JP5287135B2 - Image forming method and charged particle beam apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method for obtaining a sample image with stable clearness of a contour even with a sample likely to generate drift, as well as a charged particle beam device using the above method. <P>SOLUTION: The image forming method is to comprise a first imaging process for obtaining a first image datum by imaging a sample S in line scan, a first digitalizing process of digitalizing clearness of a contour of first image datum, a threshold value setting process for setting a threshold value Ms of the clearness from a value M1 indicating clearness of the contour of the first image datum obtained from the first digitalization process, a second imaging process of obtaining a second image datum by imaging the sample S in area scan, a second digitalization process for digitalizing clearness of a contour of the second image datum, a determination process for determining whether a value M2 indicating clearness of a contour of the second image datum satisfies the threshold value Ms, and a storage process of selecting and memorizing images based on results of the determination process. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming method and a charged particle beam apparatus used in a charged particle beam apparatus that irradiates a sample with a charged particle beam and detects a secondary signal from the sample.

In charged particle beam devices typified by scanning electron microscopes, sample images and the like are detected by irradiating a charged particle beam that is converged finely on a sample while detecting secondary electrons emitted from the sample. I get the information.
Such a charged particle beam apparatus is required to have high resolution and high magnification in accordance with the recent high integration and miniaturization of semiconductor devices.
However, in a charged particle beam device such as a scanning electron microscope, the charged particle beam is applied to the sample, so that the sample is charged up over time, and the positional relationship between the charged particle beam and the sample changes, resulting in a sample image. It is easy for drift to occur. Such a drift is known to have a great influence on a sample image particularly in a situation where observation is performed at a high magnification.

FIG. 8 is a diagram for explaining the influence of drift on the sample image. FIG. 8A is a perspective view showing a sample, and FIG. 8B is a diagram showing an ideal sample image. FIG. 8C is a diagram showing a sample image by a general line scan, and FIG. 8D is a diagram showing a sample image by a general area scan. FIGS. 8B to 8D are sample images when the region 51 shown in FIG. 8A is imaged.
As shown to Fig.8 (a), the sample 50 has the convex pattern part 50a formed on the base | substrate part 50b. As shown in FIG. 8B, it is desirable that the pattern portion 50a has a shape extending straight in the vertical direction and a clear outline as a sample image.

However, when imaging is performed by line scanning (a scanning method for obtaining one image by line integration) , if a drift occurs due to charge-up of the sample, a clear contour is obtained, but the sample image is likely to be deformed. Therefore, in a sample having a pattern such as a line shape like the pattern portion 50a of the sample 50, as shown in FIG. 8C, the outline of the pattern portion 50a is clear, but the shape of the pattern portion 50a is It becomes a deformed sample image such as a slant. If an attempt is made to measure the dimension of the pattern portion 50a using such a sample image, there is a problem that it is difficult to obtain an accurate dimension due to deformation.
Further, when an image is captured by area scanning (a scanning method for obtaining one image by frame integration) , if a drift occurs due to charge-up of the sample, the sample image is not deformed but the outline is likely to be blurred. For this reason, as shown in FIG. 8D, the pattern portion 50a is not deformed, but the contour image of the pattern portion 50a is blurred, and there is a problem that accurate length measurement cannot be performed.

An example of a method and apparatus for obtaining a sample image in which the influence of drift due to such charge-up is suppressed is disclosed in Patent Document 1. The sample image forming method and the charged particle beam apparatus disclosed in Patent Document 1 perform imaging by area scanning, synthesize a plurality of images obtained by a plurality of scans, and then form a plurality of such synthesized images. It is characterized in that a sample image is obtained by correcting a positional shift between images and synthesizing images to form a synthesized image.
International Publication No. 03/044821 Pamphlet

  However, in the sample image forming method of Patent Document 1, since the drift amount of the sample image changes depending on the imaging time even for the same sample, the clarity of the outline varies greatly depending on the imaging time. For this reason, there has been a problem that the clarity of the contour of the obtained sample image varies and the reproducibility is lowered.

  An object of the present invention is to provide an image forming method for a charged particle beam apparatus and a charged particle beam apparatus using the method, which can obtain a sample image with a stable outline even if the sample is prone to drift. That is.

The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this .

