JPH05296711A - Probe jogging mechanism - Google Patents

Abstract

PURPOSE:To reduce the effect of creep action generated with a plane scanning piezoelectric element on a measurement image, regarding the probe jogging mechanism of a scanning type tunnel microscope or the like. CONSTITUTION:This mechanism is constituted of two piezoelectric elements 3a and 3b corresponding to first and second axes orthogonal with each other for undertaking plane scanning with a probe 1 via the expansion and contraction of the elements 3a and 3b due to voltage application. In addition, the constitution is so made that rated voltage is applied to the elements 3a and 3b in such a way as generating the maximum stroke thereof almost free from creep in non-scanning state prior to the start of plane scanning operation. Also, the constitution is so made as to apply voltage causing the maximum stroke of the elements 3a and 3b determined by the predetermined scanning area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine needle movement mechanism, and more particularly to a fine needle movement mechanism suitable for a scanning tunneling microscope or the like used for measuring an atomic level fine object.

[0002]

2. Description of the Related Art A fine probe mechanism of a scanning tunneling microscope is usually constructed by using a piezoelectric element. According to the scanning tunneling microscope, it is possible to measure the uneven shape of the atomic level dimension on the sample surface. In this measurement, the probe moves so as to trace the uneven shape of the sample surface. At this time, the Z-direction piezoelectric element in the fine movement mechanism moves the probe so as to keep the interval between the probe and the sample surface constant. Move it in the height direction.

Various types of fine movement mechanisms have been proposed in the past. Generally, a tripod type fine movement mechanism in which rod-shaped piezoelectric elements are arranged in each of three axial directions of X, Y and Z orthogonal to each other is used.
According to this fine movement mechanism, when the piezoelectric element expands and contracts in each of the X and Y directions, the sample surface is scanned in a rectangular area with one side of about 10 μm, and the piezoelectric element expands and contracts in the Z direction to expand the probe and the sample surface. Adjust so that the interval is constant.

[0004]

The piezoelectric element used in the fine movement mechanism has the following problems. The piezoelectric element has the property of being distorted according to the applied voltage. By applying the required voltage, the piezoelectric element can be extended to obtain the required length. By reducing the applied voltage, the piezoelectric element contracts, reducing its length.

By the way, an example of the relationship between the applied voltage and the strain (expansion / contraction length) in the piezoelectric element is shown in the graph of FIG. Although this drawing is used in the description of the embodiments of the present invention, it will be referred to in order to explain the problem in the characteristics of the piezoelectric element. In the graph of FIG. 2, the horizontal axis represents the applied voltage, and the applied voltage increases toward the right. The vertical axis represents the strain amount, and the strain amount increases in the upward direction. As is apparent from the graph, the strain amount is 0 when the applied voltage is 0 initially. When the applied voltage is gradually increased from 0 to the rated voltage that achieves the maximum strain amount, the strain amount changes from the origin O to increase according to the change characteristic A.
The maximum stroke (extension amount) occurs at point a corresponding to the rated voltage. Next, when the applied voltage is gradually reduced from the rated voltage, the amount of strain decreases according to the change characteristic B. When the applied voltage is 0, it moves to the position of point b. In this case, the amount of strain is different when compared with the first applied voltage of 0, and the amount of strain is not completely zero. However, the amount of distortion becomes 0 with the passage of time. That is, the transition is made from the point b to the origin O.
When the applied voltage is changed from 0 to the rated voltage again before such a transition occurs, the strain amount changes according to the change characteristic C. Furthermore, in the same manner as above, the applied voltage is 0 from the rated voltage.
When it is changed to, the distortion amount changes according to the change characteristic D so as to move to the point c.

