JPH06180227A - Scanning probe microscope apparatus - Google Patents

Abstract

PURPOSE:To achieve that a shape which is closer to an actual surface shape is displayed with high definition by a method wherein the influence of a frictional force is reduced and the problem of the hysteresis in the up-and-down direction of a piezoelectric body is eliminated. CONSTITUTION:On the basis of a signal from a cantilever displacement- measuring sensor 1, a piezoelectric-body tube scanner 4 is driven. A signal for X-Y scanning is input to a tube-scanner X-Y-Z drive circuit 10 from a computer 14, and the piezoelectric-body tube scanner 4 is scanned in the X-, Y- and Z-directions. When the scanner searches a measuring point, a Z-direction modulation control circuit 12 drives the piezoelectric-body tube scanner 4 by a Z-direction modulation drive circuit 11 in such a way that a sample is moved up and down according to a modulation signal. Then, the position in the Z- direction of a cantilever in its driving position is measured by the cantilever displacement-measuring sensor 1, and its signal is sent to, and processed by, the computer 14. By repeating this operation, data is taken into, and an AFM image is displayed on a monitor 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope apparatus such as an atomic force microscope capable of observing a sample with an accuracy of atomic size order.

[0002]

2. Description of the Related Art Conventionally, a scanning tunneling microscope (STM;
g Tunnering Microscope) In the technical field of equipment,
An atomic force microscope is a microscope that can observe insulative samples that cannot be measured with the accuracy of the atomic size order.
A technique relating to an (AFM; Atomic Force Microscope) device is proposed in Japanese Patent Laid-Open No. 62-130302.
This AFM device is positioned as one of the scanning probe microscopes, and in this AFM device, a cantilever having a sharp protruding portion at the free end, that is, a probe portion is opposed to and close to the sample, and the atom at the tip of the probe is located. The movement of the cantilever that is displaced by the interaction force acting between the sample and the sample atom is measured electrically or optically, and the sample is scanned in the XY direction to determine the positional relationship between the cantilever and the probe. By relatively changing, it is possible to three-dimensionally capture the unevenness information of the sample in the atomic size order. Here, this AFM device will be described in detail with reference to the conceptual diagram of FIG.

As shown in the figure, the sample 108 to be measured is placed on the piezoelectric tube scanner 101 for XYZ scanning fixed to the base 109, and the probe 104 at the tip of the cantilever 103 is brought very close to the sample 108. It is located at. Then, the semiconductor laser 105 and the lens 10
6, a two-divided photodiode 107, and a cantilever 1
An optical sensor for measuring displacement of a cantilever called an optical lever method is formed using the back surface of 03.

The measuring method in this AFM apparatus is "contact mode" and "non-contact mode".
Although a technique related to the above has been proposed, the most widely used measurement method at present is the “contact mode”. In this “contact mode”, the AFM signal is captured in a state where a repulsive force acts between the tip of the probe 104 and the sample 108, that is, in a region where the two are almost in contact with each other, so that high lateral resolution is obtained.

Further, in the scanning probe microscope apparatus,
Generally, a piezoelectric body is used to determine the positional relationship between the probe and the sample by XYZ.
By controlling and changing the direction, extremely high resolution is realized.

[0006]

However, when measuring in the above-mentioned "contact mode", a plurality of forces act on the probe at the tip of the cantilever, and therefore, the image when measured by the AFM device and other images such as STM. There is a difference in the image when measured with a scanning probe microscope such as an apparatus.
In the scanning probe microscope operated in the “contact mode”, when the piezoelectric tube scanner 101 is moved in the direction of S in the figure with the cantilever tip 102 fixed, the probe is in contact with the sample. At the tip of the needle 104, along with a force A acting as a repulsive force from the sample in the normal direction, a frictional force B due to friction with the sample acts in the lateral direction, that is, the sample surface direction because the scanning is performed, Also receives a force C from the probe. The frictional force is the main cause of the above-mentioned inconvenient phenomenon.

Further, the piezoelectric body used in the scanning probe microscope apparatus has a problem of hysteresis. That is, the hysteresis curve of this piezoelectric body is shown in FIG.
As shown in (a), regarding the hysteresis in the Z direction, when measuring a sample for a two-step grating, while performing servo control so that the interaction force between the probe and the sample becomes constant, When the probe is scanned so that it is orthogonal to the groove and the data is taken in, due to the hysteresis of the piezoelectric body, it appears that both sides of the groove, which should have been the same height, have different heights. Cause a problem.

That is, FIG. 7C shows the height profile of the AFM image when the sample of FIG. 7B is measured, but at the steps S1 and S3 which should originally have the same height, There is a problem that S3 is expressed higher.