The first aspect of the present invention is an image forming method for obtaining a sample image in a charged particle beam apparatus, wherein the sample (S) is imaged by line scanning to obtain one image by line integration to obtain first image data. An imaging step (S101, S201, S301), and a first digitizing step (S102, S202, S302) for digitizing the clarity of the outline of the first image data after the first imaging step. Threshold value setting step (S103, S203, S303) for setting the clarity threshold value (Ms) from the numerical value (M1) representing the clarity of the outline of the first image data obtained in the first digitizing step. ) and, the sample is imaged by an area scan to obtain one image by the frame integration, and a second imaging step of obtaining the second image data (S104, S204, S304), the second imaging step Later, after the second digitizing step (S105, S205, S305) for digitizing the clarity of the contour of the second image data, and the second digitizing step, the contour of the second image data the number representing the clarity (M2) is judging process of judging whether or not satisfies the threshold (S106, S206, S306), based on the result of the determination step, and selecting the second image data storing Te and the storage step (S107, S208, S307), Bei give a until the numerical value in the determination step represents the clarity of the outline of the second image data (M2) meets the threshold (Ms), the An image forming method characterized by repeating the second imaging step to the determination step .
The invention of claim 2 is an image forming method for obtaining a sample image in a charged particle beam apparatus, wherein the sample (S) is imaged by a line scan to obtain one image by line integration, and first image data is obtained. An imaging step (S401), a drift amount quantifying step for quantifying the drift amount measured from the deformation of the image of the first image data after the first imaging step, and the quantified drift A drift amount determination step (S402) for determining whether or not the amount is equal to or less than a predetermined value, and first image data for selecting and storing the first image data based on the result of the drift amount determination step A storage step (S412), a first numerical step (S403) for digitizing the clarity of the contour of the first image data, and the first image data obtained in the first numerical step. Clear outline of A threshold value setting step (S404) for setting a clarity threshold value (Ms) from a numerical value (M1) representing the above and a sample of the sample by area scanning for obtaining one image by frame integration to obtain second image data. Second imaging step (S405), a second numerical step (S406) for digitizing the clarity of the contour of the second image data after the second imaging step, and the second numericalization. After the step, based on the result of the determination step (S407) for determining whether or not the numerical value (M2) representing the clarity of the outline of the second image data satisfies the threshold value, And a storage step (S408) for selecting and storing the second image data.
According to a third aspect of the present invention, in the image forming method according to the second aspect, in the determination step (S407) , a numerical value (M2) representing the clarity of the outline of the second image data satisfies the threshold (Ms). The image forming method is characterized by repeating the second imaging step (S405) to the determination step (S407) .
According to a fourth aspect of the present invention, in the image forming method according to the second aspect, in the determination step (S407), a numerical value (M2) representing the clarity of the outline of the second image data satisfies the threshold (Ms). In this case, the image forming method is characterized in that the second imaging step (S405) to the determination step (S407) are repeated a set number of times.
According to a fifth aspect of the present invention, in the image forming method according to the first or third aspect, the upper limit number of times for performing the second imaging step (S104, S204, S405) is preset. Image forming method.

The invention of claim 6 is the image forming method according to any one of claims 1 to 5, wherein the first numerical step (S102, S202, S302, S403 ) and the second numerical In the converting step (S105, S205, S305 , S406 ), the clarity of the contour is quantified using the maximum absolute value of the first derivative of the line profile of the first image data and the second image data. This is an image forming method characterized by that.
According to a seventh aspect of the invention, in the image forming method according to any one of claims 1 to 5, wherein in the first digitizing step and the second digitizing process, the first image An image forming method characterized in that the clarity of a contour is digitized using a difference between a maximum value and a minimum value of pixel values of data and a line profile of the second image data.
The invention of claim 8 is the image forming method according to any one of claims 1 to 5, wherein in the first digitizing step and the second digitizing process, the first image Using the width of the line profile that satisfies the set value set using the difference between the maximum value and the minimum value of the pixel values of the data and the line profile of the second image data, the clarity of the contour is quantified The image forming method characterized by the above.

Invention 請 Motomeko 9, second and electron gun portion charged particle beam a (C1) is irradiated on the sample (S) (11), said charged particle beam on the sample is released from the irradiated region primary A charged particle beam apparatus comprising: a detection unit (18) that detects a signal (C2); and an image formation unit (24) that forms an image based on the detected secondary signal, wherein the image formation unit Is an area scan that sets the threshold (Ms) by quantifying the clarity of the contour of the first image data obtained by line scanning to obtain one image by line integration, and obtains one image by frame integration of the sample. by digitizing the clarity of the outline of the second image data captured by, it determines whether they meet the threshold, select the second image data based on the determination result, the storage unit (27 ) to be stored, Eli said sample By digitizing the clarity of the outline of the second image data captured by the scan, to determine whether that number (M2) meets the threshold, repeating until the numerical value meets the threshold, Is a charged particle beam device (1).

According to the present invention, the following effects can be obtained.
(1) An image forming method according to the present invention includes a first imaging step of imaging a sample by line scanning to obtain first image data, and a first method for quantifying the clarity of the outline of the first image data. A numerical value setting step, a threshold value setting step for setting a threshold value for clarity based on a numerical value representing the clarity of the contour of the first image data, and a second method for obtaining second image data by imaging the sample by area scanning. An imaging step, a second numerical step for digitizing the clarity of the contour of the second image data, and an evaluation step for evaluating a numerical value representing the clarity of the contour of the second image data with reference to a threshold value; And a display step for displaying the result of the evaluation step, so that the second image data can be selected based on the displayed evaluation result, an image having no image deformation and having a certain level of clarity. Can be obtained stably regardless of the imaging time Kill.

(2) An image forming method according to the present invention includes a first imaging step of imaging a sample by line scanning to obtain first image data, and a first method for quantifying the clarity of the outline of the first image data. A numerical value setting step, a threshold value setting step for setting a threshold value for clarity based on a numerical value representing the clarity of the contour of the first image data, and a second method for obtaining second image data by imaging the sample by area scanning. An imaging step, a second numerical step for digitizing the clarity of the contour of the second image data, and whether or not a numerical value representing the clarity of the contour of the second image data satisfies a threshold value Since it includes a determination step and a storage step of selecting and storing the second image data based on the result of the determination step, an image having no image deformation and having a certain level of clarity is captured. It can be obtained stably without depending on.

(3) Since the second imaging process to the determination process are repeated until the numerical value representing the clarity of the contour of the second image data satisfies the threshold value in the determination process, an image having a certain level of clarity is reliably obtained. be able to.
(4) Since the upper limit number of times for performing the second imaging step is set in advance, the time required for imaging can be limited.
(5) Even when the numerical value representing the clarity of the outline of the second image data satisfies the threshold value in the determination step, the second imaging step to the determination step are repeated a set number of times, so that a clearer image can be obtained. Can be obtained.

