JP2000283909A - Surface observation device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain a concavo-convex image of a wide range of a sample by STM. When observing a wide range of uneven images of a sample, a distance between a tip of a probe and a surface of the sample is a distance through which a field emission current flows between the probe and the sample. You. The sample 2 is two-dimensionally scanned by the scanning mechanism 6. During the scanning, the position detecting device 7 detects the current position of the probe 1 in the scanning range and transfers it to the control device 10. The current detection device 8 detects a field emission current flowing through the sample 2, and the control device 10 takes it in. The control device 10 forms an uneven image of the sample surface in the scanning range based on the position data from the position detecting device 7 and the field emission current detected by the current detecting device 8 and displays the image on the display device 11, Based on the position data, an image indicating the current scanning position of the probe 1 is formed and displayed on the display device 11. By observing these two images, the operator can easily search for a part to be observed in detail.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface observing apparatus for observing a sample surface, and more particularly, to a surface observing apparatus capable of observing an uneven image of a relatively wide area of the sample surface in a short time.

[0002]

2. Description of the Related Art A scanning tunneling microscope (hereinafter, referred to as STM) is known for observing an uneven image of a sample surface. And ST
When observing the sample surface with M, it is necessary to first find out which part of the sample to observe.

For this purpose, it is conceivable to first obtain a rough image of a relatively wide area of the sample surface and observe the uneven image to determine a region to be observed in detail. Is performed by a piezoelectric scanning element, the area that can be scanned by temporary two-dimensional scanning is a rectangular area with a side of several μm at the maximum. For example, a concavo-convex image of a 4 mm × 4 mm area on the sample surface is obtained. In such a case, the operation of scanning the probe in a rectangular range of several μm on each side to obtain a concavo-convex image must be repeatedly performed while manually moving the position of the probe, which is very time consuming. Costly and inefficient.

Further, as described above, one side is several μm.
The operation of scanning the probe within the rectangular area to obtain a concavo-convex image is repeated while moving the position of the probe, and if there is a protrusion on the sample surface, the probe collides with the protrusion Thus, the possibility that the probe is damaged is increased.

[0005] In this specification, a relatively large area of the sample surface means that the probe is formed by a piezoelectric scanning element.
This means that it is sufficiently wide compared to the scanning range when performing dimensional scanning.

Accordingly, an object of the present invention is to provide a surface observation apparatus capable of obtaining a concavo-convex image of a relatively wide range of a sample surface in a shorter time than in the past.

[0007]

According to a first aspect of the present invention, there is provided a surface observation apparatus, comprising: a scanning mechanism for two-dimensionally scanning a sample;
A position detecting device for detecting a position of the probe in the scanning range, a current detecting device for detecting a field emission current or a tunnel current flowing through the sample when the sample is two-dimensionally scanned, and a position detecting device And a control device for forming a concavo-convex image of a sample surface in a scanning range on the display device based on the position data detected in the step (a) and the field emission current or the tunnel current detected by the current detection device. And According to a second aspect of the present invention, in the surface observation device of the first aspect, the line scanning in the two-dimensional scanning of the sample is not performed in one direction, and the line scanning is performed in an opposite direction in an adjacent scanning line. Features. The surface observation device according to claim 3, wherein the extraction electrode, a screen provided with a channel plate, a scanning mechanism for two-dimensionally scanning the extraction electrode, and the two-dimensional scanning of the extraction electrode, the extraction electrode has a scanning range. A first current detection device that detects a current flowing through the extraction electrode when the extraction electrode is two-dimensionally scanned, and a two-dimensional scanning of the extraction electrode. When you are
A second current detecting device for detecting a current flowing through a channel plate of the screen, position data detected by the position detecting device, a current detected by the first current detecting device, and / or a second current detecting device. A control device for forming an uneven image of the sample surface in the scanning range based on the detected current and displaying the image on a display device.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a first embodiment of a surface observation device according to the present invention, wherein 1 is a probe, 2 is a sample, 3 is a power source, 4 is a piezoelectric element, 5 is a moving mechanism, and 6 is A scanning mechanism, 7 is a position detecting device, 8 is a current detecting device, 9 is an operating device, 10 is a control device, and 11 is a display device. Hereinafter, the vertical direction in the figure is defined as a Z-axis direction, and a plane orthogonal to the Z-axis direction is defined as an XY plane.

