JP2968566B2 - Astigmatism reduction method for scanning electron microscope - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing astigmatism in a scanning electron microscope that reduces astigmatism when irradiating an electron beam converged by an objective lens onto a sample to be observed. Things.

[Conventional technology]

Generally, a scanning electron microscope has an objective lens shown in FIG. This objective lens usually has a cylindrically symmetric shape with the electron beam path 43 as a common axis.
A magnetic path 41 connecting the magnetic poles 41-1 and 41-2 is made of a magnetic material such as pure iron, and a current is applied to a coil 44 for giving a magnetomotive force to generate a magnetic field between the magnetic poles 41-1 and 41-2. Is occurring.
The electron beam passing through this magnetic field collides with the observation surface 46 of the wafer (semiconductor substrate) 42 to be observed under the convergence action, and generates secondary electrons. The secondary electrons thus generated are subjected to both the action of the longitudinal magnetic field generated by the objective lens and the electric field applied in the axial direction (Lorentz force), and the wafer undergoes a spiral motion along the axial direction. And is captured by the detector. The secondary electrons captured by the detector are image-processed and displayed on a cathode ray tube.

FIG. 10 is a schematic configuration diagram of a scanning electron microscope filed by the present inventors (patent application No. 244392).

The basic operation will be described in detail using the scanning electron microscope of FIG.

In FIG. 10, an electron beam 12 emitted from an electron gun 11 is shown.
Are focused by a focusing coil 13, converged by a focusing lens 14, and incident on an objective lens 17 via a stop 16. The electron beam further converged by the objective lens 17 irradiates the wafer 22 and scans the irradiating point by the deflection coil 25. Secondary electrons emitted from the wafer 22 are detected by the secondary electron detector 24. And a secondary electron image is displayed by performing luminance modulation on the display.

Next, the configuration and operation of a conventional scanning electron microscope will be described in detail.

In FIG. 10, a magnetic pole 19 is a magnetic pole for forming a magnetic loop for the flat magnetic pole 21.

The coil 20 applies a current to apply a magnetomotive force to the objective lens 17 to generate a lens effect.

The plate magnetic pole 21 is a plate-like magnetic pole that can move in parallel to the magnetic pole 18 facing the plate.

The wafer 22 is a sample to be observed placed on the plate magnetic pole 21.

 The holding table 23 is a table that holds the plate magnetic poles 21 in parallel.

The secondary electron detector 24 collects and detects secondary electrons generated by irradiating the wafer 22 with an electron beam.

The deflection coil 25 scans the wafer 22 with an electron beam.

The adjusting screws 26 and 26 'adjust the parallelism (that is, the parallelism with respect to a plane perpendicular to the axial direction of the objective lens) of the plate magnetic pole 21 to which the wafer is fixed on the holding table 23 by the fixtures 31 and 31'. It is a mechanism for adjusting.

The moving tables 27 and 28 are tables that can move the holding table 23 in a plane parallel to a plane perpendicular to the axial direction of the objective lens.

 The sample chamber 30 is a vacuum chamber for storing the wafer 22 and the like.

In FIG. 10, a magnetomotive force is generated by passing a current through the coil 20 constituting the objective lens 17, and a magnetic circuit is formed in a loop as shown by a dotted line in the figure. As a result, a magnetic field is generated between the inner distance between the magnetic poles (between the magnetic pole 18 and the flat magnetic pole 21) and the outer distance (between the magnetic pole 19 and the flat magnetic pole 21).
The only magnetic field that effectively acts as an objective lens on the electron beam is an axially symmetric magnetic field generated between the magnetic pole 18 and the flat magnetic pole 21. The gap between the magnetic pole 19 and the flat magnetic pole 21 is for forming a magnetic circuit. Where the flat magnetic pole
When observing the wafer 22 mounted on the flat plate magnetic pole 21 by moving the irradiation position of the electron beam in parallel by moving in parallel,
It is configured to have a size sufficiently larger than the size of the wafer 22 so that the magnetic field acting on the electron beam between the magnetic pole 18 and the plate magnetic pole 21 does not change.