The present invention has been made in view of the above problems, and an object thereof is to reduce the influence of frictional force,
By solving the problem of hysteresis in the vertical direction of the piezoelectric body, it is possible to display a shape closer to the actual surface shape with high accuracy.

[0010]

In order to achieve the above object, in the scanning probe microscope apparatus of the present invention, the probe portion at the tip of the cantilever and the surface of the sample to be measured are brought into close proximity or substantially in contact with each other, and both are relatively placed. While scanning in XY direction,
The displacement signal of the cantilever which is displaced according to the interaction force acting between the two, or the Z direction servo control signal for keeping the displacement or the contact pressure of the probe on the sample constant, is taken into the image processing device, In a scanning probe microscope apparatus that maps the displacement amount at each position of a scanning region, at the predetermined position on the surface of a measurement sample that is set in advance, the probe portion is provided in the Z direction which is a direction perpendicular to the XY scanning direction. Based on the Z-direction vibration control means that vibrates and changes the relative positional relationship with the sample, and the force curve signal at each position of the scanning region, the interaction force acting between the probe part and the sample at each position becomes constant. And a monitor means for monitoring the Z-direction servo control signal as the displacement information of the probe at the tip of the cantilever. To.

[0011]

That is, the scanning probe microscope apparatus of the present invention is
The Z-direction vibration control means vibrates and changes the relative positional relationship between the probe portion and the sample in the Z direction, which is a direction perpendicular to the XY scanning directions, at a predetermined position on the surface of the measurement sample that is preset. Based on the force curve signal at each position of the scanning region, the monitor means outputs the Z direction servo control signal when the interaction force acting between the probe portion and the sample at each position becomes constant to the tip of the cantilever. The displacement information of the probe is monitored.

[0012]

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

FIG. 1 is a diagram showing the configuration of a scanning probe microscope apparatus according to an embodiment of the present invention. In this example,
At the point of data acquisition, the probe is moved vertically in the sample surface so that the force applied in the lateral direction is released, and the data is acquired point by point.

As shown in the figure, in the scanning probe microscope apparatus according to the present embodiment, a cantilever displacement measuring sensor 1, a cantilever 2, a piezoelectric tube scanner 4, and Z.
The direction coarse movement stage 7 and the microscope casing 8 are integrally provided. Then, the cantilever displacement measuring sensor 1
Is connected to the scanning control circuit 13, and the scanning control circuit 13 is connected to the Z direction modulation control circuit 12 and the servo control circuit 9.

Further, the Z-direction modulation control circuit 12 is connected to the drive electrode 5 of the piezoelectric tube scanner 4 through the Z-direction modulation drive circuit 11, and the servo control circuit 9 connects the XYZ drive circuit 10. It is connected to the drive electrode 6 through. The servo control circuit 9 and the Z-direction modulation control circuit 12 are each connected to a computer 14, and the computer 14 is connected to a display monitor 15, a scan control circuit 13, and an XYZ drive circuit 10. .

In such a configuration, during scanning between predetermined measuring points, the signal from the cantilever displacement measuring sensor 1 is input to the servo control circuit 9 via the scanning control circuit 13, and the tube scanner XYZ drive circuit 10 is supplied. The piezoelectric tube scanner 4 is driven in the Z direction via.
When the basic signal for XY scanning is output from the computer 14, it is input to the tube scanner XYZ drive circuit 10 to scan the piezoelectric tube scanner 4 in the XY directions.

Further, the timing at which the measurement point is reached is transmitted from the computer 14 to the scan control circuit 13, and XY
The scanning of the direction is stopped while maintaining its position, and the signal flow is switched as follows. That is, when the measuring point is reached, the signal from the cantilever displacement measuring sensor 1 is switched so as to flow to the Z-direction modulation control circuit 12 where it was previously connected to the servo control circuit 9 side in the scanning control circuit 13. To be

The Z-direction modulation control circuit 12 incorporates a modulation signal generation circuit and a data acquisition point determination circuit, which are not shown, and the sample is output in accordance with the modulation signal until the end of the data acquisition is determined. The piezoelectric tube scanner 4 is driven by the Z direction modulation drive circuit 11 so as to move up and down.
Are driven in the Z direction. At this time, as the data acquisition point determination circuit, for example, a circuit for differentiating the force curve signal to detect a signal rise is used.