(6) In the first numerical value process and the second numerical value process, the clarity of the contour is increased using the maximum value of the absolute value of the first derivative of the line profile of the first image data and the second image data. Since it is digitized, the clarity of the image can be easily digitized.
(7) In the first numerical value process and the second numerical value process, by using the difference between the maximum value and the minimum value of the pixel values of the line profile of the first image data and the second image data, Since the clarity is digitized, the clarity of the image can be digitized more easily.
(8) In the first numerical value process and the second numerical value process, it is set using the difference between the maximum value and the minimum value of the pixel values of the line profile of the first image data and the second image data. Since the clarity of the contour is quantified using the width of the line profile that satisfies the set value (that is, the width of the bright part related to the contour), the clarity of the image can be easily quantified.

(9) In the charged particle beam apparatus according to the present invention, the image forming unit digitizes the clarity of the outline of the first image data obtained by imaging the sample by line scanning, sets a threshold value, and images the sample by area scanning. Since the clarity of the contour of the second image data is digitized and evaluated based on the threshold value, and the evaluation result is displayed on the display unit, the second image data is selected with reference to the displayed evaluation result. Therefore, an image having no image deformation and having a certain level of clarity can be stably obtained regardless of the imaging time.

(10) In the charged particle beam apparatus according to the present invention, the image forming unit digitizes the clarity of the outline of the first image data obtained by imaging the sample by line scanning, sets a threshold value, and images the sample by area scanning Since the clarity of the contour of the second image data is digitized, it is determined whether or not the threshold is satisfied, and the second image data is selected based on the determination result and stored in the storage unit. Therefore, it is possible to stably obtain an image whose contour has a certain level of clarity regardless of the imaging time.

(11) In the image forming method of the present invention, a sample is imaged by area scanning to obtain image data, a digitizing step for digitizing the clarity of the contour of the image data, and the clarity of the contour of the image data. A determination step of comparing whether a numerical value representing the clarity of the contour of the image data is compared with a numerical value representing the clarity of the contour of the image data already stored, The process from the process to the determination process is repeated for a set number of times, so that the outline of the image becomes clear to the set outline clarity threshold (for example, the threshold based on the clarity of the image captured by the line scan). Even if the above does not reach, an area scan image having the clearest contour can be obtained by repeating the imaging process to the determination process a set number of times.

(12) In the image forming method of the present invention, a sample is imaged by line scanning to obtain image data, and after the imaging step, a numerical value step for digitizing a drift amount (pattern bending) of the image data And a determination step for determining whether or not the drift amount is equal to or less than a predetermined value, and a storage step for selecting and storing image data based on the result of the determination step. Whether or not the drift amount is equal to or less than a predetermined value is determined for the image obtained in this manner. Therefore, for a sample with a small drift amount, damage due to an electron beam can be reduced and the time required for image formation of the sample can be shortened.

Hereinafter, embodiments of an image forming method and a charged particle beam apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, a scanning electron microscope will be described as an example of an embodiment of a charged particle beam apparatus.
(First embodiment)
FIG. 1 is a diagram illustrating a scanning electron microscope 1 according to the first embodiment. Note that FIG. 1 is a diagram schematically illustrating the size and shape of each part as appropriate for easy understanding.
The scanning electron microscope 1 according to the first embodiment includes an electron gun unit 11, a lens barrel unit 12, a stage unit 16, an exhaust unit 17, a detection unit 18, an electron beam control unit 21, a signal processing unit 22, a CPU (central processing unit). ) 23, a charged particle beam apparatus including an image forming unit 24, a display unit 25, an input / output unit 26, a memory 27, and the like.

The electron gun unit 11 is a part that emits an electron beam C1, and includes a cathode 11a and an anode 11b.
The lens barrel 12 includes a converging lens 13, a scanning coil 14, and an objective lens 15 from the electron gun unit 11 side in the traveling direction of the electron beam C1. The converging lens 13 and the objective lens 15 have a function of converging the electron beam C1 on the sample S. The scanning coil 14 has a function of deflecting the electron beam C1 in order to cause the electron beam C1 to scan a predetermined region on the sample S.
The cathode 11 a, the anode 11 b, the converging lens 13, the scanning coil 14, and the objective lens 15 are connected to the electron beam control unit 21. The electron beam control unit 21 is a circuit that controls the cathode 11 a, the scanning coil 14, and the like according to instructions from the CPU 23.
The stage unit 16 is a stage on which the sample S is arranged.
The exhaust unit 17 has a function of bringing the space in which the stage unit 16 and the sample S are arranged into a vacuum state.

The detection unit 18 has a function of detecting secondary electrons C2 emitted from the sample S when the electron beam C1 hits the sample S.
The signal processing unit 22 converts secondary electrons detected by the detection unit 18 into predetermined signals, performs amplification, and the like.
The image forming unit 24 performs various processes such as a smoothing process on the secondary electron information processed by the signal processing unit 22 to form an image.
In addition, the image forming unit 24 has a function of forming a line profile or the like based on image data formed from the detected secondary electron information. This line profile is, for example, a curve (that is, a set of luminance information on the line) generated based on luminance information or the like included in the image data of the sample obtained by scanning the electron beam C1 (FIG. 3 ( c)).

The display unit 25 is a part that converts image data into a luminance signal and displays it. For example, a cathode ray tube or the like is used. The image scan amount displayed on the display unit 25 and the deflection amount of the scanning coil 14 with respect to the electron beam C <b> 1 are controlled by the CPU 23.
The input / output unit 26 has a function of inputting an instruction to the CPU 23 and outputting the obtained image data.
The memory 27 is a part that stores image data and the like.

