JPH0843409A - Interatomic forces microscope - Google Patents

Abstract

PURPOSE:To obtain an interatomic forces microscope equipped with a mechanism which can make the surface of a sample and a scanning plane of a cantilever be parallel to each other. CONSTITUTION:A frame 1 supporting a cantilever 5, etc., is set on four shaft screws 32 of which height positions of the respective upper end faces can be regulated independently. The frame 1 is provided with a reference plane 10 parallel to a scanning plane of the cantilever 5 beforehand. On the other hand, the surface of a sample (s) is made horizontal beforehand. The inclination of the reference plane 10 is measured by a clinometer 4 and positions of the shaft screws 32 are regulated by operating a motor 31 so that the reference plane 10 be horizontal.

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 Recently developed atomic force microscopes (AF
M: Atomic Force Microscope) is capable of observing non-conductive substances such as living things, organic molecules, and insulating substances (for example, ceramics) on a nanometer scale, and thus is expected to have a wide range of applications.

The principle of the AFM and the structure of the main part will be described with reference to FIG.

The AFM comprises a pedestal 1, a pedestal 2, a triaxial vertical fine movement mechanism 3, a sample holder 20, a cantilever 5, a scanner 6, a light source 7, and a detector 8.

The sample holder 20 is a table on which the sample s is placed.

The distance between the cantilever 5 and the sample surface is
This is detected as the amount of deflection of the cantilever 5 itself. The cantilever 5 is formed in a leaf spring shape and has a probe 50 at its tip. The cantilever 5 is bent by an atomic force acting between the probe 20 and the sample surface.

The scanner 6 is for scanning the cantilever 5 in the XY directions on the sample surface. The cantilever 5 is scanned in the XY directions by the scanner 6 with the probe 50 being in mechanical contact with the sample surface.

The light source 7 and the detector 8 are the cantilever 5.
This is for detecting the amount of deflection. The light emitted from the light source 7 is applied to the cantilever 5, and the reflected light is detected by the detector 8. By measuring this reflected light, the amount of deflection of the cantilever can be measured.

The magnitude of the interatomic force acting between the sample surface and the probe changes depending on the distance between the two. Generally, on the surface of a substance, attractive force works at a long distance, and repulsive force works at a short distance. Therefore, keeping the atomic force constant (ie,
By moving the probe 50 on the sample surface while keeping the amount of deflection of the cantilever constant, it is possible to observe the unevenness of the sample surface.

By subjecting the measurement data thus obtained to an appropriate treatment, an image showing the unevenness of the sample surface can be obtained by the AFM.

The cantilever 5, the scanner 6, the light source 7, and the detector 8 described above are installed on the mount 1. Further, the gantry 1 itself is placed on the pedestal 2. Therefore,
By operating the triaxial vertical fine movement mechanism 3, the inclination and the like of the cantilever 5, the scanner 6, the light source 7, the detector 8 and the like can be adjusted without changing their relative positional relationship. On the other hand, since the sample holder 20 is installed on the pedestal 2, it is always kept at a fixed position without being affected by the operation of the triaxial vertical fine movement mechanism 3.

In the AFM having such a structure, whether or not the surface of the sample s and the scanning surface of the cantilever 5 are parallel to each other affects the detection accuracy of the uneven image. The magnitude of the influence of the tilt will be described with reference to FIG.

Hereinafter, the fact that the scanning surface of the cantilever and the surface of the sample are not parallel is simply referred to as "inclination of the sample surface" or "inclination of the sample". (It is based on the scanning plane, not the inclination with respect to the horizontal plane).

The smallest irregularity that can be detected by the AFM is
Height difference of sample surface detected by cantilever 5 ΔH (= H
It depends on the size of (max − Hmin).

For example, consider a case where data sampling is performed with 8 bits (that is, 256 steps). In this case, the minimum height h _min of the observable unevenness is determined by the following formula 1.

[0016]

## EQU1 ## h _min = (Hmax-Hmin) / 256 Hmax: maximum value of height detected by cantilever 5 in scanning range Hmin: minimum value of height detected by cantilever 5 in scanning range Cantilever 5 If the detected difference in height ΔH is large, for example, if ΔH = 5000 nm, then h _min = 2
It becomes 0 nm. That is, the unevenness of 20 nm or less on the sample surface cannot be detected. Even if the surface of the sample has unevenness with a height h = 10 nm, it cannot be observed as unevenness. On the other hand, when the height difference ΔH detected by the cantilever 5 is small, for example, when ΔH = 100 nm, h _min = 0.4 nm and the height h = 1.
Unevenness of 0 nm can be observed. If the surface of the sample is tilted, the axial direction for measuring the height position H and the measuring direction for the height h of the unevenness are deviated from each other.

By the way, the cantilever 5 itself cannot distinguish whether the height difference obtained by observation is caused by the unevenness of the sample surface or the inclination of the entire sample surface. Therefore, when the inclination of the sample surface is large, the above-mentioned height difference ΔH is determined due to the inclination of the sample surface. And, with this, the microscope cannot exert its original performance. In the worst case, the cantilever 5 may not reach the surface of the sample and may not be observed from the middle. Ideally, it is preferable that the above-mentioned Hmax and Hmin are determined by the unevenness of the sample surface itself (that is, there is no inclination or an extremely small state).

Therefore, various mechanisms for correcting this inclination have been conventionally proposed.

For example, an AFM equipped with a mechanism similar to that of the above-described example (FIG. 5) (mechanism in which the pedestal 1 is supported by the vertical fine movement mechanism 3 having three axes that can be independently moved up and down) is, for example, , USP. US515
7251 (1991.3.13: ParkScient)
It is disclosed in ific Instruments (hereinafter referred to as "prior art A").

Further, in Japanese Patent Laid-Open No. 212001/1992, before observing the sample, the probe is scanned in the measurement region on the surface of the sample to obtain the inclination of the sample surface by calculation, and based on the obtained inclination A scanning tunneling microscope having a function (correction program) for driving a support mechanism is described (hereinafter referred to as "prior art B").

[0021]

However, there are the following problems in the tilt correction and correction techniques proposed above.

In the prior art A described above, the operability was poor because the triaxial vertical fine movement mechanism was manually operated. Especially, since there is no standard or standard for whether or not it is horizontal,
The exact setting was difficult.

In the prior art B as well, the surface of the sample must be scanned before starting the observation, which requires extra time and operation.

It is an object of the present invention to provide a scanning probe microscope having a mechanism capable of quickly and easily making the scanning surface of the cantilever and the surface of the sample parallel to each other.

[0025]

Generally, in a high resolution microscope such as AFM, the pedestal 2 is placed in a sample holder 20.
The pedestal 2 is installed with sufficient care in advance so that the surface of the sample placed on is horizontal. Further, the sample s to be observed is also prepared with sufficient care so that the surface of the sample s placed in the sample holder 20 and placed on the pedestal 2 becomes horizontal. Therefore, the present invention is based on the assumption that the surface of the sample s placed in the sample holder 20 and placed on the pedestal 2 is horizontal.

The present invention has been made in order to achieve the above object, and in one aspect thereof, a cantilever configured to be deformable by an atomic force generated between the cantilever and a sample surface, and the amount of deformation of the cantilever is detected. Detecting means, a scanning means for scanning the cantilever, a frame to which the cantilever is attached, an inclination angle detecting means for detecting an inclination of a surface of the cantilever to be scanned (hereinafter referred to as "scanning surface"), An angle adjusting unit that adjusts the inclination of the scanning surface, and a control unit that operates the angle adjusting unit based on the detection result of the inclination angle detecting unit and keeps the scanning surface at a predetermined angle. An atomic force microscope is provided.

The reference plane parallel to the scanning plane may be provided, and the inclination angle detecting means may detect the inclination of the reference plane.

The reference plane may be set on the frame, and the angle adjusting means may adjust the inclination of the scanning surface by changing the inclination of the entire frame.

It is preferable that the predetermined angle is horizontal.

[0030]

The tilt angle detecting means detects the tilt of the scanning surface. The tilt is detected, for example, by detecting the tilt of the reference plane of the frame set parallel to the scanning plane.

The control means, based on the detection result of the tilt angle detection means, causes the scanning surface to have a predetermined angle (for example,
The angle adjusting means is operated so that it becomes horizontal). The angle adjusting unit adjusts the inclination of the scanning surface by changing the inclination of the entire frame, for example.

[0032]

An embodiment of the present invention will be described with reference to the drawings.

The AFM of this embodiment is as shown in FIG.
A pedestal 1, a pedestal 2, a 4-axis vertical fine movement mechanism 3, an angle detector 4, a cantilever 5, a scanner 6, a light source 7,
The detector 8 and the control unit 9 (see FIG. 2) are included.

The gantry 1 includes a cantilever 5, a scanner 6,
This is for holding the light source 7, the detector 8 and the like so that their positional relationship does not change. An angle detector 4 is installed on a reference plane 10 provided on the gantry 1. The reference surface 10 is scanned by the X- of the cantilever 5.
It is parallel to the Y plane. Further, the gantry 1 is placed on the shaft screw 32 in such a direction that the scanning directions X and Y of the cantilever 5 and the directions of the sides of the quadrangle formed by the shaft screw 32 coincide with each other (FIG. 3). reference).

The angle detector (inclinometer) 4 is for detecting the tilt angle of the reference plane 10 of the gantry 1 and its direction. As described above, the present invention is premised on that the surface of the sample s is horizontal. Therefore, if the tilt of the gantry 1 is adjusted so that the reference surface 10 is horizontal, the scanning surface of the cantilever 5 and the surface of the sample s can be made parallel to each other. The angle detector 4 outputs the detection result to the control unit 9 (see FIG. 2). In this embodiment, the angle detector 4 is a digital inclinometer manufactured by Chemika Rising Co., Ltd. (trade name) capable of detecting an inclination with an accuracy of 0.1 °.
Two TD-2B) are used. By arranging these two inclinometers at right angles to each other, it is possible to detect the tilt in each of the directions (X direction, Y direction) in which the tilt adjustment is performed by the 4-axis vertical fine movement mechanism 3. However, the inclinometer used is not limited to this.

The cantilever 5 measures the distance from the sample surface by
This is detected as the amount of deflection of the cantilever 5 itself. The cantilever 5 is formed in a leaf spring shape and has a probe 50 at its tip. The cantilever 5 is bent by the interatomic force acting between the probe 50 and the sample surface.

The scanner 6 moves the cantilever 5 in the X direction,
It is for scanning in the Y direction. In this embodiment, a piezo element is used. The cantilever 5 is scanned by the scanner 60 in the X direction and the Y direction while the probe 50 is mechanically brought into contact with the surface of the sample s. As mentioned above, this scanning plane (XY plane) is
It is parallel to the reference plane 10 of the gantry 1. The tilt of the scanning plane is adjusted by the four-axis vertical fine movement mechanism 3 which will be described later.

The scanner 6 can also move the entire cantilever 5 in the Z-axis direction so that the atomic force detected by the cantilever 5 becomes constant (that is, the deflection of the cantilever 5 becomes constant). Is configured.

The light source 7 and the detector 8 are the cantilever 5.
This is for detecting the amount of deflection. The light emitted from the light source 7 is applied to the cantilever 5, and the reflected light is detected by the detector 9. By measuring this reflected light, the amount of deflection of the cantilever can be measured. In this embodiment, a semiconductor laser is used as the light source 7.

The pedestal 2 is for supporting the entire microscope, and is made of a heavy and hard material so as not to move easily. At the center of the upper surface of the pedestal 2,
A sample holder 20 for mounting the sample s is installed. Holes 22 penetrating vertically are provided at four corners of the pedestal 2, and shaft screws 32 of a motor 31, which will be described later, are passed therethrough.

The four-axis vertical fine movement mechanism 3 is for adjusting the inclination of the gantry 1. As shown in FIG. 2, the four-axis vertical fine movement mechanism 3 includes motors 31a, b, c, d and drivers 30a, 30b, 30c, 30d.
Hereinafter, the motor 31a, the motor 31b, the motor 31c, and the motor 31d are collectively referred to simply as "motor 31".
Similarly, it is called "driver 30". Shaft screw 3 of motor 31
2 is configured to be movable in the vertical direction in FIG. 1 in accordance with the rotation of the motor. Each of the motors 31 has a shaft screw 32 passed through the hole 22 described above, and the tip end thereof supports the gantry 1. The positional relationship between the shaft screw 32 and the scanning direction of the cantilever 5 when viewed from the upper side of FIG. 1 is shown in FIG. The shaft screws 32 are respectively arranged at the apexes of a square (indicated by a chain line in the figure). Then, as will be described later, the gantry 1 is placed on the four shaft screws 32 in such an orientation that the X and Y directions in which the cantilever 5 is scanned correspond to the directions of the sides of the square, respectively. There is. Therefore, by operating the motors 31 independently of each other, the inclination of the gantry 1 can be adjusted independently in each of the X direction and the Y direction. That is, the motors 31a and 31b and the motor 31
The tilt in the X direction can be adjusted by separately operating the combination of c and 31d. Similarly, the tilt in the Y direction can be adjusted by separately operating the motors 31a and 31c and the motors 31b and 31d in combination.

In this embodiment, since fine adjustment is possible,
A step motor is used as the motor 31.

The driver 30 is a control circuit for actually operating the motor 31 in accordance with a signal from the control section 9.

The control configuration of this embodiment will be described with reference to FIG.

FIG. 2 mainly shows a control structure for horizontally adjusting the scanning surface of the cantilever 5, and omits other parts.

The control unit 9 operates the motor 31 according to the detection result input from the angle detector 4 to make the gantry 1 horizontal.

The control unit 9 includes a preamplifier 90, an arithmetic processing unit 91, and a distributor 92. Preamplifier 90
Is for amplifying the output signal of the angle detector 4 and converting it into a signal processable by the arithmetic processing unit 91 (for example, A / D conversion).

The arithmetic processing unit 91 has a function of obtaining the operation amount of the motor 31 based on the angle information input through the preamplifier 90. In this embodiment, the arithmetic processing unit 9
1 includes a microprocessor, ROM, RAM, and programs and data stored in these memories. For details of calculation by calculation processing,
The operation will be described later.

The distributor 92 is for distributing the signal output from the arithmetic processing section 91 to the driver 30 corresponding to the signal and outputting it.

The "frame" referred to in the claims corresponds to the gantry 1 in this embodiment. ”
The tilt angle detecting means "corresponds to the angle detector 4."
The “angle adjusting means” corresponds to the 4-axis vertical fine movement mechanism 3.
The control means corresponds to the control unit 9.

Next, the gantry 1 (that is, the cantilever 5
The operation of horizontally adjusting the scanning surface) will be described with reference to the flowchart of FIG.

After starting the operation, the control section 9 detects the tilt angles in the X direction and the Y direction based on the angle signal detected by the angle detector 4. Then, it is determined whether or not each inclination angle is 0.5 ° or more (step 71). As a result, 0.5 ° on either side
If it is above, the coarse adjustment of the inclination is performed (step 72). In the rough adjustment, the operation amount of the step motor 31 is increased to some extent. Tilt in X direction is 0.5
When it is equal to or more than 0 °, the motors 31a and 31b (or the motors 31c and 31d) are operated by the same amount. Although not particularly mentioned in the above description, the shaft screws 32a, 32a
The pitches of the screws b, 32c, 32d are the same. Therefore, without affecting the tilt in the Y direction,
Only the tilt in the X direction can be reduced.

When the inclination in the Y direction is 0.5 ° or more, the motors 31a and 31c (or the motors 31b and 31b,
Activate d) by the same amount. As a result, only the tilt in the Y direction can be reduced without affecting the tilt in the X direction. The inclination is 0.5 in both X and Y directions.
If there is more than °, perform in both directions.

After step 72, step 71 is performed again.
Then, the same processing is repeated until the inclination becomes less than 0.5 ° in both X and Y directions.

When the inclination becomes less than 0.5 ° in both the X and Y directions, the process proceeds to steps 73 and 74, and the inclination adjustment is repeated until the inclination becomes less than 0.1 degree.
The method of adjusting the inclination is basically the same as that in step 772. However, in order to enable finer adjustment, step 7
In 4, the amount of one-time operation of the motor 31 is smaller than that in step 72.

In step 73, if the inclination is less than 0.1 ° in both the X and Y directions, the inclination adjustment is completed and the process proceeds to step 75. In step 75, while keeping the entire gantry 1 horizontal, the gantry 1 is lowered to a range where observation by the cantilever 5 is possible. Then, the sample is observed (step 76).

Finally, the accuracy of detecting irregularities when tilt adjustment is performed in this embodiment will be described. When discussing the degree of inclination of the sample surface using the angle as a parameter, the height of the unevenness of the sample surface that can be detected is defined by the following mathematical expression 2. In Formula 2, it is assumed that data sampling is performed in 8 bits (256 steps), as in the above example.

[0058]

## EQU00002 ## h _min = (L · tan θ) / 256 θ: inclination angle of the scanning surface of the cantilever with respect to the sample surface h _min : minimum height of observable unevenness L: scanning distance In the present embodiment, inclination θ Can be set with an accuracy of 0.1 °. Further, here, if L = 20 μm = 20000 nm, then h _min ≈0.1 nm, and practically sufficient detection accuracy can be obtained.

As described above, in the present embodiment, the scanning surface of the cantilever 5 and the surface of the sample s can be made parallel to each other easily and accurately. Therefore, the original function of the AFM can be fully exerted.

In the above embodiment, the 4-axis vertical fine movement mechanism is adopted, but the inclination can be adjusted also by the 3-axis vertical fine movement mechanism. However, in that case, whichever axial screw 32 (motor 3
It is necessary to perform a process of calculating how much 1) should be operated. Alternatively, the angle detector 4 needs to be configured so as to be able to detect the tilt angles in the three directions corresponding to the respective shaft screws 32.

In the above embodiment, the angle adjustment is automated in order to facilitate the operation. However, the shaft screw 32 may be manually moved. In this case, the control unit 9 does not need a configuration for adjusting the angle, and the cost can be reduced. Even in this case, by adjusting the angle detector 4 while looking at it, the angle can be adjusted more accurately than before.

In the above embodiment, the pedestal 2 itself is constructed on the premise that it is horizontal. However, in some cases, the pedestal 2 may necessarily be tilted. Therefore, in this case, an angle detector for detecting the inclination of the pedestal 2 may be separately provided. In this case, the control unit 9 operates the 4-axis vertical fine movement mechanism so that the tilt of the gantry 1 and the tilt of the pedestal 2 match. However, also in this case, it is assumed that the surface of the sample s is parallel to the pedestal 2.

[0063]

As described above, according to the present invention, since the surface of the sample and the scanning surface of the cantilever can be made parallel to each other, the capability (resolution) originally possessed by the microscope can be maximized. it can. In addition, since it is automated, the operation is easy and even beginners can make adjustments. Also, the time required for adjustment is short.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration on control.

FIG. 3 is a positional relationship between the shaft screws 32 and the cantilever 5.
It is a figure which shows the relationship with the scanning direction of.

FIG. 4 is a flowchart showing a control operation.

FIG. 5 is a schematic diagram showing a main part configuration of a conventional AFM.

FIG. 6 is a schematic view showing how the sample surface is inclined.

[Explanation of symbols]

1 ... Frame, 2 ... Pedestal, 3 ... 4-axis vertical fine movement mechanism, 4 ... Angle detector, 5 ... Cantilever, 6 ... Scanner, 7 ... Light source,
8 ... Detector, 9 ... Control part, 20 ... Sample holder,
30 ... Driver, 31 ... Motor, 32 ... Shaft screw, 50 ...
Probe, 90 ... Preamplifier, 91 ... Arithmetic processing unit, 92 ... Distributor

Claims (4)

[Claims] 1. A cantilever configured to be deformable by an interatomic force generated between a sample surface, a detection unit for detecting a deformation amount of the cantilever, a scanning unit for scanning the cantilever, and a mounting unit for the cantilever. Frame, tilt angle detecting means for detecting the tilt of the surface on which the cantilever is operated in the scanning (hereinafter referred to as "scanning surface"), angle adjusting means for adjusting the tilt of the scanning surface, and the tilt angle. An atomic force microscope, comprising: a control unit that operates the angle adjustment unit based on a detection result of the detection unit to keep the scanning surface at a predetermined angle. 2. The atomic force microscope according to claim 1, further comprising a reference plane parallel to the scanning plane, wherein the inclination angle detecting means detects an inclination of the reference plane. 3. The reference surface is set in the frame, and the angle adjusting means adjusts the inclination of the scanning surface by changing the inclination of the entire frame. The atomic force microscope according to claim 2. 4. The atomic force microscope according to claim 1, wherein the predetermined angle is horizontal.