JPH04238202A - Scanning type probe microscope and control method thereof - Google Patents

Abstract

PURPOSE:To observe a high-accuracy image at a high speed in a scanning type probe microscope. CONSTITUTION:A probe 2a is scanned in the X, Y directions via the scanning control of a scanning wave-form generating circuit 4 by an X, Y, Z-axis piezoelectric element 2b, and it is controlled in the Z direction via the feedback control of a feedback control circuit 3. Signals of the scanning wave-form generating circuit 4 and the feedback control circuit 3 are interlinked, the scanning speed is decreased when the absolute value of the feedback signal of the feedback control is large, the scanning speed is increased when the absolute value of the feedback signal is small, thus the scanning speed is changed in response to the aspect ratio of local irregularities on the surface of a sample 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention allows surface shape and material analysis to be performed by bringing a sharply pointed probe close to the sample surface and detecting physical quantities that depend on the distance between the probe and the sample surface. This invention relates to a scanning probe microscope and its control method.

0002

[Prior Art] Scanning tunneling microscopes (hereinafter abbreviated as STM) and atomic force microscopes (hereinafter abbreviated as AFM), which are types of scanning probe microscopes, are capable of observing the surfaces of substances with high resolution on the atomic order. This has attracted attention in recent years, and it is based on the following principles. In other words, in the case of STM, when the tip of a sharply pointed probe is brought close to a distance of about 1 nm from the sample surface, a current due to a tunneling phenomenon (tunnel current) flows through the sample while a voltage is applied between the probe and the sample.・Flow between the probes, and in the case of AFM, the sample
Atomic force acts between the probes. Physical quantities such as tunneling current and atomic force greatly depend on the distance between the sample and the tip, so
By detecting this physical quantity while raster-scanning the probe in the X and Y directions, and by feedback controlling the probe in the Z direction so that this quantity remains constant, the surface shape and surface state distribution of the sample can be observed on the atomic order. At this time, X
Scan control in the Y direction and control of the sample-to-probe distance are both performed using an analog system, scan control only using a digital system, and both controls performed using a digital system. is becoming mainstream due to its flexibility in signal processing.

Now, among conventional scanning probe microscopes, an example of a scanning tunneling microscope that employs digital control is the NA manufactured by Digital Instruments Co., Ltd. shown in FIG.
This will be explained using a configuration diagram of noscope2. This conventional example includes a sample 18, a probe 19a, and a probe 19b.
control the probe 19a in the three directions of X, Y, and Z;
Z-axis piezoelectric element, 20a is an A/D converter, 20b to 20e
21 is a D/A converter, 21 is a DSP section (digital signal processor section), and 22 is a control computer.

To operate such a conventional example, first, under the control of the DSP unit 21, a tunnel bias voltage is applied to the sample 18 via the tunnel bias voltage D/A converter 20e. When the tip of the probe 19a approaches the surface of the sample 18 in this state, a tunnel current is generated on the sample 18.
8. Flows between the probe 19a. This tunnel current is sample 1
8. Since it largely depends on the distance between the probes 19a, the distance between the probes 19a
The surface shape of the sample 18 can be observed on the atomic order by feedback-controlling the probe 19a in the Z direction using the piezoelectric element 19b so that the tunneling current becomes constant while scanning the probe 19a in the X and Y directions using the piezoelectric element 19b.

Next, this feedback control will be explained in more detail. That is, the A/D converter 20a amplifies the tunnel current flowing through the probe 19a and converts it into a digital signal, which is then received by the DSP unit 21. The DSP unit 21 compares this tunnel current signal with a set current value indicated in advance by the control computer 22, and sends a Z applied voltage signal to adjust the distance between the sample 18 and the probe 19a so that they match. It is calculated using a table format instructed in advance by the control computer 22 and output to the Z applied voltage D/A converter 20b. The DSP section 21 also transfers this Z applied voltage signal and the like to the control computer 22. The Z applied voltage D/A converter 20b converts this digital signal into an analog signal, amplifies it, and outputs it to the Z applied terminal of the piezoelectric element 19b. Further, the DSP unit 21 sends a sweep signal for raster scanning the probe 19a in the X and Y directions to the X and Y sweep D/A converters 20c and 20d in a manner instructed in advance by the control computer 22. Output. The X, Y sweep D/A converters 20c, 20d each convert this digital signal into an analog signal, amplify it, and output it to the X, Y application terminals of the piezoelectric element 19b. The control computer 22 is a DSP
The sweep signal instructed to the section 21 is associated with data such as the Z applied voltage signal transferred from the DSP section 21, and the data is stored and displayed as three-dimensional data.