In the scanning electron microscope 1, the electron beam control unit 21 applies a predetermined voltage between the cathode 11a and the anode 11b according to an instruction from the CPU 23, whereby the electron beam C1 is emitted from the cathode 11a and has a predetermined speed. And is emitted from the electron gun unit 11.
The electron beam C1 emitted from the electron gun unit 11 is irradiated as a minute spot onto the sample S by the converging lens 13 and the objective lens 15, and the scanning coil 14 connected to the electron beam control unit 21 causes a predetermined surface on the sample S. Scan in a two-dimensional direction (vertical direction and horizontal direction of the imaging region).
The secondary electrons C2 emitted from the sample S by the irradiation of the electron beam C1 are detected by the detection unit 18, the signal is subjected to processing such as amplification and A / D conversion by the signal processing unit 22, and image formation by the CPU 23 is performed. An image is formed by the unit 24 and displayed on the display unit 25.
The memory 27 stores and stores predetermined image data based on an instruction from the CPU 23.

FIG. 2 is a view for explaining an image forming method of the scanning electron microscope 1 according to the first embodiment.
In the scanning electron microscope 1 of the present embodiment, as an example, it is assumed that an image having an image size of 1024 × 1024 pixels can be taken.
(A) The first step (S101) is a first imaging step in which the CPU 23 images a sample by line scanning and obtains first image data. The number of line scan integrations (line integrations) is set in advance, and in this embodiment, the number of integrations is 32.
The imaged image data (first image data) of the sample S is A / D converted by the signal processing unit 22, subjected to predetermined processing, and then sent to the image forming unit 24 of the CPU 23.

(B) In the second step (S102), the image forming unit 24 forms a line profile from the first image data of the sample obtained by the line scan in the first step (S101), and based on this line profile. This is a first numericalization step for converting the clarity of the first image data into numerical values.
FIG. 3 is a diagram for explaining a line profile and its first derivative. 3A is a cross-sectional view of the sample S, and FIG. 3B is a diagram illustrating a sample image of the image data of the sample S taken. FIG. 3C shows a line profile obtained when the electron beam C1 is irradiated along the straight line AA shown in FIG. 3B, and FIG. 3D shows the line profile shown in FIG. Is the first derivative of the line profile.
As shown in FIG. 3, the convex portion of the sample S has a slightly higher luminance than the concave portion, and the contour portion of the convex portion has a higher luminance and is observed as a white line (FIGS. 3A and 3B). )reference).
In the second step (S102), the image forming unit 24 sets an arbitrary region including the contour portion of the sample image from the first image data (for example, specifies the target region of the image by surrounding it with a box), and the sample image A line profile of the contour part (edge part) of the line is created and the line profile is first-order differentiated. Then, the maximum value of the absolute value of the first derivative of the line profile is set to a numerical value M1 that represents the clarity of the contour of the first image data.

FIG. 4 is a diagram showing the relationship between the clarity of image data and the line profile and the first derivative of the line profile. 4A shows an example of clear image data, and FIG. 4B shows an example of image data in which blur has occurred. In FIGS. 4A and 4B, the upper curve indicates the line profile, and the lower curve indicates the first derivative of the line profile.
As shown in FIG. 4, the maximum value of the line profile is larger when the outline of the sample image is clear than when the sample image is blurred.
The first derivative of the line profile is obtained by comparing the Ma part and the Mb part of the waveform of the first derivative of the line profile of the luminance value shown in FIGS. The larger the difference is, the larger the maximum absolute value is, and the clearer the contour is, the larger the numerical value representing the clarity is. Therefore, in the first-order differentiation of the line profile, when the contour of the sample image is clear, the maximum absolute value, that is, a numerical value representing the clarity, is larger than when the image is blurred.
The numerical value M1 representing the clarity of the contour of the first image data obtained in the second step (S102) is the clarity of the contour of the sample image captured by the line scan, that is, the clarity of the ideal contour. It is a numerical value representing the height.

(C) Returning to FIG. 2, in the third step (S103), the image forming unit 24 calculates the contour from the numerical value M1 indicating the clarity of the contour of the first image data obtained in the second step (S102). It is a threshold value setting process which sets the threshold value of clarity.
For example, if 80% of the clarity of the contour of the first image data obtained in the second step (S102) is set to be adopted, a numerical value obtained by multiplying the numerical value M1 by 0.8 is a threshold value Ms. It becomes. It is assumed that how many times the threshold value Ms is set with respect to the numerical value M1 representing the clarity of the ideal contour can be set as appropriate.

(D) The fourth step (S104) is a second imaging step in which the CPU 23 images the sample by area scan and obtains second image data. The number of area scan integrations (frame integrations) can be set in advance, and in this embodiment, the number of integrations is 32 as in the line scan of the first imaging step.
The second image data obtained in the fourth step (S104) is sent to the image forming unit 24.

(E) In the fifth step (S105), the image forming unit 24 creates a line profile from the second image data obtained by the area scan in the fourth step (S014), and based on this line profile, This is a second numericalization step for converting the clarity of the outline of the second image data into numerical values.
Here, a line profile is generated from the contour portion of the second image data obtained in the fourth step (S104) as in the second step (S102), and the maximum absolute value of the first derivative is obtained. And this is set as a numerical value M2 representing the clarity of the outline of the second image data.

(F) In the sixth step (S106), the image forming unit 24 obtains a numerical value M2 representing the clarity of the contour of the second image data obtained in the fifth step (S105) in the third step (S103). A determination step of determining whether or not the set threshold value Ms is satisfied is performed.
In the present embodiment, the threshold value Ms is set to be 80% of the numerical value M1 representing the clarity of the first image data. Therefore, the numerical value M2 representing the clarity of the second image data is M2 ≧ Ms. It is determined whether or not (Ms = M1 × 0.8) is satisfied.
If the numerical value M2 representing the clarity of the second image data is greater than or equal to the threshold value Ms, the process proceeds to the seventh step (S107), and if it is less than the threshold value Ms, the process proceeds to the eighth step (S108).

