JPH10206433A - Scanning-type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To bring a probe close to a sample quickly, accurately, and efficiently by enabling a control means to obtain the relationship between the amount of displacement of a scanner and that of a cantilever and extending the scanner based on it. SOLUTION: A cantilever 4 has a sharp probe 2 at its tip and is extended and contracted to change the relative distance between the probe 2 and a sample 6. A scanner displacement detector 10 detects the amount of displacement of the scanner 8 that is generated when the relative distance between the probe 2 and the sample 6 is changed, and a cantilever displacement detector 12 detects the amount of displacement of the cantilever 4 caused by the change in the relative distance between the probe 2 and the sample 6. A control means (for example, a CPU 20) obtains the relationship between the amount of displacement of the scanner 8 and that of the cantilever 4 and continuously extends or contracts the scanner 8 up to a point close to a contact point where the probe 2 at least contacts the sample 6. A piezo driver 2 performs the expansion and contraction displacement of the scanner 8 based on a control signal from the CPU 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning probe microscope (SP) for measuring surface information of a sample with high resolution.
M) relates to a technique for causing a probe of a cantilever to approach a sample surface.

[0002]

2. Description of the Related Art When a probe of a cantilever approaches a sample surface, a probe contact pressure setting operation called force curve measurement is usually performed. In this force curve measurement, when a scanner (for example, a piezoelectric tube scanner) supporting a cantilever or a sample is expanded and contracted,
The displacement of the cantilever caused by the interaction between the tip of the probe and the sample surface is optically detected by, for example, a displacement detection sensor.

FIG. 6A shows the result of measurement of a force curve in a static mode, and FIG. 6B shows the result of measurement of a force curve in a dynamic mode. force curve characteristics based on the relationship between expansion and contraction displacement (Z) and the output voltage value of the displacement sensor (V _S) are shown. In this case, the reflected light reflected from the cantilever and the reflected light reflected from the sample interfere with each other due to an optical path difference therebetween.
The force curve characteristic before the tip of the probe contacts the sample surface appears as a wavy curve that changes at a predetermined cycle in accordance with the amount of displacement of the scanner.

[0004] Then, the probe is positioned at the approach position set based on the force curve characteristics, and S
PM measurement is performed. This approach position, it is possible to define the displacement amount of the scanner (Z) and the voltage value of the displacement sensor and (V _S) by. For example, FIG.
3A and 3B, the approach position (see FIG. 3A) in the static mode is defined based on the relationship between the displacement Z1 and the voltage _VB1, and the displacement Z2 and the voltage _VB2 are defined. Based on the relationship, the approach position in the dynamic mode (see FIG. 4B) is defined.

Here, the voltage values V _B1 and V _{B2 of} each mode are
Is the approach determination reference value, in the process of extending the scanner, the voltage value V from the displacement detection sensor
_{When S} reaches the approach determination reference values V _B1 and V _B2 ,
That is, when the relationship of V _S ≧ V _B1 (see FIG. 4A) and V _S ≦ V _B2 (see FIG. 4B) is satisfied, the probe is approached to a predetermined position on the sample surface. Is determined.

Thereafter, the surface information of the sample is measured while performing feedback control of the scanner so that the output of the displacement detection sensor is maintained at the approach determination reference values V _B1 and V _B2 .

[0007]

As described above, when an approach determination reference value is set based on a force curve characteristic that changes in a wave shape, it is erroneously determined that the probe has been approached before the probe is positioned at the approach position. In some cases.

Specifically, in FIG. 6A, V _S ≧
The displacement amount (Z) of the scanner satisfying the relationship V _B1 is Z
There are two locations (Z1 ', Z1 ") on the near side of the location 1.
For this reason, before the probe is positioned at the approach position corresponding to the displacement amount Z1, it may be erroneously determined that the probe has been approached with the displacement amount Z1 'or Z1 ". Similarly, FIG. As shown in (2), in Z2 'on the near side of Z2, the relationship of V _S ≤ V _B2 is satisfied. May be erroneously determined to have been performed.

[0009] Such a problem also occurs, for example, as shown in FIG. FIG. 6C shows a force curve characteristic in a state where an electrostatic attractive force acts between the probe and the sample. In this case, assuming that the approach determination reference value is V _B3 , V _S ≧
The relationship V _B3 is already satisfied at the start of the force curve measurement. As a result, before the probe is positioned at the approach position corresponding to the displacement Z3, that is, it is erroneously determined that the probe has been approached at the displacement Z3 'corresponding to the start of the force curve measurement.

