JP2001229866A - Automatic stigma adjustment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quick and highly precise optimal adjustment of stigma intensity in a beam scanning of charged particle beam. SOLUTION: In the beam scanning, a charged particle beam is scanned two- dimensionally on a specimen in x- and y-directions to form a scanned image. This apparatus comprises two sets of stigma coils for correcting the asymmetry of the charged particle beam in different correction directions of x and y, a stigma control means for synchronizing and changing the current value supplied to the stigma coils for correcting in the same direction as the direction where the charged particle beam is scanned in the two sets of stigma coils with a scanned signal for the charged particle beam, and an astigmatic correction and calculation means for changing the current value supplied to one of the stigma coils and calculating the astigmatic correction value from a scanned image determined. The scanned image is focused and adjustments of the current value supplied to the stigma coils and calculation of the astigmatic correction value are repeated to adjust the current value supplied to the sigma coil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to beam scanning in which a charged particle beam such as an electron beam or an ion beam is two-dimensionally scanned on a sample to form a scanned image, and more particularly to astigmatism of the charged particle beam. The stigma adjusting device to be corrected can be applied to an electron beam micro analyzer, an X-ray analyzer, and the like.

[0002]

2. Description of the Related Art EDX (energy dispersive X-ray spectroscopy) and W
An electron microanalyzer (EPMA) using DX (wavelength dispersive X-ray spectroscopy), an electron beam analyzer such as a scanning electron microscope (SEM), an X-ray analyzer, or an analyzer such as an ion microanalysis (IMA). 2. Description of the Related Art A scanning beam apparatus that forms a scanned image by two-dimensionally scanning a sample with a charged particle beam of electrons or ions is known. In these scanning beam devices, a sample is irradiated with a charged particle beam such as an electron beam or an ion beam, and a secondary electron beam, a reflected electron beam, a characteristic X-ray, and the like generated from the sample by the irradiation are detected, whereby the sample is irradiated. Perform surface analysis and elemental analysis. At this time, the charged beam or the sample stage is two-dimensionally scanned and detected by a detector, thereby obtaining a two-dimensional scanned image of the unevenness of the surface of the sample and elemental analysis.

It is desirable that the charged particle beam formed on the sample has a probe diameter as small as possible, and at the same time, the probe shape should be closer to a perfect circle. FIG. 10 is a diagram for explaining the shape of a scanned image by a non-circular probe. When the probe shape is long in a certain direction as shown in FIG. 10, the formed scanned image also becomes long in that direction. For example, when the sample shown in FIGS. 10A and 10C is scanned by a probe having a long shape in a certain direction, FIG.
As shown in (b) and (d), a scanned image deformed in the direction of the probe is obtained. In particular, when the size of the sample is smaller than the size of the probe, the shape of the scanned image is greatly affected by the shape of the probe. If there are astigmatism causes such as the shape of the light source and the asymmetry of the electric and magnetic fields, the apparent probe shape on the sample does not disappear even if the strength of the objective lens is changed.

Conventionally, as the astigmatism correction, a plurality of correction values based on a combination of current values supplied to each of the stigma coils in the x and y directions are prepared, and a scan image is obtained for each correction value of each combination. A method is known in which a plurality of scanning images having different values are compared to obtain a current value to be supplied to a stigma coil to perform astigmatism correction.

[0005] Other astigmatism corrections include the x direction and the y direction.
The scan image is obtained while simultaneously changing the current value supplied to each stigma coil in the direction, the scanned image is observed, and the current value supplied to the stigma coil is obtained from the current value at which a clear image is obtained, and the astigmatism correction is performed. Methods of doing so are also known.

