WO2015050157A1

WO2015050157A1 - Charged particle beam device and method for setting correction filter thereof

Info

Publication number: WO2015050157A1
Application number: PCT/JP2014/076284
Authority: WO
Inventors: 真佐志渡辺; 千葉　寛幸; 吉延星野; 川俣　茂
Original assignee: 株式会社日立ハイテクノロジーズ
Priority date: 2013-10-03
Filing date: 2014-10-01
Publication date: 2015-04-09
Also published as: JPWO2015050157A1; JP6162813B2

Abstract

The same region of a sample is scanned with a charged particle beam at a first speed within a bandwidth range of a detection unit and a second speed which exceeds the upper bound of the bandwidth. A first amplitude spectrum which is obtained by frequency analyzing a first detection signal which is obtained by the scanning at the first speed is superpositioned with a first amplitude spectrum which is obtained in a different image capture condition. A degraded function which represents a frequency characteristic of the detection unit is computed using the superpositioned first spectrum and a second spectrum corresponding to a second detection signal. While the superpositioned frequency spectrum does not satisfy an amplitude condition, the image capture condition is changed and the process is returned to a first processing unit. If the superpositioned frequency spectrum satisfies the amplitude condition, a correction filter of the detection unit of a charged particle beam device is computed and set on the basis of an inverse function of the already computed degraded function.

Description

Charged particle beam apparatus and correction filter setting method thereof

The present invention provides a charged particle beam apparatus equipped with a correction filter setting function for correcting deterioration of a detection signal caused by a frequency band limitation of a detection unit (detector and its amplifier) when a sample is scanned at high speed with a charged particle beam. And its method.

A scanning charged particle beam apparatus (for example, a scanning electron microscope apparatus, a scanning ion microscope apparatus, or a scanning transmission electron microscope apparatus) scans the surface of a sample two-dimensionally (horizontal direction and vertical direction) with a charged particle beam, and irradiates it. A secondary signal generated from the region is detected. The scanning charged particle beam apparatus amplifies and integrates detection signals by an electric circuit, and then replaces the amplitude value with a density value of image data. The scanning charged particle beam apparatus generates a two-dimensional image by associating the density value after replacement with the scanning coordinates of the charged particle beam. This two-dimensional image is used for observation of the structure of the sample surface.

The scanning speed of the charged particle beam is determined according to the material of the sample, the purpose of observation, the characteristics of the detector that detects the secondary signal, and the like. When the scanning speed is fast, the SN ratio of the two-dimensional image is deteriorated because the integration time of the detection signal is small, but on the other hand, the response to the temporal change of the observation object is improved. Further, when the scanning speed is high, the irradiation time of the charged particle beam to one point on the sample can be shortened, and the influence of the destruction, contamination, charging, etc. of the sample by the charged particle beam can be reduced.

On the other hand, when the scanning speed is slow, the integration time of the detection signal obtained from one point on the sample surface is increased, so that the SN ratio of the two-dimensional image is improved. However, there is an influence such as destruction of the sample by the charged particle beam, contamination, and charging. To increase. Therefore, in general, when searching for an observation field on the sample, a high scanning speed is used, and when observing and storing the sample with high image quality after determining the observation position, a slow scanning speed is used.

Also, in the case of a material that is easily damaged due to the sample being destroyed, contaminated, or charged by irradiation of the charged particle beam, the influence may be alleviated by increasing the scanning speed of the charged particle beam. There are other methods such as setting the acceleration voltage of the charged particle beam to a low voltage, and reducing the charged particle beam current amount irradiated on the sample by narrowing the probe diameter of the charged particle beam. .

In addition to the above, another factor that determines the scanning speed of the charged particle beam is the detector characteristics. The characteristics of the detector are determined by the response speed from the detection of the secondary signal to the conversion to the electrical signal and the response speed of the amplifier circuit that amplifies the detection signal. The amplifier circuit has a characteristic that the response speed becomes slower as the gain is increased. Hereinafter, in the present invention, the detector and its amplifier circuit may be collectively referred to as a detection unit.

When the response speed of the detector and the response speed of the amplifier circuit are both slow, when the charged particle beam is scanned at high speed, the detection signal is band-limited in the process of passing through the detector and the amplifier circuit. For this reason, when a sample surface having a fine structure is scanned at high speed with a charged particle beam and a detection signal containing a large amount of high frequency components is input to the detector, the output of the detector becomes an impulse response, and the time for the impulse response to converge An output signal having a shape in which the detection signal in t and the above-described impulse response are superimposed is obtained.