The piezoelectric element 4 changes the position of the probe 1 in the Z-axis direction, and the variable amount of the position is controlled by a control voltage from a control device 10. The moving mechanism 5 is for integrally changing the position of the probe 1 and the piezoelectric element 4 in the Z-axis direction, and is composed of, for example, a motor. The variable amount is controlled by a control signal from the control device 10. Therefore, when the position of the probe 1 in the Z-axis direction is largely changed, the control device 10 drives the moving mechanism 5, and when the position of the probe 1 in the Z-axis direction is to be changed by a small amount, the control device 10 controls the piezoelectric element 4. Drive.

The scanning mechanism 6 moves the sample 2 in the XY plane
This is for performing dimensional scanning, and is composed of a motor. The size of the scanning range in which scanning is performed is provided from the control device 10. For scanning, four scanning modes as shown in FIG. 2 are defined. 2A is a mode in which scanning is performed from top to bottom, FIG. 2B is a mode in which scanning is performed from top to bottom, FIG. 2C is a mode in which scanning is performed from left to right, and FIG.
(D) is a mode in which scanning is performed from right to left. In any of the scanning modes, when scanning of one line is completed, line scanning is performed in the same direction from the next line scanning position. Instead, the line scanning position is changed by a predetermined width from the position where the line scanning is completed, and scanning is performed in the reverse direction. By performing such scanning, the scanning time is reduced.

Further, as shown in FIGS.
The reason why the two modes are provided is that when it is possible to predict in advance the position of the region to be observed in detail on the sample surface, a concavo-convex image can be obtained as quickly as possible according to the position. For example, as shown in FIG. 3, when the probe 1 is at the lower left, the region to be observed in detail is the sample 2
If it can be predicted that it is located in the area surrounded by the ellipse of FIG. 2, scanning in the scanning mode shown in FIG.
As compared with the case where scanning is performed in the scanning modes shown in (d) to (d), a concavo-convex image of the region can be obtained more quickly.

The position detecting device 7 detects which position in the current scanning range faces the probe 1 when scanning is being performed. This is nothing but detecting where the probe 1 is currently in the scanning range.

The current detecting device 8 detects a field emission current or a tunnel current flowing through the sample 2.

The operating device 9 is used to make various settings such as setting of a range for performing two-dimensional scanning and a scanning mode, and setting of a detailed image observation mode or a wide range image observation mode. Here, as a method of setting the scanning range, for example, the coordinates of the scanning center position and the size in the ± X direction and ± Y direction from the center position may be set, or the scanning range may be set. This may be done by setting the coordinates of one vertex of the rectangle and the size in the X and Y directions, or by setting the coordinates of two vertices that are the diagonals of the rectangle in the scanning range. Is also good.

The control device 10 gives the scanning range and the scanning mode set by the operating device 9 to the scanning mechanism 6, and based on the position data from the position detecting device 7 and the field emission current value from the current detecting device 8. A predetermined process such as a process of forming an image and displaying the image on the display device 11 is executed. As described above, since a method of forming an image from a current value is well known, a detailed description thereof will be omitted. For example, a method of forming an image by associating a current value with a luminance value may be used.

When a wide range of the image observation mode, the scanning range, and the scanning mode are set by the operating device 9, the control device 10 moves the moving mechanism 5 to a predetermined position in the Z-axis direction. give. Thereby, the moving mechanism 5
Moves the probe 1 and the piezoelectric element 4 so as to be located at the position in the Z-axis direction. The position in the Z-axis direction is a position where a field emission current flows between the probe 1 and the sample 2, and the distance between the probe 1 and the sample 2 is usually several μm.
m. The probe 1 is fixed at this Z-axis position until the wide range image observation mode ends.

At this time, the control device 10 sends the scanning range and the scanning mode set by the operation device 9 to the scanning mechanism 6, and instructs the start of scanning.

The voltage of the power supply 3 will be described as follows. In the image observation mode in a wide range, the power supply 3 needs a negative voltage of several kV, and in the detailed image observation mode, it has a negative voltage of several V. Therefore, the power supply 3
If the power supply is capable of generating a wide voltage range from a negative number V to several kV, the control device 10 controls the power supply to be a negative number kV during a wide range image observation mode and a detailed image observation mode during a detailed image observation mode. Automatic control can be performed so as to be a negative number V, but if not, the power supply voltage is previously determined by a switch between a wide range image observation mode and a detailed image observation mode. Must be switched. Here, as the power source 3, a negative number kV
Is connected, and the voltage is switched by a changeover switch.

