the defocus amount F is reduced and then the original magnification is restored for re-measurement. There is also a method of decreasing the swing angle α as a method of increasing the common portion.

In TEM, an objective aperture is often inserted in the optical axis for observation in order to increase image contrast.
When the incident direction of the electron beam is changed, the electron beam deviates from the optical axis and may not pass through the diaphragm. In order for both the electron beam with the first incident angle and the electron beam with the second incident angle to pass through the diaphragm, the swing angle α must be set smaller than the hole diameter of the diaphragm. For example, for a diaphragm with a hole diameter of ~ 10 μm, the swing angle α needs to be set to 0.5 ° or less.

Since the second TEM image is taken with the incident electron beam being tilted, the swing angle α of the incident electron beam is
If is too large, the image of the second TEM image is distorted due to the effect of the axis shift, and the common part with the first TEM image is extremely reduced, which may make analysis impossible. In this case, it is necessary to set the swing angle α smaller.

The magnification M is also necessary for calculating the defocus F. TE
M usually has a magnification error of about 5%.

Further, when an optical lens is used in the coupling portion 72 of the scintillator 71 and the CCD camera 73, a magnification error of the optical lens also occurs. Therefore, consider the effect on the focus analysis error when there is an error of M (1 + Δ), that is, Δ in the magnification. For example, suppose that the displacement D1 is measured. Original defocus F1
Is D1 / [M (1 + Δ) α] ⁻¹ −C _s α ² , but defocus F1 ′ = D1
Calculated as / [Mα] ⁻¹ −C _s α ² . The analysis error of the defocus F due to the magnification error is F1−F1 ′ = − ΔD1 / (1 + Δ) Mα.
That is, the focus analysis error due to the magnification error is proportional to the positional deviation amount D1. That is, when the positional deviation D = 0, the focus analysis error due to the magnification error is the smallest. Then, repeat the focus correction to F _s = −C _s α ² where the positional deviation D = 0. If the focus is set to F _s after the defocus F1 ′ is analyzed, (F1−F1 ′) + Fs is set. Misalignment D in this state
When 2 is measured, D2 = -ΔD1. TEM magnification error Δ is 5%
Since it is about the degree, if the focus correction is repeated several times, the position shift D
Converges to ~ = 0. As described above, if the float is set to the designated optimum focus after correcting the objective lens so that the positional deviation becomes D = 0, it can be seen that the focus analysis error due to the magnification error is sufficiently small. Note that the positional deviation D = 0
Instead, the flow may be set such that the positional deviation is near D = 0, for example, D = MC _s α ³ where F = 0, and then the optimum focus is set. In this case, the influence of the magnification error is reduced and the influence of the second peak due to the fixed pattern is reduced. Further, when the number of corrections of defocus F = 0 is set to the second or more, if the defocus F _n analyzed in the nth time becomes larger than the defocus F _n-1 analyzed in the n−1 time. , A function to stop the focus correction is also added. As a result, the number of corrections can be minimized. Considering the above, the focus correction is performed according to the flowchart shown in FIG.
First, the field of view for focus analysis is selected. This selection also includes settings such as observation magnification and objective aperture. Next, the optimum focus, the lower limit of the correlation value, the swing angle α, and the number of corrections are set using the screen shown in FIG. Although a recommended value, that is, an initial value of the optimum focus, the lower limit of the correlation value, the swing angle α, and the number of corrections is set in the computer, the operator can change the value as necessary. Optimum focus is normally set to F = 0, but it may be better to observe under focus depending on the sample.
The swing angle α is set to 0.5 °, which is the maximum swing angle that can pass through the objective diaphragm with a hole diameter of ~ 10 μm, but depending on the field of view, the effect of image distortion due to the incident electron beam angle change is large. In some cases it may be better to set a smaller value. The lower limit of the correlation value also depends on the shooting conditions such as the number of pixels of the analysis image. In order to optimize the swing angle α and the correlation value, it is necessary to provide a mode in which only focus analysis is performed and focus correction is not performed. A swing angle α of 0.2 to 0.5 degrees is generally used.
The lower limit of the swing angle α and the upper limit of the allowable accuracy are determined by the performance of the device. When the correction count setting shown on the screen of FIG. 2 is set to 0 and the focus correction execution button 93 is clicked, only measurement is performed. Further, if the operator forgets the recommended value while changing the parameters, the recommended value is called by clicking the initial setting button 92.

After the parameters are set, the electron beam detector 17
Take a pair of images using. The conventional TEM defocus detection device has a configuration in which the operator observes the vibration of the TEM image when the angle of the incident electron beam is vibrated sinusoidally using the irradiation system electron deflection lens 13. However, the conventional circuit configuration in which the TEM image constantly vibrates cannot capture the image. After receiving the signal instructing the acquisition of the first TEM image,
After receiving the signal indicating that the image capturing is started and the image capturing is completed, the angle of the incident electron beam is changed to the second angle, and the signal indicating that the change is completed is detected by the electron beam detector. A control system is needed to capture the second image after it has been received. The analysis image P (n, m) is calculated from the image pair captured using the control system, and the peak corresponding to the positional deviation is specified.

If the peak due to the positional deviation cannot be identified, a flow is provided for inferring the cause in order to stop the focus correction and give the operator a guide for the next action. The reason why the displacement could not be analyzed is that there is a problem in each image such as no sample in the field of view, the image is very blurred, and the displacement due to the incident electron beam tilt angle being too large. In some cases, D becomes too large, the image is distorted due to the influence of the incident electron beam angle change, and the common area between the image pairs decreases. For that determination, the angle of the incident electron beam is set to the first angle, and a fourth TEM image obtained by moving the image in parallel by a known amount using the imaging system electron deflection coil 16 is photographed. The displacement analysis is performed on the image and the fourth TEM image. If misalignment analysis is not possible between the first TEM image and the fourth TEM image, it is considered that there is a problem in each image, such as no sample in the field of view or the image is very blurred. In response to this, the magnification is reduced, and an instruction to execute the preliminary correction at a low magnification is issued. The lower the magnification, the wider the field of view, and the higher the probability that a sample will be in the field of view. Further, at a low magnification, the influence of image blur due to defocus is reduced, and the sharpness of the image is improved, so that the positional shift analysis becomes possible.
If misalignment analysis is possible between the first TEM image and the fourth TEM image, it is considered that the common part between the image pairs is reduced, and therefore an instruction to reduce the swing angle α is issued. The error message is displayed on the screen as shown in FIG. 2 (b), the defocus F that could not be analyzed is not displayed, and only the correlation value is displayed.

When the peak corresponding to the positional deviation can be identified, the positional deviation D is obtained from the peak, the focal deviation F is calculated using the relationship of D = Mα (F + Csα ² ), and the objective lens current is adjusted. To do. Since the relationship between the objective lens current and the focus position differs depending on the setting of the projection lens, that is, the observation magnification, the relation table or the relational expression between the objective lens current and the focus position is recorded in the computer at each observation magnification. Using the above relational table or relational expression, find the current required to achieve the set focus,
Adjust the objective lens current. If the number of times of focus correction is set to 2 times or more, the image pair is captured again, the focus is analyzed, and the objective lens current is adjusted.

The automatic focus correction system according to the present invention is equipped with the position shift analysis calculator 20 based on the phase difference analysis of the Fourier transform image, which is a digital signal processor. Position shift analysis of 256 pixel image is 30msec
It can be executed by the following. It is possible to execute a single correction including the image capture by the electron beam detector 17, the irradiation system electron deflection coil 13, and the change of the objective electron lens 14 in less than 1 second, and continuous automatic correction is possible. ing.
Clicking the continuous execution button shown in FIG. 2 starts continuous focus correction, and clicking the button that supports the stop of focus correction stops focus correction. Alternatively, clicking the continuous execution button starts continuous focus correction, and clicking the continuous execution button again stops continuous focus correction. Alternatively, double-clicking the focus correction execution button 93 starts continuous focus correction, and clicking the execution button 93 again stops continuous focus correction. During continuous focus correction, even if the sample stage is moved to change the field of view, the optimum focus is automatically set. Note that if the first TEM image and the second TEM image are taken while moving the sample stage, the positional deviation D due to parallax and the positional deviation Ds due to sample movement are mixed, but the focus correction analysis accuracy deteriorates, but the target field of view is reduced. When is found, the movement of the sample stage is stopped and the observation is started, so that the focus correction accuracy necessary for the sample observation can be obtained. When the correction accuracy deterioration due to the movement of the sample stage poses a problem, the first TEM image taken for the nth focus analysis and the first TEM image taken for the (n-1) th focus analysis are The moving speed of the sample stage is measured from the positional deviation, and the positional deviation Ds due to the sample movement between the first TEM image and the second TEM image in the n-th measurement is predicted, and the first TEM image and the second TEM The position shift D due to parallax is extracted by subtracting the position shift Ds due to sample movement from the image position shift D + Ds, and the focus is analyzed.