As a result, the above-described two-dimensional image becomes a blurred image as the image flows in the scanning direction of the charged particle beam. For this reason, it is difficult to discriminate and observe the sample structure from the acquired two-dimensional image. Therefore, it is impossible to select acquisition of a two-dimensional image by high-speed scanning in an application where it is desired to observe a sample with high gain while using a detector with a slow response speed.

In addition, the selection of the detector is determined by conditions such as the type of secondary signal to be detected, the atmosphere in the sample chamber, and the detection sensitivity. For this reason, depending on the observation conditions, the scanning speed of the charged particle beam may be lowered in accordance with a detector having a slow response speed. However, in this case, there is a problem that the scanning speed cannot be increased for searching the field of view or reducing the sample damage.

A method for solving the above problem is proposed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-165450). Patent Document 1 discloses (1) a detection signal stored by scanning a charged particle beam at a speed within the bandwidth of the detector and its amplifier circuit, and a charged particle beam at a speed exceeding the upper limit of the bandwidth. (2) Calculate the deterioration function by dividing the result of Fourier transform of these two detection signals, and (3) then calculate the inverse function of the calculated deterioration function. (4) A method in which the amplitude of the signal corresponding to the time t at which the impulse response converges is used as a weighting factor for a one-dimensional filter that corrects image deterioration due to the detector and its amplifier circuit. Is disclosed.

Patent Document 1 applies a one-dimensional filter generated by such a method to a detection signal stored at a scanning speed exceeding the upper limit of the bandwidth of the detector and its amplifier circuit or a two-dimensional image based on the detection signal. Thus, a method for restoring the original two-dimensional image from the detection signal or the detection signal without reducing the throughput of the input signal is disclosed.

JP 2011-165450 A

However, the amplitude of the signal corresponding to the time t at which the impulse response used when Patent Document 1 generates a one-dimensional filter converges is not an impulse input in the original sense. That is, the signal generated by scanning the charged particle beam contains only a frequency component depending on the sample structure, and is not an ideal impulse waveform. For this reason, with the method described in Patent Document 1, it is not always possible to calculate an accurate one-dimensional filter corresponding to the detector mounted on the charged particle beam apparatus and its amplifier circuit.

In order to solve the above-described problems, the present invention adopts, for example, the configuration described in the claims. The present specification includes a plurality of means for solving the above problems. To give an example, a charged particle source that outputs a charged particle beam, a scanning unit that scans the sample with the charged particle beam, and the like. Detecting a secondary signal generated from the irradiation region of the charged particle beam and amplifying the amplitude of the detection signal; and under a certain imaging condition, the same region of the sample is Detected by scanning the charged particle beam at a second speed exceeding the upper limit of the bandwidth of the first detection signal and the detection unit detected by scanning the charged particle beam at a first speed within a range A first processing unit that stores a second detection signal in a storage unit; a second processing unit that performs frequency analysis of the first detection signal; and a first amplitude spectrum obtained by the frequency analysis The other first acquired for imaging conditions different from the conditions Based on a third processing unit that superimposes the amplitude spectrum, and the first amplitude spectrum after superimposition and the second amplitude spectrum obtained by frequency analysis of the second detection signal, the frequency of the detection unit A fourth processing unit that calculates a degradation function that represents the characteristics; a fifth processing unit that determines whether the amplitude spectrum after superimposition satisfies the first amplitude condition; and the amplitude spectrum after superimposition is the first A sixth processing unit that changes the imaging condition and returns to the processing of the first processing unit while the amplitude condition is not satisfied, and the fourth spectrum when the amplitude spectrum after superposition satisfies the first amplitude condition, A seventh processing unit that calculates a correction filter of the detection unit based on an inverse function of the deterioration function calculated by the processing unit, and the calculated correction filter is acquired at the second speed. Set for correction of second detection signal That the charged particle beam device having a processing unit of the eighth.

According to the present invention, even when a detector having a slow response speed and a high amplification gain is used for a charged particle beam apparatus, a correction filter with higher accuracy than that of the conventional method can be calculated. It is possible to improve the image quality of an image acquired through scanning. Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

1 is a diagram illustrating a configuration of an electron microscope apparatus according to Embodiment 1. FIG. 5 is a flowchart for explaining a procedure for creating a deterioration function and a corrected one-dimensional filter in the first embodiment. The figure which shows the relationship between the frequency according to frequency of the amplitude spectrum acquired about slow scanning speed, and a threshold value. 9 is a flowchart for explaining a procedure for creating a deterioration function and a corrected one-dimensional filter in the second embodiment. The figure which shows the relationship of the frequency according to the frequency of an amplitude spectrum acquired about slow scanning speed, and an upper limit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments of the present invention are not limited to the embodiments described later, and various modifications are possible within the scope of the technical idea.