The scanning mechanism 6 two-dimensionally scans the set scanning range in the set scanning mode according to an instruction from the control device 10. The scanning position is detected by the position detecting device 7, and the control device 10 Passed. At each scanning position, a field emission current corresponding to the distance between the probe 1 and the surface of the sample 2 flows through the sample 2, and the field emission current is detected by the current detection device 8 and passed to the control device 10. It is.

Then, the control device 10 controls the position detecting device 7
An image is formed on the basis of the position data from the current detecting device 8 and the field emission current value from the current detecting device 8 and displayed on a predetermined area of the display device 11, while the scanning range set by the operating device 9 and the position detection Based on the position data from the device 7, an image indicating the current position of the probe 1 in the scanning range and the scanning position is displayed on the display device 11.
Is displayed in a predetermined area.

Here, in the former image formed based on the field emission current value, the luminance value of each pixel of the image corresponds to the field emission current value at the scanning position. Since the value corresponds to the distance between the tip of the probe 1 and the surface of the sample, the image is ultimately an image representing the unevenness of the surface of the sample in the scanning range. Therefore, by observing the image, it is possible to find an area to be observed in detail.

FIG. 4 shows an example of the latter image showing the current scanning position of the probe 1. FIG. 4 shows the setting of the scanning range.
The figure shows the case where the scanning is performed by setting the coordinates of the scanning center position and the size in the ± X direction and ± Y direction from the center position, and the black point in the figure indicates the current scanning position of the probe 1. On the lower side, the X and Y coordinate values of the scanning position are displayed. The coordinate values are displayed as the amount of deviation from the set scanning center position. In addition, R in a figure,
L, U, and D mean right (right), left (left), up (up), and down (down), respectively.

By displaying such two images, the operator can easily know the position of the area to be observed in detail. In order to display two images on the display device 11 as described above,
The display area of the display device 11 may be divided into two and displayed.

When the scanning mechanism 6 scans the scanning range once, the scanning is completed. That is, for example, when scanning is performed in the scanning mode shown in FIG. 2A, scanning is performed from the lower left end of FIG. 2A, and the scanning ends when the scanning reaches the upper left end.
The same applies to other scanning modes. In the image observation mode in a wide range, it is only necessary to know the outline of the unevenness on the surface of the sample, so that only one scan is required.

Then, the control device 10 controls the position detecting device 7
When it is detected that the scanning is completed based on the position data from, the processing in the wide range image observation mode is completed.

When the region to be observed in detail is determined by the image formed based on the field emission current value and the image indicating the current scanning position of the probe 1, the operator operates the operation device 9 to perform a detailed image observation mode. , A scanning range is set, and an image is observed. This detailed image observation mode is the same as the image observation of the sample surface using the conventional STM.
This detailed image observation mode is well known and is not essential in the present invention, so a detailed description is omitted,
The outline is as follows.

In the detailed image observation mode, the power supply 3 is set to a negative number V, and the control device 10 controls the control voltage applied to the piezoelectric element 4 so that the tunnel current value from the current detection device 8 becomes constant. Under the control, an operation of keeping the distance between the probe 1 and the surface of the sample 2 constant is performed, and an uneven image of the surface of the sample 2 is formed and displayed on the display device 11.

As described above, according to this surface observation apparatus, the sample 2 is scanned by the scanning mechanism 6 constituted by a motor, so that the sample is compared with the case where the probe 1 is scanned by the piezoelectric scanning element. A relatively large area of the surface can be scanned. In the wide range image observation mode,
Since the probe 1 is placed at a distance of several μm from the surface of the sample 2, the possibility that the tip of the probe 1 collides with the protrusion of the sample 2 is very small. Further, since an image formed based on the field emission current value and an image indicating the current scanning position of the probe 1 are displayed, the operator can easily search for a region to be observed in detail. Further, since a plurality of scanning modes are provided, an uneven image at an arbitrary position can be obtained efficiently. Further, in the image observation mode for a wide range, the line scanning is performed not in one direction but in the adjacent scanning lines in the opposite direction, so that the scanning time can be reduced.