This system has a malfunction check function of not changing the focus when the correlation value is less than the lower limit value. The TEM image generally has a low S / N ratio, and an image with a low S / N ratio has a high probability of being incapable of displacement analysis. If the cause of the misalignment analysis being probabilistic is probabilistic, it is highly possible that correct analysis results will be obtained in the next analysis. Therefore, we set the upper limit of the number of errors in focus analysis, and when the number of times the correlation value was below the lower limit exceeds the upper limit, the electron beam was blocked by the diaphragm, etc., so the TEM image of the sample structure was captured by the electron beam detector. It is judged that there was an accident such as not being performed, and an error message is displayed on the screen.

During the focus correction continuous operation, the first TEM image at the first incident angle and the second TEM image at the second incident angle are alternately displayed on the screen. The display may be perceived as flickering on the screen, which may give an operator an unpleasant sensation or hinder the observation of the fine structure. Therefore, only the TEM image observed at the first incident angle is displayed on the screen, and the TEM image observed at the second incident angle is not displayed on the screen.
Alternatively, if the circuit configuration is such that the TEM image observed at the first incident angle and the TEM image observed at the second incident angle are displayed on different screens, the effect of image distortion due to the axis shift of the incident electron beam is required. You can also check accordingly. Example 2 FIG. 19 shows a basic configuration diagram of a TEM used in an automatic inspection device. Electron gun 11 and its control circuit 11 ', irradiation lens 12 and its control circuit 12', irradiation system electron deflection coil 13 and its control circuit 13 ', objective lens 14 and its control circuit 14', projection lens 15 and its control circuit 15 ', Imaging electron deflection coil
16 and its control software 16 ', an electron beam detector 17 and its control circuit 17', a sample stage 18 and its control circuit 18 ', and a computer 19 equipped with control software and image processing software. Each control circuit receives a control command sent from the control software of the computer, and when the control is completed, sends a return value to the computer 19. An image shift function for translating the TEM image in parallel using the irradiation electron deflection coil 13 and the irradiation electron deflection coil 16 is provided. The electron beam detector 17 is an electron beam detector composed of a large number of pixels such as a CCD camera, and the obtained image signal is based on the recording device of the computer 19 or the phase analysis of the Fourier transform image with a cable for image transmission. It is transmitted at high speed to the arithmetic unit 20 for position shift analysis. The calculator 19 is connected to the position shift analysis calculator 20 based on the phase analysis of the Fourier transform image, and is equipped with the pattern inspection / measurement software.

FIG. 10 shows a processing flow of the automatic inspection device using TEM. First, an accelerating voltage is applied to the electrons generated by the electron gun 11, and the irradiation system electron beam deflection coil 13 is used to adjust the electron beam so that the electron beam passes on the optical axis.
Confirm that the electron beam reaches. The direction parallel to the optical axis
The plane orthogonal to the z direction and the optical axis is defined as the xy plane. Irradiation lens
After adjusting 12, the sample 21 is inserted into the sample chamber. Sample 2
1 is thinned so that an electron beam can pass through it, and then fixed to a metal support called a mesh 22 (Fig. 11).
(a)). The mesh 22 is placed on the sample holder, and the sample holder is placed on the sample stage for observation. The mesh 22 has a diameter of about 3 mm, and it is difficult to place the mesh 22 on the sample holder by accurately specifying the direction and position. Therefore, an image of the mesh 22 observed at a low magnification is recorded, and the direction, position and shape of the mesh 22 are analyzed according to the flow of FIG. Electrons can pass through a hole area called hole 23. First, the captured image is binarized, the connected component is obtained, and each region is labeled (FIG. 11 (b)). Next, the area of each label area is calculated. Since the size of the hole is almost constant, the mode of the area can be specified as the area of the hole. Specifically, of the areas labeled as shown in FIG. 11 (b), the entire hole is shown in the area having an area near the mode value 4, 5, 7,
Label areas are 8, 9, 12, and 13. In order to analyze the direction of the mesh 22, the center of gravity 24 of the label area in which the entire hole 23 is reflected is calculated. A combination that minimizes the distance between the centers of gravity of the regions is obtained (FIG. 11 (c)). For example, the center of gravity 24 of the label area 4 is closest to the center of gravity 24 of the label area 5 and the label area 8.
Is. The direction connecting the centers of gravity 24 of the label areas 4 and 5 is specified as the x direction, and the direction connecting the centers of gravity 24 of the label areas 4 and 8 is specified as the y direction. Further, since the shape of the hole 23 is known, the length H of one side of the hole 23 can be calculated from the area of the hole 23. Further, the width M of the mesh 22 is calculated by subtracting the length H of one side of the hole 23 from the distance between the centers of gravity of the closest points. After the above steps are completed, a screen in which the xy direction of the mesh 22 and the horizontal and vertical directions of the screen are aligned is displayed. Each hole of mesh 22
The number is displayed on 23. The operator can confirm from this display that labeling is being performed correctly. It is also possible to shorten the inspection time by designating the position of the hole 23 in which the sample 21 exists, that is, the hole 23 to be inspected, by using this number, and not inspecting the other holes.

The presence / absence of the sample in the hole can be automatically determined by image processing. The histogram of the image intensity in the hole and the Fourier transform image are used for this determination. In the determination using the Fourier transform image, the determination is made based on the ratio of high frequency components in the Fourier transform image. As shown in FIG. 17B, when the sample does not exist in the analysis area, the image intensity slightly changes due to the distribution of the irradiation electron current density and the like, but the Fourier transform image has only low frequency components. When there is a sample, especially a sample with a fine structure like a biological sample,
The proportion of high frequency components in the Fourier transform image increases (FIG. 17 (a)). When the ratio of the high frequency component to the low frequency component exceeds a certain value, it is determined that the sample exists in the analysis area. In the determination using the image intensity histogram, the presence or absence of the sample is determined based on the number of peaks existing in the image intensity histogram. If the sample does not exist in the hole, the image intensity varies somewhat due to the distribution of the irradiation electron current density and the like, but there is only one peak (FIG. 13).
(b)). On the other hand, there are a plurality of peaks in the histogram of the image intensity where the sample exists in the hole (FIG. 13 (a)). Therefore, if there are a plurality of peaks in the image intensity histogram, it is judged that the sample exists in the hole. For samples in which peaks overlap due to extremely low sample contrast, the presence or absence of the sample is determined based on the half-width of the beak.

Before analyzing the direction and shape of the mesh 22,
It is better to adjust the height of the sample holder. There is a possibility that the sample holder is placed outside the focus range in which the objective lens can be set due to improper setting of the sample stage. Even if the sample holder is placed in the focus range, the magnification of the objective lens current may change due to a change in the lens condition, so that the magnification may change. Therefore, it is preferable that the height of the sample holder be substantially constant.
A focus analyzer which will be described later analyzes the height of the sample holder, and a function of automatically adjusting the height of the sample holder using the sample stage control mechanism 18 'is added.

In some cases, the sample holder may be slantly inserted due to improper setting of the sample stage 18. If the sample holder is greatly inclined, the observation conditions will change depending on the position of the holes in the mesh 22. Therefore, a plurality of points are selected from the mesh 22 and the position of the points and the sample height obtained from the result of defocus analysis are recorded. The tilt angle of the sample holder is calculated from the sample height at each position, and the tilt angle of the sample holder is adjusted. The sample stage control mechanism 18 'is also provided with an automatic correction function for the inclination of the sample holder.