[Outline of signal processing to be adopted]
Also in the charged particle beam apparatus according to the embodiment, a correction filter that corrects deterioration due to a detector when a detector having a slow response speed and a high amplification gain (including the amplifier circuit; the same applies hereinafter) is used. Is basically created according to the following procedure.

(1) A first detection signal detected by scanning a charged particle beam (e.g., an electron beam) at a first speed that is within the bandwidth of the detector, and the same first detection signal acquired. Storing a second detection signal detected by scanning the charged particle beam at a second speed exceeding the upper limit of the bandwidth of the detector in a storage unit (for example, a memory); and (2) a first detection signal. The first amplitude spectrum obtained by frequency analysis (for example, Fourier transform) is divided by the second amplitude spectrum obtained by frequency analysis (for example, Fourier transform) of the second detection signal to calculate a deterioration function. (3) The inverse function of the calculated degradation function is Fourier-transformed to calculate a correction filter, and (4) the calculated correction filter is stored in the storage unit.

However, an accurate correction filter cannot be calculated only by the above procedure. Therefore, the charged particle beam apparatus according to the embodiment further executes the following processing.

(1) It is determined whether or not the newly acquired first amplitude spectrum includes a frequency component sufficient for the impulse input, and (2) the frequency of the first amplitude spectrum for the impulse input. If the component is insufficient, change the field of view movement, enlargement / reduction, rotation, focus variation, charged particle beam tilt, sample tilt, etc. (that is, change the imaging conditions), (3) After changing the imaging conditions, The first detection signal obtained by scanning the charged particle beam at a first speed within the range of the detector bandwidth is stored in the storage unit, and the first region exceeding the upper limit of the detector bandwidth for the same region is stored. A second detection signal obtained by scanning a charged particle beam at a speed of 2 is stored in a storage unit, and (4) a first amplitude spectrum obtained by frequency analysis (for example, Fourier transform) of the first detection signal. Acquired for different imaging conditions (5) The first amplitude spectrum after superimposition is divided by the second amplitude spectrum obtained by frequency analysis (for example, Fourier transform) of the second detection signal, and deteriorated. A function is calculated, (6) it is determined whether or not the first amplitude spectrum after superimposition includes a sufficient frequency component with respect to the impulse input, and (7) further different when the frequency component is insufficient. The first and second detection signals are acquired for the imaging conditions, and the first amplitude spectrum obtained by frequency analysis of the first detection signals is superimposed on the other first amplitude spectra acquired for the different imaging conditions. Then, the process after the change of the imaging condition is repeated until it is determined that the first amplitude spectrum after the superimposition includes a sufficient frequency component compared with the impulse input, and (8) when the frequency component is sufficient, All the memorized degradation functions are averaged (the averaging may be performed sequentially while the detection is repeated), and (9) the inverse response of the averaged degradation function is inversely transformed by Fourier transform so that the impulse response is The amplitude of the signal corresponding to the convergence time t is calculated as the weighting coefficient of the correction filter (one-dimensional filter).

In other words, a superimposed amplitude spectrum including a sufficient frequency component is created by superimposing a plurality of first amplitude spectra that are sequentially acquired for different imaging conditions, and a deterioration function is created for the superimposed amplitude spectrum. The amplitude of the signal corresponding to the time t at which the impulse response converges is calculated as a weighting coefficient of the correction filter (one-dimensional filter) by Fourier-transforming the inverse function of the deterioration function.

[Example 1]
FIG. 1 shows a configuration example of an electron microscope apparatus according to the first embodiment. An electron beam 2 generated from the electron gun 1 is converged by a converging lens 3. Thereafter, the electron beam 2 passes through the objective lens 4 and is converged to the minimum diameter on the surface of the sample 5. The deflection coil 6 is disposed between the converging lens 3 and the objective lens 4, and changes the magnetic field intensity according to the time change of the deflection current supplied from the deflection control circuit 7. Due to the change in the magnetic field intensity, the electron beam 2 scans the surface of the sample 5 two-dimensionally (horizontal direction and vertical direction).