A wafer 22 to be observed is placed in close contact with the flat magnetic pole 21 and fixed by fixtures 31 and 31 '. Further, the plate magnetic pole 21 is configured to be in close contact with a holding base 23 having a sufficient thickness and strength to maintain flatness. In order to adjust the parallelism of the parallel magnetic pole 21 to the magnetic pole 18, the holding table 23 fixes moving tables 27 and 28 (movable in X and Y axes) in an adjustable manner by adjusting screws 26 and 26 '. ing. The adjusting screws 26, 26 'are also provided in a direction perpendicular to a straight line connecting the 26 and 26', and can adjust the X and Y axes. The adjustment screws 26 and 26 'are adjusted while observing the secondary electron image or using an optical microscope so that the height of the observation point does not change when the movable tables 27 and 28 are moved. I have. The adjusting screws 26 and 26 'are adjusted and fixed so that the astigmatism does not increase due to the movement of the movable table. This is because the astigmatic distortion of the objective lens is caused by the non-uniformity of the objective lens magnetic field in the paraxial direction of the electron beam trajectory. Therefore, it is very important to maintain the parallelism between the magnetic poles 18 and 19 and the flat magnetic pole 21 and form a uniform magnetic field.

As described above, in the scanning electron microscope, in order to stably obtain the best image originally possessed by the scanning electron microscope, the parallelism between the first magnetic poles 18 and 19 and the second flat magnetic pole 21 is improved. It is indispensable to reduce the astigmatism of the objective lens.

[Problems to be solved by the invention]

However, in the above configuration, since there is no mechanism for automatically reducing the astigmatism, there is a problem that the operator has no other method than correcting the astigmatism while visually checking the image displayed on the display. . Also, the first magnetic poles 18, 19,
The degree of parallelism of the second plate magnetic pole 21 largely depends on the mechanical processing accuracy and the assembling accuracy, and there was no other way than to adjust it by manual alignment.

The present invention has been made in view of the above circumstances, and has as its object to provide a scanning electron microscope capable of performing automatic astigmatism reduction.

[Means for solving the problem]

The present invention relates to a first magnetic pole 18 which is axially symmetric, has a hole at the center for passing an electron beam, and is conical and flat at the tip.
An objective lens 17 having a second flat plate magnetic pole 21 movable in a plane perpendicular to the axis opposite to the first magnetic pole 18, and an objective lens 17 for correcting astigmatism generated by the objective lens 17; A point correction coil 5 and stage height control motors 40 to 43 for controlling the height and inclination of the moving table (stage) are provided. The sample to be observed is mounted on the second flat magnetic pole 21 mounted on the moving table. The astigmatism correction coil 5 and the coil of the objective lens 17 when the movable table is moved to perform astigmatism correction in advance on arbitrary points (for example, coordinate values (x, y)) of the sample to be observed. The current value (voltage value) flowing through 20 and the indicated value of the stage height control motors 40 to 43 are respectively stored, and when the sample to be observed is moved and observed, the stored current value (voltage value) is stored. To the astigmatism correction coil 5 (or the astigmatism correction coil 5 and the coil 2 of the objective lens 17). 0) and a signal corresponding to the stored indicated value to the stage height control motors 40 to 43. Also,
This scanning electron microscope is provided with a magnetic field sensor, detects the asymmetry of the magnetic field of the objective lens 17, and supplies a correction signal to the stage height control motors 40 to 43.

[Action]

According to the present invention, the current value (voltage value) obtained and stored in advance in association with the position of the sample to be observed by the above-described configuration.
Is supplied to the astigmatism correction coil 5 (or the astigmatism correction coil 5 and the coil 20 of the objective lens 17), and a signal corresponding to the indicated value is supplied to the stage height control motors 40 to 43 to perform astigmatism reduction. Additional magnetic field sensors 1 to 4 as required
The deviation amount of the detected magnetic field is obtained, and a correction signal generated based on the deviation amount is supplied to the stage height control motors 40 to 43 so as to reduce astigmatism. These astigmatism reductions make it possible to always observe the sample under observation in the best condition.