Next, FIG. 9 shows the relationship between the shape of the sample surface, the X sweep signal, and the Z applied voltage signal. The X sweep signal is shown in Figure 9(b)
) is a triangular wave with a constant scanning speed, so the probe repeatedly moves back and forth in the X direction at a constant speed. If the sample surface has the shape shown in FIG. 9(a), the Z applied voltage signal has a waveform similar to that shown in FIG. 9(a) due to feedback control, indicating the shape of the sample surface.

[0007]

[Problems to be Solved by the Invention] However, in the scanning tunneling microscope (STM) according to the above-mentioned conventional technology,
The scanning of the probe in the X and Y directions is controlled independently of feedback control regarding the distance between the sample and the probe. In other words,
The scanning speed is always constant during the collection of one microscopic image,
It does not depend on the aspect ratio of local unevenness on the sample surface. Therefore, in order to prevent the probe from colliding with the sample surface, settings such as the scanning speed must be set so that the feedback control follows the part with the highest aspect ratio of the unevenness in the observed part of the sample. However, if there is even one part with a large aspect ratio, the scanning speed must be considerably slowed down. On the other hand, if there is even one part in the observation area that has a large aspect ratio relative to the scanning speed,
There was a problem in that the probe came into contact with the sample surface and the tip of the probe became deformed.

Furthermore, if the feedback control coefficient is set to an appropriate value for a portion with a large aspect ratio, the feedback control will easily oscillate in a portion with a small aspect ratio. Conversely, if the feedback control coefficient is made small so as not to oscillate in areas with a small aspect ratio, there is a problem in that the probe collides with the sample surface in areas with a large aspect ratio. Such problems not only cause observations with a scanning probe microscope to take longer than necessary, but also reduce the spatial resolution, accuracy, and credibility of microscopic images due to deformation of the tip of the probe. do.

In addition, in the case of STM, if a part of the sample surface is an insulating material due to dirt or oxidation, when the probe approaches the insulating material part, the tip of the probe will not touch the surface of the insulating material. Even when brought close, no tunneling current flows, so the probe is pressed against the sample, crushing the tip of the probe and losing high spatial resolution. In other words, since only a small portion of the sample surface is made of an insulating material, there is a problem in that the entire image cannot be observed stably.

The present invention was made to solve the above problems, and its purpose is to enable highly accurate images to be observed at high speed, and to provide a part of the sample surface that is physically convenient for observation. An object of the present invention is to provide a scanning probe microscope and a control method thereof, which allow proper observation of most other parts even if there are parts with bad properties.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the scanning probe microscope of the present invention includes a sample, a probe, and an in-plane direction of the sample surface between the sample and the probe. In a scanning probe microscope, the scanning probe microscope is comprised of a scanning control unit that scans and controls the relative position of the sample and the probe, and a feedback control unit that feedback controls the relative position of the sample and the probe in a direction perpendicular to the sample surface. , the scanning control section is characterized in that the scanning control section takes in a signal from the feedback control section and performs the scanning control in association with the signal.

[0012] Also, in order to achieve the above object,
In the scanning probe microscope control method of the present invention,
Scanning control and feedback control are digital controls, and when the absolute value of the feedback signal of the feedback control is a certain value or more, the scanning is temporarily stopped at the scanning point at that point, and the feedback control is continued, and the absolute value of the feedback signal is When the value becomes smaller than the certain value within a certain time or a certain number of times, the scanning point is advanced to the next scanning point, and the absolute value of the feedback signal is greater than or equal to the certain value for the certain period of time or a certain number of times. If the number of scans exceeds a certain value, the distance between the sample and the probe is temporarily increased, and the scanning point is advanced to the next scanning point.

[0013]

[Operation] In the scanning probe microscope and the control method thereof of the present invention, signals from the scanning control section and the feedback control section are connected, and when the absolute value of the feedback signal of the feedback control is large, the scanning speed is decreased, and the feedback signal is When the absolute value of is small, the scanning speed is increased, thereby changing the scanning speed in accordance with the aspect ratio of local irregularities on the sample surface. This reduces the time for image observation, and also covers the entire observation area.
Enables observation under conditions of appropriate feedback control.