The first embodiment has been described above. Next, the second embodiment will be described.

In the above-described first embodiment, the field emission current flowing through the sample 2 is detected in the image observation mode in a wide range. In the second embodiment, the tunnel current is detected. FIG. 5 shows an example of the configuration. Although the configuration shown in FIG. 5 is the same as that shown in FIG. 1, this embodiment differs from the first embodiment in that the current detection device 8 detects the tunnel current even in the image observation mode in a wide range. Is different. Therefore, in this embodiment, in the image observation mode in a wide range, the position of the probe 1 in the Z-axis direction is set to a position where the distance from the sample 2 is about several nm, and the power supply 3 is set to a negative number V. You. The other points are the same as in the first embodiment.

As described above, according to the surface observation apparatus, a relatively wide range of the sample surface can be scanned, as in the first embodiment. Further, an image formed based on the tunnel current value and an image indicating the current scanning position of the probe 1 are displayed, so that the operator can easily search for a region to be observed in detail.

In the second embodiment, however, the distance between the probe 1 and the sample 2 is about several nm, which is considerably shorter than that in the first embodiment. In order to avoid collision, it is necessary for the control device 10 to control the piezoelectric element 4 when the tunnel current increases and to move the probe 1 upward in the drawing.

Next, a third embodiment will be described.
In the first and second embodiments described above, the case where the STM observes the uneven image of the sample over a relatively wide range is described. In this way, first, an image of the sample over a relatively wide range is obtained, and the image is obtained. The task of observing and searching for a portion to be observed in detail is required not only in STM.

For example, recently, research on a scanning atom probe device (hereinafter referred to as SAP) for evaluating the composition distribution and the electronic state of the tip of a sharp projection such as a scanning probe at an atomic level. Development is underway. The principle of the analysis of the protruding portion using the SAP device will be briefly described as follows. As shown in FIG.
A funnel-shaped extraction electrode 21 is arranged near the tip of the projection, and a positive high voltage is applied to the sample 20. This allows
Ions fly out of the tip of the protrusion of the sample 20. Some of these ions collide with the screen 22 having the channel plate 23 and are converted into current by the channel plate 23 and detected by a current detector (not shown). Passes through a probe hole 24 formed at the center of the sample, and is subjected to mass analysis by a mass spectrometer (not shown). Then, by comprehensively analyzing the current detected by the channel plate 23, the result of mass spectrometry, and the like, the composition distribution and the electronic state at the tip of the projection can be evaluated.

Now, in such an SAP apparatus,
It is necessary to check which part of the sample has the protruding portion. At present, however, the extraction electrode 21 is manually moved by trial and error.

Therefore, in the SAP apparatus, first, a concavo-convex image of a relatively wide area of the sample is obtained, and if the concavo-convex image can be searched for a projection to be analyzed in detail, the extraction electrode is automatically moved to a desired position. Since it is possible to move the target efficiently, the analysis efficiency can be improved.

In the third embodiment, in the SAP device,
The purpose of this is to obtain a concavo-convex image by scanning a relatively wide range of the sample, and an example of the configuration is shown in FIG. In FIG. 7, 20 is a sample, 21 is an extraction electrode, 22 is a screen, 23 is a channel plate, 24 is a probe hole, 25 is a piezoelectric element, 26 is a moving mechanism, 27 is a power supply,
Reference numeral 28 denotes a scanning mechanism, 29 denotes a current detection device, 30 denotes a position detection device, 31 denotes a current detection device, 32 denotes a control device, 33 denotes a display device, and 34 denotes an operation device. In this embodiment, the left-right direction in the drawing is the Z-axis direction, and the plane orthogonal to the Z-axis direction is the XY plane.

The piezoelectric element 25 changes the position of the sample 20 in the Z-axis direction, and the amount of change in the position is controlled by a control voltage from the control device 32. FIG.
Here, the control signal line is omitted. The moving mechanism 26 is for integrally changing the position of the sample 20 and the piezoelectric element 25 in the Z-axis direction, and is constituted by, for example, a motor. The variable amount is controlled by a control signal from the control device 10. In FIG. 7, the control signal lines are omitted. Therefore, when the position of the sample 20 in the Z-axis direction is largely changed, the control device 32 drives the moving mechanism 26 to
The controller 32 drives the piezoelectric element 25 when changing the position in the Z-axis direction by a small amount.