(G) In the seventh step (S107), the image forming unit 24 selects the second image data in which the numerical value M2 representing the clarity is equal to or greater than the threshold value Ms, and the memory 27 selects the selected second image. It is a storage process for storing data.
After storing the second image data in the memory 27, the image forming unit 24 ends the process related to the image formation of the sample. If necessary, length measurement or the like may be performed from the sample image of the second image data stored in the memory 27.

(H) In the eighth step (S108), the second image data determined by the image forming unit 24 that does not satisfy the threshold Ms in the sixth step (S106) This is a step of determining whether or not the image data is the clearest.
For example, if the imaging by the area scan in the above-described fourth step (S104) is the first time, it is determined that the current second image data is the clearest.
In addition, if the imaging by the area scan in the above-described fourth step (S104) is the second or more times, a numerical value M2a representing the clarity of the previous second image data stored in the memory 27 at that time, and this time The numerical value M2b representing the clarity of the second image data imaged in the fourth step (S104) is compared, and the clearer one (the larger numeric value representing the clarity in this embodiment) is the most contoured. Is determined to be clear.
When it is determined that the second image data captured this time is the most clear of the second image data of the sample captured so far, the process proceeds to the ninth step (S109), and the second image data is not the most clear. If it is determined, the process proceeds to the tenth step (S110).

(I) In the ninth step (S109), the image forming unit 24 selects the second image data determined to be the most clear in the eighth step (S108), and the selected second image data is selected. This is a process stored in the memory 27.
Here, the second image data stored in the memory 27 is used for determination in the eighth step (S108) after the next time.
If the ninth step (S109) is the second or subsequent time, the previous second image data stored as the most clear before is discarded, and it is newly determined that the most clear. The second image data thus obtained is stored in the memory 27.

(J) The tenth step (S110) is a step in which the image forming unit 24 determines whether or not the imaging by the area scan in the fourth step (S104) has reached a preset upper limit number.
If the upper limit number of times of imaging by area scanning in the fourth step (S104) has been reached, the image formation is terminated. If the upper limit number of times of image capturing by area scanning in the fourth step (S104) has not been reached, the process returns to the fourth step (S104) to perform image capturing by area scanning again, and the contour of the obtained image data The fourth step (S104) to the tenth step (S110) are repeated, such as determining whether the clarity satisfies the threshold.
Note that the second image data satisfying the threshold value Ms is not obtained, but if it is determined in the tenth step (S110) that the upper limit number set in advance has been reached, the second image that has been imaged a predetermined number of times. The clearest second image data among the image data is stored in the memory 27.

According to this embodiment, the following effects can be achieved.
(1) A threshold Ms of the clarity of the contour of the sample image is set from the first image data obtained by the line scan, and expresses the clarity of the contour of the sample image of the second image data obtained by the area scan. Since it is determined whether or not the numerical value M2 satisfies the threshold value Ms and the second image data that satisfies the threshold value Ms is stored, the clarity of the image data of the sample S stored in the memory 27 becomes stable, and imaging is performed. Image data having a desired level of clarity can be obtained regardless of the timing, drift amount, and the like.
In addition, since the second image data stored by determining whether or not the numerical value representing the clarity of the outline satisfies the threshold is selected by the image forming unit 24, even if the operator is absent, a certain level is obtained. It is possible to automatically obtain image data having the following clarity. Therefore, unattended automatic operation or the like of the scanning electron microscope 1 becomes possible, and work efficiency can be improved.

(2) Since the second image data stored in the memory 27 is imaged by area scanning, even when drift occurs, deformation due to drift of the sample image is small. In addition, since the second image data is stored when the threshold value set from the first image data by line scanning is satisfied, an image having a certain level of clarity can be stabilized regardless of the imaging timing and the drift amount. Can be obtained. Accordingly, it is possible to obtain a sample image with a more accurate shape, dimensions, and the like.
Thereby, when measuring the dimension of a sample using the obtained sample image, the length measurement accuracy is improved.

(3) When it is determined that the numerical value M2 representing the clarity of the second image data satisfies the threshold value Ms, the second image data is stored in the memory 27, and imaging by area scanning has reached the upper limit number of times. Even if it is not, since the image formation is completed, clear image data can be obtained in a shorter time.

(4) The fourth step (S104) to the tenth step (S110) are repeated a set number of times, but the numerical value representing the clarity of the second image data does not satisfy the threshold Ms in the sixth step (S106). In this case, since the second image data having the numerical value M2 closest to the threshold value Ms is stored in the memory 27, even when the second image data satisfying the threshold value Ms cannot be obtained, the sample image of the second image data is the most. Second image data with a clear outline can be obtained.

(Second Embodiment)
FIG. 5 is a diagram illustrating an image forming method of the scanning microscope according to the second embodiment.
The scanning electron microscope of the second embodiment is substantially the same as the scanning electron microscope 1 shown in the first embodiment, except that the image forming method is partially different. Therefore, parts having the same functions as those of the first embodiment are denoted by the same reference numerals or the same reference numerals at the end thereof, and repeated description is appropriately omitted.
The image forming method of the scanning electron microscope according to the second embodiment includes the first step (S201) to the eleventh step (S211).
In the image forming method of the second embodiment, the first step (S201) to the sixth step (S206), and the ninth step (S209) to the eleventh step (S211) are the first steps shown in the first embodiment ( The same processing as that from S101) to the sixth step (S106) and from the eighth step (S108) to the tenth step (S210) is performed.