〔Example〕

Next, the configuration and operation of one embodiment of the present invention will be sequentially described in detail with reference to FIGS.

FIG. 1 is a schematic sectional view of a scanning electron microscope of the present invention, and FIG. 2 is a sectional view of a main structure of the present invention.

1 and 2, the magnetic field sensors 1 to 4
Is a sensor (for example, a Hall element, see FIG. 8) for measuring the intensity of the magnetic field generated between the magnetic pole 18 of the objective lens 17 and the flat magnetic pole 21. These magnetic field sensors 1 to 4
As shown in FIG. 2, two are provided in the X and Y directions of the rectangular coordinate system, respectively, to measure the magnetic field strength in the Z-axis (center axis of the lens) direction component.

The astigmatism correction coil 5 is a coil for correcting astigmatism generated by the objective lens 17, and is, for example, an eight-pole air-core (having no magnetic material) coil, and includes an N pole and an N pole (or an S pole). And the S pole) and the S pole and the S pole (or the N pole and the N pole).

The magnetic field sensors 6 to 9 are magnetic poles outside the objective lens 17.
This is a sensor (for example, a Hall element) for measuring the strength of a magnetic field generated between 19 and the plate magnetic pole 21. The magnetic field sensors 6 to 9 are provided two each in the X and Y directions of the rectangular coordinate system, measure the magnetic field strength in the Z-axis (center axis of the lens) direction component, and measure the parallelism between the magnetic pole 19 and the flat magnetic pole 21. Is to adjust.

The stage height control motors 40 to 43 are for adjusting the height of the moving table 27 'mounted on the moving table 27 (arbitrarily adjusting in the X and Y directions).

Next, the astigmatism reduction method will be described in detail with reference to FIG. Here, the initial adjustment is performed only once, and the initial adjustment is performed each time the image observation is performed.

In FIG. 3, the wafer 22 is divided into nine areas. In this method, the observable range of the wear 22, which is the sample to be observed, is divided into nine areas including, for example, a 3 × 3 matrix using stage coordinates.

Performs astigmatism correction by the operator at the center of each area. In this method, an operator performs astigmatism correction manually at the center of each of the nine divided areas.

Detects magnetic field information with a magnetic field sensor and stores it in a memory. In this method, when the worker manually performs astigmatism correction in each of the nine divided areas, the magnetic field intensity measured by the magnetic field sensors 1 to 4 is stored in a memory (memory area) prepared in advance for each area.

Stores the indicated values of the coil 20, the stigmator coil 5, the stage height control motors 40 to 43, and the stage coordinates (x, y) in the memory. As a result, the current value flowing through the astigmatism correction coil 5 in the astigmatism corrected state, the magnetic field intensity measured by the magnetic field sensors 1 to 4, the current value of the coil 20 (the current value of the objective lens 17) for all the divided areas , And the indicated values of the stage height control motors 40 to 43 are stored in the memory.

 The initial adjustment is completed by the above processing.

 Next, processing at the time of image observation will be described.

In FIG. 3, the stage is moved. This means that the observer moves the stage to observe an image at a desired position.

Determines the area from the stage coordinates. this is,
In response to the movement of the stage, it is determined which of the divided areas from the coordinate values.

Determines whether the area is the same as before the movement. YES
In the case of (1), the image observation work is performed in and. on the other hand,
In the case of NO (when the area is different from the one before the movement), the current value or voltage value stored in the corresponding area is converted to the astigmatism correction coil 5, the coil 20, the stage height control motors 40 to 43, and
When the difference between the magnetic field measured by the magnetic field sensors 1 to 4 and the stored magnetic field is equal to or greater than a specified value when the reproduction is performed, a correction signal (correction voltage) corresponding to the difference is provided. Is supplied to the stage height control motors 40 to 43 to perform a magnetic field reproduction sequence (described later with reference to FIG. 4).

