JP2000346782A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the action of an excessive force on a sample and to improve measurement accuracy in surface shape observation and adsorption force measurement by a scanning probe microscope. Kind Code: A1 A limit value of compression and tension of an acting force acting between a cantilever 2 and a sample S is set, and the position of the cantilever or the sample is adjusted so that the measured acting force falls within a range defined by the set limit value. A force curve measuring means 11 for performing control and measuring an acting force acting between the cantilever and the sample based on the displacement of the cantilever is provided. The adsorption force measurement using the position data as a value is performed while moving the cantilever on the sample surface at each measurement point. Specify the range for measuring the force curve by the amount of deflection of the cantilever, and limit the applied force to the sample within the set limit value to prevent excessive force from acting

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a scanning probe microscope, and more particularly to observation of a surface shape and measurement of adsorption force mapping.

[0002]

2. Description of the Related Art As a scanning probe microscope, a scanning atomic force microscope (AFM) using an atomic force acting between a probe and a sample surface is known. A scanning atomic force microscope is equipped with a probe, a cantilever supporting the probe, and a displacement measurement system for detecting bending of the cantilever, and detects an atomic force (attractive force or repulsive force) between the probe and the sample. Thus, the shape of the sample surface is observed, and non-conductive substances such as living organisms, organic molecules, and insulators can be observed. Observation with a scanning atomic force microscope can be applied to measurement of a surface shape in various measurement modes such as a contact mode, a contact height mode, a non-contact mode, and a dynamic mode. The surface shape measurement in the contact mode detects the deflection of the cantilever, and the surface shape measurement in the dynamic mode detects the amplitude of the cantilever.

The scanning atomic force microscope has a force curve measuring function for measuring the acting force acting between the sample and the cantilever, in addition to the surface shape observation. In the force curve measurement, the distance between the sample and the cantilever is changed, the acting force acting between the sample and the cantilever is measured, and the change in the acting force with respect to the distance is determined. By measuring the force curve, the adsorption force of the sample can be measured.

[0004]

In a scanning probe microscope, when the surface shape is measured by the contact mode or the dynamic mode, the probe of the cantilever is pushed into the sample with a force of the order of nN, so that it is very soft. In the case of a sample, the sample may be broken by the pressing force of the probe. When the cantilever and the sample are relatively moved and scanned, the direction of the force applied to the sample by the probe changes depending on the surface shape, the scanning direction, and the like, and is not necessarily perpendicular to the sample. Another problem is that the measurement conditions for observing the surface shape are not the same.

When a force curve is measured by a scanning probe microscope, a mechanism for controlling the position of the cantilever or the sample causes a position where the cantilever is farthest from and closest to the sample, or a case where the sample is closest to the cantilever. The distant position and the closest position are designated, and the distance between the sample and the cantilever is changed within the range of these set positions. In the conventional scanning probe microscope, since the measurement range of the force curve is determined by specifying the position of the cantilever or the position of the sample, there is a possibility that the cantilever or the sample may be damaged due to a positional deviation from the specified position.

FIG. 5 is a schematic sectional view for explaining the positional relationship between the cantilever and the sample. When the distance between the cantilever 2 and the sample S is reduced, the probe 20 of the cantilever 2 comes into contact with the sample S at a point Pa as shown in FIG. When the distance between the cantilever 2 and the sample S fluctuates, the sample S and the cantilever 2 may be damaged as shown in FIG. 5B or 5C. FIG.
In (b), since the cantilever 2 and the sample S are too close to each other, an excessive compressive force acts on the sample S and the cantilever 2 at the contact point Pb. Also, the cantilever 2 and the sample S
When the two are separated after contacting with each other, a tensile force acts on the sample S as shown in FIG. 5C by the meniscus force (adhesive force) of the liquid L present on the surface of the sample S.

In the diagram showing the relationship between the position and the acting force in the force curve measurement of FIG. 6, the measurement range is determined by designating the position such as the closest position Zu and the farthest position Zl. Therefore, when the position exceeds Zu (closest position) due to a position shift due to temperature drift or the like, an acting force exceeding the maximum compression limit Fu is applied.
If it exceeds Zl (the most distant position), an acting force exceeding the maximum pulling limit Fu will be applied. Therefore, in the case of the conventional position designation, unnecessary acting force may be applied.