Next, inspection items are set. In automatic inspection of living things, the shape and number of viruses are often searched. Inspection items such as image preprocessing and geometrical features to be measured are set by each virus and recorded in the computer 19 as a macro program. For example, about 20 diameters dispersed in the sample
Consider the case of measuring the number of spherical viruses of nm to 30 nm and the diameter of each. Since the only information to be examined is the number and diameter of viruses, it is necessary to check
The TEM image is captured by the electron beam detector 17, and the captured image is binarized to extract a stained region, that is, a virus, and the diameter of the virus is measured by geometrical feature analysis. First, the size of the analysis area is set according to this purpose. The number of pixels of the image used for virus inspection is 512 x 512
When measuring the diameter with an error of about 10%, it is appropriate that the length of one side of the analysis area is about 1 μm so that the diameter of one virus is about 10 pixels. If the length of one side of the holes is 30 μm, one hole is divided into 30 × 30 areas, and 31 × 31 areas are divided by setting an overlapping area of about 30 nm between the areas to prevent counting. When the area division is completed, the screen as shown in Fig. 11 (d) is displayed.
The analysis area is shown.

Since the sample does not always exist in all the analysis areas, if the sample does not exist in the analysis area, the inspection time can be shortened by moving to the next analysis area immediately. It is also equipped with a function to determine the presence or absence of a sample in the analysis area by using the histogram of the image intensity in the area and the Fourier transform image. Since the sample preparation method in which only the virus is strongly stained as described above is used, it can be assumed that the image intensity of the region where the sample is present is different from the image intensity of the region where the sample is not present. When the sample exists in the analysis area, the image intensity histogram has a plurality of peaks as shown in FIG. Figure 13 (b)
As shown in (1), when there is no sample in the analysis area, the image intensity varies slightly depending on the distribution of the irradiation electron current density and the like, but there is only one peak. Therefore, the presence or absence of a virus can be determined by the number of peaks existing in the histogram of the image intensity. In the determination using the Fourier transform image, the determination is made based on the ratio of high frequency components in the Fourier transform image. As shown in FIG. 17 (b), when the sample does not exist in the analysis area, the Fourier transform image has only low-frequency components, but when a sample having a fine structure such as a biological sample exists, the Fourier transform is performed. The proportion of high frequency components in the image increases (FIG. 17 (a)). When the ratio of the high frequency component to the low frequency component exceeds a certain value, it can be determined that the sample exists in the analysis area.

For a 30 μm hole on one side, the diagonal distance is 42.
Since it is μm, if the sample holder is tilted by 1 °, defocus of 0.74 μm will occur in the hole. The contrast of TEM images is sensitive to defocus, and if there is submicron defocus, image contrast changes and image blurring occur, so virus inspection must always be performed on images taken with a fixed focus. Before starting the virus inspection, it is necessary to perform focus correction with submicron accuracy.

A focus analysis method using parallax is applied to the focus analysis in this focus correction. A first TEM image taken by injecting an electron beam from a first angle substantially parallel to the optical axis and a second TEM image taken by entering an electron beam at a second angle inclined by an angle α from the optical axis. To use. As shown in FIG. 4, when the focal point is deviated, a positional deviation occurs between the first TEM image and the second TEM image. D = M for defocus F and displacement D due to parallax
There is a relationship of α (F + Csα ² ). The operator sets the magnification M and the swing angle α. Since the spherical aberration coefficient Cs is fixed to the device, if the positional deviation D between the image pairs can be measured, the defocus F can be specified. The cross-correlation method and the least-squares method have been conventionally used as the displacement analysis method based on parallax. There wasn't. The present invention is characterized in that an analysis method based on the phase difference analysis of the Fourier transform image is applied to the analysis of the positional deviation D. As shown in FIG. 1, the first and second TEMs in which the incident angle of the electron beam with respect to the sample is changed by using the angle deflecting means 13 provided above the objective lens 14.
An image is taken using the electron beam detector 17. The first shot
And the second TEM image are transmitted to the arithmetic unit 20 for positional deviation analysis based on the phase difference analysis of the Fourier transform image, and the positional deviation D as the analysis result is sent to the computer 19. Misalignment D on computer 19
The defocus F is calculated from the objective defocus F to obtain the objective current I _obj required to set the desired focal point, and the focus of the objective lens 14 is corrected based on the objective current I _obj .

FIG. 5 shows an explanatory diagram of the displacement analysis method applied to the present invention. Image pair S1 (n, with misregistration D = (dx, dy)
m) = S2 (n + dx, m + dy), the two-dimensional discrete Fourier transform of S1 (n, m), S2 (n, m) is converted into S1 '(k, l), S2' (k , l). F (S (n + dx, m + dy)} = F {S (n, m)} exp (idxk + i for Fourier transform
dyl) formula, S1 '(k, l) = S2' (k, l) exp (idxk +
It can be transformed with idyl). That is, the difference between S1 '(k, l) and S2' (k, l) is represented by the phase difference exp (idxk + idyl) = P '(k, l). P '
Since (k, l) is also a wave with a period of (dx, dy), the phase difference image
The image obtained by inverse Fourier transform of P '(k, l) is (dx, dy) for P (n, m).
A δ-like peak occurs at the position. Since it can be assumed that there is only a δ-like peak in the image P (n, m), if the center of gravity of the δ-like peak is calculated, the position of the δ-like peak will be correctly positioned even if it contains a decimal point. Desired.

After normalizing the intensity of the entire image P (n, m), δ
When the peak intensity is calculated, the peak intensity becomes weaker when there are many noise components, that is, portions where image pairs do not match. If this peak intensity is indicated as a correlation value, the operator can identify the noise component ratio, that is, the reliability of the analysis result. There is no guarantee that an automatic correction device will always perform correct analysis in all areas. Therefore, the lower limit value of the correlation value is set, and if the calculated correlation value is less than or equal to the lower limit value, the objective lens is not adjusted and the correlation value is recorded together with the address of the analysis area. For example, if the mesh position is displaced due to a malfunction during movement of the sample stage, more than half of the captured TEM image at the end of the hole 23 becomes the mesh 22,
Since the common part of the image pair is reduced, there are columns of analysis areas that cannot be analyzed. After the automatic inspection, the operator can infer from the distribution of the analysis area where analysis is not possible, that the mesh is mixed in the analysis area due to the malfunction of the sample stage, and at what time the malfunction of the stage has occurred. . If the displacement amount D can be analyzed, D = Mα (F + Csα
^The focus F is calculated using the relationship of ² ), the current required to achieve the set optimum focus is obtained, and the objective lens current is adjusted. After the objective lens is corrected, the focus analysis by parallax is performed again, and the correlation value and the objective lens current in the position shift analysis are recorded together with the address of the analysis area, so that the inspection state can be recorded in more detail. The height distribution of the sample can be obtained from the objective lens current in the optimum focus. Further, by using the correlation value calculated with the same positional deviation D, the image quality such as sharpness can be compared.

After the focus correction is completed, the virus inspection is executed according to the flow shown in FIG. A new TEM image for inspection may be taken, but the TEM image at incident electron beam angle 1 taken with Optimum focus has already been recorded, so using this for virus inspection will shorten the imaging time. . In the virus inspection, the TEM image is first binarized, the connected components are obtained, and the regions are labeled. Next, the area of each label area is calculated, and the area having a fixed area or less is judged as noise and erased. Next, the characteristic quantities of the biological sample such as the circularity and moment of each label area are calculated, the area determined to be close to a perfect circle is identified as a virus, and the diameter (biological information) is calculated from the area. The number of viruses and the diameter of each are recorded together with the address of the analysis area as before.

When the inspection is completed in one analysis area, the sample is moved using the sample stage 18, and the inspection in the next analysis area is started. The fine movement accuracy of the sample stage 18 is described by the positioning accuracy and backlash. The movement accuracy in the constant movement direction of the sample stage is the positioning accuracy, and the sliding distance in the direction change is the backlash. The positioning accuracy of current products is about 1.2 nm, and the backlash is about 0.02 μm. If the size of the analysis area is 30 μm, sample movement can be performed by the sample stage 18.

