JP2000323081A - electronic microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically perform magnification correction to improve magnification accuracy of a microscope, and shorten an adjusting period, by finding the current correction amount of an image formation lens from a magnification error of a transmission image derived by calculating matching degree of different images. SOLUTION: A sample position is adjusted by a sample position adjusting mechanism 45 inserting a reference sample 5. A magnification changeover R.E (rotary encoder) 39 is rotated, and the corresponding magnification is displayed on a CRT 35 referring to data of a ROM 42. A transmission image projected to a scintillator 33 using a TV control portion 43 is taken by a TV 11, an enlarged image is stored as the transmission image in an HD 31, and the magnification is compared with a previously photographed and stored image of the reference sample 5. An magnification error of the newly taken transmission image for the image of the reference sample 5 is calculated by an ALU 32 and a correction amount of an image formation lens is calculated. This correction amount is added to a stored data in the ROM 42, new data is stored in a RAM 41, and this value is displayed on the CRT 35.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope, and more particularly, to a magnification adjusting method in a transmission electron microscope.

[0002]

2. Description of the Related Art In a conventional transmission electron microscope, an electron beam transmitted through a sample is enlarged by an electron lens and displayed on a fluorescent screen. A reference value is set for the current of the imaging lens that determines the magnification of the transmission electron image for each of a plurality of magnification steps, and the image is formed so that the magnification error falls within a certain range using a reference sample when adjusting the transmission electron microscope. Fine adjustment of the reference current of the lens.

[0003]

SUMMARY OF THE INVENTION In a transmission electron microscope,
In many cases, the magnification of an image actually obtained is deviated from the magnification displayed by a transmission electron microscope due to a manufacturing tolerance of an electron lens or a magnetic path or a tolerance at the time of assembly. Furthermore, measurement errors occur depending on the skill of the operator who performs the magnification measurement and the sample used. Therefore, the magnification actually displayed on the electron microscope has a certain error range.

On the other hand, at the time of adjustment, a magnification error is measured using a reference sample, and the reference current of the imaging lens is finely adjusted and reset so that the amount of deviation falls within the above-mentioned error range. This process needs to be performed for each of a plurality of magnification steps.
Therefore, when there are a plurality of magnification steps, it takes time and effort to adjust the magnification.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and to automatically correct magnification from a transmission image of a reference sample and a previously stored reference image when adjusting an electron microscope, thereby further improving magnification accuracy. An object of the present invention is to provide an electron microscope with a reduced length and shorten the adjustment period.

[0006]

In order to achieve the above object, an electron microscope according to the present invention is different from an image pickup apparatus for photographing and recording a transmission image and a means for recording an image captured by the apparatus. Means for calculating the degree of coincidence between the two images; means for calculating a magnification error of the transmitted image from the calculated degree of coincidence; means for calculating the current correction amount of the imaging lens from the magnification error; It comprises means for storing a plurality of amounts and means for correcting the magnification according to the correction amount for each of a plurality of magnifications.

[0007] The operation of the present invention will be described based on the above configuration means. Set the reference sample on the transmission electron microscope for which you want to adjust the magnification, and take a transmission image at any magnification.
Record. The magnification of the image of the reference sample photographed and recorded in advance is compared with the image of the same magnification. It is desirable to use the same reference sample before and after, but it is also possible to use a sample in which the distance such as the lattice spacing is invariable using, for example, a gold single crystal.

When the magnification is deviated from the reference,
The magnification of the imaging lens is calculated by calculating how much the current of the imaging lens should be corrected from the reference current and resetting the imaging lens current.

At this time, since the magnification is adjusted to the reference sample, the magnification setting accuracy is improved.
The magnification is corrected using the phase correlation method, a position is calculated from the degree of coincidence between the two images, and the magnification is calculated from the difference between the preceding and succeeding peak positions. Hereinafter, for simplicity, description will be made using a circular hole as a reference sample.

A reference image of a transmission image is recorded as f1 (m, n) in a storage device with M × N pixels. Next, a transmission image at an arbitrary magnification is stored in the storage device with f2 (m,
n).

However, both are natural images, and m = 0,
, M-1, n = 0, 1, 2,..., N-1.