The scanning speed of the electron beam 2 can be changed in multiple stages by changing the change period of the deflection current supplied from the deflection control circuit 7. The operator can input an arbitrary scanning speed to the CPU 9 through the control input device 8. The CPU 9 sets a scanning speed for the deflection control circuit 7 and changes the scanning speed of the electron beam 2. The sample stage 10 that supports the sample 5 moves the coordinates of the sample 5 manually or by motor drive. By moving the coordinates of the sample 5, the irradiation range (observation field of view) of the electron beam 2 irradiated on the surface of the sample 5 can be moved.

A secondary signal 11 is generated from the region of the sample 5 irradiated by the electron beam 2, and the detector 12 detects the secondary signal 11. The detector 12 converts the detected secondary signal into an electrical signal and outputs it as a detection signal. The detection signal is amplified to a signal having a sufficient amplitude by the amplifier 13. In preparation for the case where the amplitude of the detection signal is very small, the electron microscope apparatus employs a configuration in which a plurality of amplifiers having different amplification factors are provided, or a configuration in which one variable amplifier capable of arbitrarily changing the amplification factor is provided. As the detector 12, in addition to a secondary electron detector that detects secondary electrons, a reflected electron detector that detects reflected electrons may be employed. Further, a detector that detects current flowing in the sample 5 irradiated by the electron beam 2 such as EBIC (Electron Beam Induced Current) or absorption current may be employed.

In the case of the electron microscope apparatus shown in FIG. 1, a configuration in which an amplifier 13 having a minimum amplification factor, an amplifier 14 having an intermediate amplification factor, and an amplifier 15 having a maximum amplification factor is employed, and the amplification factor is switched by a switch 16. The number of amplifiers may be determined in accordance with the required amplification factor range. The operator inputs the amplification factor to the CPU 9 by the control input device 8, and the CPU 9 switches and controls the switch 16 so that the amplifier having the input amplification factor is connected. The detector 12 and the

amplifiers

13, 14, and 15 are collectively referred to as an amplifying unit.

The detection signal amplified in any amplifier is input to the analog-to-digital converter 17 and converted into a digital signal so that the intensity of the detection signal corresponds to the density value of the gray scale image. The digitized detection signal is stored in the frame memory 18 so that the horizontal and vertical scanning coordinates of the electron beam 2 correspond to the horizontal and vertical coordinates of the two-dimensional image data. When the switch 20 is closed, the two-dimensional image data read from the frame memory 18 is output to the image display device 19. As a result, the surface structure of the sample 5 irradiated with the electron beam 2 is displayed on the screen of the image display device 19 so as to be observable as a grayscale two-dimensional image.

The electron microscope apparatus according to the present embodiment further includes an image processing apparatus 21 that calculates an image degradation function and a corrected one-dimensional filter when the electron beam 2 is scanned at a speed exceeding the bandwidth of the detection unit. The image processing device 21 is connected to the frame memory 18 and stores from the frame memory 18 an image stored at a low scanning speed that falls within the bandwidth of the detection unit and an image stored at a high scanning speed that exceeds the bandwidth of the detection unit. read out. A slow scanning speed image and a fast scanning speed image are acquired for the same field of view (region). Also, an image with a slow scanning speed and an image with a fast scanning speed are acquired with the same amplification factor. That is, two images with different scanning speeds are acquired for the same region under the same imaging conditions other than the viewing area and the scanning speed.

The calculated corrected one-dimensional filter is set in the filtering unit 22. The filtering unit 22 is connected to the frame memory 18, corrects an image stored at a scanning speed exceeding the bandwidth of the detector 12 and its amplification circuit, and outputs the corrected image to the frame memory 23. The frame memory 23 is connected to the image display device 19 through the switch 24. When the switch 24 is closed, the image read from the frame memory 23 is displayed on the image display device 19.

FIG. 2 illustrates a correction one-dimensional filter setting operation executed by the image processing apparatus 21 mounted on the electron microscope apparatus according to the first embodiment. The processing procedure shown in FIG. 2 mainly assumes a case where the processing procedure is executed before the use of the electron microscope apparatus is started. But you may perform at the time of the maintenance after the use start of an electron microscope apparatus, etc.

(Step S10)
The image processing device 21 acquires, from the frame memory 18, an image f (x, y) obtained by scanning the electron beam 2 at a slow scanning speed within the bandwidth of the detector 12 and its amplifier as an image without deterioration. To do.

(Step S20)
The image processing device 21 acquires, from the frame memory 18, an image g (x, y) when the electron beam 2 is scanned at a high scanning speed at which deterioration occurs for the same field of view as the image f (x, y).

Note that step S10 and step S20 are out of order, and either may be performed first.