However, when the sample stage 18 is moved, a sample drift due to inertia of the sample stage 18 occurs even after receiving a signal for stopping the stage movement. In the focus analysis using the parallax, if the positional shift Ds due to the sample drift is mixed with the positional shift D due to the parallax, the precision of the focus analysis is reduced. Therefore, at the second time different from the time when the first TEM image was taken, the third TE imaged at the first incident electron beam angle was taken.
Use M image. The sample drift is calculated from the amount of positional deviation between the first TEM image and the third TEM image. This positional shift analysis is also performed by the positional shift analysis method based on the phase difference analysis of the Fourier transform image. Unless the positional deviation Ds due to the sample drift is analyzed with the same analysis accuracy as the positional deviation D due to parallax, the focus analysis accuracy will deteriorate. Further, the measurement of the sample drift needs to be executed in a short time, and the amount of displacement due to the sample drift is very small. The conventional positional deviation analysis method, in which the analysis accuracy is limited by the size of one pixel, is clearly insufficient in accuracy. First
Subtracting the positional deviation Ds due to sample drift from the positional deviations in the second and TEM images, the positional deviation D due to parallax
Can be asked. Furthermore, the position shift due to sample drift
By performing automatic drift correction by operating the imaging system electron deflection coil 16 so as to cancel Ds, the blur of the captured image due to the drift can be removed.

The sample drift that impairs the focus analysis is caused by the time until the temperature unevenness of the mirror body and the stabilization of the electron gun after the power of the electron microscope is turned on, immediately after the moving sample stage 18 is stopped, etc. , To some extent predictable. Since increasing the number of captured images lowers the inspection efficiency, the observation conditions for capturing the third TEM image for drift correction are specified in advance, and under the specified observation conditions, the first and second TEM images as well as the first Take the TEM image of 3 and remove the effect of drift. Drift is reduced, that is, the first TEM image and the third
After the position shift amount of the TEM image of
If the algorithm is used to capture only the TEM of, the focus can be accurately corrected with the minimum number of TEM images.

If the third TEM image, which is an image for correcting the sample drift, is taken every time the sample stage 18 is moved, the efficiency of the inspection is deteriorated. Therefore, the sample stage 18 is moved only between the holes. The movement between the analysis areas is performed by the imaging system electron deflection coil 16. The correction of the sample drift due to the inertia of the stage movement is performed only during the movement between the holes, so that the number of captured third TEM images is considerably reduced. In addition, when it is necessary to move the analysis area by the imaging system electron deflection coil 16, the analysis area is divided into small parts, and therefore the precision of the fine movement of the sample stage 18 causes insufficient accuracy in the movement of the analysis area. is there.

If the size of the hole is so wide that the electron deflection coil 16 of the imaging system cannot follow it, the sample stage
18 is moved at a substantially constant speed, and the imaging system electron deflection coil 16
There is also a method in which the image is shifted by using the imaging system deflection coil 16 at substantially the same speed as the sample stage moving speed. FIG. 18 (c) shows the position of the observation field, the setting position of the imaging system electron deflection coil 16 and the sample stage when the analysis stage is moved in combination with the sample stage movement and the image shift movement.
18 Indicates the set position over time. The time required to capture the TEM image is T _C , the time required to move the visual field by the sample stage is T _S ,
The time required to move the field of view by the imaging system electron deflection coil 16
T _I. In the visual field movement by the sample stage 18, there is an upper limit to the speedup due to the influence of backlash and inertia of the stage movement, and it cannot be faster than the visual field movement by the imaging system electron deflection coil 16. If the visual field is moved only by the sample stage 18, the inspection time becomes long as shown in FIG. On the other hand, the imaging system electron deflection coil 16 has a problem that the moving range is narrow. As shown in FIG. 18B, when the movement range of the imaging system electron deflection coil 16 is exceeded, the sample needs to be moved by the sample stage 18. Therefore, as shown in FIG. 18C, if the sample stage 18 is moved at a substantially constant speed and the movement of the sample stage is offset by the image shift by the imaging system electron deflection coil 16, the sample stage 18 moves. Despite that, you can still shoot still images in each analysis area. A wide range of field movement can be executed at high speed without being affected by backlash or inertia of the sample stage 18.

A wider range of analysis can be performed if the set position of the image forming system electron deflection coil 16 at the time when the inspection of each analysis area starts is almost constant (see FIG. 18). The time T required for correction and inspection executed in each analysis area is calculated, and the moving speed of the sample stage 18 is set so that the movement of the sample stage 18 to the next analysis area is completed at that time. In order to cancel the determined moving speed of the sample stage 18,
The image shift by the image forming system electronic deflection coil 16 is controlled. In order to match the moving speed of the sample stage 18 and the moving speed of the imaging system electron deflection coil 16, the position shift analysis of the observation visual field is performed by the position shift analysis method based on the phase difference analysis of the Fourier transform image. As shown in FIG. 26, the first time and the second time are set, and the first TEM image at the first time and the third TEM image at the second time are set to the electron beam detector 17
To shoot. The photographed first and second TEM images are transmitted to the arithmetic unit 20 for positional deviation analysis based on the phase difference analysis of the Fourier transform image, and the positional deviation D as the analysis result is calculated by the computer 19
Sent to. The computer 19 calculates the moving speed of the observation visual field from the positional deviation D, and obtains the setting value of the imaging system electron deflection coil 16 necessary for the moving speed of the observation visual field to become zero. Adjust and correct coil 16.

Since the accuracy of setting the position of the sample stage 18 is higher when the moving speed of the sample stage 18 is constant, the inspection time T of each analysis area is desired to be constant. In other words, we want to keep the number of shots in each analysis area constant. If a third TEM image for analyzing the displacement of the analysis area is taken for each analysis area, the precision of the displacement correction and the accuracy of the focus analysis are improved,
Inspection efficiency deteriorates. Therefore, the adjustment of the observation visual field movement using the sample stage 18 and the imaging system electronic deflection coil 16 is executed at the stage of the apparatus adjustment before the virus inspection. Alternatively, an analysis area unsuitable for virus inspection is designated in advance and focus correction is not performed in the analysis area, and the first TEM image and the third
Take a TEM image of and adjust the observation field of view. Assuming that the observation field of view is almost stopped in the normal analysis area,
A first TEM image and a second TEM image are taken for focus correction.

The operator selects the display item during the inspection as required. For example, the display items shown in FIG. 15 are prepared. An image obtained by dividing the captured image of the mesh 22 into analysis areas is displayed, and the analysis areas that have been inspected, inspected, and uninspected are displayed in different colors, and are used to grasp the current examination progress status and predict the end time. . A table 94 for sequentially displaying the inspection results in each analysis area and a histogram 95 for displaying the cumulative value of the inspection results are also provided. A window for displaying the focus analysis result is also provided, and the height of the sample calculated based on the correlation value of the image pair and the focus analysis result is displayed. The reference point of the sample height is designated by selecting an appropriate position in the sample before or after the inspection and pressing the reset button 96. Also used for virus inspection TEM
The image display is provided with a layer that displays a circle 97 indicating the position and size of the identified virus. The operator can observe the virus inspection result, the focus correction result and the TEM image, and can stop the inspection when an abnormality is found on the way. Also, among the virus inspection results, focus correction results, and TEM images, the items specified by the operator are recorded in the memory, so after the inspection is completed, an analysis that is expected to be abnormal based on information such as correlation values and sample height. You can also check the inspection status by displaying the inspection results of the area.

Mesh for displaying analysis results after inspection
Use 22. The measured hole is divided into analysis areas. By selecting display items, the analysis results of each analysis area are displayed in monochrome or color by color. For example, when the number of viruses is selected as a display item, each analysis area is color-coded according to the number as shown in FIG. 16 (b). The photographed TEM image of each analysis area is displayed by specifying the analysis area number, for example, by double-clicking the position of the analysis area. Of the items recorded in the memory, the display items specified by the operator are displayed on the screen. For example, together with the display of the TEM image, the virus inspection result in the analysis area, the sample height, and the correlation value are displayed (FIG. 16 (a)).