[0014] Furthermore, if the absolute value of the feedback signal of the feedback control is equal to or greater than a predetermined value for a predetermined period of time or a predetermined number of times, it is determined that that portion has a property that is not convenient for observation; By skipping the measurement and proceeding to the next scanning point, the tip collides with the sample surface and avoids parts of the sample surface that are physically inconvenient for observation. Even if there are some areas, it is possible to properly observe most other areas.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. This example shows the configuration of STM, and this example includes 1 a sample, 2a a probe, 2b an XY
A Z-axis piezoelectric element, 3 a feedback control circuit, 4 a scanning waveform generation circuit, 5 a bias voltage generation circuit, and 6 a storage oscilloscope.

In the above, the bias voltage generation circuit 5 applies a bias voltage to the sample 1. In this state, when the tip of the probe 2a approaches the surface of the sample 1 by controlling the piezoelectric element 2b, a tunnel current flows between the sample 1 and the probe 2a.
The feedback control circuit 3 receives this signal. The feedback control circuit 3 uses a difference circuit to obtain a signal representing the difference between the tunnel current signal and a preset current value, and uses the feedback control result as a feedback signal to apply Z to the piezoelectric element 2b as a Z applied voltage signal. Output to terminal and storage oscilloscope 6. That is, the feedback signal, which is the difference between the tunnel current signal and the set current signal, is integrated with a preset time constant, a signal proportional to the feedback signal is added thereto, and the resulting signal is amplified and output as a Z applied voltage signal. The scanning waveform generating circuit 4 inputs the feedback signal from the feedback control circuit 3 and outputs X, Y sweep signals generated by a method described later to the X, Y application terminals of the piezoelectric element 2b. The storage oscilloscope 6 has a feedback control circuit 3
The Z applied voltage signal inputted from the scanning waveform generation circuit 4 is associated with the X, Y sweep signals inputted from the scanning waveform generation circuit 4, and the microscopic image is displayed as a three-dimensional figure or a gray scale diagram.

FIG. 2 is a block diagram of a part of the scanning waveform generating circuit 4 used in the above embodiment. In the figure, 8a is an input terminal, 8b is an output terminal, 9 is an absolute value circuit, 10 is a rectangular wave generation circuit, 11 is a code conversion circuit, and 12 is an addition/integration circuit.

In the above, the absolute value circuit 9 inputs the feedback signal of the feedback control circuit at the input terminal 8a, and outputs the absolute value of the feedback signal to the code conversion circuit 11. On the other hand, the rectangular wave generation circuit 10 generates a rectangular wave, and the sign conversion circuit 11 outputs a signal of the absolute value of the feedback signal having the opposite sign to the rectangular wave to the addition/integration circuit 12. This signal is added and integrated with the rectangular wave in the addition/integration circuit 12,
It is output as an X sweep signal from the output terminal 8b. The X sweep signal is also output to the rectangular wave generating circuit 10, and the rectangular wave generating circuit 10 inverts the sign of the generated rectangular wave when the X sweep signal reaches a specific value. When the absolute value of the feedback signal is large, the addition/integration circuit 12 cancels out the rectangular wave and integrates it, so the slope of the output X sweep signal becomes small; conversely, when the absolute value of the feedback signal is small, , the slope of the X sweep signal increases, so the scanning speed changes in a monotonically decreasing relationship with respect to the absolute value of the feedback signal of the feedback control. The same configuration may be used for the Y sweep signal by simply changing the integration time constant of the addition/integration circuit.

The operation and effects of the first embodiment configured as above will be described.

FIGS. 3(a), (b), and (c) are diagrams for explaining the operation, and show the relationship between the shape of the sample surface, the feedback signal of the feedback control, the X sweep signal, and the Z applied voltage signal. ing. When the sample has the shape shown in Figure 3(a),
The feedback signal of the feedback control is (b-1) in Fig. 3(b).
), the absolute value of the feedback signal increases and the slope of the X-sweep signal decreases in the part where the aspect ratio of the unevenness of the sample shape is high, so the X-sweep signal becomes (b- 2). Therefore, as a result of the feedback control, the Z applied voltage signal becomes as shown in FIG. 3(c), and has a smooth waveform regardless of local changes in the aspect ratio of the unevenness of the sample shape. Since the storage oscilloscope 6 displays the X sweep signal and the Z applied voltage signal in association with each other, it reproduces the image of the sample shape shown in FIG. 3(a). In this way, the feedback signal for feedback control changes depending on the local unevenness of the sample surface, so the scanning speed is reduced in areas with a large aspect ratio, and increased in areas with a small aspect ratio. , automatic change of scanning speed can be realized.