In the seventh step (S207) of the image forming method of the second embodiment, the threshold Ms is applied to the second image data that the image forming unit 24 determines to satisfy the threshold Ms in the sixth step (S206). It is determined whether or not the second image data satisfying the condition is the clearest.
Here, if the seventh step (S207) is the first time, the second image data is selected to be the clearest, and the process proceeds to the eighth step (S208), where the memory 27 stores the second image data. Remember.
If the seventh step (S207) is the second and subsequent times, the clearness is compared with the previous second image data determined in the previous seventh step (S207) and stored in the memory 27.

If it is determined that the current second image data is clearer than the previous second image data, the current second image data is selected, and the process proceeds to the eighth step (S208). In the eighth step (S208), the memory 27 stores the second image data this time, and proceeds to the eleventh step (S211).
If it is determined that the current second image data is not clearer than the previous second image data, the current second image data is discarded, and the process proceeds to the eleventh step (S211).
Then, in the eleventh step (S211), it is determined whether or not the imaging by the area scan performed in the fourth step (S204) has reached the upper limit number.
As described above, in the present embodiment, even when the second image data satisfying the threshold value Ms is obtained, the image capturing by the area scan and the threshold value determination are performed until the preset upper limit number of image capturing by the area scan is reached. The fourth step (S104) to the tenth step (S210) are repeated.

Therefore, for example, when the threshold value Ms is set to 80% of the numerical value M1 representing the clarity of the contour by line scanning, the numerical value M2 representing the clarity in the first fourth step (S204) is 82% of the threshold value. Even if the second image data is obtained, the second step (S204) to the eleventh step (S211) are repeated up to the upper limit number of times, thereby making the second image data clearer (for example, representing clarity). There is a possibility that the numerical value M2 satisfies the threshold Ms and second image data (89%, 96%, etc.) of the numerical value M1) can be obtained.
Therefore, according to this embodiment, a clearer sample image can be obtained.

(Third embodiment)
FIG. 6 is a diagram for explaining an image forming method of the scanning microscope according to the third embodiment.
The scanning electron microscope of the third embodiment is substantially the same as the scanning electron microscope 1 shown in the first embodiment, except that the image forming method is partially different. Therefore, parts having the same functions as those of the first embodiment are denoted by the same reference numerals or the same reference numerals at the end thereof, and repeated description is appropriately omitted.
The image forming method of the scanning electron microscope according to the third embodiment includes a first step (S301) to a seventh step (S307).
The first step (S301) to the fifth step (S305) of the image forming method of the third embodiment corresponds to the first step (S101) to the fifth step (S105) of the first embodiment.

  In the sixth step (S306) of the third embodiment, the numerical value M2 representing the clarity of the second image data captured by the image forming unit 24 in the area scan in the fourth step (S304) is the third step (S306). This is a determination step for determining whether or not the threshold value Ms generated in S303) is satisfied. If the numerical value M2 is greater than or equal to the threshold value Ms, the process proceeds to the seventh step (S307), and the memory 27 stores the second image data. When the numerical value M2 is less than the threshold value Ms, the process returns to the fourth step (S304), and the fourth step (S304) to the sixth step (S306) are repeated.

In the present embodiment, the upper limit number of times of imaging by area scanning performed in the fourth step (S304) is not defined. Therefore, the fourth step (S304) to the sixth step (S306) are repeated until the second image data having clarity that satisfies the threshold Ms is obtained.
Therefore, it is possible to reliably obtain the second image data having the clarity of the outline that satisfies the threshold value Ms.
In the third embodiment, when the second image data having the clearness of the contour that satisfies the threshold Ms cannot be obtained, there is a problem that the image formation is continued permanently, which is inconvenient. This problem can be solved, for example, by measuring the time related to image formation with a timer and finishing the image formation when a predetermined time elapses and proceeding to image formation of the next sample. .

(Deformation)
Without being limited to the embodiments described above, various modifications and changes are possible, and these are also within the scope of the present invention.
(1) In each embodiment, in the first step, imaging by line scanning is performed, and after obtaining the first image data, the clarity of the contour of the first image data is digitized in the second step. Although shown, you may have the process of determining whether the sample image of 1st image data has deform | transformed by drift between this 1st step and 2nd step.
FIG. 7 is a diagram illustrating a modification of the image forming method.
The image forming method according to the modification shown in FIG. 7 includes a first step (S401) to a twelfth step (S412). Note that, as an example, a modification of the image forming method shown in the first embodiment is shown. However, the image forming method can be appropriately applied to the second embodiment and the third embodiment.

The first step (S401), the third step (S403) to the eleventh step (S411) of the modified form are the first step (S101) and the second step (102) to the tenth step (shown in the first embodiment). (S110) The same process.
In the second step (S402) of the deformation mode, the image forming unit 24 determines whether deformation due to drift has occurred in the sample image of the first image data obtained in the first step (S401).
If there is no deformation due to drift in the sample image (that is, a straight line that runs in the vertical direction and the sample to be observed tilts the pattern diagonally, etc.) (that is, the drift amount is below a predetermined value) Then, the process proceeds to the twelfth step (S412), the memory 27 stores the first image data, and the process ends. When the sample image is deformed (that is, when the drift amount is larger than the predetermined value), the process proceeds to the third step (S403), and the image forming unit 24 clears the outline of the first image data. Quantify the height.