 Performs an image observation operation.

Determines whether the observation has been completed. If YES,
The image observation ends. In the case of NO, the subsequent steps are repeated.

By the above processing, the current value flowing through the astigmatism correction coil 5, the coil 20 and the voltage value applied to the stage height control motors 40 to 43 are automatically corrected in a state stored in advance with the stage movement, Magnetic field sensor 1 when reproduced further
When the difference detected by (4) is equal to or more than a specified value, the correction voltage corresponding to the difference is supplied to the stage height control motors 40 to 43 to reduce astigmatism, thereby automatically changing the movement of the sample to be observed. Astigmatism can be reduced.

The example of the magnetic field reproduction sequence shown in FIG. 3 will be described in detail with reference to FIG.

In FIG. 4, the information of the area is called from the memory to the memory on the CPU. Here, the magnetic field B _zi0 (i = 1, 2, 3,
4) Take out the above to the memory on the CPU.

Controls and reproduces the coil 20, the astigmatism correction coil 5, and the stage height control motors 40 to 43. this is,
Is supplied to the coil 20, the astigmatism correction coil 5, and the stage height control motors 40 to 43 to reproduce the initial state.

Detects magnetic field information by the magnetic field sensors 1 to 4 and stores it in a memory. This is the magnetic field detected by the magnetic field sensors 1 to 4 in the current state of the stage.
B _zi (i = 1, 2, 3, 4) is stored in the memory.

Compares the magnetic field information at the time of initial adjustment with the latest information,
Calculate ΔB _zi . This calculates ΔB _zi = B _zi −B _zoi (i = 1, 2, 3, 4).

Determines whether ΔB _zi <ΔB _s (standard value). This is because magnetic field information B _zoi at the time of initial adjustment and current magnetic field information B _zi
It is determined whether or not the difference ΔB _zi is smaller than the standard value ΔB _s . In the case of YES, it is determined that the difference ΔB _zi is smaller than the standard value ΔB _s , so that it is determined that the astigmatism has been reduced, and the process ends, and the process proceeds to FIG. On the other hand, in the case of NO, the difference ΔB _zi
Since but is determined to be greater than the standard value .DELTA.B _s, perform ,, regarded as not being astigmatic correction.

Calculates ΔB _X = ΔB _z2 −ΔB _z1 ΔB _Y = ΔB _z3 −ΔB _z4 . This is the magnetic field sensor 1 shown in FIG.
The difference between the displacement of the magnetic field in the X direction by the magnetic field sensor 2 and ΔB _X
, And similarly the magnetic field sensor 3 and the magnetic field sensor 4
The difference between the displacement amount of the magnetic field in the Y direction by calculating as .DELTA.B _Y.

Is, .DELTA.B _X, corrects the voltage of the stage height control motors 40-43 in the direction of reducing ΔB _Y (ΔB _X, seeking to previously measured relationship between supply voltage .DELTA.B _Y and the stage height control motors 40 to 43 This is not the corrected state, and this is repeated.

Through the above processing, in response to movement of the stage, reproduced astigmatic correction state at the time of initial adjustment, further from the current time of initial adjustment field shift amount .DELTA.B _X, .DELTA.B _Y in advance when the specified value or more delta _s By supplying the correction voltage measured and obtained to the stage height control motors 40 to 43 to reduce the astigmatism, the astigmatism can be automatically reduced in accordance with the movement of the stage.

Next, another astigmatism reduction method will be described with reference to FIG.

In FIG. 5, the wafer is divided into nine areas. In this case, as in FIG. 3, the observable range of the wafer 22, which is the sample to be observed, is divided into nine areas composed of a 3 × 3 matrix using the stage coordinates.

Performs astigmatism correction by the operator at the center of each area. In this case, as in FIG. 3, the operator manually performs astigmatism correction at the center of each of the nine divided areas.