The discrete Fourier images F1 (m, n) and F2 (m, n) of f1 (m, n) and f2 (m, n) are (1),
Defined in (2).

[0013]

(Equation 1)

In the phase correlation, when there is a parallel movement of an image between two images, the position of the correlation peak is shifted by the amount of movement.

A method for deriving the movement amount will be described below.

First, assuming that the original image f2 (m, n) has moved by r 'in the m direction, f4 (m, n) = f2 (m +
r ', n).

Equation (2) is transformed into equation (3).

[0018]

(Equation 2)

By setting the amplitude spectrum B (u, v) as a constant, a phase image independent of the image contrast can be obtained. The phase image F′4 (u, v) of f4 is represented by Expression (4).

[0020]

(Equation 3)

The phase image F'1 (u, v) is added to F'2 (u, v).
The composite image H14 (u,
v) is given by equation (5).

[0022]

(Equation 4)

The correlation strength image G14 (r, s) is given by equation (6) by performing an inverse Fourier transform on the composite image H14 (u, v).

[0024]

(Equation 5)

According to equation (6), when there is a displacement r 'in the m direction between the two images, the peak position of the correlation intensity image is shifted by -r'.

For example, if there is a displacement of 2 pixels in the m direction between two images, the composite image becomes a two-period wave. When this is inverse Fourier transformed, it becomes a correlation strength image, and 2 pi from the center
A peak occurs at a position shifted by xel.

[0027] When the peak position (r _12, s ₁₂₎ can be identified, the front edge performs edge detection in the r direction in the position of _{s 12 Δf (r f, s} 12) and the rear edge Delta] f (r _b, s ₁₂₎ obtains a distance D ₁₂ between.

[0028]

[6] _{Δf (r f, s 12)} = f (r f, s 12) -f (r f -1, s 12) ... (7) Δf (r b, s 12) = f (r b, _{s 12) -f (r b -1} , s 12) ... (8) D 12 = Δf (r f, s 12) -Δf (r b, s 12) ... (9) the distance unit in example pixel including I do not care. Previously determining the ratio R ₁₂ of the reference distance D ₀ and D ₁₂ were measured by using a reference sample at the same magnification.

[0029]

R ₁₂ = D ₁₂ / D ₀ (10) The correction amount I ₁₂ of the imaging lens current can be calculated from the magnification Mag obtained by measuring the magnification error and the ratio R ₁₂ .

[0030]

I ₁ = A ₁ (Mag × (1- (1 / R ₁₂ ))) + C ₁ (11) A ₁ and C ₁ are constants.

In equation (11), for example, the correction is performed by one imaging lens such as the second projection lens. However, the correction may be performed by using a plurality of imaging lenses.

Normally, when correction is performed with one imaging lens, the image is rotated depending on the amount of lens current to be corrected and the number of turns of the lens. However, imaging lenses 2 having different polarities from each other
If the number is used, for example, if the correction is performed using the second intermediate lens and the first projection lens, the rotation of the image at the time of the magnification correction can be corrected.

In the electron microscope, a coil for correcting the lens and a coil for moving the image are incorporated in the imaging lens portion. Depending on the combination of the imaging lenses, the coil may not be effective. However, if three or more lenses are combined, it becomes possible to set conditions effective for the coil in addition to the magnification and rotation of the image.

[0034]

(Embodiment 1) An embodiment of the present invention will be described below with reference to FIG. 1 and according to the flowchart of FIG. The reference sample 5 (circular hole) is inserted, and the sample position is adjusted by the sample position adjusting mechanism 45.

In order to input the magnification M, the pulse wave generated by rotating the magnification switching rotary encoder 39 is converted into an I / F signal.
The digital signal is input to a digital signal 36 for conversion. The microprocessor 30 determines the value of the digital signal in the ROM 42
Is displayed on the CRT 35 using the CRT controller 34 by referring to the magnification display data set in advance. At the same time, the first
The lens data of the irradiation lens, the second irradiation lens, the third irradiation lens, the objective lens, the first intermediate lens, the second intermediate lens, the first projection lens, and the second projection lens are stored in DACs 21 and 22, respectively.
2, 25 to 29 to convert lens system data into analog signals. Analog signals are output from the DACs 21, 22, 25 to 29 to the excitation power supplies 12, 13, 16 to 20, and lens currents are output to the lens coils 2, 3, 6 to 10 of each lens system.

