JP4489869B2 - Scanning probe microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning probe microscope, and relates to surface shape observation and adsorption force mapping measurement.
[0002]
[Prior 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 that supports the probe, and a displacement measurement system that detects bending of the cantilever, and detects the atomic force (attraction 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 the surface shape by various measurement modes such as a contact mode, a contact height mode, a non-contact mode, and a dynamic mode. The surface shape measurement by contact mode detects the deflection of the cantilever, and the surface shape measurement by dynamic mode detects the amplitude of the cantilever.
[0003]
The scanning atomic force microscope has a force curve measurement function for measuring the acting force acting between the sample and the cantilever in addition to the above 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 obtained. By measuring the force curve, the adsorption force of the sample can be measured.
[0004]
[Problems to be solved by the invention]
In the 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 nN order. Therefore, in the case of a very soft sample, the probe There is a risk of destruction by pressing force.
When the cantilever and the sample are moved relative to each other and scanned, the direction of the force that the probe acts on the sample changes depending on the surface shape, the scanning direction, etc., and is not necessarily perpendicular to the sample. There is also a problem that the measurement conditions for surface shape observation are not the same.
[0005]
When measuring the force curve with a scanning probe microscope, the position where the cantilever is closest to the sample or the position where the sample is farthest from the cantilever by the mechanism that controls the position of the cantilever or sample. The closest position is 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, the measurement range of the force curve is determined by designating the position of the cantilever or the position of the sample. Therefore, the cantilever or the sample may be damaged due to the displacement from the designated position.
[0006]
FIG. 5 is a schematic cross-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 contacts the sample S at a point Pa as shown in FIG. If the distance between the cantilever 2 and the sample S varies, the sample S and the cantilever 2 may be damaged as shown in FIG. 5B or 5C. In FIG. 5B, 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.
In addition, when the cantilever 2 and the sample S come into contact with each other and are separated from each other, a pulling force is applied to the sample S as shown in FIG. 5C by the meniscus force (adhesion force) due to the liquid L existing on the surface of the sample S. Works.
[0007]
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 as the closest approach position Zu and the most separated position Zl. Therefore, when Zu (closest approach position) is exceeded due to a position shift due to temperature drift or the like, an action force exceeding the maximum compression limit Fu is applied, and when Zl (maximum separation position) is exceeded, the maximum tensile limit is exceeded. An acting force exceeding Fu is applied. Therefore, in the case of the conventional position designation, unnecessary acting force may be applied.
[0008]
As described above, the conventional scanning probe microscope has a problem that an excessive force is applied to the sample in surface shape observation and adsorption force measurement.
Further, when the adsorption force is measured by force curve measurement, the acting force immediately before the cantilever is separated from the sample is measured. In FIG. 6, Fp immediately before the probe is separated from 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 a photodetector. However, since the point P is a change point of the acting force and is a sudden change, there is a problem that high resolution cannot be expected by measurement using a photodetector.
[0009]
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-described conventional problems and to prevent an excessive force from acting on a sample and improve measurement accuracy in surface shape observation and adsorption force measurement using a scanning probe microscope. .
[0010]
[Means for Solving the Problems]
In the force curve measurement performed in surface shape observation and adsorption force measurement using a scanning probe microscope, the present invention replaces the range in which the force curve is measured with the designation of the position of the cantilever or the position of the sample. Specifies the acting force acting on the sample. As a result, the acting force applied to the sample is limited within a set limit value to prevent 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 conditions with the acting force on the sample as a vertical direction.
[0011]
The scanning probe microscope of the present invention sets the limit value of compression and tension of the acting force acting between the cantilever and the sample, and the cantilever or the cantilever so that the measured acting force is within the range determined by the setting limit value. Force curve measurement means that controls the position of the sample and measures the acting force acting between the cantilever and the sample based on the displacement of the cantilever, measures the surface shape using the position data that is the compression set limit value, and pulls Adsorption force measurement using position data that is a set limit value is performed while moving the cantilever for each measurement point on the sample surface.
[0012]
The force curve measuring means of the scanning probe microscope of the present invention sets the upper and lower limits of the acting force acting between the cantilever and the sample as the compression setting limit value and the tension setting limit value, and the acting force is the set limit value. The position of the cantilever or sample is controlled so as to be within a predetermined range. Since the acting force and the deflection of the cantilever are proportional, the setting and measurement can be performed with the amount of deflection of the cantilever instead of the acting force.