As described above, the conventional scanning probe microscope has a problem that an excessive force is applied to the sample in observing the surface shape and measuring the attraction force. Further, when the adsorption force is measured by force curve measurement, the acting force immediately before the cantilever separates from the sample is measured. In FIG. 6, Fp immediately before the probe leaves the sample because it cannot withstand the pulling force is used as the adsorption force, and the deflection of the cantilever at this time is detected by the photodetector. However, since the point P is a point where the acting force changes and is abrupt, there is a problem that high resolution cannot be expected in the measurement by the photodetector.

Accordingly, the present invention solves the above-mentioned conventional problems, and in the observation of the surface shape and the measurement of the attraction force using a scanning probe microscope, it is necessary to prevent the action of an excessive force on the sample and to improve the measurement accuracy. Aim.

[0010]

According to the present invention, in a force curve measurement performed in surface shape observation and adsorption force measurement using a scanning probe microscope, a range for measuring a force curve is determined by a position of a cantilever or a position of a sample. Instead of specifying, the action force acting between the cantilever and the sample is specified. Thereby, the acting force applied to the sample is limited within a set limit value, thereby preventing an excessive force from acting. In addition, by performing measurement at each measurement point, measurement accuracy is increased by performing measurement under the same measurement condition with the acting force on the sample being vertical.

In the scanning probe microscope of the present invention, the limit value of the compression and the tension of the acting force acting between the cantilever and the sample is set so that the measured acting force is within the range defined by the set limit value. Equipped with force curve measuring means that controls the position of the cantilever or sample and measures the acting force acting between the cantilever and the sample based on the displacement of the cantilever, and measures the surface shape using the position data that is the compression set limit value And the measurement of the attraction force using the position data serving as the pull setting limit value are performed while the cantilever is moved at each measurement point on the sample surface.

The force curve measuring means of the scanning probe microscope according to the present invention sets the upper and lower limits of the acting force acting between the cantilever and the sample as a compression set limit value and a tension set limit value, and the action force is set. The position of the cantilever or the sample is controlled so as to be within the range defined by the limit value. Since the acting force is proportional to the deflection of the cantilever, the setting and measurement can be performed using the amount of deflection of the cantilever instead of the acting force.

According to the present invention, in the force curve measuring means, data relating to the surface shape is measured from the position data serving as the compression set limit value, and data relating to the attraction force is measured from the position data serving as the pull set limit value. By obtaining the acquired surface shape data and adsorption force data at a plurality of measurement points on the sample surface, surface shape and adsorption force mapping can be obtained. According to the scanning probe microscope of the present invention, the force acting between the cantilever and the sample during the measurement of the force curve is limited, and the position of the cantilever or the sample is controlled so as to be within a set limit value. By doing so, surface shape and adsorption force mapping can be obtained without damaging the sample or the cantilever.

Further, by performing each measurement for each measurement point, it is possible to prevent the sample from being damaged by the cantilever and to increase the measurement accuracy by making the acting direction of the acting force the same in each measurement.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of a scanning probe microscope of the present invention, and is a diagram illustrating a scanning atomic force microscope as an example. The scanning probe microscope shown in FIG. 1 includes a probe 20, a cantilever 2 supporting the probe 20, a displacement measuring system 3 for detecting the bending of the cantilever 2,
And a drive system 4 for moving the sample S in the Z-axis direction and the X-axis and Y-axis directions, and detects an atomic force (attractive force or repulsive force) between the probe 20 and the sample S by the amount of deflection of the cantilever. Then, the shape of the sample surface is observed and the adsorption force is mapped using the obtained deflection amount.

The displacement measuring system 3 includes a light source such as a laser oscillator 31, an optical system such as mirrors 32 and 33, and a photodetector such as a photodiode 34. Laser light emitted from the laser oscillator 31 and reflected by the cantilever 2 is provided. Is detected by the photodiode 34, so that the cantilever 2
Measure the displacement of A force curve is measured from the displacement of the cantilever 2. The displacement signal detected by the photodiode 34 is converted into a digital signal by the A / D converter 35 and then sent to the force curve measuring means 1 of the measuring means 1.

The measuring means 1 includes a force curve measuring means 11 for measuring a force curve, a surface shape measuring means 12 for obtaining a surface shape based on data acquired by the force curve measuring means 11, and an attraction force for obtaining an attraction force. A mapping measurement unit 13 is provided. The force curve measuring means 11 calculates an acting force corresponding to the displacement of the cantilever 2 and outputs a control signal to the drive system 4. The drive system 4 includes a D / A converter 41 that converts a digital control signal from the force curve measuring unit 1 into an analog signal.
And a scanner driver 42 for driving the scanner 43 in the Z-axis direction by the analog signal. The scanner driver 42 receives a control signal from a control device (not shown) and drives the scanner 43 in the X-axis direction and the Y-axis direction.
The sample S can be scanned.