As described above, between the applied voltage and the strain amount in the piezoelectric element, there is a hysteresis characteristic that the change characteristics of the strain amount are different in the increasing direction and the decreasing direction of the applied voltage. Further, when the applied voltage is repeatedly increased and decreased, the change characteristic has a characteristic that the amount of strain gradually increases. Creep characteristics are characteristics that change and the amount of strain decreases when the applied voltage is held constant for a predetermined time. In the creep characteristics, the change in strain is particularly remarkable when the applied voltage is 0, but it also occurs at other intermediate points, for example, point d. That is, as time passes, point d changes to point e. In other words, the creep phenomenon is such that the change characteristic of the strain amount corresponding to the applied voltage changes in the direction in which the strain amount increases when the applied voltage is repeatedly increased and decreased, and the strain amount decreases when the applied voltage is kept constant. It is a phenomenon that changes in the direction of.

[0007] In the measurement by the scanning tunneling microscope, the creep characteristic of the piezoelectric element has a great influence on the measurement data as follows.

As described above, the probe is composed of the X-direction piezoelectric element and the Y-direction.
The rectangular piezoelectric element on the sample surface is scanned by the directional piezoelectric element. In this plane scanning, a rectangular area 31 is set on the sample surface as shown in FIG. 6 (A). FIG. 6A shows a partial surface of the sample, and the vertical line 32 shows an example of a pattern on the sample surface. In the rectangular area 31, the horizontal axis means the X axis and the vertical axis means the Y axis. In order to scan the rectangular area 31 in a plane, a driving voltage is applied to each of the X-axis direction piezoelectric element and the Y-axis direction piezoelectric element as shown in FIG. The magnitude of the voltage applied to each piezoelectric element is determined corresponding to the scanning area. A triangular wave voltage is applied to the X-axis direction piezoelectric element to repeat the reciprocating movement. A step-like voltage is applied to the Y-axis direction piezoelectric element in order to move the position at a constant distance corresponding to each of the triangular wave voltages. The applied voltage starts from 0 for both piezoelectric elements. In this way, the probe scans the rectangular area 31 in a plane by the piezoelectric elements in the X and Y directions.

However, since the piezoelectric element has creep characteristics, the creep phenomenon occurs in the piezoelectric element in the X-axis direction immediately after the start of scanning, and the accuracy of the measurement data deteriorates. In the conventional control method, the initial value of the applied voltage to the piezoelectric element is 0, and the range of the applied voltage uses the voltage region in which creep is particularly remarkable. As a result, as shown in FIG. 6B, the image portion 34 measured immediately after the scanning of the measurement image 33 starts to be disturbed occurs.

The above-mentioned problems similarly occur in other types of probe fine movement mechanisms.

An object of the present invention is to provide a fine movement mechanism of a probe, such as a scanning tunneling microscope, in which the creeping effect of a piezoelectric element is less likely to affect the measurement image.

[0012]

A probe fine movement mechanism according to the present invention has two piezoelectric elements respectively corresponding to a first axis and a second axis which are orthogonal to each other, and a voltage is applied to each of these piezoelectric elements. It is configured to perform planar scanning of the probe by applying and expanding and contracting it, and at the time of non-scanning before starting the planar scanning,
The two piezoelectric elements are configured to be applied with a rated voltage that causes a maximum stroke in which almost no creep occurs.

The probe fine movement mechanism according to the present invention has two piezoelectric elements respectively corresponding to the first axis and the second axis which are orthogonal to each other, and a voltage is applied to each of these piezoelectric elements to expand and contract. Is configured to perform flat scanning of the probe with
Further, during non-scanning before starting the planar scanning, a voltage that causes a maximum stroke determined by the set scanning region is applied to the two piezoelectric elements. This voltage is a voltage that keeps the probe in the scanning area and corresponds to a location in the scanning area where creep is least generated.

[0014]

According to the present invention, when the scanning tunneling microscope or the like is used to start the measurement, when the probe is made to scan the surface area to be measured in the plane, two piezoelectric elements related to the plane scan during the non-scan before the start of the plane scan. Apply the rated voltage to the device. This rated voltage sets the piezoelectric element to a maximum stroke, so that the piezoelectric element is held in a state where almost no creep occurs. Therefore, when the plane scanning is started for the measurement, the plane scanning is started from the state in which the rated voltage is applied, so that the plane scanning can be stably performed immediately after the measurement is started without being affected by the creep.