[0006]

In the conventional astigmatism correction,
In order to obtain a scan image for each of a plurality of correction values composed of a combination of current values, it is necessary to obtain a plurality of scan images while variously changing the combination of current values in order to obtain an optimum correction value. For this reason, there is a problem that it takes a long time, and since the operator compares each scanned image, there is a problem that labor of the operator is required and individual differences between operators occur. Also, in astigmatism correction for obtaining a scanned image while simultaneously changing the current value supplied to each stigma coil, the combination of the current values in the x direction and the y direction is limited, so that an optimum correction value is not necessarily obtained. There is a problem in correction accuracy. Therefore, an object of the present invention is to solve the above-described conventional problems and to perform optimal stigma correction in a short time and with high accuracy in beam scanning of a charged particle beam.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a scan image obtained by changing a current value supplied to a stigma coil in a focused scan image, and correcting a stigma coil astigmatism from the obtained scan image. Is calculated alternately for each stigma coil, thereby sequentially obtaining high-precision correction values.

According to the present invention, since one correction value is obtained for one scanning image, the correction values in the x direction and the y direction can be obtained from the two scanning images. The processing time can be reduced. Further, the processing for obtaining the correction value is alternately performed for each stigma coil and repeated, thereby improving the correction accuracy.

Therefore, the automatic stigma adjusting apparatus according to the present invention uses the charged particle beam to scan the sample in two dimensions in the x and y directions to form a scanned image. The current value supplied to the two sets of stigma coils for correcting in the different correction directions of the direction and the y direction, and the stigma coil for correcting the same direction as the scanning direction of the charged particle beam in the two sets of stigma coils, is a charged particle beam. A stigma control means for changing the current value supplied to one of the stigma coils to obtain a scan image, and a stigma control means for changing the current value supplied to one of the stigma coils, and an image in the same scan direction as the change direction in the scan image. The process of calculating the astigmatism correction value of one stigma coil based on the image position where the signal intensity change is maximum is performed in the x direction and y And an astigmatism correction calculating unit that alternates in the direction, adjusts the current value supplied to the stigma coil based on the astigmatism correction value by focusing the charged particle beam on the scanned image, and supplies the current by the stigma control unit. The current value supplied to the stigma coil is adjusted by repeating the change of the current value and the calculation of the astigmatism correction value by the astigmatism correction calculation means.

The two sets of stigma coils in the x-direction and the y-direction are supplied with automatically adjusted current values, thereby correcting the probe-shaped astigmatism of the charged particle beam. The stigma control unit of the present invention is a unit for controlling a current value supplied to two sets of stigma coils in the x direction and the y direction, and a unit for performing astigmatism correction and an astigmatism correction value for performing astigmatism correction. It is also possible to adopt a configuration that also serves as a means for obtaining.

To obtain the astigmatism correction value, the charged particle beam is scanned by the scanning coil, and at the same time, the current supplied to the stigma coil in the same direction as the scanning direction is synchronized with the scanning signal of the charged particle beam by the stigma control means. To obtain a scanned image for one frame. In the obtained one-frame scan image, a shift due to the astigmatism of the charged particle beam appears as a change in image signal intensity. The astigmatism correction calculating means obtains a shift due to astigmatism from the image position where the image signal intensity change is maximum, and obtains an astigmatism correction value of each stigma coil. The astigmatism correction value can be obtained as an amount for compensating the deviation. The astigmatism correction is performed with the obtained astigmatism correction value, and the current value supplied to the stigma coil is alternately repeated in the x direction and the y direction while changing the current value supplied to the stigma coil in a minute range with the astigmatism correction value as a center. Find the point correction value. After obtaining the astigmatism correction value, the stigma control means sets the stigma intensity for driving each stigma coil to an optimum value based on the astigmatism correction value.