Thereafter, conditions are met from the fourth step (S404) to the eleventh step (S411) corresponding to the third step (S103) to the tenth step (S110) described in the first embodiment. Until the image is formed, and the image data is stored in the memory 27. As a result, it is possible to obtain image data having a desired level of clarity regardless of the drift amount.
Note that the determination of whether or not the sample image of the first image data is deformed due to drift is performed by measuring the amount of drift based on how the image is deformed, as described in JP-A-2002-222633, for example. This can be determined by using the method and setting the allowable amount of drift in advance.

In the modified form, when the sample image of the first image data obtained by the line scan obtained in the first step (S401) is not deformed due to the drift, the image can be adopted and stored in the memory 27. It is.
Therefore, the time required for image formation of the sample can be shortened, and a clearer sample image can be obtained.

(2) In each embodiment, the image forming method includes a step in which the image forming unit 24 determines whether or not the numerical value M2 representing the clarity of the outline of the second image data satisfies the threshold Ms. However, the present invention is not limited to this, and the numerical value M2 may be evaluated based on the threshold value Ms, and the evaluation result may be output to the display unit.
FIG. 9 is a diagram illustrating a modification of the image forming method.
9 includes the first step (S501) to the tenth step (S510), omitting the sixth step (S106) of the first embodiment, and the first embodiment. Except for having a ninth step (S509) and a tenth step (S510) that are not in the form, the second embodiment has substantially the same steps as the first embodiment.
In the image forming method shown in FIG. 9, the first step (S501) to the fifth step (S505) correspond to the first step (S501) to the fifth step (S105) of the first embodiment. The sixth step (S506), the seventh step (S507), and the eighth step (S508) are respectively the eighth step (S108), the ninth step (S109), and the tenth step (S110) of the first embodiment. It corresponds to each.

In the image forming method shown in FIG. 9, the fourth step (S504) to the eighth step (S508) are repeated a predetermined upper limit number of times. At this time, in the sixth step (S506), a numerical value M2 representing the clarity of the contour of the second image data obtained by imaging the sample S by area scanning is used as the second image data taken before that. Compared with the numerical value M2 representing the clarity of the contour, an image having a larger numerical value M2 (that is, a clearer image) is selected, and stored (overwritten) in the memory 27 in the seventh step (S507).
As a result of repeatedly executing the fourth step (S504) to the eighth step (S508) until the predetermined upper limit is reached, the memory 27 stores the numerical value M2 among the second image data imaged a predetermined number of times. Is stored, that is, the second image data with the clearest outline is stored.

The ninth step (S509) is a numerical value M2 representing the clarity of the contour among a predetermined number of second image data obtained by repeating the fourth step (S504) to the eighth step (S508) a predetermined number of times. Is compared with the threshold value Ms related to the clarity of the ideal contour set in the third step (S503) as a reference value, and the clarity of the contour of the second image data stored in the memory 27 is evaluated. It is a process to do.
As this evaluation method, evaluation is performed using the ratio (M2 / Ms) of the numerical value M2 to the threshold value Ms (in this case, the closer the M2 / Ms is to 1, the clearer the determination is). Or to evaluate.

  In the tenth step (S510), the evaluation result in the ninth step (S509) is stored and displayed on the display unit 25. As the display method of the evaluation result, the most clearly stored second image (the one with the largest numerical value M2 representing the clarity of the contour) is displayed. At this time, the ratio (M2 / Ms) between the numerical value M2 representing the clearness of the contour of the second clearest image and the set threshold value Ms is displayed as a percentage, or the determination result of whether M2 satisfies Ms is displayed. A display form such as displaying or arranging M2 and Ms so that they can be compared can be selected as appropriate.

In the modified form of the image forming method shown in FIG. 9, the steps of obtaining the ideal clarity of the contour of the image data by line scanning (S501, S502) and the step of obtaining the clarity threshold Ms (S503) are performed. The order may be performed at any step position as long as it is before the step of comparing the numerical value M2 representing the clarity of the contour of the second image data with the threshold value Ms (S509).
For example, after the step of determining whether the number of times of imaging has reached the upper limit number (S508), the step of imaging the first image data of the sample S by line scanning (S501), and the clarity of the contour of the image data is digitized. After executing the step (S502) and the step (S503) for obtaining the threshold of the clarity of the contour, the order of the steps (S509) for comparing the clarity of the contour with the threshold can be implemented without any problem.

(3) In each embodiment, in the second step and the fifth step, an example is shown in which the line profile of image data is linearly differentiated as a numerical value representing the clarity of the contour, and the maximum absolute value of the primary differential is used. However, the present invention is not limited to this, and other known methods, for example, a line profile pixel value range, a line profile width that satisfies a set value generated from the line profile pixel value range, etc. May be.
The range of the pixel value of the line profile is a difference between the maximum value and the minimum value of the pixel value of the line profile of the image data, and this can be used as a numerical value representing clarity. For example, when the maximum value of the pixel value of the line profile is 230 and the minimum value is 50 in the contour portion of the sample of the image data, the range is 180, and this numerical value is expressed as a numerical value representing the clarity of the image data. Use. In this case, the larger numerical value means clearer.

In addition, the setting value is determined from the pixel value range of the line profile, and the width of the line profile that satisfies the setting value (the width of the portion where the peak portion having the maximum value of the line profile curve exceeds the threshold) ) Can also be used as a numerical value for clarity. For example, when the maximum value of the pixel values of the line profile is 230, the minimum value is 50, and the range is 180, if the set value is 50% of the range, the pixel value that is the set value is 140. The dimension of the curve width of the line profile exceeding the set value is used as a numerical value representing clarity. In this case, if the sample image is blurred, the width becomes thick, and if it is clear, the width becomes narrow.
In addition, as a method for digitizing the clarity of the contour of the sample image, methods other than these methods described above can be used as appropriate.
Furthermore, smoothing processing and filtering processing for the purpose of noise removal that are generally performed may be performed before the above-described profile processing. Such smoothing processing and filtering processing are techniques that are normally performed, and therefore, detailed description thereof is omitted in this specification.