[0010] When such a problem occurs, it is difficult and time-consuming to make the probe approach the set approach position accurately, so that there is also a problem that the approach operation cannot be performed efficiently. I do.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a scanning probe microscope in which a probe can accurately and accurately approach a sample in a short time. Is to do.

[0012]

In order to achieve the above object, a scanning probe microscope according to the present invention comprises a cantilever having a sharpened tip at the tip and a relative position between the cantilever and the sample. A scanner that can be extended and retracted to change the distance, a scanner displacement detector that detects the amount of displacement of the scanner that occurs when the relative distance between the probe and the sample changes, the probe and the sample A cantilever displacement detector for detecting a displacement amount of the cantilever caused by a change in a relative distance between the probe and a probe, and a relationship between a displacement amount of the scanner and a displacement amount of the cantilever is obtained. And control means capable of continuously extending the scanner to at least a position near a contact point where the scanner contacts the sample.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning probe microscope according to one embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the scanning probe microscope according to the present embodiment expands and contracts so as to change the relative distance between the cantilever 4 having the sharpened tip 2 at the tip and the sample 6. A possible scanner 8 (for example, a piezoelectric tube scanner), a scanner displacement detector 10 for detecting the amount of displacement of the scanner 8 that occurs when the relative distance between the probe 2 and the sample 6 is changed, and the probe 2 A cantilever displacement detector 12 for detecting a displacement amount of the cantilever 4 caused by a change in a relative distance between the cantilever 4 and the sample 6, and a relationship between the displacement amount of the scanner 8 and the displacement amount of the cantilever 4 is obtained. Control means capable of continuously extending the scanner 8 to at least a position near a contact point where the probe 2 contacts the sample 6.

The scanner 8 has a base end supported on a coarse movement mechanism 14, and a sample stage 16 on which the sample 6 can be mounted is attached to the tip end. A coarse movement driver 18 is connected to the coarse movement mechanism 14.
The scanner 8 can be moved in the XYZ directions based on a control signal output from the PU 20 via the D / A converter 22.

The scanner 8 includes a piezo driver 2.
4 is connected, and the D / A converter 26
The scanner 8 can be expanded and contracted in the XYZ directions based on a control signal output through the scanner 8.

The scanner displacement detector 10 is configured to detect the amount of displacement of the scanner 8 in the Z direction when the relative distance between the probe 2 and the sample 6 is changed by the scanner 8. I have. This scanner displacement detector 10
Is output to the feedback circuit 30 and the A / D converter 32 via the amplifier 28.
The detection signal output to the feedback circuit 30 is input to the piezo driver 24, while the detection signal output to the A / D converter 32 is input to the CPU 20.

The cantilever displacement detector 12 includes a detector body 34 and light detecting means capable of optically detecting the amount of displacement of the cantilever 4. Supported.

As the light detecting means, an optical lever method, a focus detecting method, or the like can be applied. In the present embodiment, for example, a light detecting means using an optical lever method is used. And The optical lever type light detecting means includes a semiconductor laser 3 capable of irradiating the back surface of the cantilever 4 (the surface opposite to the surface on which the probe 2 is formed) with laser light.
6 and a photodetector 38 capable of receiving light reflected from the back surface of the cantilever 4. The semiconductor laser 36 and the photodetector 38 are both attached to the detector main body 34.

The semiconductor laser 36 includes a laser driver 4
It is configured so that a predetermined laser beam can be emitted based on a signal from 0. Further, the photodetector 38 is configured to output an electric signal corresponding to the amount of received light. The electric signal from the photodetector 38 is output to the feedback circuit 44 and the A / D converter 46 via the amplifier 42. The detection signal output to the feedback circuit 44 is input to the piezo driver 24, while the detection signal output to the A / D converter 46 is input to the CPU 20.

The cantilever 4 is provided with a piezoelectric body 48 for cantilever excitation.
Is applied to the piezoelectric body 48 via the piezo driver 52 via the D / A converter 50 to cause the cantilever 4 to vibrate at a resonance frequency according to the intended use. Have been.

A memory 54 is connected to the CPU 20, and a processing program for each signal input to the CPU 20 (for example, a program for calculating a second-order difference to be described later) and a CP
The control program of each control signal output from U20, each input signal and a predetermined calculation result can be stored. In the present embodiment, as an example, the CPU 20 determines, based on the relationship between the amount of displacement of the scanner 8 and the amount of displacement of the cantilever 4, at least a contact point at which the probe 2 comes into contact with the sample 6. A scanner extension amount setting means for extending the scanner 8 to a desired nearby position is provided.