The above is an example using analog control, but even with the digital control configuration shown in FIG.
By rewriting the software executed in step 1, when the aspect ratio of the irregularities on the sample surface is large and the absolute value of the feedback signal is large, the scanning speed is reduced, and the aspect ratio is small and the absolute value of the feedback signal is small. Sometimes the speed of scanning can be increased.

As described above, the effect of being able to change the scanning speed according to the unevenness of the sample is that when a part of the sample has a large aspect ratio, the scanning speed for the small aspect ratio part is faster. This means that the time needed to observe the entire image is reduced. In addition, it is possible to avoid contact of the probe with the sample surface in areas with a large aspect ratio, and if the feedback control conditions are set appropriately for areas with a relatively small aspect ratio, it is possible to scan even areas with a large aspect ratio. Since the speed is reduced, it is possible to observe the entire sample under appropriate feedback control conditions, which increases the accuracy and credibility of the microscopic image.

Next, a second embodiment of the present invention will be explained.

FIG. 4 is a block diagram of the STM showing its structure. As components of this example, 1 is a sample, 2a
1 is a probe, 2b is an XYZ-axis piezoelectric element, 13a is a feedback control circuit, 13b is an A/D converter, 14a is an absolute value circuit, 14b is a threshold circuit, 14c is an AND circuit, 1
4d and 14e are triangular wave generation circuits, 14f and 14g are D/
15 is a bias voltage generation circuit, 16 is an interface, and 17 is a control computer.

In the above, sample 1, probe 2a, XYZ
The axial piezoelectric element 2b, the feedback control circuit 13a, and the bias voltage generation circuit 15 are the same as the sample 1, the probe 2a, the XYZ-axis piezoelectric element 2b, the feedback control circuit 3, and the bias voltage generation circuit 5 in FIG. 1 of Example 1 in this order. It has the following functions. The feedback control circuit 13a is
A Z applied voltage signal is output to the control computer 17 via the A/D converter 13b and the interface 16. The absolute value circuit 14a applies a low-pass filter to the feedback signal of the feedback control inputted from the feedback control circuit 13a, and then converts the signal into a signal having an absolute value. The threshold circuit 14b outputs a signal of 1 when the signal converted by the absolute value circuit 14a is below a certain threshold, and outputs a signal of 0 when the signal is above a certain threshold. The AND circuit 14c outputs the AND (logical product) of this 1 or 0 signal and the pulse signal inputted from the control computer 17 via the interface 16 to the triangular wave generation circuit 14d as a timing signal. The triangular wave generating circuit 14d is a circuit that generates a triangular wave as a digital signal when a pulse signal at a constant interval is input.Here, the triangular wave generating circuit 14d generates a triangular wave within the amplitude range only when receiving the timing signal pulse from the AND circuit 14c. Output the incremented X sweep signal to advance the scan to the next scan point. This amplitude and waveform increment are given in advance from the control computer 17 via the interface 16. The D/A converter 14f converts the digital X sweep signal into an analog signal and outputs it to the X application terminal of the piezoelectric element 2b. The triangular wave generating circuit 14d outputs a pulse signal to the triangular wave generating circuit 14e every round trip of the output waveform, so that the triangular wave generating circuit 14e and the D/A converter 14g transmit the Y sweep signal to the Y application terminal of the piezoelectric element 2b. Output to. The control computer 17 receives the Z applied voltage signal input from the feedback control circuit 13a via the interface 16,
The X and Y sweep signals inputted from the triangular wave generation circuits 14d and 14e are associated, and the microscopic image is displayed and stored as a three-dimensional figure or a gray scale diagram.

The operation and effect of the second embodiment configured as above will be described.