, Detects magnetic field information with a magnetic field sensor and stores it in a memory. This is because, when the astigmatism correction is manually performed in each of the nine divided areas by the operator, the magnetic field sensors 1 to 4
Is stored in a memory (memory area) prepared in advance for each area.

Makes a curve approximation of the magnetic field strength in the coordinate system of the stage.
For example, as described on the right side, B _zi ≒ f _i (x, y) (i = 1, 2) (1) B _zj ≒ f _j (x, y) (j = 3, 4) ( 2) and the magnetic field strengths B _zi and B _zj are each approximated by a curve. Here, the magnetic field intensity _Bzi indicates the magnetic field intensity indicated by the magnetic field sensors i and j, and both are functions of the (x, y) coordinates.

Saves the approximate expression in memory. This stores the equations (1) and (2) approximated by a curve in a memory.

 The initial adjustment is completed by the above processing.

 Next, processing at the time of image observation will be described.

In FIG. 5, the stage is moved. This means that the observer moves the stage to observe an image at a desired position.

Calculates magnetic field information at the position from the stage coordinates and the approximate expression. This calculates the magnetic field information at the current position from the coordinates (x, y) of the current stage and the approximate expressions (1) and (2).

Controls the voltage of the stage height control motors 40-43,
Reproduce the magnetic field at that position. This is so that the stage height control motors 40 to 43 are set so that the magnetic field information calculated by the magnetic field information measured by the magnetic field sensors 1 to 4 at the current position becomes equal.
Is controlled to reproduce the magnetic field at the time of the initial adjustment.

 Performs an image observation operation.

Determines whether the observation has been completed. If YES,
The image observation ends. If NO, do the following.

By the above processing, the voltage of the stage height control motors 40 to 43 is controlled so as to reproduce the state of the magnetic field information calculated based on the approximate expression obtained and stored in advance with the movement of the stage. Astigmatism reduction can be performed automatically as the observation sample moves.

In the above embodiment, the method of reducing the astigmatism by storing the magnetic field information after the astigmatism correction in advance and reproducing the stored magnetic field state as much as possible has been described.
This is because normally, astigmatism cannot be completely corrected simply by forming a uniform symmetric magnetic field in the axial direction. However,
If the astigmatism can be reduced sufficiently for practical use only by forming a uniform axially symmetric magnetic field by improving the processing and assembly accuracy, the astigmatism reduction method shown in FIG. 6 is very practical and useful. Come the way. This will be described below with reference to FIG.

FIG. 6 is a flowchart showing the astigmatism reduction operation of the present invention.

In FIG. 6, during the stage assembly adjustment, the parallelism is adjusted by adjusting screws 26 and 26 '. This is adjusted by adjusting screws 26, 26 'in FIG. 1 so that the flat magnetic pole 21 mounted on the holding base 23 and the magnetic poles 18, 19 are parallel.

Performing the above adjustments at the stage assembly
The gap between 18 and the plate magnetic pole 21 is parallel, and the astigmatism resulting from the spatial positional relationship of the magnetic field is minimized.

Next, during actual observation, the magnetic field strength is measured by a magnetic field sensor. This is because when the stage is moved and the sample to be observed is positioned at a desired position, the magnetic field B _zi (i =
1, 2, 3, 4) are measured.

Calculates the deviation from the axially symmetric component _Bzo .

Where the axially symmetric component B _zo is The shift amount ΔB _zi (i = 1, 2, 3, 4) is ΔB _zi = B _zi −B _zo (i = 1, 2, 3, 4) (4).

Determines whether B _zo and ΔB _zi (i = 1, 2, 3, 4) are within the standard. In the case of YES, the automatic astigmatism reduction work ends. In the case of NO, the correction operation (correction by the stage control motor or the like) is performed in and the subsequent steps are performed.