When the region to be measured is a limited region, the applied voltage corresponding to the portion where the degree of creep generation is smallest in the measurement region is applied to the piezoelectric element instead of the rated voltage. Also in this case, the influence of creep can be reduced immediately after the start of measurement.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the basic structure of a scanning tunneling microscope, and schematically shows a fine movement mechanism of a probe of the scanning tunneling microscope, a control mechanism for controlling its operation, and a signal processing mechanism. In this embodiment, a fine movement mechanism of a probe applied to a scanning tunneling microscope will be described. The probe fine movement mechanism includes its control mechanism.

The tip 1 of the probe 1 is vertically arranged with its tip facing the measurement surface of the sample 2. The probe 1 is fixed to the three-dimensional piezoelectric actuator 3. The actuator 3 has X, Y,
It has piezoelectric elements 3a, 3b, 3c in the respective Z-axis directions. The probe 1 is attached to a vertical intersection of the three piezoelectric elements 3a to 3c. The piezoelectric elements 3a and 3b are driving means for performing XY scanning (planar scanning) of the probe 1 along the surface of the sample 2. The piezoelectric element 3c is a Z-direction driving unit for adjusting the distance (height) between the probe 1 and the surface of the sample 2 by changing the position of the probe in the Z direction.

A power source 4 is connected between the probe 1 and the sample 2, and when the distance between the probe 1 and the sample 2 approaches within a predetermined range, a tunnel current flows between the probe and the sample. Is composed of. When the probe 1 approaches the surface of the sample 2 at a distance as large as the atomic level, a tunnel current flows between them. This phenomenon occurs based on the tunnel phenomenon caused by the quantum effect. The adjustment of the distance between the probe 1 and the surface of the sample 2 is performed by the expansion / contraction operation of the piezoelectric element 3c described above. The amount of expansion / contraction of the piezoelectric element 3c is determined by the voltage applied to the piezoelectric element 3c. The voltage applied to the piezoelectric element 3c is given from the servo circuit 5.

In the measurement operation of the scanning tunneling microscope, the distance between the probe 1 and the sample 2 is first set to a constant distance (set based on the magnitude of the tunnel current), and the probe 1 is scanned. By detecting the tunnel current and holding the tunnel current constant, the piezoelectric element 3 is held so that the distance between the probe 1 and the sample 2 is held at the above-mentioned constant distance.
Servo control c. By doing so, the probe 1 moves by tracing the atomic level unevenness on the surface of the sample 2, so that the unevenness of the sample surface can be measured based on the control data for moving the probe 1. .. In FIG.
Reference numeral 6 denotes a tunnel current detection / distance conversion circuit having a function of detecting and amplifying a tunnel current and further converting the current value into a distance (voltage value). The signal output from the tunnel current detection / distance conversion circuit 6 is given to the servo circuit 5. The servo circuit 5 sets a voltage for determining the movement of the probe 1 so that the output signal of the tunnel current detection / distance conversion circuit 6 has a predetermined constant value, and supplies the voltage to the piezoelectric element 3c.

Reference numeral 7 is a piezoelectric element 3 for scanning the probe 1.
It is an XY scanning circuit that controls the operations of a and 3b.

For the purpose of causing the probe 1 to perform a measurement operation, the expansion / contraction operation of the piezoelectric elements 3a to 3c is controlled. At this time, the Z direction control data generated by the servo circuit 5 and the X and Y direction control data generated by the XY scanning circuit 7 are supplied to and stored in the memory 8. The control data for performing the measurement operation of the probe 1 stored in the memory 8 becomes the measurement data representing the uneven shape of the sample surface as it is. This measurement data is data-processed by the signal processing circuit 9, and the image of the measured sample surface is displayed on the screen of the display device 10 based on the image data created thereby.