FIG. 1 is a diagram for explaining astigmatism correction by the automatic stigma adjusting apparatus according to the present invention, and shows astigmatism on a scanned image. In the automatic stigma adjusting apparatus according to the present invention, astigmatism is detected and adjusted using an image in which the focal position is focused on a scanned image. The image shape of the charged particle beam is a circular shape when focused, and a non-circular shape deformed by 90 degrees in x and y directions across the focused position when not focused Becomes When the power of the objective lens is adjusted, the image shape displayed on the scanned image becomes a deformed image in which the deformation direction is different by 90 degrees with respect to the circular image. When focused, a circular image is formed, and the degree of deformation increases as the image is defocused. Focusing the image on the scanned image can be performed by adjusting the power of the objective lens so that the image is in the middle of the deformed images in the deformed directions different by 90 degrees.

When the image is focused on the scanned image, the position and size of the circular image displayed on the scanned image indicate the degree of astigmatism. Here, assuming that the beam passes through the center position of the x and y coordinates when there is no astigmatism, the diameter of the circular image becomes minimum at the center position. In FIG. 1A,
When there is astigmatism, a position where there is no astigmatism on the scanned image is represented by a point Q in the figure, and the degree of the astigmatism is represented by a deviation from the center position. In the present invention,
When obtaining a correction value for the stigma in the x direction, FIG.
As shown in (b), when scanning the charged particle beam in the x-axis direction, the current value supplied to the stigma coil is changed from -100% to 100% in synchronization with the scanning. The shape of the probe P changes according to the value of the current supplied to the stigma coil, and becomes smaller as the probe P becomes more appropriate.

When there is astigmatism, the probe image P becomes minimum at a position shifted by the astigmatism. The current value supplied to the stigma coil when the probe image P is minimized becomes the astigmatism correction value. Here, by fixing the value of the current supplied to the stigma coil in the y-direction near 0, only the change in the x-direction can be displayed on the scanned image. By performing this scanning over the entire area in the y direction, a scanned image of one frame can be obtained, and the position of the astigmatism direction is determined by the change in the intensity of the scanned image in the x direction (in the y direction indicated by the hatched portion in the figure). (Extended band), and a stigma correction value in the x direction can be obtained from this position.

Similarly, when obtaining the stigma correction value in the y direction, as shown in FIG. 1C, when scanning the charged particle beam in the y axis direction, the charged particle beam is supplied to the stigma coil in synchronization with the scanning. A scanned image is obtained by changing the current value from -100% to 100%, and y is obtained from the intensity change in the y direction.
Find the stigma correction value for the direction. The optimum value of the astigmatism correction is set with higher accuracy by repeating the correction of the current value supplied to the stigma coil based on the obtained correction value and the process of obtaining the stigma correction value in the x direction and the y direction several times. Can be. In this repetition, by narrowing the change range of the stigma value in order, it is possible to set the optimum value of the astigmatism correction with higher accuracy.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the automatic stigma adjusting apparatus of the present invention, as the configuration of the stigma coil for performing astigmatism correction, an 8-pole stigma correction coil or a 60-degree oblique 4-pole stigma correction coil can be applied. The eight-pole stigma correction coil is configured to perform astigmatism correction in the x and y directions by two sets of coils each having four poles.
The 60-degree oblique 4-pole stigma correction coil is configured to perform astigmatism correction in the x and y directions by setting the 4 poles to an angle of 60 degrees (π / 3). In any of the correction coils, the astigmatism correction in the x and y directions can be performed by adjusting the current supplied to each set of stigma coils.

FIG. 2 shows an example of the configuration of an automatic stigma adjusting apparatus according to the present invention, which is applied to a scanning electron microscope. The scanning electron microscope 1 includes a beam source 2,
A scanning coil 6 for scanning the charged particle beam 3 irradiated from the beam source 2 on the sample stage S, a scanning controller 16 for controlling the scanning coil 6, a stigma coil 5 for correcting astigmatism of the charged particle beam 3, and Stigma coil 5
, A scan signal forming unit 14 for inputting a scan signal to the stigma control unit 15 and the scan control unit 16, a secondary electron emitted from the sample,
A detector 8 such as a PMT for detecting a line or the like, an amplifier 9 for amplifying a detection signal, an A / D converter 10 for converting an analog detection signal into a digital signal, a storage unit 17 for storing the detection signal, An image processing unit 12 and a control unit 11 including an astigmatism correction calculation unit 13 are provided.