Next, the transmission image projected on the scintillator 33 is captured by the TV 11 using the TV control unit 43, and the enlarged image of the magnification M is named and stored as the transmission image 2 in the storage device 31 from the image capturing interface 44. . The magnification is compared with the image 1 of the reference sample of the magnification M previously photographed and recorded in the storage device 31.

The arithmetic unit 32 calculates the magnification error of the newly acquired transmitted image 2 with respect to the image 1 of the reference sample of magnification M previously photographed and recorded. The number of pixels of the captured image is equal to the number of pixels of the reference image 1 stored in advance. For example, when the previously stored image 1 has M × N pixels, the number of pixels of the captured image 2 is also set to M × N. The data of the image 1 and the image 2 are read into the arithmetic unit 32, and the reference image 1 and the transmission image 2 are Fourier-transformed respectively. If the combined image is subjected to inverse Fourier transform by subtracting the data of the phase component after the conversion, a correlation strength image is obtained. Regarding the transmission image 2,
The leading edge Δf (r _f , s ₁₂ ) and the trailing edge Δf (r
_b , s ₁₂ ), the distance D ₁₂ becomes the maximum at s ₁₂ , so from equation (9), the front edge Δf (r
_f, s ₁₂₎ and the rear edge Δf (r _b, s ₁₂₎ the distance between D
_Ask for ₁₂ . Then (10) determining the ratio R ₁₂ of the reference distance D ₀ and D ₁₂ were measured by using a reference sample by formula. From the magnification M and the ratio R _12, calculates the correction amount I ₁₂ of the imaging lens current used for correction by equation (11).

The arithmetic unit 32 correction amount I ₁₂ of the resulting imaging lens current by calculation by adding the data of the imaging lens current stored in advance in the ROM42 magnification M, the imaging system of the newly magnification M The data is stored in the RAM 41 as lens data.

After the magnification is set, when the magnification M is selected by the magnification switching rotary encoder 39, the microprocessor 30 refers to magnification display data preset in the ROM 42 based on the value of the digital signal, and sets the corresponding magnification to the CRT. It is displayed on the CRT 35 using the controller 34. At the same time, the first illumination lens, the second illumination lens, the third illumination lens, the objective lens,
The lens data of the first intermediate lens, the second intermediate lens, the first projection lens, and the lens data after magnification correction newly stored in the RAM 41 are stored in the DACs 21, 22, 25 to 29.
To convert the lens system data into an analog signal. However, the number of irradiation lenses is not limited to three. Each DAC
Exciting power supplies 12, 13, 16 from 21, 22, 25 to 29
Output analog signals to the lens coils 2, 3,
The lens current is output to 4, 6 and the lens coils 7 to 10
Output the lens current after magnification correction.

As a result, the setting accuracy of the magnification of the transmission electron microscope becomes more precise, and the adjustment period is shortened because the magnification is automatically corrected.

(Embodiment 2) Hereinafter, description will be made with reference to the flowchart of FIG.

In the electron microscope of the first embodiment, the transmission image captured by the TV 11 is named and stored in the storage device 31 by the image capture interface 44 as the transmission image 2 of the magnification M. At this time, if the entire sample is not recorded on the transmission image 2, the degree of coincidence due to the phase correlation becomes small and a magnification error occurs. For this reason, when the degree of coincidence is small, the entire reference image 1 is not used, and the half or 1 /
The calculation is performed by the arithmetic unit 32 while changing the area of the comparison of the degree of coincidence with that of the area No. 4. In the case of 1/2, the degree of coincidence is sequentially calculated for the upper, lower, left and right by the arithmetic unit 32. Next, in the case of １ ／, the calculation unit 32 sequentially calculates the data from each of the four equal parts at 90 ° intervals. As a result of the calculation, a part of the reference image 1 having the highest matching degree is stored as the image 3, and magnification correction is performed using the image 3.