The CPU 20 is connected to a host computer 58 via a communication board 56, and is configured to be able to display calculation results and surface information of the sample 6 on a monitor 60.

According to such a configuration, first, the scanner 8 is moved by a predetermined amount in the Z direction by the coarse movement mechanism 14, and then the contact pressure between the probe 2 and the sample 6 is set by force curve measurement. Is done. Subsequently, as the contact pressure is maintained, on the basis of the output voltage value V _S and CPU20 photodetectors 38 to the reference signal output through the D / A converter 62, the piezoelectric driver 24 from the feedback circuit 44 A predetermined feedback signal is applied to the scanner 8 via the scanner 8 to perform feedback control of the scanner 8 along the Z direction. While the feedback control is being performed, the piezo driver 2 is controlled based on a control signal output from the CPU 20 via the D / A converter 26.
4 applies a predetermined XY scanning signal to the scanner 8 to displace the scanner 8. At this time, the probe 2 is relatively scanned along the sample 6 in the XY directions, and the surface information of the sample 6 is measured. The measured surface information is CUP
After being input to the host computer 58 via the CPU 20 and subjected to predetermined image processing, the image is displayed on the monitor 60 as a three-dimensional image. This three-dimensional image is
It can also be stored in the memory 54.

When the SPM measurement is performed efficiently, the contact pressure between the probe 2 and the sample 6 is set by force curve measurement, and then the probe 2 is accurately and accurately applied to the sample 6 in a short time. It is necessary to approach.

In order to fulfill this demand, the following approach is applied to the scanning probe microscope of the present embodiment. Hereinafter, this approach method will be described with reference to FIGS. 1 and 3 according to the flowchart of FIG.

FIG. 3A shows the result of force curve measurement in the static mode, and FIG. 3B shows the result of force curve measurement in the dynamic mode. Detector 10
Force curve characteristic based on the relationship between expansion and contraction displacement and (Z) output voltage value of the cantilever displacement detector 12 (V _S) of the scanner 8 detected is indicated by. In this case, since the reflected light reflected from the cantilever 4 and the reflected light reflected from the sample 6 interfere with each other due to a difference in optical path therebetween, the force curve characteristic before the tip of the probe 2 contacts the surface of the sample 6 is: The waveform becomes a wavy curve that changes in a predetermined cycle in accordance with the displacement amount of the scanner 8 (see S1 in FIG. 2).

Conventionally, SPM measurement is performed with the probe 4 positioned at the approach position on the sample 6 so that the contact pressure is set based on the force curve characteristics.
By the way, this approach position is determined by the cantilever displacement detector 12 when the cantilever 4 is flexed and displaced by a desired amount.
_Can be defined by the voltage value (V _S ) output from.

[0028] For example, FIG. 3 (a), in the measurement mode (b), respectively, approaches the position of the respective modes on the basis of the voltage value V _B is defined. Note that the voltage value V _B is temporarily taken into the CPU 20 for use in subsequent signal processing.

Here, assuming that the voltage value V _B of each mode is an approach determination reference value, in this embodiment, an approach determination start point is set separately from this approach determination reference value V _B. In this case, the approach determination start point is a scanner 8 that can continuously extend the scanner 8 without any limitation and unconditionally during the approach operation.
2 is a value (Z _B ) that defines the amount of displacement (Z) of the
2).

In order to perform the approach operation efficiently in a short time, it is preferable that the approach determination start point Z _B is set as close to the approach determination reference value V _B as possible. For example, in the measurement mode (dynamic mode) of FIG. 3B, the frequency band should be set very close to the resonance frequency of the cantilever 4 according to the purpose of use, and very close to the point where the amplitude value of the cantilever 4 starts to decrease. Is preferred.

As described above, the approach determination reference value V
After setting the _B and approach judgment start point Z _B, CPU
20 to a piezo driver 24 via a D / A converter 26
Scanner 8 based on the approach control signal output to
The is unconditional and continuously extended to approach judgment start point Z _B in the Z direction (see S3 in Fig. 2). In this case, based on a detection signal from the scanner displacement detector 10 and a reference signal output from the CPU 20 via the D / A converter 64, a predetermined feedback signal is sent from the feedback circuit 30 to the scanner 8 via the piezo driver 24. Is applied to perform feedback control on the scanner 8. Furthermore, the operation of extending the scanner 8 to approach judgment start point Z _B may be performed without considering certain conditions based on the change of the voltage value V _S from the cantilever displacement detector 12 as described below . As a result, the precise scanner 8 without being affected by the interference light can be extended unconditionally to approach judgment start point Z _B.