(Step S30)
The image processing device 21 performs a window function on the image f (x, y) and the image g (x, y) to obtain the image f ′ (x, y) and the image g ′ (x, y). The window function is a general processing function used to suppress an error component (artifact) that appears due to a sudden change in the starting point and the ending point of a signal in the process of performing Fourier transform in the next step. In this embodiment, a Hanning window is used as the window function, and the signal at the start point and the end point is suppressed to zero. This can reduce the vertical error component (artifact) in the corrected image after applying the filter, but other window functions other than the Hanning window may be used.

In the scanning of the two-dimensional electron beam 2, generally, the scanning is first performed in the horizontal direction (X direction), then moved by one line in the vertical direction (Y direction), and the horizontal direction (X Direction). Due to the characteristics of this scanning, deterioration when scanning the electron beam 2 at high speed occurs in the horizontal direction (X direction) where the moving speed is high. For this reason, the calculation of the deterioration function may be executed only for the line unit extending in the horizontal direction (X direction). That is, the window function processing in step S30 need not be performed two-dimensionally on the image, but may be performed on the start and end points of data in the horizontal direction (X direction).

(Step S40)
The image processing device 21 performs Fourier transform on the image f ′ (x, y) for each image f ′ (t) for one line in the horizontal direction (X direction) to obtain F (s).

(Step S41)
The image processing device 21 obtains the amplitude spectrum from F (s) acquired in the previous step S40 and superimposes it on the amplitude spectrum stored in step S63 of the previous loop. If there is no amplitude spectrum stored in step S63 of the previous loop (at the first execution), an amplitude spectrum is obtained from F (s).

(Step S50)
The image processing device 21 outputs an image g ′ (one line in the horizontal direction (X direction) of the image g ′ (x, y) obtained by applying a window function to g (x, y) corresponding to a high scanning speed. Fourier transform is performed every t) to obtain G (s).

(Step S60)
The image processing device 21 obtains the deterioration function H ⁻¹ (s) by the following formula 1.
[Equation 1]
H ⁻¹ (s) = F (s) / G (s) (Formula 1)

(Step S61)
The image processing apparatus 21 adds the deterioration function H ⁻¹ (s) acquired in step S60 of the current loop to the deterioration function ΣH ⁻¹ (s) / (n−1) stored in step S64 of the previous loop, and averages it. And a new deterioration function given by the following Equation 2 is obtained.
[Equation 2]
ΣH ⁻¹ (s) / n (Formula 2)

Here, ΣH ⁻¹ (s) represents an addition value of all deterioration functions obtained in the current and past step S60, and n represents the number of times the deterioration functions are added (the number of loops). If there is no deterioration function stored in step S64 of the previous loop (at the first execution), this averaging process is not particularly necessary. A deterioration function reflecting all past calculation results can be obtained by averaging.

(Step S62)
When the frequency characteristic of the amplitude spectrum after superimposition obtained in step S41 of the current loop is insufficient (if the frequency is insufficient for the impulse input or the frequency of each frequency for all frequencies) If the threshold value has not reached the threshold value), the process proceeds to step S63.

FIG. 3 shows the relationship between the frequency and the threshold value for each frequency component of the amplitude spectrum after overlapping obtained in step S41. In the case of the present embodiment, specifically, the image processing device 21 determines whether or not the frequency of the amplitude spectrum (after superposition) acquired for the slow scanning speed has exceeded the threshold value for all frequencies. To do. The threshold value does not have to be the same for all frequencies as shown in FIG. 3, and the threshold value may be changed depending on the frequency. In any case, when the frequency of each frequency does not exceed the respective threshold values for all frequencies, the process proceeds to step S63.

(Step S63)
The image processing device 21 stores the amplitude spectrum after superimposition obtained in step S41 in a storage unit (for example, a hard disk device or a semiconductor memory).

(Step S64)
The image processing device 21 stores the averaged deterioration function ΣH ⁻¹ (s) / n obtained in step S61.

(Step S65)
The image processing device 21 changes image acquisition conditions such as field of view movement, enlargement / reduction, rotation, focus variation, charged particle beam tilt, sample tilt in the electron microscope device. The above is one loop. Thereafter, the image processing apparatus 21 returns to step S10 and enters the next loop. In step S62, the loop configured by the above-described processing is repeated until the frequency in the amplitude spectrum after superimposition obtained in step S41 is sufficient for the impulse input or reaches the frequency determined as the threshold value. If the frequency in the amplitude spectrum after superimposition obtained in step S41 is sufficient for the impulse input or reaches the frequency determined as the threshold value, the process proceeds to step S70.