Next, piezoelectric elements 3a and 3b for plane scanning.
The operation control of will be described.

When the probe 1 is scanned in a plane on the measurement surface of the sample 2, the expansion and contraction operations of the piezoelectric elements 3a and 3b are controlled at predetermined timings. The plane scanning by the expansion / contraction operation of the piezoelectric elements 3a and 3b is performed based on the scanning signal given from the XY scanning circuit 7. The scanning signal from the XY scanning circuit 7 is generated based on the control command given from the computer 11.

FIG. 2 shows the relationship between the applied voltage and the amount of strain in the piezoelectric element. As is apparent from FIG. 2, in the piezoelectric element, when the first applied voltage is 0 and the applied voltage is repeated between the voltage 0 and the rated voltage, the change characteristics A, B, C, D follow the order. The amount of strain changes according to the applied voltage. In the change characteristic of FIG. 2, the creep characteristic occurs as described above except the point a. In the change characteristic, the creep phenomenon occurs small in the region near the point a corresponding to the rated voltage and large in the region corresponding to zero voltage. When performing a plane scan by the conventional fine movement mechanism of the probe, the applied voltage is usually 0 in the initial state of the piezoelectric elements 3a and 3b.
Was set to. As shown in FIG. 2, the region where the voltage is 0 is a region where large creep occurs. Therefore, when performing the plane scan by the conventional fine movement mechanism, a large amount of creep is likely to occur in the piezoelectric elements 3a and 3b that perform the plane scan, and the measured image is greatly affected by the creep immediately after the start of measurement, and the position due to the creep characteristic is increased. There was a gap.

Therefore, in the present embodiment, in order to reduce the influence of creep in planar scanning as much as possible, planar scanning is performed by applying a voltage to the piezoelectric element 3a in the X direction and the piezoelectric element 3b in the Y direction to expand and contract. In this case, the piezoelectric elements 3a and 3b are set to have a rated voltage applied thereto before the start of the plane scanning. The applied voltage does not have to exactly match the rated voltage. A voltage close to the rated voltage is sufficient.

As described above, if the rated voltage is applied to each of the piezoelectric elements 3a and 3b during the non-scanning before the start of the plane scanning, when the plane scanning is started, the stable state shifts relatively quickly. The effect of creep can be reduced.

FIG. 3 shows, as a hardware configuration, an apparatus configuration for setting the applied voltage to the piezoelectric elements 3a and 3b to the rated voltage before the plane scanning is started as described above. This configuration is included in the XY scanning circuit 7. According to this configuration, the set command given from the computer 11 is sent to the D / A converter 12
Is converted into an analog voltage signal by the buffer amplifier 13, amplified by the buffer amplifier 13, and supplied to each of the piezoelectric elements 3a and 3b.

The fact that the rated voltage is applied to each of the piezoelectric elements 3a and 3b before the start of the plane scanning means that each piezoelectric element is in the state of the maximum stroke. Therefore, since the planar scanning is started in such a state, the scanning is started in the direction in which the distortion amount of the piezoelectric element decreases, that is, in the contracting direction. It is also possible to temporarily set each of the piezoelectric elements 3a and 3b in the maximum stroke state to the minimum stroke state, increase the applied voltage before the occurrence of creep, start scanning, and perform planar scanning. The control of the expansion / contraction operation of the piezoelectric elements 3a and 3b for plane scanning is executed based on the control command supplied from the computer 11. The contents of control of the expansion / contraction operation of the piezoelectric elements 3a and 3b are set inside the computer 11 by software.