FIGS. 5(a), (b), (c), (d), (
e) is a waveform diagram for explaining the operation, and shows the relationship between the absolute value of the feedback signal of the feedback control, the output signal of the threshold circuit, the pulse signal, the timing signal, and the X sweep signal. When the absolute value of the feedback signal of the feedback control is shown by the solid line in FIG. 5(a) and the threshold value of the threshold circuit 14b is shown by the broken line, the output signal of the threshold circuit 14b is as shown in FIG. 5(b), and the timing signal obtained by ANDing this and the pulse signal from the control computer 17 with the pulse signal of FIG. 5(c) is as shown in FIG. 5(d). Become. At this time, the X sweep signal becomes as shown in Fig. 5(e), and when the absolute value of the feedback signal of feedback control is above a certain value, the scanning is temporarily stopped, and when the absolute value of the feedback signal becomes smaller than the certain value. The scan will proceed to the next scan point. In other words, scanning is stopped until the feedback control follows a portion of the sample shape with a large aspect ratio, and the data finally obtained is obtained when the absolute value of the feedback signal is sufficiently small.

This ensures that the Z applied voltage signal is collected under conditions in which the absolute value of the feedback signal is less than or equal to a certain value. This means that the accuracy of the obtained data is high. In addition, by making the distance between scanning points in the X direction sufficiently small and setting the feedback control system to a small value, the scanning speed can be adjusted to be slower in areas with a large aspect ratio and faster in areas with a small aspect ratio, depending on the local unevenness of the sample surface. In this way, automatic changes in scanning speed can be realized.

Next, a third embodiment of the present invention will be described.

FIG. 6 is a flowchart showing this embodiment. The second embodiment described above is an embodiment using a feedback control section using analog control and a scanning control section using digital control, but this embodiment uses D shown in FIG.
Even with an all-digital control configuration using the SP unit 21, D
This is an example in which a similar control method is realized by rewriting the software executed by the SP section 21. Figure 6 shows the DS
This is a flowchart of software executed by the P section 21, where I is a tunnel current signal value and Z is a Z applied voltage signal value. Ist is a value that feedback controls the probe in the Z direction so that the tunnel current remains constant at this value (I-I
st) becomes a feedback signal for feedback control. ΔI is a tolerance of the feedback signal, and F is a feedback control function for determining the Z applied voltage signal value from the feedback signal (I-Ist).

The DSP unit 21 inputs the tunnel current signal I as feedback control, substitutes I into a feedback control function F given in advance, calculates Z=F
(I-Ist) is output as a Z applied voltage signal. After that, scanning control is performed so that the absolute value of the feedback signal (I-Ist) is △I
If it is smaller, ie, the tunneling current is sufficiently close to the set current, the scan advances to the next scan point. If the absolute value of the feedback signal is larger than ΔI, it is determined that the aspect ratio of the unevenness on the sample surface is large, and feedback control is repeated at the same scanning point. Feedback control is repeated several times, and when the absolute value of the feedback signal becomes smaller than ΔI, scanning proceeds to the next scanning point.

For example, when the absolute value of the feedback signal of feedback control is as shown in FIG. 5(a), the X sweep signal becomes as shown in FIG. 5(e), and the absolute value of the feedback signal of feedback control is constant. When the absolute value of the feedback signal is greater than the fixed value, scanning is temporarily stopped, and when the absolute value of the feedback signal becomes smaller than a certain value, scanning is advanced to the next scanning point. In other words, scanning is stopped until the feedback control follows a portion of the sample shape with a large aspect ratio, and the data finally obtained is obtained when the absolute value of the feedback signal is sufficiently small.

In this way, it is guaranteed that the Z applied voltage signal is collected under conditions in which the absolute value of the feedback signal is less than or equal to a certain value, which means that the accuracy of the obtained data is high. Furthermore, by making the distance between the scanning points in the X direction sufficiently small and setting the feedback control coefficient to a small value, the scanning speed is slow in areas with a large aspect ratio and fast in areas with a small aspect ratio, depending on the local unevenness of the sample surface. In this way, automatic changes in scanning speed can be realized.

The effect of being able to change the scanning speed according to the unevenness of the sample is that if a part of the sample has a large aspect ratio, the scanning speed for the small aspect ratio part can be fast, so the image The total observation time is short. In addition, it is possible to avoid contact of the probe with the sample surface in areas with a large aspect ratio, and if the feedback control conditions are set appropriately for areas with a relatively small aspect ratio, it is possible to scan even areas with a large aspect ratio. Since the speed is reduced, it is possible to observe the entire sample under appropriate feedback control conditions, and the accuracy and credibility of the microscopic image can be improved.

Next, a fourth embodiment of the present invention will be described.