The scanning coil 6 moves the charged particle beam 3 in the xy directions based on a scanning signal from the scanning controller 16 to scan the sample stage 8 two-dimensionally. The detector 8 detects secondary electrons, X-rays, and the like emitted from the sample (not shown), thereby obtaining a two-dimensional scanning image of the surface of the sample and the elemental analysis. The stigma coil 5 adjusts a current value to be supplied based on the correction value input from the stigma control unit 15. By adjusting the current value, the asymmetry of the charged particle beam 3 can be corrected to correct astigmatism, and the amount of astigmatism correction can be detected.

The scanning signal forming section 14 forms a scanning signal and supplies it to the stigma control section 15 and the scanning control section 16. By using the common scanning signal, the stigma controller 15 can change the current value supplied to the stigma coil in synchronization with the scanning of the scanning controller 16. When obtaining a scanned image of the sample, the control unit 13 controls the scanning signal forming unit 14 to determine the scanning speed, the scanning range, and the like, and controls the stigma control unit 15 to perform astigmatism correction. When the astigmatism correction value is obtained, the scan image is obtained while controlling the stigma control unit 15 to change the current value supplied to the stigma coil.
The astigmatism correction value is calculated from the change in the signal intensity of the scanned image obtained by 2 and the astigmatism correction calculator 13.

Here, the image processing unit 12 obtains the distribution of the image signal intensity of the scanned image, and obtains the intensity change of the image signal in the x direction or the y direction. The change in the intensity of the image signal can be obtained, for example, from the difference in signal intensity between adjacent pixels. At this time, the change in signal intensity between adjacent pixels is small in an image with large astigmatism, and the change in signal intensity between adjacent pixels is large in an image with small astigmatism. Therefore, the degree of astigmatism can be estimated based on the magnitude of the signal intensity change, and the image position where the signal intensity change is the maximum indicates the position where the astigmatism is the smallest.
The astigmatism correction calculation unit 13 examines a change in the image signal intensity of the scanned image, obtains a shift of the stigma corresponding to the astigmatism position from the image position where the change in the signal intensity is maximum, and calculates an astigmatism correction value from the stigma shift. Is calculated. Note that the control unit 11
Scanning image signal from the / D converter 10 or the storage unit 17
Can be used.

Therefore, the automatic stigma adjusting apparatus according to the present invention comprises the stigma coil 5, the stigma controller 1
5 and an image processing unit 12 and an astigmatism correction calculation unit 13, and cooperates with a configuration for obtaining a scanned image, such as a scanning coil 6, a scanning control unit 16, a detector 8, a scanning signal forming unit 14, and the like. To determine the astigmatism correction amount.

The operation of the automatic stigma adjusting apparatus according to the present invention will be described below. FIG. 3 is a schematic diagram showing the relationship between the stigma correction and the probe shape. The rectangle in the figure indicates the outer peripheral portion of the scanned image, each coordinate (xy coordinate) in the scanned image indicates the correction direction by the stigma coil, and the spread of the circular probe indicates the degree of astigmatism. Note that the probe shape shown in the figure has a circular shape because it shows a case where the scanning beam is focused on the scanning image plane.
The stigma correction indicates a case where the scanning image is changed from −100% to + 100% from the left side to the right side and from the upper side to the lower side. For example, at the upper left position of the scanning image, the stigma correction of the x coordinate and the y coordinate is performed. Both -100
%.