(Step S70)
The image processing device 21 inversely transforms ΣH ⁻¹ (s) / n to obtain h ⁻¹ (t). Here, h ⁻¹ (t) is a repair function for the deteriorated image in the real image space, and the deterioration can be repaired by multiplying h ⁻¹ (t) by the deteriorated image data g (t). .

(Step S80)
The image processing device 21 sets a value until the amplitude of h ⁻¹ (t) converges to 0 as a weighting coefficient of the correction one-dimensional filter, and creates a correction one-dimensional filter.

(Summary)
As described above, according to the present embodiment, even when a detector (detector 12 and

amplifiers

13, 14, and 15) having a slow response speed and a high amplification gain is used, the frequency characteristics can be accurately corrected. A one-dimensional filter can be calculated. For this reason, if the corrected one-dimensional filter is applied to the filtering unit 22, the image quality of an image acquired when the electron beam 2 is scanned at high speed can be improved.

[Example 2]
Subsequently, a method of creating a corrected one-dimensional filter by the electron microscope apparatus according to the second embodiment will be described. The second embodiment automatically corrects the deviation between the change in the deterioration function (characteristic change in the detector 12 and the amplifier 13 and the like) and the corrected one-dimensional filter during the long-term operation, and applies it to the filtering unit 22. An electron microscope apparatus equipped with the function will be described. The apparatus configuration of the electron microscope apparatus according to the present embodiment is the same as that of the first embodiment.

FIG. 4 illustrates processing operations executed by the image processing apparatus 21 mounted on the electron microscope apparatus according to the second embodiment. The image processing apparatus 21 of the electron microscope apparatus stores the superimposed amplitude spectrum and the degradation function generated by the method of the first embodiment, and the filtering unit 22 has a one-dimensional correction filter set in advance. Yes.

(Step S110)
During normal use, the operator searches the observation target portion while viewing the image after applying the corrected one-dimensional filter displayed on the image display device 19 when the electron beam 2 is scanned at high speed. When searching, the operator changes image acquisition conditions such as visual field movement, enlargement / reduction, rotation, focus fluctuation, charged particle beam tilt, sample tilt, and the like through the control input device 8.

The image processing apparatus 21 monitors the operation content of the operator and the execution operation of the electron microscope apparatus through the CPU 9, and determines whether images in the same region have been acquired for both the slow scanning speed and the fast scanning speed. . Here, the slow scanning speed means a speed within the bandwidth range of the detector 12 and the amplifier 13 and the fast scanning speed means a speed exceeding the upper limit of the bandwidth of the detector 12 and the amplifier 13. . If a positive result is obtained in step S110, the image processing apparatus 21 proceeds to step S120, and repeats the above determination process while a negative result is obtained.

(Step S120)
The image processing device 21 applies a window function to the image f (x, y) acquired at a low scanning speed and the image g (x, y) acquired at a high scanning speed, and the image f ′ (x, y) and An image g ′ (x, y) is obtained.

(Step S130)
The image processing device 21 performs Fourier transform for each image f ′ (t) of one line in the horizontal direction (X direction) of the image f ′ (x, y) to obtain F (s).

(Step S140)
The image processing device 21 calculates the average value (300 in FIG. 5) and the upper limit value (301 in FIG. 5) of the spectrum frequency stored in the storage unit. The upper limit value is set to a value larger than the average value. The upper limit value is, for example, a value obtained by adding a fixed value set in advance to the average value, a value obtained by multiplying the average value by (1 + α) (where α> 0), a value obtained by multiplying the average value by (1 + σ) (where σ is Standard deviation value).

(Step S150)
The image processing device 21 superimposes the amplitude spectrum of F (s) acquired in step S130 on the amplitude spectrum stored in the built-in memory.

(Step S160)
The image processing device 21 determines whether or not there is a frequency having a threshold value exceeding the upper limit value (301 in FIG. 5) in the amplitude spectrum after superimposition obtained in step S150. If there is no frequency having a frequency exceeding the upper limit value, the image processing device 21 stores the superimposed amplitude spectrum acquired in step S150 as it is. On the other hand, if there is a frequency (302 in FIG. 5) having a frequency exceeding the upper limit (301 in FIG. 5), the image processing device 21 returns to step S110 without storing the superimposed amplitude spectrum.

(Step S170)
If an affirmative result is obtained in step S160, the image processing device 21 applies the window function to g (x, y) corresponding to the high scanning speed and applies the horizontal direction (X G (s) is obtained by performing Fourier transform for each image g ′ (t) in one direction).