By the above processing, the stage control motor is controlled so that the deviation from the axially symmetric component measured by the magnetic field sensors 1 to 4 is within the standard when actually observing, with high accuracy can be formed uniform and axisymmetric axial magnetic field B _z, it is possible to automatically reduce the astigmatic. Forming a uniform and axially symmetric uniform magnetic field is macroscopically equivalent to the magnetic poles 18, 19 and the second flat magnetic pole.
It is nothing but improving the parallelism of 21. Therefore, by inserting the following operation shown in FIG. 7 between that shown in FIG. 6, the astigmatism reduction operation when the parallelism is largely shifted can be performed quickly.

 FIG. 7 is a diagram for explaining correction of magnetic pole parallelism according to the present invention.

FIG. 7 (a) shows a state before the parallel correction, and
FIG. 21 shows a state in which 21 is downward-sloping as shown. In this state, the _{B zo '= B z8 = B} z9, B z6> B z7. Here, the suffixes 6 and 7 represent two magnetic fields of the magnetic pole 19 in the X direction, and the suffixes 8 and 9 represent two magnetic fields of the magnetic pole 19 in the Y direction.

FIG. 7 (b) shows a state after the parallel correction, and
21 shows how they are parallel as shown. In this state, the _{B zo '= B z6 = B} z7 = B z8 = B z9. here, It is.

In the above-described astigmatism reduction method, a case where four magnetic field sensors are used by dividing the area into nine areas has been described for the sake of simplicity, but the present invention is not limited to this. Instead, the area may be divided into an arbitrary number and a larger number of magnetic field sensors may be used.

 FIG. 8 shows an example of a magnetic field sensor according to the present invention.

FIG. 8 (a) shows a magnetic field sensor 32 attached to the magnetic pole 18 on the objective lens.
The state in which was provided is shown.

FIG. 8 (b) shows an enlarged view of the magnetic field sensor 32. In the magnetic field sensor 32, a plurality of (for example, 256) Hall elements are provided in a circular shape on a semiconductor substrate, and these Hall elements are provided one by one or a predetermined number (for example,
In the case shown in FIG. As described above, since the Hall element is formed on the semiconductor substrate by the LSI technology, the magnetic field sensor 32 having a uniform magnetic field detection characteristic can be easily formed. For example, the magnetic field sensor 32 can be easily configured to measure an axial magnetic field (vertical magnetic field) between the magnetic pole 18 and the plate magnetic pole 21 or a magnetic field in a direction perpendicular to the axial direction.

〔The invention's effect〕

As described above, according to the present invention, one of the magnetic poles constituting the objective lens is a movable flat magnetic pole,
The astigmatism correction is performed in advance to store the current flowing through the astigmatism correction coil 5 and the coil 20, and the voltage applied to the stage height control motors 40 to 43. The initial voltage is applied to the astigmatism correction coil 5 (or the astigmatism correction coil 5 and the coil 20) and the stored voltage is applied to the stage height control motors 40 to 43 to perform the astigmatism correction (adjustment by the operator). By adopting a configuration that reproduces the magnetic field of the state and corrects astigmatism and, if necessary, the reproduction magnetic field based on the deviation of the magnetic field detected by the magnetic field sensor, distortion due to astigmatism is minimized. It is possible to observe stably with the best image quality originally possessed by the scanning electron microscope. Therefore, the practical effects of the present invention are very large.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a conceptual configuration of a scanning electron microscope of the present invention. FIG. 2 shows a sectional view of the main structure of the present invention. FIG. 3 shows a flowchart (part 1) of the astigmatism reduction method according to the present invention. FIG. 4 shows an example of a magnetic field reproduction sequence according to the present invention. FIG. 5 shows a flowchart (part 2) of the astigmatism reduction method according to the present invention. FIG. 6 is a flowchart showing the main operation of the astigmatism reduction according to the present invention. FIG. 7 is a diagram for explaining correction of magnetic pole parallelism according to the present invention. FIG. 8 shows an example of a magnetic field sensor according to the present invention. FIG. 9 and FIG. 10 are explanatory diagrams of the prior art. In the figure, 1 to 4 are magnetic field sensors for measuring the magnetic field of the magnetic pole 18, 5 is an astigmatism correction coil, 6 to 9 are magnetic field sensors for measuring the magnetic field of the magnetic pole 19, 17 is an objective lens, 18 and 19 are magnetic poles,
20 is a coil, 21 is a plate magnetic pole, 22 is a wafer, 23 is a holding table,
24 is a secondary electron detector, 26 and 26 'are adjustment screws, 27 and 27',
Reference numeral 28 denotes a moving table, reference numerals 31 and 31 'denote fixtures, and reference numerals 40 to 43 denote stage height control motors.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenji Hatto 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Taichi Koizumi 1006 Kadoma Kadoma, Kadoma, Osaka Pref. In-company (72) Inventor Norimichi Anazawa 2-2-1 Shinjuku, Shinjuku-ku, Tokyo Holon Co., Ltd. (56) References JP-A-1-197951 (JP, A) JP-A-54-122970 (JP, A) JP-A-57-66637 (JP, A) JP-A-57-50756 (JP, A) JP-A-63-200444 (JP, A) JP-A-61-2249 (JP, A) −156172 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 37/00-37/36