The force curve measuring means 11 provided in the scanning probe microscope of the present invention comprises a cantilever 2 and a sample S
Is set, and the position of the cantilever 2 or the sample S is controlled so that the measured acting force falls within a range defined by the set limit value. Note that the amount of deflection of the cantilever can be used as the set limit value of the acting force. Hereinafter, an example in which the set limit value is determined based on the deflection amount will be described.

FIG. 2 shows the amount of deflection ΔZ acting on the cantilever.
It is a figure for explaining the relation of the limit value of (action force), and position control. In FIG. 2, the vertical axis indicates the amount of deflection ΔZ acting on the cantilever, and the horizontal axis indicates the position of the cantilever with respect to the sample, which is indicated by the position of the scanner in the Z-axis direction.
In FIG. 2, a portion indicated by A indicates a state where the cantilever is attracted to the sample side by a meniscus force due to a liquid layer existing on the sample surface when the cantilever approaches the sample, and a portion indicated by B Indicates a state in which the cantilever which has compressed the sample is returned, and a portion indicated by C indicates a state in which the cantilever is attracted to the sample side by a meniscus force due to a liquid layer existing on the sample surface when the cantilever separates from the sample.

In the present invention, the measurement range of the force curve is determined by setting a limit value for the amount of deflection acting on the cantilever. In FIG. 2, an upper limit value ΔZ (max) is defined as a limit value of a deflection amount applied to the direction in which the cantilever compresses the sample, and a lower limit value ΔZ (min) is set as a limit value of the acting force applied in the direction in which the cantilever pulls the sample.
Is determined. The upper limit ΔZ (max) and the lower limit ΔZ (min)
Is the maximum value at which the cantilever or sample is not damaged by the action force generated between the cantilever and the sample,
Alternatively, a value obtained by multiplying the maximum value by a predetermined safety factor can be used. The position control of the sample and the cantilever is performed so that the deflection amount ΔZ of the cantilever falls within a range between the set upper limit value ΔZ (max) and the lower limit value ΔZ (min). The position in the direction moves within the range between Zi (max) and Zi (min). As a result, the acting force acting between the cantilever and the sample is limited to the acting force represented by the amount of deflection between the upper limit ΔZ (max) and the lower limit Z (min).

Next, the configuration of the measuring means will be described with reference to the block diagram of FIG. 3, the measuring means 1 includes a force curve measuring means 11, a surface shape measuring means 12, an attraction force mapping measuring means 13, and a storage means 14. The force curve measuring means 11 is a part having a function of limiting the amount of deflection (action force) and determining a measurement range of the force curve based on position control based on the limitation.
As a configuration for measuring the position at the limit value, the comparing means 1
1a and a scanner position calculating means 11b. The comparing means 11a compares the detected deflection amount ΔZ with the limit value ΔZ (ma
x), ΔZ (min) and scanner position calculating means 1
1b calculates the scanner positions Zi (max) and Zi (min) at the limit value based on the comparison result of the comparing means 11a. The setting value Zs (initial position of the scanner) and the limit values ΔZ (max) and ΔZ (min) used by the comparing means 11a and the scanner position calculating means 11b can be set by the setting means 5. Further, the force curve measuring means 11
Calculates the scanner position Zi corresponding to the amount of deflection, and sends the scanner position Zi to the driver side (D / A converter 41,
The data is sent to the scanner driver 42) to perform control in the Z direction.
Scanner position Z calculated by scanner position calculation means 11b
i (max) and Zi (min) are stored in the storage unit 15.

The surface shape measuring means 12 calculates height data Di of the sample surface using the scanner position Zi (max) in the sample height calculating means 12a, and stores the surface shape data together with the X and Y coordinate data of the measurement point. 12b. Further, the adsorption force mapping measurement means 13 calculates height data di of the sample surface having the same adsorption force using the scanner position Zi (min) in the adsorption force calculation means 13a,
It is stored in the suction force distribution storage means 13b as the suction force distribution together with the X and Y coordinate data of the measurement point. Surface shape storage means 1
The data stored in 2b and the suction force distribution storage means 13b can be displayed as an image on the display means 6.

Next, the operation performed by the measuring means will be described with reference to the flowchart of FIG. First, the scanner operation start position Zs and the upper limit value of the deflection amount ΔZ (ma
x) and the lower limit Z (min) are input. The scanner operation start position Zs is the first position of the scanner in the force curve measurement, and is usually set to be a position where the cantilever and the sample are sufficiently separated. In FIG. 2, the coordinates indicating the scanner position Zi are indicated by Zi in the left direction of the figure.
Is increasing.

The upper limit value ΔZ (max) is the maximum amount of deflection when the cantilever is compressed, and corresponds to the limit value of the acting force applied in the direction in which the cantilever compresses the sample.
The lower limit Z (min) is the maximum amount of deflection when the cantilever is pulled, and is the limit value of the acting force applied in the direction in which the cantilever pulls the sample. Upper limit ΔZ
(Max) and the lower limit Z (min) correspond to the maximum value at which the cantilever or the sample is not damaged by the action force generated between the cantilever and the sample, or a value obtained by multiplying the maximum value by a predetermined safety factor. Use things (Step S
1).

The scanner is moved in the x and y directions to a measurement point (step S2), and the scanner position Zi is set to the initial position Zs in order to operate the scanner's Z axis and measure a force curve. Also, the initial movement direction of the Z axis of the scanner is set. Here, as the moving direction, the cantilever and the sample approach each other, and the polarity P in the moving direction in which a compressive force is generated is (+), and the polarity P in the moving direction in which the cantilever is separated from the sample and a tensile force is generated is (+). As −), the initial movement direction is set to (+) (Step S)
3).

While moving the scanner position Zi, the deflection amount ΔZ of the cantilever is measured (step S4), and compared with the upper limit value ΔZ (max) in the comparison means 11a.
The scanner position Zi is moved until the deflection amount ΔZ reaches the upper limit value ΔZ (max), and the deflection amount ΔZ is shifted to the upper limit value ΔZ (ma
x), the movement of the scanner position Zi is stopped (step S5), and the scanner position Zi (ma
x) is stored (step S6).

Next, the polarity of the scanner in the moving direction is set to (-), and the cantilever is moved in a direction of releasing from the sample (step S7). The deflection ΔZ of the cantilever is measured while moving the scanner position Zi (step S8),
The comparator 11a compares the value with the lower limit value ΔZ (min). The scanner position Zi is moved until the deflection amount ΔZ becomes the lower limit value ΔZ (min), and the deflection amount ΔZ is reduced to the lower limit value ΔZ.
(Min)), the movement of the scanner position Zi is stopped (step S5), and the scanner position Zi at this time is stopped.
(Min) is stored (step S10). Step S3
By repeating the steps from S10 to S10 while moving the measurement point, the surface shape and the adsorption force distribution of the measurement area on the sample surface can be obtained.

[0028]

As described above, in the observation of the surface shape and the measurement of the attraction force by the scanning probe microscope, it is possible to prevent the action of an excessive force on the sample and to improve the measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a scanning probe microscope of the present invention, and is a diagram illustrating a scanning atomic force microscope as an example.

FIG. 2 is a diagram for explaining a relationship between a limit value of a deflection amount ΔZ (action force) acting on a cantilever and position control.

FIG. 3 is a block diagram illustrating a configuration of a measuring unit according to the present invention.

FIG. 4 is a flowchart for explaining the operation performed by the measuring means of the present invention.

FIG. 5 is a schematic cross-sectional view for explaining a positional relationship between a cantilever and a sample.

FIG. 6 is a diagram showing a relationship between a position and an acting force in a force curve measurement.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Measurement part, 2 ... Cantilever, 3 ... Displacement detection system, 4 ...
Drive system, 5 setting means, 6 display unit, 11 force curve measuring means, 11a comparing means, 11b scanner position calculating means, 12 surface shape measuring means, 12a sample height calculating means, 12b surface Shape memory means, 13 ... Attraction force mapping measurement means, 13a ... Attraction force calculation means, 13b
... attracting force distribution storage means, 14 ... storage means, 20 ... probe,
31 laser oscillator, 32, 33 mirror, 34 photodiode, 35 A / D converter, 41 D / A converter, 42 scanner driver, 43 scanner, S
sample.

Claims (1)

[Claims] 1. A method for controlling the position of a cantilever or a sample so as to set a limit value of compression and tension of an acting force acting between a cantilever and a sample, and to set a measured acting force within a range defined by a set limit value. Performing force curve measurement means for measuring the acting force acting between the cantilever and the sample based on the displacement of the cantilever, surface shape measurement using the position data serving as the compression set limit value, and the tension set limit value A scanning probe microscope characterized in that an adsorption force measurement using position data is performed while moving a cantilever at each measurement point on a sample surface.