(Step S180)
The image processing device 21 obtains the deterioration function H ⁻¹ (s) by the following Expression 3.
[Equation 3]
H ⁻¹ (s) = F (s) / G (s) (Formula 3)

(Step S190)
The image processing device 21 obtains and stores a deterioration function ΣH ⁻¹ (s) / n obtained by averaging the deterioration function of the amplitude spectrum obtained in step S190 of the previous loop and the deterioration function obtained in step S180 of the current loop. Here, ΣH ⁻¹ (s) represents an addition value of all deterioration functions obtained in the previous loop and the current loop, and n represents the number of times the deterioration functions are added (the number of loops). A deterioration function reflecting all past calculation results can be obtained by averaging.

(Step S200)
The image processing device 21 inversely transforms ΣH ⁻¹ (s) / n to obtain h ⁻¹ (t). Here, h ⁻¹ (t) is a repair function for the deteriorated image in the real image space, and the deterioration can be repaired by multiplying h ⁻¹ (t) by the deteriorated image data g (t). .

(Step S210)
The image processing device 21 sets a value until the amplitude of h ⁻¹ (t) converges to 0 as a weighting coefficient of the correction one-dimensional filter, and creates a correction one-dimensional filter.

(Step S220)
The image processing device 21 resets the corrected one-dimensional filter created in step S210. By repeating the above processing procedure, it is possible to incorporate a correction one-dimensional filter generation and resetting process into a series of processes in which an operator observes, and always correct correction 1 even if the status of the apparatus changes. It is possible to provide a dimensional filter.

(Summary)
As described above, according to the present embodiment, in addition to the technical effects of the first embodiment, it is possible to automatically update the correction one-dimensional filter while the apparatus is in use. Thereby, even when the electron microscope apparatus is used for a long period of time, it is possible to always apply the optimum correction one-dimensional filter.

[Other embodiments]
The present invention is not limited to the configuration of the embodiment described above, and includes various modifications. For example, in the above-described embodiments, in order to explain the present invention in an easy-to-understand manner, some embodiments are described in detail, and it is not always necessary to include all the configurations described. Further, a part of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. It is also possible to add other configurations to the configuration of each embodiment, replace a partial configuration of each embodiment with another configuration, or delete a partial configuration of each embodiment.

In addition, each of the above-described configurations, functions, processing units, processing means, and the like may be partly or entirely realized as, for example, an integrated circuit or other hardware. Each of the above-described configurations, functions, and the like may be realized by a processor interpreting and executing a program that realizes each function. That is, each configuration may be realized by software. In this case, information such as programs, tables, and files for realizing each function can be stored in a storage device such as a memory, a hard disk, an SSD (Solid State Drive), or a storage medium such as an IC card, an SD card, or a DVD. .

Also, the control lines and information lines indicate what is considered necessary for explanation, and do not represent all control lines and information lines necessary for the product. In practice, it can be considered that almost all components are connected to each other.

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron beam, 3 ... Converging lens, 4 ... Objective lens, 5 ... Sample, 6 ... Deflection coil, 7 ... Deflection control circuit, 8 ... Control input device, 9 ... CPU, 10 ... Sample stand, DESCRIPTION OF SYMBOLS 11 ... Secondary signal, 12 ... Detector, 13, 14, 15 ... Amplifier, 16 ... Switching machine, 17 ... Analog-digital converter, 18, 23 ... Frame memory, 19 ... Image display apparatus, 20, 24 ... Switch, 21: Image processing device, 22: Filtering unit.