When the data acquisition point is determined in this way, the displacement or position of the cantilever in the Z direction at that position is measured by the cantilever displacement measuring sensor 1, and the signal is not used for servo control, but the computer 14 And processed to construct an image. After this scanning is completed, the computer 14 is again activated.
Based on the signal from, the scan control circuit 13 returns to the state immediately before the previous servo control is turned off, and switches to start XY scanning and servo control. The above operation is repeated to capture the data and finally display the AFM image on the monitor 15. Next, the operation of the tip of the probe of the scanning probe microscope of this embodiment will be described in more detail. First, the first measurement operation will be described with reference to the drawings. FIG. 2B is a diagram showing a trajectory S2 of the movement of the tip of the probe 16 with respect to the surface of the sample 3 when the measurement is performed according to the present embodiment.

As is clear from comparison with the locus S1 of the movement of the probe of the conventional scanning probe microscope shown in FIG. 2A for comparison, the operation of the probe 16 at the initial stage of measurement is The probe 16 approaching / contacting with is scanned laterally so as to trace the sample shape with the start of measurement. At this time, feedback servo is applied by the servo circuit so that the contact pressure or the needle pressure at which the probe 16 contacts the sample 3 becomes constant. That is, the displacement of the cantilever with the probe 16 is measured by using an optical displacement measuring means or the like, and the sample table or the like is moved up and down so that the signal becomes constant. Then, when the first measurement point a1 is reached, the scanning of the probe in the lateral direction is stopped and the feedback servo for keeping the stylus pressure constant is also stopped, and then the probe 16 or the sample 3 is perpendicular to the scanning direction. Up and down. That is, the force curve is taken at the measurement point a1. This force curve is obtained when the probe 16 or the sample 3 is moved up and down.
6 shows the deflection signal of the cantilever 2 obtained from the displacement measuring means of the cantilever 2 with respect to the distance between 6 and the sample surface, and FIGS. 3 (a) and 3 (b) show typical force curves measured in a liquid. 3 (c) and 3 (d) show typical force curves measured in the atmosphere. The vertical axis represents the amount of displacement of the cantilever, and the horizontal axis represents the amount of displacement of the actuator that adjusts the distance between the cantilever and the sample.

In FIG. 3, a voltage signal applied to the piezoelectric tube scanner at the bending point of the force curve indicated by "2" is taken into the computer 15. The detection of the bending point can be easily performed by passing the force curve signal through the differentiating circuit. Further, if the point of taking in the voltage signal applied to the piezoelectric tube scanner is set between "2" and "3" in the figure, data at a predetermined contact pressure will be taken, and the setting is not necessarily "2". It doesn't have to be a point. In an apparatus called an atomic force microscope, this contact pressure is 10 ^-6 to 10 ^-11. It is set to about N. In this way, when this detection is completed, feedback servo is applied again, the stylus pressure is made constant, and scanning is performed up to a2 in FIG.

Then, when reaching the new data acquisition point a2, similarly, the scanning of the probe 16 is stopped, the feedback servo is also stopped, and the probe 16 or the sample 3 is vertically moved up and down to acquire the data. Then, it moves to the next measurement point a3 and repeats the above operation. still,
The locus of the tip of the probe at this time is as shown in FIG.

Then, for example, the data of one line is 128
In the case of expressing with points, this is repeated 128 times per line, and scanning is performed for XY raster scanning to 128 times.
Data of x128 points is taken in and imaged on the screen of the computer 14. As described above, in the first measurement operation, the influence of the frictional force at each point is eliminated, and the shape closer to the actual sample surface can be imaged. In addition to the first measurement operation, various measurement operations can be considered.

For example, as shown in FIG. 2D, a method may be considered in which feedback servo is not applied between measurement points and scanning is performed up to the next measurement point and the measurement point is moved up and down in the Z direction. In this case, a high frequency component near the resonance frequency of the cantilever may be further superimposed on the locus shown in FIG. 2 (d) (FIG. 2 (e)). The amplitude of the high frequency component at that time is preferably about 1 nm to 500 nm at a position away from the sample.

Alternatively, in the third measurement operation shown in FIG. 4, the probe is moved up and down only at the measurement point in the first and second measurement operations, whereas the probe 16 is moved up and down as shown in FIG. Is moved like a sawtooth wave, and when the probe 16 comes into contact with the sample 3, the data is captured. In this measurement operation, the distance between the probe and the sample, which is separated from each position such as the positions a to d where the probe comes into contact with the sample, that is, the distance between the measurement point and the next point, is a constant value D. Unlike the first measurement operation in which the feedback servo is applied, the feedback servo is not applied between the measurement points. As described above, according to the third measurement operation, the scanning speed can be increased by moving like a sawtooth wave.

Further, in the fourth measuring operation shown in FIG. 5, the motion of the probe is made like a cycloid curve to smooth the motion. The part above the partial dotted line indicated by S in the same figure is a cycloid curve, and the part indicated by L below that is a part which is linearly connected smoothly to the upper part. The positions e to g that move linearly are the measurement points. As described above, according to the third measurement operation, since there is no place where the change is abrupt, the influence of vibration is reduced.

As described above in detail, according to the present invention, the influence of the frictional force is eliminated, so that it is possible to form one image without line skipping even if data is fetched and displayed both on the way back and forth. However, in this case, when the piezoelectric tube scanner is used to scan the sample, it is premised that a means for correcting the hysteresis in the XY directions is taken.

Further, in the measuring method of the present invention, the measuring environment such as the atmosphere, the gas atmosphere, the liquid or the vacuum can be selected, but the force when the force curve is measured can be controlled because the control of the probe operation becomes simple. It is especially effective when the curve is applied to the measurement in a liquid in which a hysteresis due to contamination of water on the sample surface does not occur. For example, FIG. 8 is a diagram showing how to perform measurement in a liquid according to the present invention.

In the figure, the measuring cell 113 in the liquid is shown.
The sample 108 is immersed in a liquid such as water 114 by the upper surface of the piezoelectric tube scanner 101 and the O-ring 115. In the figure, the state where water 114 has already been injected is shown. In this example, the piezoelectric body 112 for Z-direction modulation is provided close to the Z-direction modulation cantilever.

It is needless to say that the scanning probe microscope of the present invention is not limited to the above embodiment, and various improvements and changes can be made. For example, the torsion of the cantilever may be monitored instead of utilizing the displacement of the cantilever in the cantilever axial direction in order to monitor the force applied to the probe.

[0031]

According to the present invention, by reducing the influence of frictional force and eliminating the problem of hysteresis in the vertical direction of the piezoelectric body, it is possible to display a shape closer to the actual surface shape with high accuracy. A scanning probe microscope capable of being provided can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a scanning probe microscope apparatus according to an embodiment of the present invention.

2A to 2D are diagrams showing a first measurement operation of the scanning probe microscope apparatus according to the embodiment.

3A and 3B are force curves in a liquid,
(C) And (d) is a figure which shows the force curve in the atmosphere.

FIG. 4 is a second example of the scanning probe microscope apparatus according to the embodiment.
It is a figure which shows the measurement operation of.

FIG. 5 is a third view of the scanning probe microscope apparatus according to the embodiment.
It is a figure which shows the measurement operation of.

FIG. 6 is a conceptual diagram of a conventional AFM device.

FIG. 7A is a diagram for explaining hysteresis of a piezoelectric body, and FIGS. 7B and 7C are diagrams for explaining influence of hysteresis.

FIG. 8 is a diagram showing how a measurement in a liquid is performed by the scanning probe microscope apparatus of the present invention.

[Explanation of symbols]

1 ... Cantilever displacement measuring sensor, 2 ... Cantilever,
3 ... Sample, 4 ... Piezoelectric tube scanner, 5, 6 ... Drive electrode, 7 ... Z direction coarse movement stage, 8 ... Housing, 9 ... Servo control circuit, 10 ... XYZ drive circuit, 11 ... Z direction modulation drive circuit , 12 ... Z-direction modulation control circuit, 13 ... Scan control circuit, 14 ... Computer, 15 ... Monitor, 16 ... Probe.

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[Procedure amendment]

[Submission date] January 29, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

[Procedure amendment]

[Submission date] July 20, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

2A to 2E are diagrams showing a first measurement operation of the scanning probe microscope apparatus according to the embodiment.

Claims (1)

[Claims] 1. A cantilever which is displaced in accordance with an interaction force acting between them while the probe portion at the tip of the cantilever and the surface of the sample to be measured are brought into close proximity or almost in contact with each other while relatively scanning them in the XY directions. The displacement signal, or the Z-direction servo control signal for keeping the displacement or the contact pressure of the probe on the sample constant, is fetched into the image processing device,
In a scanning probe microscope apparatus for mapping the displacement amount at each position of a scanning site, at the predetermined position on the surface of a measurement sample which is set in advance, the probe portion is also provided in the Z direction which is a direction perpendicular to the XY scanning direction. Z for changing the relative positional relationship with the sample by vibration
Based on the directional vibration control means and the force curve signal at each position of the scanning region, the Z-direction servo control signal when the interaction force acting between the probe portion and the sample at each position becomes constant is described above. A scanning probe microscope apparatus, comprising: a monitor unit that monitors displacement information of the probe section at the tip of the cantilever.