The scanning mechanism 28 connects the extraction electrode 21 to the X-
This is for performing two-dimensional scanning in the Y plane, and is constituted by a motor. The size of the scanning range in which scanning is performed is provided from the control device 32. For the two-dimensional scanning of the extraction electrode 21, the four scanning modes shown in FIG. 2 are defined similarly to the above-described embodiment, and the scanning time is shortened.

The position detecting device 30 detects the position of the extraction electrode 21 in the scanning range when the extraction electrode 21 is being scanned.

The current detector 29 detects the current I _e flowing through the extraction electrode 21 (this current is referred to as the extraction electrode current).
Is to be detected. The current detection device 31 detects the current I _s converted by the channel plate 23 (this current is referred to as a screen current).

The operating device 34 has a range for performing two-dimensional scanning,
And various settings such as setting of a scanning mode, setting of a detailed analysis mode or a wide range of image observation mode, and the like. Here, as a method of setting the scanning range, for example, the coordinates of the scanning center position and the size in the ± X direction and ± Y direction from the center position may be set, or the scanning range may be set. This may be done by setting the coordinates of one vertex of the rectangle and the size in the X and Y directions, or by setting the coordinates of two vertices that are the diagonals of the rectangle in the scanning range. Is also good.

The control device 32 gives the scanning range and the scanning mode set by the operating device 34 to the scanning mechanism 28, and based on the position data from the position detecting device 30 and the extraction electrode current _Ie from the current detecting device 29. Te, also on the basis of the screen current I _s of the position data and the current detector 31 from the position detecting device 30, to form an image, executes the predetermined processing of the processing for displaying on the display device 33.

Now, when the image observation mode, the scanning range, and the scanning mode in a wide range are set by the operation device 34, the control device 32 sends a predetermined position in the Z-axis direction to the moving mechanism 26. give. Accordingly, the moving mechanism 26 moves the sample 20 and the piezoelectric element 25 so as to be located at the position in the Z-axis direction. The position in the Z-axis direction may be set appropriately. At this time, the control device 32
Sends the scanning range and the scanning mode set by the operation device 34 to the scanning mechanism 28, and instructs to start scanning.

The voltage of the power supply 27 will be described as follows. As described above, when analyzing the protrusions of the sample 20 in detail, the power supply 27 is set to a positive high voltage, but in a wide range image observation mode, the power supply 27 is set to a negative high voltage. The power supply voltage can be switched between the detailed analysis mode and the wide range image observation mode by an appropriate method.

The scanning mechanism 28 two-dimensionally scans the set scanning range in the set scanning mode in accordance with an instruction from the control device 32.
0 is detected and passed to the control device 32. Also,
At each scanning position, the surface of the sample 20 and the extraction electrode 21 are separated from the surface of the sample 20 facing the extraction electrode 21.
And an amount of electrons corresponding to the distance between them is emitted, a part of which is taken into the extraction electrode 21 and the other extraction electrodes 21
The electrons that have passed through are captured by the screen 22,
The extraction electrode 21 and the channel plate 23 include:
Each of the extraction electrode current _Ie and the screen current _Ie according to the distance between the surface of the sample 20 and the extraction electrode 21
_s flows and is detected by the current detection devices 29 and 31, respectively, and the control device 32 takes in it.

Then, the control device 32 controls the position detecting device 3
And position data from the 1, to form an image on the basis of the screen current I _s from the extraction electrode current I _e and the position data and the current detector 31, from the current detection unit 29, a predetermined area of each display device 33 And an image indicating the current position of the extraction electrode 21 in the scanning range based on the scanning range set by the operation device 34 and the position data from the position detecting device 31. Is displayed in a predetermined area of the display device 33.

[0048] Here, the extraction electrode current I _e image formed on the basis of, and screen currents I _s image formed on the basis of the both samples at the luminance value of each pixel of the image is the scanning position Since these two images correspond to the distance between the surface of the sample 20 and the extraction electrode 21, these two images are ultimately nothing less than the images showing the unevenness of the sample surface in the scanning range. Therefore, by observing the image, it is possible to find out the position of the protrusion. Further, an image indicating the current scanning position of the extraction electrode 21 is displayed as shown in FIG. 4, as in the first embodiment.