When the charged particle beam has no astigmatism, the probe shape has the smallest diameter at the position where the stigma correction of the x coordinate and the y coordinate is 0, that is, at the center position O of the scanned image. The diameter of the probe shape increases as the position shifts. On the other hand, when the charged particle beam has astigmatism, the diameter of the probe shape becomes minimum at a position shifted from the center position O of the scanned image. The difference between the position where the diameter of the probe shape is minimum and the center position O corresponds to the degree of astigmatism, and the current value supplied to the stigma coil to compensate for the astigmatism is the stigma correction value. Therefore, the astigmatism can be corrected by correcting the current applied to the stigma coil using the stigma correction value. With this correction, the diameter of the probe shape formed on the scanned image is reduced at the center position O. The smallest.

Next, the operation of the stigma adjustment will be described with reference to the flowcharts of FIGS. 4 and 5 and the probe shape diagrams on the scanned images of FIGS. Prior to astigmatism correction, step S
A focusing operation for focusing the charged particle beam on the position of the scanned image plane is performed by steps 1 and 2. In the focusing operation, a scanning signal (sweep signal) is input in the x direction and the y direction of the deflector of the scanning coil 6, and the charged particle beam is scanned on the sample to obtain and display a scanned image (Step S).
1) Adjusting the power of the objective lens 7 while observing the scanned image. By adjusting the probe shape to be smaller, the focal point position can be adjusted.
By focusing on the scanning image plane position, the probe shape obtained from the scanning image becomes circular (step S2).

In the next steps S3 to S10, a stigma correction value for performing astigmatism correction is obtained. In the present invention, the stigma correction value in the x direction and the stigma correction value in the y direction are obtained alternately. The deviation of the stigma in the x direction is obtained by steps S3 to S5, and step S6
Obtains the stigma correction value. First, change x
Set the stigma intensity width in the direction. This width setting is performed by first determining the degree of astigmatism from the wide detection range, then determining the accuracy of the astigmatism correction in step S11, and repeating while narrowing the detection range in order according to the accuracy.
This is for obtaining the stigma value of the astigmatism correction with higher accuracy (step S3).

The power of the stigma in the y direction is set, for example, near 0 and fixed (step S4), and the deviation of the stigma in the x direction is obtained (step S5). The flowchart in FIG. 5A describes a procedure for obtaining the displacement of the stigma in the x direction. In order to determine the displacement of the stigma in the x direction, a scan signal in the x direction is input to the scan coil 6 to perform the scan in the x direction.
The scanning signal in the x direction synchronized with the scanning signal in the x direction is -1.
It is changed in the intensity range from 00% to + 100%.

FIGS. 6 and 7 show the x-direction scanning signal (a), the x-direction stigma correction amount (b), and the probe shape (c) on the scanned image at this time, and FIG. 6 shows no stigma. FIG. 7 shows a case where there is a dot. As shown in FIG. 6, when there is no astigmatism, the diameter of the probe becomes smaller as the stigma correction amount changes from -100% to 0% toward the center of the scanned image, and the stigma correction amount becomes zero. % Is minimum. Thereafter, the stigma correction amount is increased from 0% to +10 from the center of the scanned image toward the outside.
As the value changes to 0%, the diameter of the probe becomes larger again.

On the other hand, as shown in FIG. 7, when there is an astigmatism, the stigma correction amount decreases toward the center of the scanned image.
The diameter of the probe shape becomes smaller as it changes from 100% to + 100%, becomes smallest at a certain stigma correction amount, and then becomes larger again. The deviation (the amount of displacement in the x direction) between the position where the diameter of the probe shape is minimum and the center position is a stigma correction value for correcting astigmatism. Note that the stigma correction value for correcting astigmatism means that the displacement of the charged particle beam when a current is supplied to the stigma coil with the stigma correction value of that magnitude is the same as the displacement due to astigmatism. There is (step S51). The scanning in the x direction in step S51 is repeated while scanning in the y direction (step S52) to obtain a scanned image. The obtained change in the intensity of the image signal in the x direction of the scanned image appears as a band extending in the y direction through the position where astigmatism exists (step S53).