(4) In each embodiment, the scanning electron microscope has been described as an example of the charged particle beam apparatus. However, the present invention is not limited to this, and is applied to other apparatuses using a charged particle beam such as a transmission electron microscope. It is also possible.
In addition, although this embodiment and modification can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited by the embodiments described above.

It is a figure explaining the scanning electron microscope 1 of 1st Embodiment. It is a figure explaining the image formation method of the scanning electron microscope 1 of 1st Embodiment. It is a figure explaining a line profile and its 1st derivative. It is a figure which shows the relationship between the clarity of image data, and the first derivative of a line profile and a line profile. It is a figure explaining the image formation method of the scanning microscope of 2nd Embodiment. It is a figure explaining the image formation method of the scanning microscope of 3rd Embodiment. It is a figure which shows the modification of an image forming method. It is a figure explaining the influence which a drift has on a sample image. It is a figure which shows the modification of an image forming method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scanning electron microscope 11 Electron gun part 12 Lens barrel part 13 Converging lens 14 Scanning coil 15 Objective lens 16 Stage part 17 Exhaust part 18 Detection part 21 Control part 22 Signal processing part 23 CPU
24 Image forming unit 25 Display unit 26 Input / output unit 27 Memory

Claims (9)

An image forming method for obtaining a sample image in a charged particle beam apparatus,
A first imaging step of capturing a sample by line scanning to obtain one image by line integration and obtaining first image data;
A first quantification step for quantifying the clarity of the contour of the first image data after the first imaging step;
A threshold setting step for setting a clarity threshold value from a numerical value representing the clarity of the contour of the first image data obtained in the first digitization step;
A second imaging step in which the sample is imaged by area scanning to obtain one image by frame integration to obtain second image data;
A second quantification step for quantifying the clarity of the outline of the second image data after the second imaging step;
A determination step of determining whether or not a numerical value representing the clarity of the outline of the second image data satisfies the threshold value after the second numerical value step;
A storage step based on said result of the determination process, and stores the selected said second image data,
Bei to give a,
Repeating from the second imaging step to the determination step until a numerical value representing the clarity of the outline of the second image data satisfies the threshold in the determination step;
An image forming method. An image forming method for obtaining a sample image in a charged particle beam apparatus,
A first imaging step of capturing a sample by line scanning to obtain one image by line integration and obtaining first image data;
After the first imaging step, a drift amount quantification step for quantifying the drift amount measured from the degree of deformation of the image of the first image data;
A drift amount determination step for determining whether or not the digitized drift amount is equal to or less than a predetermined value;
A first image data storage step of selecting and storing the first image data based on a result of the drift amount determination step;
A first digitizing step for digitizing the clarity of the outline of the first image data;
A threshold setting step for setting a clarity threshold value from a numerical value representing the clarity of the contour of the first image data obtained in the first digitization step;
A second imaging step in which the sample is imaged by area scanning to obtain one image by frame integration to obtain second image data;
A second quantification step for quantifying the clarity of the outline of the second image data after the second imaging step;
A determination step of determining whether or not a numerical value representing the clarity of the outline of the second image data satisfies the threshold value after the second numerical value step;
A storage step of selecting and storing the second image data based on a result of the determination step;
Providing
An image forming method. The image forming method according to claim 2.
Repeating from the second imaging step to the determination step until a numerical value representing the clarity of the outline of the second image data satisfies the threshold in the determination step;
An image forming method. The image forming method according to claim 2.
Repeating the set number of times from the second imaging step to the determination step even when the numerical value representing the clarity of the outline of the second image data satisfies the threshold in the determination step;
An image forming method. The image forming method according to claim 1 or 3,
The upper limit number of times for performing the second imaging step is set in advance;
An image forming method. The image forming method according to any one of claims 1 to 5, wherein:
In the first numerical value process and the second numerical value process, the contour is clarified using the maximum absolute value of the first derivative of the line profile of the first image data and the second image data. Quantifying
An image forming method. The image forming method according to any one of claims 1 to 5, wherein:
In the first numerical value process and the second numerical value process, a contour is obtained by using a difference between a maximum value and a minimum value of pixel values of a line profile of the first image data and the second image data. Quantifying the clarity of
An image forming method. The image forming method according to any one of claims 1 to 5, wherein:
In the first numerical value process and the second numerical value process, the first image data and the second image data are set using a difference between the maximum value and the minimum value of the pixel values of the line profile of the second image data. Quantifying the clarity of the contour using the width of the line profile that satisfies the set value,
An image forming method. An electron gun that irradiates the sample with a charged particle beam;
A detection unit for detecting a secondary signal emitted from an area irradiated with the charged particle beam on the sample;
An image forming unit that forms an image based on the detected secondary signal;
A charged particle beam device comprising:
The image forming unit includes:
Set the threshold value by quantifying the clarity of the contour of the first image data obtained by line scanning of the sample to obtain one image by line integration ;
Quantifying the clarity of the outline of the second image data obtained by area scanning for obtaining one image of the sample by frame integration, and determining whether or not the threshold is satisfied;
Based on the result of the determination, the second image data is selected and stored in a storage unit ,
It is repeated until the numerical value satisfies the threshold value, by converting the clarity of the outline of the second image data obtained by imaging the sample by area scanning and determining whether the numerical value satisfies the threshold value. ,
Charged particle beam device characterized by the above.