By displaying such an image,
The operator can easily know the position of the protrusion of the sample to be analyzed in detail.

When the scanning mechanism 28 scans the scanning range once, the scanning ends. In the image observation mode in a wide range, it is only necessary to know the outline of the unevenness on the surface of the sample, so that only one scan is required.

Then, the control device 32 controls the position detecting device 3
When the end of the scanning is detected based on the position data from 0, the processing of the image observation mode in the wide range is ended.

[0052] When the lead-out electrode current I _e image formed on the basis of the image formed on the basis of the screen current I _s, the position to be analyzed in detail by the image indicating the current scanning position of the extraction electrode 21 fixed, The operator sets a detailed analysis mode and an analysis position using the operation device 34 and performs analysis. This detailed analysis mode is the same as described above.

In the above description, the image formed based on the extraction electrode current I _e and the screen current I _s
And the image formed based on the
Only one of the images may be displayed.

As described above, according to this surface observation apparatus, the scanning mechanism 28 constituted by a motor scans the extraction electrode 21, so that a relatively wide range of the sample surface can be scanned. Further, the image formed on the basis of the extraction electrode current I _e, the image formed on the basis of the screen current I _s, since the image indicating the current scanning position of the extraction electrode 21 is displayed, the operator, for further analysis The position of the projection of the sample to be obtained can be easily found, and the analysis efficiency can be improved. Furthermore,
Since a plurality of scanning modes are provided, an uneven image at an arbitrary position can be obtained efficiently. Further, in the image observation mode for a wide range, the line scanning is performed not in one direction but in the adjacent scanning lines in the opposite direction, so that the scanning time can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a surface observation device according to the present invention.

FIG. 2 is a diagram showing a scanning mode of a scanning mechanism 6;

FIG. 3 is a diagram for explaining the meaning of providing the four scanning modes shown in FIG. 2;

FIG. 4 is a diagram showing an example of an image indicating the current scanning position of the probe 1;

FIG. 5 is a diagram showing a second embodiment of the surface observation device according to the present invention.

FIG. 6 is a diagram for explaining the outline of the principle of analysis using a scanning atom probe (SAP) device.

FIG. 7 is a diagram showing a third embodiment of the surface observation device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Probe, 2 ... Sample, 3 ... Power supply, 4 ... Piezoelectric element, 5 ... Moving mechanism, 6 ... Scanning mechanism, 7 ... Position detecting device, 8 ... Current detecting device, 9 ... Operating device, 10 ... Control device, 11 display device, 20 sample, 21 extraction electrode, 22 screen, 23 channel plate, 24 probe hole, 25 piezoelectric element, 26 moving mechanism, 27 power supply, 2
8 scanning mechanism, 29 current detection device, 30 position detection device, 31 current detection device, 32 control device, 33 display device, 34 operation device.

Claims (3)

[Claims] A scanning mechanism for two-dimensionally scanning a sample; a position detecting device for detecting a position of a probe in a scanning range when the sample is two-dimensionally scanned; A current detection device that detects a field emission current or a tunnel current flowing through the sample during scanning, a position data detected by the position detection device, and a field emission current or a tunnel current detected by the current detection device. A control device for forming a concave-convex image of the sample surface in a scanning range and displaying the image on a display device. 2. The surface observation apparatus according to claim 1, wherein the line scanning in the two-dimensional scanning of the sample is not performed in one direction, and the line scanning is performed in an opposite direction on an adjacent scanning line. 3. A screen provided with an extraction electrode, a channel plate, a scanning mechanism for two-dimensionally scanning the extraction electrode, and where in the scanning range the extraction electrode is located when the extraction electrode is two-dimensionally scanned. A first current detection device for detecting a current flowing through the extraction electrode when the extraction electrode is two-dimensionally scanned; and a screen when the extraction electrode is two-dimensionally scanned. A second current detecting device for detecting a current flowing through the channel plate of the first position detecting device, position data detected by the position detecting device, current detected by the first current detecting device and / or detected by the second current detecting device A control device for forming an uneven image of the sample surface in a scanning range based on the supplied current and displaying the image on a display device.