In order to determine the position of astigmatism, an intensity change curve of the image signal is obtained from the scanned image, and an area where the change is large (see the hatched area in FIG. 1B) is obtained. This change curve can be obtained by calculating the difference in signal intensity between adjacent pixels in the image data taken into the storage unit. When the astigmatism is large, the change in signal intensity between adjacent pixels is small, and when the astigmatism is small, the change in signal intensity between adjacent pixels is large. Therefore, the image position where the change in signal intensity is the maximum indicates the position where the astigmatism is the smallest.

The change curve can also be calculated by integrating the image data fetched into the storage section in the y direction and calculating the difference in the x direction with respect to the integrated value (step S54). In the scanned image, the deviation of the stigma in the X direction is obtained from the deviation between the center position and the position obtained in step S54 (step S55). Step S5
An astigmatism correction value for compensating for the stigma deviation obtained in step (1) is calculated, and a current value to be supplied to the stigma coil is calculated (step S6).

Next, the deviation of the stigma in the y direction is determined in steps S7 to S10. Step S
Steps 7 to S10 can be similarly performed by exchanging the x direction and the y direction in the steps shown in steps S3 to S6, and after setting the scanning width in the y direction (step S7), The stigma correction value in the x direction calculated in S6 is set (step S6).
8) Find the displacement of the stigma in the y direction (step S)
9) A current value to be supplied to the stigma coil is calculated by calculating the astigmatism correction value in the y direction (step S10). In addition,
The flowchart illustrating the process of step S9 in FIG. 5B is the same as the flowchart illustrating the process of step S5 in FIG.

The astigmatism is corrected by adjusting the stigma coil with the stigma correction value obtained in the above process (step S).
11), determine the accuracy of astigmatism correction (step S1)
2). If the accuracy of the astigmatism correction is insufficient, the stigma correction value obtained in the above-described process is set as a central value and step S3
The process of step S10 is performed by setting the scanning width to, for example, 1/2, 1
/ 4 in order and repeated for a narrow range to increase the accuracy of the astigmatism correction amount. This repetition may be performed a predetermined number of times, or may be performed until the difference from the previous time becomes equal to or smaller than the threshold value. Note that the order of the step of obtaining the stigma value of the astigmatism correction in the x direction in steps S3 to S6 and the step of obtaining the stigma value of the astigmatism correction in the y direction of steps S7 to S10 can be reversed.

FIGS. 8 and 9 show steps S3 to S10.
It is a figure which shows an example of the process of. FIG. 8A shows the same scanning image of the stigma shift in the x direction and the stigma shift in the y direction when there is no astigmatism. In this example, when an intensity change curve of an image signal of a scanned image (curves shown to the left and below in the figure) is obtained, a region (shaded portion) where the intensity change is large is located at the center position in both the x and y directions. Has passed. On the other hand, FIG. 8B shows a case where there is astigmatism, and similarly to FIG. 8A, the stigma shift in the x direction and the stigma shift in the y direction are shown in the same scan image. In this example, an area (shaded area) where the intensity change is large in the intensity change curve of the image signal of the scanned image passes through a position shifted from the center position in both the x direction and the y direction. In FIG. 8, when the scan width in the x direction and the y direction is set to 10 and the range is, for example, -5 to 5, the shift in the x direction is in a region near 2 and the shift in the y direction is near -2. It is shown in the area of.

FIG. 9 shows an example of obtaining a more accurate stigma correction value using the stigma correction value obtained in FIG. FIG. 9A shows that the stigma correction value in the x direction is 2 based on the stigma correction value obtained in FIG.
, And the stigma correction value in the y direction is set to -2.
The scanning image corrected by this correction value is shown. In FIG. 9A, the scanning width in the x direction and the y direction is set to 2 which is 1/4 times, and the range is from about 1 to 3 in the x direction.
And in the y direction from near -3 to near -1. This indicates that the shift in the x direction obtained in this manner is in a region near 2.2 and the shift in the y direction is in a region near -2.2.