The height distribution and the correlation value of the sample can be used to grasp the inspection state and evaluate the reliability of the inspection result. Biological samples are usually sliced to a thickness of several tens of nm, and it can be assumed that they are almost flat. The change in sample height is caused by the warp and inclination of the mesh on which the sample is placed, and when the height distribution of the sample is plotted, it should be an almost smooth curved surface. Therefore, in the analysis area where the sample height is extremely changed, it is estimated that a malfunction of the focus analysis occurs or the sample thin film is rolled up for some reason. In any case, it can be said that the reliability of the inspection result of the analysis area is poor. For example, in FIG.
In the sample height distribution shown in (c), the sample height is different only in the region 25, and it is estimated that the reliability of the inspection result in this region is poor. In order to remove the inspection result of this area, it is possible not to use the inspection result of the analysis area where the sample height is out of the specified range. That is, the height distribution of the sample can be used as a filter for the inspection result. Further, instead of the filter based on the height of the sample, the filter can be set by the curvature obtained from the height distribution. It is also assumed that the correlation value distribution shown in FIG. 16 (d) is obtained. The correlation value can be used to evaluate the sharpness of the TEM image. In the case of a biological sample, if the sample is prepared, for example, if the sample is thick, only a blurred image can be obtained even when the sample is observed with the optimal focus. When the image is blurred, the correlation value decreases and
Since the error in binarization becomes large, the accuracy of virus diameter measurement decreases. Similar to the height distribution of the sample, the correlation value distribution can be used as a filter so that the analysis result in the region 26 where the correlation value is low is not used. It is also possible to estimate the measurement error of the virus diameter from the correlation value and use the measurement error as a weighting function when creating the virus diameter distribution map. Example 3 FIG. 19 is a basic configuration diagram of a transmission electron microscope used in an example of the present invention. Electron gun 11 and its control circuit 11 ', irradiation lens 12 and its control circuit 12', irradiation system electron deflection coil 13 and its control circuit 13 ', objective lens 14 and its control circuit 14', projection lens 15 and its control circuit 15 ', imaging system electron deflection coil 16 and its control circuit 16', electron beam detector
17 and its control circuit 17 ', the sample stage 18 and its control circuit 18', and a computer 19 equipped with control software and image processing software. Each control circuit receives the control command sent from the control software of the computer 19, and when the control ends, sends a return value to the computer. The electron beam detector 17 is an electron beam detector 17 composed of a large number of pixels such as a CCD camera,
The obtained image signal is transmitted at high speed to the recording device of the computer 19 or the position shift analysis calculator 20 based on the phase analysis of the Fourier transform image by a cable for image transmission. The calculator 19 is connected to a calculator 20 for positional deviation analysis based on the phase analysis of Fourier transform images.

FIG. 3 shows a flowchart of TEM image photography. First, an accelerating voltage is applied to the electron beam generated by the electron gun 11,
The electron beam is adjusted using the irradiation system electron beam deflection coil 13 so that the electron beam passes on the optical axis, and it is confirmed that the electron beam reaches the electron beam detector 17. Next, after adjusting the irradiation system lens 12, the sample 21 is inserted, and after confirming the TEM image of the sample 21 at a low magnification, an objective aperture is inserted in the optical axis to increase the TEM image contrast. The observation visual field is selected while increasing the magnification of the projection lens 15, the focus is corrected, and a necessary TEM image is captured.

A focus analysis method using parallax is applied to the focus analysis in this focus correction. A first TEM image taken by injecting an electron beam from a first angle substantially parallel to the optical axis and a second TEM image taken by entering an electron beam at a second angle inclined by an angle α from the optical axis. To use. A function of intentionally changing the irradiation angle of the electron beam to the sample by using the irradiation system electron deflection coil 13 shown in FIG. 19 is called a wobbler. By using this, defocus can be converted into parallax. Therefore, first, the operating principle of the wobbler and the mechanism of causing parallax will be described with reference to FIG. FIG. 24 (a) shows an electron optical diagram when the sample is at the regular focal position (F = 0) and the electron beam is incident parallel to the optical axis (α = 0). In the figure, the electron beam is incident on the sample indicated by the arrow from above the paper. In the sample, a part of the electron beam is diffracted, and in the crystalline sample, for example, the electron beam is scattered in a specific direction satisfying the Bragg condition as shown in the figure, and the rest is directly transmitted without changing the direction. The objective lens under the sample has the same property as a normal optical convex lens and has an action of converging an electron beam. Therefore, a so-called diffractive image plane (rear focal plane) in which electrons in the same scattering direction converge to one point directly below the lens is formed. Next, a TEM image plane is formed in which electrons scattered and transmitted at the same point are converged at one point. At this time, according to the projection magnification M of the lens, the sample is magnified M times in the TEM image plane. When F = 0 and α = 0, the arrow image on the TEM image plane is not displaced from the optical axis as shown in FIG. 24 (a) (D = 0).
On the other hand, although the sample is in the normal focus position (F = 0), when the electron beam is obliquely incident at an angle α due to the wobbler function, FIG. 24 (b)
As described above, since the electron beam is converged at a position deviated from the central axis of the objective lens, it is affected by the spherical aberration peculiar to the convex lens like the optical lens, and the field shift D = CsMα ³ occurs. Here, Cs is a spherical aberration coefficient which is an eigenvalue of the lens. Finally, when the sample is not in the regular focus position and the electron beam obliquely enters at an angle α due to the wobbler function, the positional deviation further increases as shown in FIG. 24 (c). When the amount of defocus is F,
Since the sample position shifts αF laterally with respect to the optical axis, TEM
On the image plane, the magnification is increased by the lens magnification M, and MαF parallax occurs. Therefore, the parallax is an amount represented by D = Mα (F + Csα ² ) together with the shift amount due to spherical aberration. As is clear from this equation, α = 0 even if the sample is not in the focal position.
Then the parallax D is zero. Therefore, by capturing two types of image pairs with different α using the wobbler function in this way, the focus shift F can be specified from the positional shift amount D of the image pair. Since the parallax due to aberration (CsMα ³ ) is usually one digit or more smaller than the parallax (MαF) caused by defocus, highly accurate focus correction is possible by minimizing the parallax. Can be considered complete if CsMα ³ or less.

The positional deviation D of the image pair is obtained by an analysis method using the phase component of Fourier transform. An explanatory diagram of this method is shown in FIG. Image pair S1 (n, with misregistration D = (dx, dy)
m) = S2 (n + dx, m + dy), the two-dimensional discrete Fourier transform of S1 (n, m), S2 (n, m) is converted into S1 '(k, l), S2' (k , l). F {S (n + dx, m + dy)} = F {S (n, m)} exp (idxk + id for Fourier transform
yl), so S1 '(k, l) = S2' (k, l) exp (idxk + id
yl) can be transformed. That is, the positional shift between S1 '(k, l) and S2' (k, l) is represented by the phase difference exp (idxk + idyl) = P '(k, l).
Since P '(k, l) is also a wave with a period of (dx, dy), the image P (n, m) obtained by inverse Fourier transform of the phase difference image P' (k, l) has (dx, d)
A δ-like peak occurs at the position of y). Image P (n, m) has δ
Since it can be assumed that only the peaks that are δ-like exist, the position of the δ-like peaks can be correctly calculated even if the position of the δ-like peaks includes a decimal point by calculating the center of gravity of the δ-like peaks.

After normalizing the intensity of the entire image P (n, m), δ
When the peak intensity is calculated, the peak intensity becomes weaker when there are many noise components, that is, portions where image pairs do not match. If this peak intensity is indicated as a correlation value, the degree of coincidence between image pairs can be evaluated.

Using the apparatus shown in FIG. 5, focus correction is performed according to the flowchart shown in FIG. First, a field of view for focus analysis is selected by the sample fine movement mechanism provided on the sample stage 18. This selection also includes settings such as observation magnification and objective aperture diameter. Next, the optimum focus, the lower limit of the correlation value, the swing angle α, and the number of corrections are set using the monitor screen shown in FIG. After the parameter setting is completed, the electron beam detector 17 is used to capture an image pair. The analysis image P (n, m) is calculated from the captured image pair, and the peak corresponding to the positional deviation is specified. When the peak corresponding to the positional deviation can be specified, the positional deviation D is obtained from the peak, and the calculated D value is transferred to the computer 19 equipped with the control software and the image processing software. Here, the focus F is calculated using the relationship of D = Mα (F + Csα ² ), the objective current value Iobj to be corrected corresponding to the focus F is calculated, and this value is transferred to the objective lens control circuit 14 ′. Then, the objective lens current is adjusted.