Claims

A charged particle source that outputs a charged particle beam;
A scanning unit that scans the charged particle beam with respect to the sample;
Detecting a secondary signal generated from the irradiation region of the charged particle beam and amplifying the amplitude of the detection signal;
The first detection signal detected by scanning the charged particle beam at the first speed within the bandwidth of the detection unit and the band of the detection unit under the same imaging condition A first processing unit that stores, in a storage unit, a second detection signal detected by scanning the charged particle beam at a second speed exceeding an upper limit of the width;
A second processing unit for frequency analysis of the first detection signal;
A third processing unit that superimposes the first amplitude spectrum obtained by the frequency analysis on the other first amplitude spectrum acquired for an imaging condition different from the imaging condition;
Fourth processing for calculating a degradation function representing the frequency characteristics of the detection unit based on the first amplitude spectrum after superimposition and the second amplitude spectrum obtained by frequency analysis of the second detection signal. And
A fifth processing unit that determines whether the amplitude spectrum after superposition satisfies the first amplitude condition;
A sixth processing unit that changes the imaging condition and returns to the processing of the first processing unit while the amplitude spectrum after superimposition does not satisfy the first amplitude condition;
A seventh processing unit that calculates a correction filter of the detection unit based on an inverse function of the deterioration function calculated by the fourth processing unit when the amplitude spectrum after superimposition satisfies the first amplitude condition; ,
A charged particle beam apparatus comprising: an eighth processing unit configured to set the calculated correction filter for correction of the second detection signal acquired at the second speed.
The charged particle beam apparatus according to claim 1,
The charged particle beam apparatus characterized in that the first imaging condition is given by any one or any plural of visual field movement, enlargement / reduction, rotation, focus variation, charged particle beam tilt and sample tilt. .
The charged particle beam apparatus according to claim 1,
The fifth processing unit determines that the first amplitude condition is satisfied when the frequency of each frequency component exceeds a threshold for all frequencies of the first amplitude spectrum after the superimposition. A charged particle beam device.
The charged particle beam apparatus according to claim 1,
The seventh processing unit calculates an average value of the deterioration function calculated by the fourth processing unit until the first amplitude condition is satisfied by the sixth processing unit, and calculates A charged particle beam apparatus, wherein a correction filter of the detection unit is calculated based on an inverse function of the average value of the deterioration function.
The charged particle beam apparatus according to claim 1,
When the process of scanning the same region of the sample at the first speed and the second speed is detected during use of the charged particle beam apparatus, the detected first detection signal and the second detection signal are detected. A ninth processing unit for storing the detection signal in the storage unit;
A tenth processing unit for analyzing the frequency of the first detection signal;
An eleventh processing unit that superimposes the first amplitude spectrum obtained by the frequency analysis with the other first amplitude spectrum acquired for an imaging condition different from the first imaging condition;
A twelfth processing unit that determines whether or not the amplitude spectrum after superposition satisfies the second amplitude condition;
A thirteenth processing unit that returns to the processing of the ninth processing unit while the superimposed amplitude spectrum does not satisfy the second amplitude condition;
When the amplitude spectrum after superimposition satisfies the second amplitude condition, based on the first amplitude spectrum after superposition and the second amplitude spectrum obtained by frequency analysis of the second detection signal, A fourteenth processing unit that calculates a deterioration function representing the frequency characteristic of the detection unit;
A fifteenth processing unit that calculates a correction filter of the detection unit based on an inverse function of the deterioration function calculated by the fourteenth processing unit;
A charged particle beam apparatus comprising: a sixteenth processing unit that resets the calculated correction filter for correcting the second detection signal acquired at the second speed.
In the charged particle beam device according to claim 5,
The twelfth processing unit determines that the second amplitude condition is not satisfied when a frequency component having a frequency exceeding an upper limit value exists in the first amplitude spectrum after the superimposition. A charged particle beam device.
In the charged particle beam device according to claim 5,
The fourteenth processing unit calculates an average value of the deterioration function calculated so far, and calculates a correction filter of the detection unit based on an inverse function of the calculated average value of the deterioration function. Characterized charged particle beam device.
A charged particle source that outputs a charged particle beam, a scanning unit that scans the charged particle beam with respect to the sample, and a secondary signal generated from the irradiation region of the charged particle beam are detected, and the amplitude of the detection signal is amplified. In a method of setting a correction filter of the detection unit in a charged particle beam apparatus having a detection unit to perform,
The calculation part
The first detection signal detected by scanning the charged particle beam at the first speed within the bandwidth of the detection unit and the band of the detection unit under the same imaging condition A first process of storing in a storage unit a second detection signal detected by scanning the charged particle beam at a second speed exceeding an upper limit of the width;
A second process for analyzing the frequency of the first detection signal;
A third process of superimposing the first amplitude spectrum obtained by the frequency analysis with the other first amplitude spectrum acquired for an imaging condition different from the imaging condition;
Fourth processing for calculating a degradation function representing the frequency characteristics of the detection unit based on the first amplitude spectrum after superimposition and the second amplitude spectrum obtained by frequency analysis of the second detection signal. When,
A fifth process for determining whether the amplitude spectrum after superposition satisfies the first amplitude condition;
A sixth process of changing the imaging condition and returning to the process of the first processing unit while the superimposed amplitude spectrum does not satisfy the first amplitude condition;
A seventh process of calculating a correction filter of the detection unit based on an inverse function of the deterioration function calculated in the fourth process when the amplitude spectrum after superposition satisfies the first amplitude condition;
A correction filter setting for a charged particle beam apparatus, wherein the calculated correction filter is set to an eighth process for correcting the second detection signal acquired at the second speed. Method.