Further, FIG. 9B shows that, based on the stigma correction value obtained in FIG. 9A, the stigma correction value in the x direction is set to 2.2 and the stigma correction value in the y direction is-.
The scanning image obtained after setting to 2.2 is shown. In FIG. 9B, the scan width in the x direction and the y direction is further set to 0.5, which is 1/4 times larger, and the range is set from about 2.0 to about 2.4 in the x direction. The direction is from about -2.4 to about -2.0. At this time,
The shift in the x direction is in a region near 2.16, and the shift in the y direction is in a region near -2.24. As described above, the accuracy of the astigmatism correction amount can be improved by repeating the scan range while sequentially narrowing the scan range.

According to the embodiment of the present invention, the present invention can be applied to any configuration of the stigma coil including the 8-pole stigma correction coil and the 60-degree oblique 4-pole stigma correction coil. Also, the gradient (angle) of the combined coordinates of the stigma magnetic poles and the magnetic field strength of the stigma can be set only by the magnitude of the current applied to each stigma coil.

[0037]

As described above, according to the automatic stigma adjusting apparatus of the present invention, optimal stigma correction can be performed in a short time and with high accuracy in beam scanning of a charged particle beam.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining detection of astigmatism correction by an automatic stigma adjustment device of the present invention.

FIG. 2 is a configuration example of an automatic stigma adjusting apparatus according to the present invention, and is a diagram illustrating a case where the apparatus is applied to a scanning electron microscope.

FIG. 3 is a schematic diagram showing the relationship between stigma intensity and probe shape.

FIG. 4 is a flowchart illustrating an operation of stigma adjustment.

FIG. 5 is a flowchart for explaining the operation of stigma adjustment.

FIG. 6 is a probe shape diagram on a scanned image for explaining the operation of stigma adjustment.

FIG. 7 is a probe shape diagram on a scanned image for explaining the operation of stigma adjustment.

FIG. 8 is a diagram showing an example of a process by the automatic stigma adjusting device of the present invention.

FIG. 9 is a diagram showing an example of a process by the automatic stigma adjusting device of the present invention.

FIG. 10 is a diagram for explaining a scan image shape by a non-circular probe.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Scanning microscope, 2 ... Beam source, 3 ... Charged particle beam, 4 ... Condenser lens, 5 ... Stigma coil, 6
... Scan coil, 7 Objective lens, 8 Detector, 9 Amplifier, 10 A / D converter, 11 Controller, 12 Image processor, 13 Astigmatism correction calculator, 14 Scan signal formation Department,
15: Stigma control unit, 16: Scanning control unit, 17
... storage unit.

Continuation of front page (72) Inventor Kazumi Nakayama 2-11 Nishinokyo Sanjobocho, Nakagyo-ku, Kyoto-shi, Kyoto Prefecture F-term (reference) 5C033 FF03 JJ02

Claims (1)

[Claims] In beam scanning for scanning a charged particle beam on a sample in two dimensions in x and y directions to form a scanned image, the asymmetry of the charged particle beam is corrected in different correction directions in the x and y directions. Two sets of stigma coils to be corrected, and a current value supplied to the stigma coil for correcting the same direction as the scanning direction of the charged particle beam in the two sets of stigma coils is changed in synchronization with the scanning signal of the charged particle beam. A stigma control unit for causing the stigma control unit to change a current value supplied to one of the stigma coils to obtain a scan image, and an image position at which the image signal intensity change in the same scan direction as the change direction in the scan image is maximum. Astigmatism correction calculating means for alternately performing a process of calculating the astigmatism correction value of one stigma coil based on the x direction and the y direction, Focusing the charged particle beam on the scanned image, adjusting the current value supplied to the stigma coil based on the astigmatism correction value, changing the supply current value by the stigma control means, and astigmatism correction value by the astigmatism correction calculating means An automatic stigma adjusting device, wherein the current value supplied to the stigma coil is adjusted by repeating the calculation of the stigma coil.