FIG. 7 is a flowchart of a method of feedback control and scanning control of a digital control STM showing an example thereof, and this example can also be realized with the configuration of the digital control STM shown in FIG. . In this embodiment, similarly to the third embodiment, calculations for feedback control and scanning control are performed by the DSP unit 21. In FIG. 7, I
is the tunnel current signal value, and Z is the Z applied voltage signal value. Ist is a value for feedback controlling the probe in the Z direction so that the tunnel current is constant at this value, and (I-Ist) is a feedback signal for feedback control. ΔI is the tolerance error of the feedback signal, m is the number of times the feedback signal is continuously greater than or equal to the tolerance error, n is the maximum number of times feedback control is repeated at the same scanning point, and ΔZ is the number of times that scanning is stopped when m is greater than or equal to n. This is a value added to the Z applied voltage signal in order to temporarily increase the distance between the sample and the probe when proceeding to the next scanning point. F is a feedback control function that determines the Z applied voltage signal value from the feedback signal (I-Ist).

As feedback control, the DSP section 21 first inputs the tunnel current signal I, substitutes I into a feedback control function F given in advance, calculates Z.
=F(I-Ist) is output as a Z applied voltage signal. From then on, all scanning is controlled, and if the absolute value of the feedback signal (I-Ist) is smaller than ΔI, that is, if the tunnel current is sufficiently close to the set current, scanning is advanced to the next scanning point. If the absolute value of the feedback signal is larger than ΔI, there is a possibility that the aspect ratio of unevenness on the sample surface is large, so feedback control is repeated at the same scanning point. When the feedback control is repeated several times and the absolute value of the feedback signal becomes smaller than ΔI, scanning proceeds to the next scanning point. If the absolute value of the feedback signal is larger than ΔI at the same scanning point for n times or more (for example, 2 times or more and 100 times or less), that part of the sample surface is covered with an insulating material. etc., it is determined that the scanning point is not suitable for observation, gives up on observation at that scanning point, outputs Z=Z+ΔZ as a Z applied voltage signal, pulls up the probe, and advances scanning to the next scanning point.

In this way, if there is a part of the sample surface that is not suitable for observation, such as an insulating material, it is possible to advance scanning to the next scanning point without pressing the probe against the sample until a current flows. I can do it. In addition, the measurement is slow in areas with a large aspect ratio, depending on the local unevenness of the sample.
It is possible to realize automatic changes in scanning speed, such as increasing speed in areas with small aspect ratios. Even if there is an insulating material on a part of the sample surface, the scanning can proceed to the next scanning point without crushing the tip of the probe. When performing STM observation under conditions in which particles are attached, it is possible to observe most of the conductive parts of the sample surface while maintaining high spatial resolution without crushing the tip of the probe. The effect of being able to change the scanning speed according to the unevenness of the sample is that if there is a part of the sample with a large aspect ratio, the scanning speed of the part with a small aspect ratio can be fast, making it easier to observe the entire image. The key is to have less time. In addition, it is possible to avoid contact of the probe with the sample surface in areas with a large aspect ratio, and if the feedback control conditions are set appropriately for areas with a relatively small aspect ratio, it is possible to scan even areas with a large aspect ratio. Since the speed is reduced, it is possible to observe the entire sample under appropriate feedback control conditions, which increases the accuracy and credibility of the microscopic image.

[0040] The above-mentioned embodiments of the present invention are based on S
The explanation was about TM, but the atomic force microscope (AF
Similar effects can be obtained by using similar configurations and controls for the feedback control section and scanning control section of other scanning probe microscopes such as M) and photon STM. Furthermore, in the embodiments of the present invention described above, the relative position of the sample surface in the in-plane direction between the sample and the probe is controlled by the scanning control unit driving the probe. Even when the scan control unit drives the sample to control the relative position in the in-plane direction of the sample surface between the sample and the probe, the same effect can be achieved by using the same configuration and control for the feedback control unit and scan control. That's what you get. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with the gist thereof.

[0041]

Effects of the Invention As is clear from the above explanation, according to the scanning probe microscope and its control method of the present invention, by changing the scanning speed according to the unevenness of the sample,
Even if there is a part of the sample with a large aspect ratio, the scanning speed of the part with a small aspect ratio can be increased.
The observation time for the entire image can be kept short. In addition, it is possible to avoid contact of the probe with the sample surface in areas with a large aspect ratio, and if the feedback control conditions are set appropriately for areas with a relatively small aspect ratio, the scanning speed can be increased even in areas with a large aspect ratio. Since the image size becomes smaller, it is possible to observe the entire sample under appropriate feedback control conditions, increasing the accuracy and credibility of the microscopic image.