Claims (3)

(57) [Claims] 1. A scanning electron microscope for irradiating an electron beam converged by an objective lens onto a sample to be observed and observing an image of the sample, wherein the scanning electron microscope has an axially symmetric hole having a hole through which the electron beam passes, and a conical shape. An objective lens having a first magnetic pole having a flattened tip, a second flat-plate magnetic pole opposed to the first magnetic pole and movable in a plane perpendicular to an axis, and an astigmatism generated by the objective lens An astigmatism correction coil for correcting aberrations, a stage height control mechanism for controlling the height and tilt of the moving table, and a sample to be observed mounted on the second flat plate magnetic pole mounted on the moving table. The astigmatism correction coil (5) when the astigmatism correction is performed in advance on any of a plurality of points (for example, coordinate values (x, y)) of the observed sample by moving the movable table, and the coil of the objective lens Current (voltage value) and stay The instruction values of the high control mechanism are stored, and when the sample to be observed is moved and observed, the stored current value (voltage value) is stored in the astigmatism correction coil (or the astigmatism correction coil and the objective). A scanning electron microscope configured to supply a signal corresponding to the stored instruction value to the stage height control mechanism. 2. A magnetic field sensor for detecting asymmetry of a magnetic field of the objective lens is provided near an axis of the objective lens, and a sample to be observed is mounted on the second flat magnetic pole mounted on the moving table. The astigmatism correction coil (5) and the objective lens are moved when the movable table is moved to perform astigmatism correction in advance on a plurality of arbitrary points (for example, coordinate values (x, y)) of the sample to be observed. The current value flowing through the coil, the instruction value of the stage height control mechanism, and the magnetic field of the objective lens detected by the magnetic field sensor are stored, and the stored current is used when moving the sample to be observed for observation. When the value is supplied to the astigmatism correction coil (5) (or the astigmatism correction coil (5) and the coil of the objective lens) and a signal corresponding to the stored indicated value is supplied to the stage height control mechanism. The above magnetic When the difference between the magnetic field detected by the field sensor and the stored magnetic field is equal to or greater than a predetermined value, a correction signal corresponding to the difference is supplied to the stage height control mechanism. The scanning electron microscope according to item (1). 3. As an arbitrary plurality of points, an observable range of a sample to be observed is divided into a plurality of meshes, and an astigmatism correction coil (5) is preliminarily subjected to astigmatism correction at an approximate center thereof. The current value flowing through the coil of the lens, the instruction value of the stage height control mechanism, and further store the magnetic field of the objective lens detected by the magnetic field sensor, if necessary,
At the time of observation, the stored values (current value, voltage value, magnetic field) are used at the time of the position in the mesh, or at the time of observation, a value calculated for the current position based on an approximate curve determined from values stored in advance (current value 3. The scanning electron microscope according to claim 1, wherein the scanning electron microscope is configured to use a value, a voltage value, and a magnetic field.