[0013]
In the present invention, the force curve measuring means measures the data related to the surface shape from the position data that becomes the compression setting limit value, and measures the data related to the suction force from the position data that becomes the tension setting limit value. By obtaining the acquired surface shape data and adsorption force data at a plurality of measurement points on the sample surface, the 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 is limited during the force curve measurement, and the position of the cantilever or the sample is controlled so as to be within the set limit range. By doing so, surface shape and adsorption force mapping can be obtained without damaging the sample or the cantilever.
[0014]
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 direction of the acting force the same in each measurement.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram of a scanning probe microscope according to the present invention, which is an example of a scanning atomic force microscope. The scanning probe microscope shown in FIG. 1 includes a probe 20, a cantilever 2 that supports the probe 20, a displacement measuring system 3 that detects bending of the cantilever 2, and a sample S in the Z-axis direction, the X-axis direction, and the Y-axis direction. A drive system 4 that moves the probe to the surface of the sample S, detects an atomic force (attraction or repulsive force) between the probe 20 and the sample S by the amount of deflection of the cantilever, and uses the obtained amount of deflection to observe the shape of the sample surface and Perform adsorption force mapping.
[0016]
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 photo detector such as a photodiode 34, and the laser beam emitted from the laser oscillator 31 and reflected by the cantilever 2 is a photodiode. By detecting at 34, the displacement of the cantilever 2 is measured. The 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.
[0017]
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 adsorption force mapping measuring means for obtaining an adsorption force. 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 that drives the scanner 43 in the Z-axis direction using the analog signal. The scanner driver 42 can scan the sample S by receiving a control signal from a control device (not shown) and driving the scanner 43 in the X-axis direction and the Y-axis direction.
[0018]
The force curve measuring means 11 provided in the scanning probe microscope of the present invention sets a limit value of the acting force acting between the cantilever 2 and the sample S, and the measured acting force is within a range determined by the set limit value. Thus, the position control of the cantilever 2 or the sample S is performed. Note that the deflection amount of the cantilever can be used as the setting limit value of the acting force. Hereinafter, an example in which the setting limit value is determined by the amount of deflection will be described.
[0019]
FIG. 2 is a diagram for explaining the relationship between the limit value of the deflection amount ΔZ (acting force) acting on the cantilever and the 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 in the Z-axis direction of the scanner.
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 compressed with 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 leaves the sample.
[0020]
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 the amount of deflection applied in the direction in which the cantilever compresses the sample, and a lower limit value ΔZ (min) is defined as a limit value of the acting force applied in the direction in which the cantilever pulls the sample. . The upper limit value ΔZ (max) and the lower limit value ΔZ (min) are the maximum value at which the cantilever or the sample is not damaged by the acting force generated between the cantilever and the sample, or the maximum value is multiplied by a predetermined safety factor. Values 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 the range between the set upper limit value ΔZ (max) and lower limit value ΔZ (min). The position in the direction moves within the range of 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 deflection amount of the upper limit value ΔZ (max) and the lower limit value Z (min).
[0021]
Next, the configuration of the measuring means will be described using the block diagram of FIG. In FIG. 3, the measuring unit 1 includes a force curve measuring unit 11, a surface shape measuring unit 12, an adsorption force mapping measuring unit 13, and a storage unit 14.
The force curve measuring means 11 is a part having a function of determining the measurement range of the force curve based on the restriction of the deflection amount (acting force) and the position control based on the restriction, and the comparison means is configured to measure the position at the limit value. 11a and scanner position calculation means 11b. The comparison unit 11a compares the detected deflection amount ΔZ with the limit values ΔZ (max) and ΔZ (min), and the scanner position calculation unit 11b calculates the scanner position Zi at the limit value based on the comparison result of the comparison unit 11a. (Max) and Zi (min) are calculated. The setting value Zs (initial position of the scanner) and limit values ΔZ (max) and ΔZ (min) used in the comparison unit 11a and the scanner position calculation unit 11b can be set from the setting unit 5. The force curve measuring means 11 calculates a scanner position Zi corresponding to the deflection amount, and sends the scanner position Zi to the driver side (D / A converter 41, scanner driver 42) to perform control in the Z direction. . The scanner positions Zi (max) and Zi (min) calculated by the scanner position calculation unit 11 b are stored in the storage unit 15.
[0022]
The surface shape measuring means 12 calculates the sample surface height data Di using the scanner position Zi (max) in the sample height calculating means 12a, and stores it in the surface shape storage means 12b together with the X and Y coordinate data of the measurement points. To do.
Further, the adsorption force mapping measurement means 13 calculates the 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, and together with the X and Y coordinate data of the measurement points. The adsorption force distribution is stored in the adsorption force distribution storage unit 13b. The data stored in the surface shape storage unit 12b and the adsorption force distribution storage unit 13b can be displayed as an image on the display unit 6.
[0023]
Next, the operation performed by the measuring means will be described using the flowchart of FIG. First, the scanner operation start position Zs, the deflection upper limit value ΔZ (max) and the lower limit value Z (min) are input from the setting means 5. The scanner operation start position Zs is the first position of the scanner in the force curve measurement, and is normally set so that the cantilever and the sample are sufficiently separated from each other. In FIG. 2, the coordinates indicating the scanner position Zi are such that the left direction in the figure is the direction in which Zi increases.
[0024]
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 value 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. The upper limit value ΔZ (max) and the lower limit value Z (min) are the maximum value at which the cantilever or the sample is not damaged by the acting force generated between the cantilever and the sample, or a value obtained by multiplying the maximum value by a predetermined safety factor. The one corresponding to is used (step S1).
[0025]
The scanner is scanned in the x and y directions and moved to the measurement point (step S2), and the scanner position Zi is set to the initial position Zs in order to measure the force curve by operating the Z axis of the scanner. Also, the first 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 the compressive force is generated is (+), and the cantilever and the sample are separated from each other and the polarity P in the moving direction in which the tensile force is generated is ( −), The initial moving direction is set to (+) (step S3).
[0026]
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). When the deflection amount ΔZ reaches the upper limit value ΔZ (max), the movement of the scanner position Zi is stopped (step S5). The scanner position Zi (max) is stored (step S6).
[0027]
Next, the moving direction polarity of the scanner is set to (-), and the cantilever is moved in a direction to release it from the sample (step S7). While moving the scanner position Zi, the deflection amount ΔZ of the cantilever is measured (step S8) and compared with the lower limit value ΔZ (min) in the comparison means 11a. The scanner position Zi is moved until the deflection amount ΔZ reaches the lower limit value ΔZ (min)). When the deflection amount ΔZ reaches the lower limit value ΔZ (min)), the movement of the scanner position Zi is stopped (step S5). The scanner position Zi (min) at this time is stored (step S10).
By repeating the steps from step S3 to step S10 while moving the measurement point, the surface shape and adsorption force distribution of the measurement region on the sample surface can be obtained.
[0028]
【The invention's effect】
As described above, in surface shape observation and adsorption force measurement using a scanning probe microscope, it is possible to prevent an excessive force from acting on the sample and to increase measurement accuracy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a scanning probe microscope according to the present invention, and illustrates 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 (acting force) acting on a cantilever and position control.
FIG. 3 is a block diagram illustrating the configuration of the measuring means of 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 the positional relationship between a cantilever and a sample.
FIG. 6 is a diagram showing the relationship between position and acting force in 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 part, 11 ... Force curve measurement means, 11a ... Comparison means, 11b ... Scanner position calculation means, 12 ... surface shape measuring means, 12a ... sample height calculating means, 12b ... surface shape storing means, 13 ... adsorption force mapping measuring means, 13a ... adsorption force calculating means, 13b ... adsorption force distribution storing means, 14 ... storage means, 20 DESCRIPTION OF SYMBOLS ... 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)

Set the limit value of compression and tension of the acting force acting between the cantilever and the sample, and control the position of the cantilever or sample so that the measured acting force is within the range defined by the setting limit value. A force curve measuring means for measuring the acting force acting between the cantilever and the sample based on the displacement;
The compression setting limit value that sets the compression limit value and the tension setting limit value that sets the tension limit value are the maximum values that do not cause damage to the cantilever or the sample due to the acting force generated between the cantilever and the sample, Or the maximum value multiplied by the safety factor,
The compression set limits a position data profilometer using, and a suction force distribution measurement using the position data serving as the tensile set limits, while the cantilever is moved for each measurement point on the sample surface Scanning probe microscope characterized by performing.

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