[0042] Furthermore, if the absolute value of the feedback signal in feedback control is greater than or equal to a certain value for a certain period of time or a certain number of times, the distance between the sample and the probe is increased, and the scanning is repeated to the next scanning. By advancing to the point, even if there is a part of the sample surface that is physically inconvenient for observation, it can be seen from most other parts without crushing the tip of the sample and maintaining high spatial resolution. A proper microscopic image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a portion of the scanning waveform generation circuit used in the first embodiment.

[Fig. 3] (a), (b), and (c) show examples of the relationship between the shape of the sample surface and the feedback signal of the feedback control, the X sweep signal, and the Z applied voltage signal, showing the operation of the first embodiment. figure

[
FIG. 4 is a configuration diagram showing a second embodiment of the present invention

[Figure 5] (a
), (b), (c), (d), and (e) are the feedback signals of the feedback control indicating the operation of the second embodiment, the output signal of the threshold circuit, the pulse signal, the timing signal, and
Diagram showing an example of the relationship between sweep signals

FIG. 6 is a flowchart showing a third embodiment of the present invention.

FIG. 7 is a flowchart showing a fourth embodiment of the present invention.

[Figure 8] Configuration diagram of a conventional scanning tunnel microscope using digital control

[Figure 9] (a) and (b) are waveform diagrams showing the shape of the sample surface and an example of the X-sweep signal of a conventional scanning tunnel microscope.

[Explanation of symbols]

1... Sample, 2a... Probe, 2b... XYZ-axis piezoelectric element, 3...
Feedback control circuit, 4...Scanning waveform generation circuit, 5...
Bias voltage generation circuit, 6... Storage oscilloscope, 8a... Input terminal, 8b... Output terminal, 9... Absolute value circuit,
DESCRIPTION OF SYMBOLS 10... Rectangular wave generation circuit, 11... Code conversion circuit, 12... Addition/integration circuit, 13a... Feedback control circuit, 13
b...A/D converter, 14a...Absolute value circuit, 14b...Threshold value circuit, 14c...AND circuit, 14d, 14e...Triangle generation circuit, 14f, 14g...D/A converter, 15...Bias voltage generation circuit , 16...interface, 17...
Control computer, 18... Sample, 19a... Probe, 19
b...XYZ-axis piezoelectric element, 20a...A/D converter, 20b
~20e...D/A converter, 21...DSP section, 22...control computer.

Claims (4)

[Claims] 1. A scan control unit that scans and controls the relative position of the sample and the probe in the in-plane direction of the sample surface between the sample and the probe; In a scanning probe microscope, the scanning probe microscope is configured to include a feedback control section that performs feedback control of a relative position in a direction perpendicular to the sample surface, wherein the scanning control section takes in a signal from the feedback control section and controls the scanning in association with the signal. A scanning probe microscope that is characterized by the ability to: 2. In scan control, the scanning speed with respect to the relative position in the in-plane direction of the sample surface between the sample and the probe is determined by the relative position between the sample and the probe in the direction perpendicular to the sample surface. A method for controlling a scanning probe microscope, characterized in that the control method uses a function that uses a feedback signal as a parameter for feedback control of a position. 3. In the method for controlling a scanning probe microscope according to claim 2, when the scanning control is digital control and the absolute value of the feedback signal for performing feedback control is greater than or equal to a certain value, the scanning point at that time Control of a scanning probe microscope characterized in that scanning is temporarily stopped at and then the feedback control is performed, and when the absolute value of the feedback signal becomes smaller than the constant value, the scanning point is advanced to the next scanning point. Method. 4. A method for controlling a scanning probe microscope according to claim 2, wherein the scanning control and the feedback control are digital controls, and when the absolute value of the feedback signal of the feedback control is a certain value or more, the scanning at that point once stopping scanning at a point and continuing to perform the feedback control, and advancing the scanning point to the next scanning point when the absolute value of the feedback signal becomes smaller than the certain value within a certain time or a certain number of times; If the absolute value of the feedback signal is equal to or greater than a predetermined value for the predetermined time or a predetermined number of times, the distance between the sample and the probe is temporarily increased, and the scanning point is advanced to the next scanning point. A method for controlling a scanning probe microscope, characterized in that: