JPH05306925A - Interatomic force microscope - Google Patents

Abstract

PURPOSE:To obtain an interatomic force microscope which is simplified in the structure of a displacement measuring system for detecting the displacement of a probe and which can perform highly accurate measurement. CONSTITUTION:This microscope holds a probe 4 on a cantilever 20 and is equipped with a displacement measuring means 22 which measures the displacement of the cantilever 20. The means 22 measures an interatomic force from the displacement of the cantilever 20 and, at the same time, detects a fine shape on the surface of an object S to be measured by scanning the surface of the object S while the interatomic force is maintained constant. The means 22 is constituted of a piezo-electric thin film 22A covering the rear of the cantilever 20.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an atomic force microscope.

[0002]

2. Description of the Related Art As an ultra-precision surface roughness meter, a scanning tunneling microscope (ST) is used.
M) is being put to practical use. This STM is a microscope that utilizes the fact that the value of the tunnel current flowing between the sample surface and the probe correlates with the distance between the sample surface and the probe.

However, this STM cannot be measured unless a tunnel current flows between the sample surface and the probe. That is, measurement cannot be performed unless the sample surface is a conductor. Of course,
The sample to be actually measured includes not only a conductor but also a nonconductor, and a microscope capable of reliably measuring the surface of a nonconductor with a resolution of several nm is desired.

Using the STM technique, an SXM (S
There is a microscope called canning X Microscope. Here, the local information X is force, light, sound, ionic conduction, or the like.

As a typical example thereof, an atomic force microscope (Atomic Force Microscope) utilizing the atomic force acting between atoms is used.
Microscope (AFM). Unlike the above-mentioned STM, this is expected to have a wide range of applications because the surface of a material having no electrical conductivity and organic molecules can be observed on the nm (nanometer) scale. As shown in FIG. 7, a conventional atomic force microscope is constructed.

An XYZ drive system 2 which is, for example, a tube type scanner is provided on the main body 1, and an object to be measured S which is a sample is placed on the XYZ drive system 2. The object to be measured S is displaced in the XYZ directions by the drive system 2.

A holder 3 made of a lever modulation piezoelectric element is provided on the upper portion of the main body 1. A leaf spring-shaped cantilever 5 having a small probe 4 at the tip is attached to the holder 3, and a cantilever portion 6 is constituted by these. The cantilever 5 is made of fine metal foil or SiO.
Made of ₂ thin films.

Further, the main body 1 is provided with the above cantilever 5.
Displacement measuring means 7, which will be described later, is provided which is a system for measuring the bend. The displacement measuring means 7 is electrically connected to a first control circuit 9 which outputs a Z control signal via an amplifier circuit 8. The XYZ drive system 2 includes the first control circuit 9
And a second control circuit 10 that outputs an XY scanning signal.

The surface of the object S to be measured is brought close to the probe 4 until the interatomic force acts as a repulsive force. It is well known that, in general, a non-polar substance surface exerts an attractive force by a dispersive force at a long distance and a repulsive force by a Pauli exclusion rule at a short distance.

The tip of the cantilever 5 having the probe 4 tends to move away from the object S to be measured, so that the cantilever 5 is bent and deformed. The second control circuit 10 outputs an XY scanning signal based on the state in which the cantilever 5 is bent to an appropriate value, and scans the measured object S in the XY directions.

Then, the distance between the probe 4 and the surface of the object S to be measured changes depending on the unevenness of the surface of the object S to be measured.
The magnitude of the interatomic force changes, and the amount of bending of the cantilever 5 changes. This displacement amount is measured by the displacement measuring means 7, and the XYZ drive system 2 moves the object S to be measured in the Z direction which is the vertical direction so that the displacement amount becomes a reference amount. At this time, the change distribution of the voltage applied to the drive system 2 is proportional to the uneven shape of the surface of the measured object S. That is, the Z control signal output of the first control circuit 9 becomes the locus of the probe 4 and reflects the surface shape of the measured object S, so that the surface shape can be known.

[0012]

By the way, in this type of atomic force microscope, the accuracy is how much the cantilever 5 is flexibly displaced in accordance with the change in the atomic force, and to what extent the displacement is. It depends on whether it can be read with the accuracy of. Conventionally, the specific means for measuring the displacement of the cantilever 5 is selected from the means shown in FIGS. 8 (A), (B) and (C).

In FIG. 1A, a bias voltage is applied from the cantilever 5 to the comparison circuit 11. A tunnel tip 12 is provided at the tip of the cantilever 5 provided with the probe 4 through a narrow gap, and exerts a force on the cantilever 5. The comparison circuit 11 compares the values from the cantilever 5 and the tunnel chip 12 and sends the corresponding value as a detection signal.

In this case, the tunnel tip 12 has a relatively simple structure and high sensitivity in principle, but the tunnel tip 12 provided on the back side of the cantilever 5 has various adsorptions at the tip of the tip 12 and the back side of the cantilever 5. A force is exerted on the cantilever 5 through the layers and vice versa. Therefore, there is a drawback that the detection sensitivity of the force is limited and the operation becomes unstable.

In FIG. 1B, the tip of the cantilever 5 is opposed to the optical fiber 15 which guides the laser light oscillated from the He-Ne laser oscillator 13 by converging to the tip of the cantilever 5 via the polarization separation element 14. Is provided. In addition, the light reflected by the polarization separation element 14 is detected by the photodetector 16
This is a so-called light wave interference method in which the light is extracted as described above and sent as a detection signal.

In FIG. 1C, an optical fiber 17 that converges and guides the laser light emitted from the He-Ne laser oscillator 16 to the tip of the cantilever 5 is provided. This reflected light is detected by the two-split photodetector 18, and this is detected by the differential amplifier 1
9 is a so-called optical lever system, which sends a detection signal according to the difference between two divisions.

In the configurations shown in FIGS. 1B and 1C, the detectors 16 and 1 that converge the laser light from the optical fibers 15 and 17 and project it on the cantilever 5 or receive the reflected light.
Since the cantilever 5 is extremely fine with a size of about several μm, alignment for alignment is extremely troublesome and troublesome.

On the other hand, in this atomic force microscope, the probe 4 has to be brought closer to the surface of the object S to be measured, as compared with a scanning tunneling microscope or the like. It is easily affected.

In particular, if foreign matter such as water adheres to the surface of the object S to be measured, the probe 4 will be attracted to the foreign matter.
Accurate measurement is not possible. That is, when the foreign matter attracted to the probe 4 separates for some reason, the impact at that time appears as vibration of the cantilever 5 and changes to a pulsed nozzle on the image display of the measurement data.

The present invention has been made in view of the above circumstances, and its first object is to simplify the structure of a displacement measuring system for detecting the displacement of a probe and to perform high-precision measurement. An atomic force microscope made possible.

A second object is to provide an atomic force microscope in which the influence of foreign matter adhering to the surface of the object to be measured can be surely removed and its shape can be accurately observed.

[0022]

In order to achieve the above object, the first invention comprises a cantilever for holding a probe and a displacement measuring means for measuring the displacement of the cantilever. In the atomic force microscope, which measures the atomic force with a displacement measuring means and scans the surface of the object to be measured while keeping the atomic force constant, the atomic force microscope detects the fine shape of the surface of the object to be measured. The measuring means is an atomic force microscope, which is directly provided on the cantilever. A second invention is the atomic force microscope according to claim 1, wherein the displacement measuring means is a thin film piezoelectric material that covers the surface of the cantilever. A third invention is the atomic force microscope according to claim 1, wherein the displacement measuring means is a semiconductor strain gauge attached to the surface of the cantilever.

A fourth invention comprises a cantilever for holding the probe and a displacement measuring means for measuring the displacement of the cantilever, the atomic force is measured from the displacement of the cantilever by the displacement measuring means, and this atomic force is measured. In the atomic force microscope that detects the fine shape of the surface of the object to be measured by scanning the surface of the object to be measured while keeping the force constant, the foreign matter adhering to the surface of the object to be measured immediately before the scanning of the cantilever. The atomic force microscope is characterized by comprising a dummy cantilever for holding a probe for removing the.

[0024]

In the first to third inventions, the displacement of the probe is detected by the piezoelectric material or the semiconductor strain gauge formed on the thin film on the cantilever, so that the displacement measuring means is simplified and the position relative to the cantilever is increased. No alignment required,
Highly accurate measurement is possible. In the fourth aspect of the invention, the dummy cantilever can be used to remove the influence of foreign matter adhering to the surface of the object to be measured, and to realize accurate observation of the surface fine shape.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a conventional atomic force microscope is constructed.

An XYZ drive system 2 which is, for example, a tube type scanner is provided on the main body 1, and an object to be measured S which is a sample is placed on the XYZ drive system 2. The object S to be measured is displaced and scanned in the XYZ directions by the drive system 2.

Further, a holder 3 composed of a piezoelectric element for lever modulation is provided on the upper part of the main body 1, and a cantilever 20 described later having a small probe 4 at the tip thereof is attached to the holder 3 to form a cantilever portion 21. Composed.

The cantilever 20 still has the shape of a leaf spring made of a fine metal foil or a SiO ₂ thin film. Displacement measuring means 22 is provided directly on the back surface thereof.

As shown in FIG. 2, the above cantilever 20 is used.
A piezoelectric material thin film, which is a displacement measuring means, that is, a PZT (lead zirconate titanate) thin film 22A, is formed on the back surface side of the above.

This PZT has the property of expanding and contracting when a voltage is applied. By applying the technique of directly synthesizing a crystalline thin film on a substrate from gel-like PZT developed recently, the film thickness can be reduced from 0.01 μm. It is possible to control up to about 1 μm. As shown in FIG. 1 again, the PZT thin film 22A is electrically connected to the first control circuit 9 which issues the Z control signal through the amplifier circuit 8. X above
The YZ drive system 2 is electrically connected to the first control circuit 9 and the second control circuit 10 which issues an XY operation signal.

The surface of the object S to be measured is brought close to the probe 4 until the interatomic force acts as a repulsive force. Since the tip of the cantilever 20 equipped with the probe 4 tends to move away from the object S to be measured, bending deformation occurs. With the state in which the cantilever 20 bends to an appropriate value as a reference, the measured object S is XY
Scan in the direction.

Then, the distance between the probe 4 and the surface of the object S to be measured changes depending on the unevenness of the surface of the object S to be measured.
The magnitude of the interatomic force changes, and the amount of bending of the cantilever 20 changes. A voltage proportional to this bending stress is applied to the PZT thin film 2
Get out of 2A.

That is, as shown in FIG. 2 (A), the PZT in a state in which the cantilever 20 has almost no bending deformation
The output voltage of the thin film 22A is V ₀ , and the cantilever 20 is flexed and deformed to some extent as shown in FIG.
Stress is generated in the T thin film 22A, and an output voltage V ₁ that is a voltage proportional to the stress at this time is generated. In other words,
A voltage proportional to the displacement of the cantilever 20 will be generated.

Therefore, in the first control circuit 9, (V ₀ −
A Z control signal is output to control the position in the Z direction so that V ₁ ) is always 0. The cantilever 20 is always kept in a constant state, and the change distribution of the voltage applied to the XYZ drive system 2 represents the surface shape of the measured object S.

The PZT thin film 22A is the cantilever 2.
Since it is equipped directly on the back side, there is no need to arrange a separate measurement system or troublesome positioning, and a simple configuration is required. Then, stress is generated in accordance with the bending deformation of the cantilever 20, and a voltage proportional to the deformation is accurately output. Therefore, of course, there is no measurement error, the operation is stable, and highly accurate detection can be performed.

Although the PZT thin film 22A is formed on the back surface of the cantilever 22 in the above embodiment, the present invention is not limited to this, and it may be formed on the surface provided with the probe 4. The same effect can be obtained. Also, this is not limited to PZT. Optical distortion element such as PLZT,
A polymer piezoelectric material such as PVDF (polyvinylidene fluoride) or ZnO may be used.

As shown in FIG. 3, a strain gauge 22B as a displacement measuring means may be provided on the back surface of the cantilever 20. In this case, if the strain on the cantilever 20 is controlled to be constant, the same operational effect as that of the above-described embodiment can be obtained.

As shown in FIG. 4, a dummy cantilever 30 may be provided in series with the cantilever 20 on the back surface of which the PZT thin film 22A serving as the displacement measuring means is formed, as described above.

In this case, the dummy cantilever 30 is used.
Must be provided at the position just before scanning of the regular cantilever 30 whose displacement is measured. A probe 4 is provided at the tip of the probe, and a probe having the same shape and structure is used except that the PZT thin film 22A is not formed. However, there is no electrical connection to other components,
It can be installed by itself.

When scanning is carried out in the direction of the arrow in the figure and foreign matter, for example water droplets W, adheres to the surface of the object to be measured S, the cantilever 2 which should detect the surface texture of the object to be measured S.
Just before 0 reaches the water drop W, the dummy cantilever 30
And the probe 4 provided therein hits the water droplet W.

The water droplet W, which is a foreign substance, is pushed away by the tip of the dummy cantilever 30 and the probe 4, or is hooked by these and is dragged. In any case, when the probe 4 of the cantilever 20 on which the PZT thin film 22A is formed reaches that portion, no foreign matter is present, so that the surface texture of the measured object S can be accurately detected.

Naturally, the pulse-like noise generated due to the presence of the foreign matter W is eliminated, and the measurement accuracy is improved. Further, with respect to these noises, when the same region is repeatedly measured, it is guaranteed that the foreign matter W attached on the scanning line is removed by the probe 4 of the dummy cantilever 30.

As shown in FIG. 4, the displacement measuring means P
A plurality (three in this case) of dummy cantilevers 30 ... May be provided in series at predetermined intervals at a position immediately before scanning of the cantilever 20 on which the ZT thin film 22A is formed on the back surface.

The shape and structure of each dummy cantilever 30 is as described above. In this case, the foreign matter removal scanning can be performed a plurality of times by one scanning, and the time can be saved.

As shown in FIG. 5, when the scanning direction is the left-right direction in the figure, the PZT thin film 2 which is the displacement measuring means.
A plurality of (two in this case) dummy cantilevers 30 ... May be provided in series at predetermined intervals at the left and right positions of the cantilever 20 having 2A formed on the back surface.

That is, regardless of whether the scanning direction is left or right, each dummy cantilever 30 carries out foreign matter removal scanning a plurality of times by one scanning, and time can be saved.

[0047]

As described above, according to the present invention, the cantilever displacement measuring means is provided directly on the surface of the cantilever. The displacement measuring means is a thin film piezoelectric material that covers the surface of the cantilever, or is a semiconductor strain gauge attached to the surface of the cantilever.

Therefore, it is not necessary to dispose a displacement measuring system separately, and there is no need for troublesome positioning. This structure can be simplified, and the effect that the force can be exerted on the cantilever and the detection sensitivity of the force is not limited, the operation is stable, and highly accurate measurement can be performed.

Further, according to the present invention, since the dummy cantilever holding the probe for removing the foreign matter adhering to the surface of the object to be measured is provided immediately before the scanning of the cantilever, the foreign matter adhering to the surface of the object to be measured is provided. The effect of being able to remove the influence of is surely observed, and the surface texture can be observed accurately.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an atomic force microscope showing an embodiment of the present invention.

FIG. 2A is a schematic configuration diagram of a cantilever of the same embodiment. FIG. 6B is a schematic configuration diagram of the cantilever in a state different from that of FIG.

FIG. 3 is a schematic configuration diagram of a cantilever according to another embodiment.

FIG. 4 is a schematic configuration diagram of a part of an atomic force microscope according to still another embodiment.

FIG. 5 is a schematic configuration diagram of a part of an atomic force microscope according to still another embodiment.

FIG. 6 is a schematic configuration diagram of a part of an atomic force microscope according to still another embodiment.

FIG. 7 is a schematic configuration diagram of an atomic force microscope showing a conventional example of the present invention.

8A to 8C are schematic configuration diagrams of a part of an atomic force microscope different from each other in a conventional example.

[Explanation of symbols]

4 ... probe, 20 ... cantilever, 22 ... displacement measuring means,
22A ... Thin film piezoelectric material (PZT thin film), 22B ... Semiconductor strain gauge, 30 ... Dummy cantilever.

Claims (4)

[Claims] 1. A cantilever for holding a probe and a displacement measuring means for measuring the displacement of the cantilever, the atomic force is measured from the displacement of the cantilever by the displacement measuring means, and the atomic force is constant. By scanning the measured object surface while holding, in the atomic force microscope to detect the fine shape of the measured object surface, the displacement measuring means,
An atomic force microscope characterized by being directly provided on the cantilever. 2. The atomic force microscope according to claim 1, wherein the displacement measuring means is a thin film piezoelectric material that covers the surface of the cantilever. 3. The atomic force microscope according to claim 1, wherein the displacement measuring means is a semiconductor strain gauge attached to the surface of the cantilever. 4. A cantilever holding a probe and a displacement measuring means for measuring the displacement of the cantilever, the atomic force is measured from the displacement of the cantilever by the displacement measuring means, and the atomic force is constant. By scanning the surface of the object to be measured while holding it in an atomic force microscope that detects the fine shape of the surface of the object to be measured, in order to remove foreign matter adhering to the surface of the object to be measured, immediately before the scanning of the cantilever. Atomic force microscope equipped with a dummy cantilever for holding the probe.