After the peak position of the correlation intensity image is specified by the arithmetic unit 32, the front and rear edges or the upper and lower edges are obtained from the image 3. Upper and lower edges can be obtained in the same manner as the front edge from the peak position r _12.

[0044] Since the radius of the sample stored in the transmission image 2 and the peak position r ₁₂ obtained by calculation from the edge position is obtained, the magnification error of the transmission image 2 is obtained. Thereafter, magnification correction is performed in the same manner as in Example 1, the precision of setting the magnification of the transmission electron microscope is further refined, and the adjustment period is shortened because the magnification correction is performed automatically.

(Embodiment 3) Hereinafter, description will be made with reference to the flowchart of FIG.

With the electron microscopes of Example 1 and Example 2,
When selecting the magnification M by the rotary encoder 39, from the reference distance ratio R ₁₂ of the transmission image 2 calculated by the arithmetic unit 32 reference image 1, calculates the actual ratio M2 of the transmission image 2 by the arithmetic unit 32. The actual magnification M2 is stored in the RAM 42 as the actual magnification M3 when the magnification M is selected. When the magnification M is selected again by the rotary encoder 39 after the magnification adjustment, the microprocessor refers to the magnification M3 newly stored in the RAM 42 based on the value of the digital signal, and causes the CRT controller 34 to display the magnification M3 on the CRT 35.

Thus, the accuracy of setting the magnification of the transmission electron microscope is improved.

[0048]

According to the present invention, the following effects can be obtained.

1) The magnification accuracy is improved.

2) The adjustment period can be shortened by automatically performing magnification correction.

When adjusting the electron microscope, it is possible to provide an electron microscope whose magnification accuracy is further improved by automatically correcting the magnification from the transmission image and the reference image, and the adjustment period can be shortened.

[Brief description of the drawings]

FIG. 1 is a diagram showing a transmission electron microscope of the present invention.

FIG. 2 is a flowchart of the transmission electron microscope of the present invention.

FIG. 3 is a diagram showing a transmission electron microscope of the present invention.

FIG. 4 is a flowchart of the transmission electron microscope of the present invention.

FIG. 5 is a flowchart of the transmission electron microscope of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... 1st irradiation lens coil, 3 ... 2nd irradiation lens coil, 4 ... 3rd irradiation lens coil, 5 ... Reference sample, 6 ... Objective lens coil, 7 ... 1st intermediate lens coil, 8 ... 2nd intermediate lens coil, 9 ... 1st projection lens coil, 10 ... 2nd projection lens coil, 11 ... T
V, 12 to 20: excitation power supply, 21 to 29: DAC, 30
... Microprocessor, 31 ... Storage device, 32 ... Operation device, 33 ... Scintillator, 34 ... CRT controller,
35: CRT, 36 to 37: I / F, 39: Rotary encoder for switching magnification, 41: RAM, 42: ROM,
43: TV control unit, 44: Image capturing interface, 45: Sample position adjusting mechanism, 52: Electron beam.

Claims (3)

[Claims] A transmission image is taken by a transmission electron microscope.
An imaging device for recording, a unit for recording an image captured by the device, a unit for calculating a coincidence between two different images, and a unit for calculating a magnification error of a transmission image from the calculated coincidence Means for calculating a current correction amount of the imaging lens from the magnification error, means for storing a plurality of the correction amounts, and means for correcting the magnification according to the correction amount for each of a plurality of magnifications. And electron microscope. 2. A transmission electron microscope according to claim 1, further comprising: means for dividing two different images into portions; means for calculating a degree of coincidence from the two different images; and Means for calculating the magnification error of the transmission image from the degree of coincidence,
A means for calculating a current correction amount of the imaging lens from the magnification error; a means for storing a plurality of the correction amounts; and a means for correcting the magnification according to the correction amount for each of a plurality of magnifications. electronic microscope. 3. A transmission electron microscope according to claim 1, wherein said means for calculating the degree of coincidence between two different images, and means for calculating the actual magnification of the transmission image from said calculated degree of coincidence. An electron microscope comprising: means for storing a plurality of actual magnifications; and means for displaying the actual magnification for each of a plurality of magnifications.