FIG. 5 shows piezoelectric elements 3a and 3b for XY plane scanning.
2 shows the scannable range by. Rectangular area 14
Is an area representing the scannable range. In the rectangular area 14, the horizontal axis is the X axis and the vertical axis is the Y axis. In the case of the above-described embodiment, since the rated voltage is applied to the piezoelectric elements 3a and 3b at the time of starting the planar scanning, the probe 1 is determined in the region 14 corresponding to the maximum stroke of each of the piezoelectric elements 3a and 3b. Exists at point Q. Similarly, at the point O, the applied voltage to the piezoelectric elements 3a and 3b is 0, at the point P, the applied voltage to the piezoelectric element 3a is the rated voltage, and the applied voltage to the piezoelectric element 3b is 0, R.
At this point, the applied voltage to the piezoelectric element 3a is 0, and the applied voltage to the piezoelectric element 3b is the rated voltage.

Next, another embodiment concerning the setting of the applied voltage before the start of the planar scanning of the XY scanning piezoelectric elements 3a and 3b will be described.

In the measurement by the scanning tunneling microscope, the measurement area on the surface of the sample 2 can be arbitrarily set within the scannable range 14. In other words, the scan area to be measured in the scannable range 14 is set arbitrarily. In FIG. 5, reference numeral 15 indicates a set scanning area. In this way, the scanning area 1 to be measured is
When 5 is set as a partial area of the scannable range 14, it is not necessary to apply the rated voltage to each of the piezoelectric elements 3a and 3b to set the maximum stroke as in the above-described embodiment. That is, in the scanning area 15, the piezoelectric element 3a, the probe 1 is arranged so that the probe 1 exists at the point S closest to the point Q.
The applied voltage of 3b can also be set. This S point is
When the scanning area 15 is scanned by the piezoelectric elements 3a and 3b, it is determined by the maximum applied voltage of each of the X and Y axes. In this way, when the applied voltage to the piezoelectric elements 3a and 3b during the non-scanning before the start of the plane scanning is set, the scanning operation can be smoothly performed in a short time because the probe 1 exists in the scanning region 15. Also, the influence of creep can be minimized.

In order to realize the above embodiment, the control command given from the computer 11 in FIG.
It is sufficient to support the maximum applied voltage of each axis in the scanning area 15.

[0034]

As is apparent from the above description, according to the present invention, in a fine movement mechanism of a probe such as a scanning tunneling microscope, two piezoelectric elements that perform planar scanning are used for non-scanning before the start of planar scanning. Since the voltage corresponding to the state in which the creep phenomenon is small is applied, the measurement can be performed in the stable state in which the influence of creep is reduced immediately after the start when the measurement is performed after the plane scanning is started. You can
It is possible to obtain a measurement image with good accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a probe fine movement mechanism of a scanning tunneling microscope showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an applied voltage and a strain amount in a piezoelectric element.

FIG. 3 is a circuit configuration diagram showing a configuration for applying a predetermined voltage to a piezoelectric element.

FIG. 4 is an explanatory diagram showing a relationship between a scannable range and a scan area and a voltage applied to a planar scanning piezoelectric element.

FIG. 5 is a graph showing change characteristics of each voltage applied to two piezoelectric elements for plane scanning.

FIG. 6 is a diagram showing a relationship between a measurement surface of a sample to be measured and a measurement image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe 2 ... Sample 3 ... Three-dimensional piezoelectric actuator 3a, 3b ... Planar scanning piezoelectric element 3c ... Height adjustment piezoelectric element

Claims (2)

[Claims] 1. A probe having two piezoelectric elements respectively corresponding to a first axis and a second axis which are orthogonal to each other, and applying a voltage to each of these piezoelectric elements to perform planar scanning of a probe by its expanding and contracting operation. The fine needle movement mechanism includes a voltage applying unit that applies a voltage that causes a maximum stroke to the two piezoelectric elements during non-scanning before starting the plane scanning. 2. A probe having two piezoelectric elements respectively corresponding to a first axis and a second axis which are orthogonal to each other, and applying a voltage to each of these piezoelectric elements to perform planar scanning of a probe by its expanding and contracting operation. The fine needle movement mechanism is provided with a voltage applying unit that applies a voltage that causes a maximum stroke determined by a set scanning region to the two piezoelectric elements during non-scanning before starting the planar scanning. Fine movement mechanism of the probe.