Here, an example of a virus or semiconductor memory defect inspection by an electron microscope using the above focus correction will be described. Since electron microscopes have atomic-level resolution and can obtain various contrasts due to the sample structure, various target samples have been observed regardless of whether they are living or non-living. Among them, for viruses such as AIDS and influenza, which cannot be evaluated with an optical microscope because of their small size, it is necessary to quickly determine the presence or absence of infection in a large number of patients. In order to meet such requirements, humans have conventionally inserted a sample into an electron microscope that operates manually and evaluated it visually. Similar example
This is a defect inspection in a semiconductor memory. Pull out as appropriate,
The sample processed into an observable shape is set in an electron microscope and observed. However, with high integration in recent years, the field of view for observation has dramatically increased, and it has become a limit for humans to manually detect defects. In addition, many samples are not flat, and the samples are not always placed on a plane perpendicular to the electron beam, so when the observation field of view is changed one after another, the focus becomes out of focus. Focus correction is required each time, and improvement of observation throughput by automatic control of the inspection process is becoming extremely important. Therefore, utilizing the automatic focus correction function of the present application, first, referring to FIG. 20, an example of virus inspection will be described. The positional deviation D is calculated from the two captured images as in the first embodiment, and then the focal deviation F and the objective current I _obj corresponding thereto are calculated. Based on these values, the objective lens 14 is immediately corrected and an image is captured again. In the image capturing, the sample fine movement and the focus correction may be repeated several times, and the image may be captured again for inspection after the desired visual field is captured in the image. After that, a comparison is made with the registered image of the virus to be extracted in advance.

Here as well, when the positional deviation D is analyzed,
The shape matching rate is evaluated by image processing based on the phase difference analysis between the two Fourier transform images, the correlation value is calculated, and if the set lower limit of the correlation value is exceeded, it is considered that a virus has been detected, and the virus has been detected. The x, y coordinates of the sample stage 18 and the sample number are registered. If no virus is found in the observation visual field, the visual field is changed. At this time, in order to change the field of view, the x, y, z fine movement mechanism in the sample stage 18 may be operated, and the electron beam position may be moved by the imaging system electron deflection coil 16. In addition, the electron beam detector 17
The electron beam detector 17 may be moved by providing a fine movement function in the portion attached to the electron microscope. As described above, the change of the sample position and the drift correction are nothing but changing the irradiation position of the electron beam transmitted through the sample and the relative position of the electron beam detector, and can be selectively used depending on the case. There are multiple methods for focus correction as well.
In the above-described embodiment, the focus correction is performed by changing the objective current value and changing the focal length.However, as a result of detecting the positional deviation D, the sample stage 18 is used, and if the position of the sample, for example, the focal position is electron beam incidence. The focus can also be corrected by slightly moving the sample in the axial direction. This is as shown in the flow in which the sample stage z is moved after the defocus F is calculated in FIG. In the case of sample drift, the sample stage 18 may be moved in a plane vertical to the electron beam incident direction in accordance with the positional deviation D, or the installation position of the electron beam detector 17 may be finely moved.

Next, a semiconductor evaluation example will be described with reference to FIG. An image (a so-called plane image) observed from above a typical memory cell transferred from the electron beam detector 17 is in a state as shown in the lower part of the figure. In many cases, the semiconductor patterns usually have regular patterns such as these.
Then, the contrast resulting from defective defects and foreign matter is mixed in a very small part of them. Also in FIG. 21, linear defects and round foreign matters are observed around the pattern. First, the focus is corrected by the method already described, and then it is compared with the registered pattern. Here, an example of the comparison method will be described with reference to FIG. Utilizing the fact that the patterns to be inspected are regularly arranged, the field size of the pattern interval is trimmed and cut out. Therefore, it is appropriate that the registered images have the same size. Here, the degree of coincidence of shapes similar to viruses is evaluated, and if the correlation value exceeds the set lower limit value,
Register the corresponding memory address. Next, the trimming position is changed and the same shape matching degree is evaluated. When the inspection of the entire surface of the image thus taken is completed, the visual field is changed by the sample stage 18 and the imaging system electron deflection coil 16, the focus is corrected again, and the same inspection is performed. In the above, the image taken by the electron beam detector initially contained a plurality of memory cell patterns, but it is possible that the defect to be evaluated is small or the contrast is weak, so take a sufficient observation magnification. It may be necessary. At this time, the electron microscope magnification may be increased, an image of one memory cell may be photographed from the beginning, and the image may be compared with the registered image on a one-to-one basis without trimming. In FIG. 22, the trimming position is moved from left to right of the sample, but as shown in FIG. 23, various inspection orders are possible. This should be set according to the fine movement performance of the sample stage and the deflection accuracy of the deflection coil.

Further, the examples in the present specification are based on the transmission electron microscope (T
Although an example using EM) was described, scanning electron microscope (SE
M), scanning transmission electron microscope (STEM), ion microscope (SIM), etc., and is widely applicable to an image observation apparatus using a charged particle beam of electrons, ions, etc. Example 4 In an apparatus for observing or inspecting a sample by continuously moving the sample stage, when the sample stage becomes a high speed of 5 m / S or more, it is equivalent that the sample stage moves at a predetermined speed due to an error due to vibration and speed irregularity rail accuracy It gets harder. In such a case, as in the present invention, the first charged particle beam itself serves as a probe to irradiate the sample with this probe, and the second charged particle beam from the sample is detected to detect the target position from a plurality of images. It is possible to solve the problem by calculating the error between and by the phase limiting method and feeding back to the deflector which deflects the sample stage or the probe until the image of the sample to be inspected next is acquired. This makes it possible to reduce erroneous determinations in the inspection of continuously moving samples. Specifically, a first charged particle beam which is a probe is converged, a predetermined area of the sample is scanned through a deflector and an objective lens, a second charged particle beam from the sample is detected by a detector, and an analog signal is obtained. Is converted into a digital signal and then stored in the storage means. The memory starting point is always fixed, and it is operated by time control or a signal from the stage or a mark on the sample. The second image is captured a predetermined time after the first image is captured. The first and second images are Fourier-transformed to find the phase difference, inverse-Fourier-transformed, the deviation from the origin position is obtained from the address amount of the storage means, and returned to the control unit of the sample stand or the deflector. It is possible to reduce the erroneous determination at the time of comparison between the first image and the second image due to the erroneous operation at the time of moving. Example 5 In Example 1, an example using a CCD camera as an imaging device was described. The basic configuration of the CCD camera used here is the scintillator 71 and the connecting portion 7 as described in FIG.
2. The CCD camera 73 is used, and the image formed on the scintillator 71 is always formed on the CCD camera 73 at a constant projection magnification. In the present embodiment, by using a zoom lens in the coupling portion 72, an example in which the projection magnification can be freely changed in accordance with the displacement analysis result is shown in FIG.
Will be explained. An electron beam detector 17 is attached to the lower part of the electron microscope as in FIG. Details of the configuration are shown in the figure. First, the electron beam image is converted into a light enhancement by the scintillator 101 in vacuum. The scintillator 101 is attached on the glass substrate 103 and has an optimum thickness, for example, 10
It is polished to a thickness of about 50-120 μm for 0 kV-400 kV accelerated electron beams. The optical image formed by the scintillator 101 is formed on the image sensor 106 by the optical lens 105. The optical lens 105 and the image sensor 106 are preferably used in the atmosphere due to their fine structure. Therefore, only the scintillator 101 is placed in a vacuum by the vacuum seal 102, and the optical image shields the vacuum from the atmosphere.
It is taken out into the atmosphere through 03. Image sensor 1
As for 06, other than CCD, two-dimensional detectors such as various image pickup tubes can be widely used. The procedure until obtaining the focus shift F corresponding to the positional shift D between the first and second images is the same as in the first embodiment. Generally, when the defocus amount decreases, the positional deviation D between the two images also decreases. Therefore, in order to calculate the positional deviation D with high accuracy, a method of enlarging the imaging magnification and increasing the positional deviation when the positional deviation D becomes a certain amount or less is effective. In order to increase the imaging magnification, it is sufficient to increase the magnification of the electron microscope, but in addition to changing the field of view range, changing the conditions of the electron optical system is often not preferable in terms of changing the image contrast. . Therefore, it was considered to change the zoom magnification of the optical lens 105 in order to change the imaging magnification without changing the electron microscope side at all. A commercially available motor-driven lens can be used as the zoom lens 105 here. As shown in the lower right of the figure, when the positional deviation D becomes small and the peak indicating the positional deviation approaches the origin, the zoom magnification of the optical lens 105 is increased by 1.5 times, for example. If two images are taken again under this condition, the new misalignment D'is 1.
Expanded 5 times. In this way, by feeding back the analysis image result to the electron beam detector 17, it becomes possible to perform more accurate focus correction, drift correction and the like. Sixth Embodiment In the first embodiment, the focus correction device using parallax has been described, but an astigmatism correction device using parallax can also be realized. Astigmatism is a phenomenon in which the focus has an elliptical distribution around the optical axis because the electromagnetic field generated in the objective lens 14 has an elliptical distribution around the optical axis (Z axis) as shown in FIG. That is, the focal point has a distribution of F (β) = F + Acos2 (β−βA) depending on the azimuth angle β. Here, F is an average value of F (β), which is a value generally called a defocus amount. A is a value called astigmatism, and βA is called an astigmatic direction.

Using the apparatus and flow shown in FIG. 29, the focus distribution around the optical axis is obtained by the focus analysis method using parallax, the astigmatism amount and direction are analyzed, and the result is fed back to the astigmatism correction coil 141. A first TEM image was taken by injecting an electron beam from a first direction substantially parallel to the optical axis, that is, the Z-axis, and the electron beam was incident from a second direction tilted by an angle α from the Z-axis. The second TEM image taken by The azimuth angle of the second direction with respect to the X axis is β ₂ . The positional shift D (β ₂ ) between the first TEM image and the second TEM image is analyzed using the positional shift analysis calculator 20 based on the phase difference analysis of the Fourier transform image, and the analyzed positional shift D (β ₂ ) is sent to computer 19,
The defocus F (β ₂ ) at the azimuth β ₂ is calculated. Then Z
A third TEM imaged by injecting an electron beam from a third direction inclined by an angle α from the axis and having an azimuth angle of β ₃ with the X axis.
Image is taken, and the positional deviation D between the first TEM image and the third TEM image
(β ₃ ) is analyzed and the defocus F at the azimuth β ₃ with the X axis is
Analyze (β ₃ ). The same analysis is performed for a plurality of azimuth angles β _n to obtain the azimuth angle distribution of the focus.

Using a fitting method such as the least squares method,
The defocus amount, the astigmatism amount, and the astigmatism direction are specified from the focus F (β _n ) in each direction. Regarding the astigmatic direction, the azimuth angle of the incident electron beam and the direction of the position shift vector may not be parallel due to the influence of the image rotation generated in the electron lens. The difference between the azimuth of the incident electron beam and the direction of the position shift vector can be specified if the lens conditions such as the magnification are determined. Correct the direction.

Astigmatism A is 0 based on the result of the astigmatism analysis.
Current value Isx, Is of the astigmatism correction coil 141 required to be
The y is calculated, and the astigmatism correction coil 141 is adjusted via the astigmatism correction coil control circuit 141 ′.

The astigmatism analysis requires accuracy of two digits higher than that of the defocus analysis. It is very difficult to meet the accuracy required for astigmatism correction with a conventional focus analysis system that uses cross-correlation for position shift analysis. Further, the astigmatism analysis is an analysis of the focus distribution, and it is necessary to analyze the displacements many times.
This system is a digital signal processor, which is a calculator for misalignment analysis based on phase difference analysis of Fourier transform image.
Since the 20 is installed, the focus analysis time per time is less than 1 second, and astigmatism correction is possible within a few seconds.

[0069]

The performance of the apparatus for correcting the electron microscope from the positional deviation between the electron microscope images, such as focus analysis utilizing parallax, largely depends on the positional deviation analysis method. In the displacement analysis method that has been used in the conventional correction system, the analysis accuracy does not become smaller than the size of one pixel of the electron beam detector 17 in principle, but by adopting this analysis method, the analysis accuracy less than the pixel size can be obtained. As a result, the focus can be corrected with the same accuracy as that of a skilled operator. It should be noted that if the performance of the device is improved, for example, by making the image used for analysis in the position shift analysis smaller in order to improve the focus analysis accuracy, the analysis time and device cost will increase, but the position shift analysis method changes In the present invention that improves the analysis accuracy, it is possible to improve the focus analysis accuracy while maintaining the analysis time and the apparatus cost.

Furthermore, since the degree of coincidence of the image pairs is clearly indicated as a correlation value, the operator can confirm the reliability of the output analysis result. If the lower limit of the correlation value is set and the calculated correlation value is less than or equal to the lower limit value, the lens adjustment is not performed to prevent malfunction. Further, in the automatic inspection apparatus, if the correlation value in the focus analysis and the focus analysis result are recorded, it can be verified later whether the automatic correction is normally executed, so that it can be operated unmanned.

Further, since the position shift analysis method used in the present invention is a method using the phase component of the image, it is not easily affected by the change in the background, and even if the shadow of the aperture is mixed, a sufficient common part can be obtained for the image pair. If there is, it can be analyzed. TE
Since it is possible to operate even if the M adjustment is a little inadequate, it is possible to use an operator who is unfamiliar with TEM operation.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an automatic focus correction process using parallax.

FIG. 2 is a schematic diagram of a screen for parameter setting and analysis result display in focus correction.

FIG. 3 is a flowchart showing steps of TEM image photography.

FIG. 4 is an explanatory diagram of the principle of a focus analysis method using parallax.

FIG. 5 is an explanatory diagram showing a calculation process of displacement analysis.

FIG. 6 is a basic configuration diagram of an electron beam detector 17 for TEM.

FIG. 7 is an explanatory diagram showing the positions and intensities of peaks in an analysis image, where (a) shows a case where the sample structure has a high contrast, (b) shows a case where the sample structure has a low contrast, and (c) shows the sample structure. The case where the displacement is small is shown.

8A and 8B are flowcharts showing a step of identifying a peak corresponding to a positional deviation from an analysis image, wherein FIG. 8A is a step of using an origin mask, and FIG. 8B is a step of outputting two peaks.

FIG. 9 is a flowchart showing steps of focus correction.

FIG. 10 is a flowchart showing an automatic inspection process using TEM.

FIG. 11 is an explanatory diagram showing a step of analyzing the direction and shape of the mesh 22 and designating an analysis area, (a) a TEM image of the mesh 22 photographed at a low magnification, (b) binarization, and a label. The attached image, (c) a diagram showing the positional relationship of the center of gravity 24 of the hole 23 and the direction of the mesh 22, and (d) a diagram showing a state in which the designated hole 23 is divided into analysis areas.

FIG. 12 is a flowchart showing a process of analyzing the direction and shape of a mesh.

FIG. 13 is an explanatory diagram showing a method for determining the presence or absence of a sample in a TEM image, where (a) is a TEM image in the presence of the sample and (b) is a TEM image in the absence of the sample and its image intensity histogram. Is.

FIG. 14 is a flowchart showing the steps of virus inspection in the analysis area.

FIG. 15 is a schematic view of a screen used for parameter setting and display of inspection progress in automatic inspection.

FIG. 16 is a schematic view of a screen displaying the result of automatic inspection.

FIG. 17 is an explanatory diagram showing a method for determining the presence / absence of a sample in a TEM image. Explanatory drawing which shows the high frequency component ratio in a conversion image.

FIG. 18 is an observation field of view when the analysis area is moved by (a) sample movement by the sample stage 18, (b) image shift by the imaging system electron deflection coil 16, and (c) sample movement and image shift. FIG. 3 is an explanatory diagram showing the lapse of time at the position, the image shift setting position, and the sample stage setting position.

FIG. 19 is a schematic view of an electron microscope used in the present invention.

FIG. 20 is an explanatory view showing an inspection process of virus inspection using TEM.

FIG. 21 is an explanatory diagram showing an evaluation process of semiconductor evaluation using TEM.

FIG. 22 is an explanatory view showing a process of trimming an inspection target pattern from a TEM image and comparing each pattern.

FIG. 23 is an explanatory diagram showing an inspection sequence when the inspection field of view is changed by the sample stage 18 and the imaging system deflection coil 16.

FIG. 24 is a diagram for explaining the principle of a focus analysis method using parallax, where (a) the sample at the positive focus position is irradiated with the incident electron beam in parallel, (b) the incident electron beam to the sample at the normal focus position. FIG. 3B is an electron optical diagram when (b) is obliquely irradiated with an incident electron beam, when (b) is obliquely irradiated to a sample at a position deviated from the regular focus.

FIG. 25 is an explanatory diagram showing an automatic focus correction process using parallax.

FIG. 26 is an explanatory diagram showing a process of automatically correcting the position shift of the sample by the imaging system electron deflection coil 16.

FIG. 27 is an explanatory diagram showing a process of improving the positional deviation analysis accuracy of a sample using a zoom lens.

FIG. 28 is an explanatory diagram showing a focus distribution around an optical axis in an electron lens having astigmatism.

FIG. 29 is an explanatory diagram showing a step of astigmatism correction in the electron microscope.

[Explanation of symbols]

11 ... Electron gun, 11 '... Electron gun control circuit, 12 ... Irradiation lens,
12 '... Irradiation lens control circuit, 13 ... Irradiation system electronic deflection coil, 13' ... Irradiation system electronic deflection coil control circuit, 14 ... Objective lens, 14 '... Objective lens control circuit, 141 ... Astigmatism correction coil, 141' ... Astigmatism correction coil control circuit, 15 ... Projection lens, 15 '... Projection lens control circuit, 16 ... Imaging system electron deflection coil, 16' ... Imaging system electron deflection coil control circuit, 17 ... Electron beam detector, 17 ' ... Electron beam detector control circuit, 18 ... Sample stage, 18 '... Sample stage control circuit, 19 ... Computer equipped with control software and image processing software, 20 ... Calculation for positional deviation based on phase difference analysis of Fourier transform image Container, 21 ... Thinned sample, 22 ... Mesh, 23 ... Hole, 24 ... Center of gravity of hole, 25 ... Region where sample height is outside specified range, 26 ... Region where correlation value is below a certain value, 31 ... Misalignment Corresponding to the first peak, 32 ... the second peak due to the fixed pattern of the detector, 33 ... the original Maximum intensity peak before applying mask, 34 ... Maximum intensity peak after applying origin mask, 35 ... Noise component, 71 ... Scintillator, 72 ... Coupling part, 73 ... CCD camera, 91 ... Continuous focus correction execution button, 92 ... Auto focus correction parameter initialization button, 93 ... Focus correction execution button, 94 ... Inspection result table, 95 ...
Inspection result histogram, 96 ... Specimen height reset button, 97
... A circle indicating the position and size of the detected virus.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Isao Nagaoki             882 Ichimo, Hitachinaka City, Ibaraki Stock Association             Company Hitachi Ltd. measuring instrument group (72) Inventor Hiroyuki Kobayashi             882 Ichimo, Hitachinaka City, Ibaraki Stock Association             Company Hitachi Ltd. measuring instrument group F-term (reference) 5C001 AA03 CC03                 5C033 EE06 LL03 SS01 SS02

Claims (11)

[Claims] 1. A detector for focusing a first electron beam using a lens, irradiating the focused electron beam onto a sample, and detecting a second electron beam transmitted from the sample, and a sample stage for holding the sample. And a means for recording a first electron microscope image photographed from a first time and a second electron microscope image photographed from a second time, and an electron microscope of the first and second electron microscope images. The first from the peak generated in the analysis image obtained by performing orthogonal transformation or inverse orthogonal transformation on the composite image of orthogonal transformation images
2. An electron microscope comprising: a means for analyzing the positional deviation between the electron microscope image and the second electron microscope image, a means for displaying or recording the sample moving speed, and a means for canceling the movement of the sample. 2. The electron microscope according to claim 1, wherein the means for canceling the movement of the sample moves the position of the sample taken into the detector by an image shift deflecting means. 3. The electron microscope according to claim 1, wherein the means for offsetting the movement of the sample moves the sample position with respect to the electron lens by a sample stage. 4. An electron source, a lens that focuses an electron beam from the electron source, and camera means that irradiates the sample with the electron beam focused by the lens to detect a transmission electron image from the sample.
In an electron microscope equipped with a deflector for deflecting a transmission electron image and a sample stage, means for moving the sample position with respect to the lens by the sample stage, and deflection of the sample position for capturing the transmission electron image by the camera means. A first electron microscope image taken from the first time and a second electron microscope image taken from the second time.
And a first electron microscope image from a peak generated in an analysis image obtained by performing Fourier transform or inverse Fourier transform on a composite image of Fourier transform images of the first and second electron microscope images. Means for analyzing the position shift of the second electron microscope image and adjustment using the deflector so that the sample position taken in by the camera means does not change even if the sample position of the lens moves by the sample stage. An electron microscope characterized by that. 5. A charged particle source and a first from said charged particle source.
Lens means for controlling the charged particle beam of the sample, a sample stage for holding a sample, a control means for controlling the sample stage, the first
Generated by irradiation of a charged particle beam on a sample
In a charged particle beam apparatus comprising a detector for detecting the charged particle beam image of 1 and a deflection means for deflecting the second charged particle beam image, a memory for acquiring and storing a plurality of images by an image signal from the detector. Means, Fourier transform for the plurality of images, computing means for obtaining the phase difference between the images and performing inverse Fourier transform or Fourier transform, and controlling the position of the charged particle beam image captured by the detector. The charged particle beam device, wherein the charged particle beam device returns to any one of the deflection unit, the control unit, and the detection unit. 6. An electron beam apparatus, a camera means arranged in the electron beam apparatus, and an image processing means connected to the camera means are used, and the first charged particle beam is sampled by the electron beam apparatus. The first image acquisition signal from the second charged particle beam from the sample to the image processing means, receiving the first acquisition completion signal from the image processing means, and the image. A step of sending a second image acquisition signal to a processing means, and a correlation value and a positional deviation amount of the first and second images are output from the image processing means, and a correction signal for correcting the positional deviation is output. A recording medium incorporating a step of determining whether or not it is based on the correlation value, and a program for outputting a correction signal to the electron beam apparatus based on the determination step. 7. A sample stage for holding a sample and a stage control means for continuously moving the sample, an angle deflecting means for deflecting an incident angle of the first charged particle beam to the sample, and a sample transmitting means. Detection means for detecting the second charged particle beam;
First from the detection means to the sample by the angle deflection means
A second image based on a second incident angle signal on the sample, the first image and the second image
Means for correcting the focus by obtaining the image shift amount from the image of
A transmission electron beam apparatus, wherein the signal from the correcting means is returned to the stage control unit. 8. A detection method, comprising: a sample stage for holding a sample; and a control means for moving the sample stage, irradiating the sample with a first charged particle beam and detecting a second charged particle beam from the sample. And means for forming an image from the second charged particle beam, and means for acquiring a plurality of images by the image forming means and calculating that the sample is displaced from a predetermined position. An electron beam apparatus for returning a first electron beam to a deflector for deflecting the first electron beam. 9. The electron beam apparatus according to claim 8, wherein the calculating means calculates in 30 milliseconds or less. 10. A charged particle source, lens means for controlling a first charged particle beam from the charged particle source, a sample stage for holding a sample, and irradiation of the sample with the first charged particle beam. In a charged particle beam apparatus including a detector for detecting a second charged particle beam image generated by the detector and display means for displaying the second charged particle image from the detector, continuous movement control of the sample stage is performed. The control means and the first sample on the sample stage are irradiated with the first charged particle beam until the out-of-focus second charged particle image obtains the second charged particle image of the second sample. A charged particle beam device for obtaining a second charged particle image focused on the. 11. A step of setting a sample on a sample stage,
A step of moving the sample stage, a step of irradiating the sample with a first electron beam, a step of capturing an image of a second electron beam from the sample, and a step of acquiring and storing a plurality of the captured images. And a step of obtaining a correlation between images from the plurality of images by image processing, and a step of obtaining a deviation amount between the images,
And a step of returning to the sample stage or the deflector based on the correlation value.