[0032] After this, further extending the scanner 8 gradually from approach judgment start point Z _B to the displacement amount [Delta] Z _B corresponding to approach criterion value V _B (see S4 in FIG. 2). In this approach process, the CPU 20, the comparison process between the voltage value V _S and approach determination reference value V _B from the cantilever displacement detector 12 is carried out (FIG. 2
S5). During the process, the feedback control is performed on the scanner 8.

When the voltage value V _S from the cantilever displacement detector 12 reaches the approach determination reference value V _B , that is, V _S ≧ V _B (see FIG. 3A), V _S ≦ V _B
When a certain condition is satisfied (see FIG. 3B), it is determined that the probe 2 has approached a predetermined position of the sample 6 by bending the cantilever 4 by a desired amount (S6 in FIG. 2). reference).

Further, the approach method of this embodiment is as follows.
For example, as shown in FIG. 3C, the present invention can be applied to a measurement mode in which an electrostatic attractive force acts between the probe 2 and the sample 6. That is, after the scanner 8 is unconditional and continuously extended to approach judgment start point Z _B in the Z direction, V
_The scanner 8 may be gradually extended to the displacement amount ΔZ _B until a certain condition of _S ≧ V _B is satisfied.

The approach determination start point Z _B can be arbitrarily set to a desired value by the measurer operating the host computer 58 (see FIG. 1).
Thus, according to this embodiment, it is possible to extend the unconditional and continuously scanner 8 to the vicinity position Z _B of no approach determination reference value V _B being affected by the interference light at the time of the force curve measured Therefore, the probe 2 can efficiently and accurately approach the sample 6 in a short time.

Further, if the approach method of the present embodiment is used, even when a soft sample such as a biological sample is measured in the static mode, the probe 2 can be safely and reliably scanned with respect to the sample. .

The present invention is not limited to the above-described embodiment, and can be variously modified without adding new matter. For example, a principle has been conventionally known in which, when a second-order difference operation is performed on a predetermined characteristic curve, a delta function-like peak is obtained at a point where the curve changes abruptly. Therefore, when this principle is applied to the force curve characteristic curve (see FIGS. 4 and 5), a peak value can be obtained at a point where the probe 2 comes into contact with the sample 6. Therefore, if this peak value is defined as the approach determination start point, the scanner 8 can be unconditionally and continuously extended to the approach determination start point based on the approach method of the above embodiment.
The probe 2 can efficiently and accurately approach the sample 6 in a short time.

Hereinafter, an approach method according to such a modification will be described in a measurement mode (see FIG. 4) affected by interference light.
A description will be given of an approach operation in a case where the method is applied to a measurement mode (see FIG. 5) in which electrostatic attraction acts between the probe 2 and the sample 6 without being affected by interference light, respectively.

First, a force curve measurement is performed in the same manner as in the above embodiment, and a force curve characteristic curve as shown in FIGS. 4A and 5A is detected. The data of the force curve characteristic curve, that is, the amount of displacement of the scanner 8 and the amount of deflection of the cantilever 4 corresponding to the amount of displacement are A
/ D converters 46 and 32 and memory 54 via CPU 20
Are sequentially stored as digital data. A force curve characteristic curve is displayed on the monitor 60 via the communication board 56.

Next, after the cantilever 4 sets the voltage value V _B output from the cantilever displacement detector 12 when flexed by a desired amount as an approach determination reference value, the second-order difference with respect to the force curve characteristic curve Perform an operation. In addition,
The second-order difference calculation is performed according to a calculation program input to the CPU 20 in advance.

First, a plurality of points are specified at regular intervals on the force curve characteristic curve, and the difference between the points is plotted (first step). Next, a characteristic curve is calculated from the plurality of values plotted in the first step (second step). Subsequently, a plurality of points are specified at regular intervals on the characteristic curve calculated in the second step, and the difference values between the points are plotted (third step). Then, a characteristic curve is calculated from the plurality of values plotted in the third step (fourth step). As a result, as shown in FIGS. 4B and 5B, the probe 2 comes into contact with the sample 6 in the relationship between the displacement amount (Z) of the scanner 8 and the second-order difference value (U _S ). A delta function peak value is obtained at the point.

More specifically, the digital data of the force curve characteristic curve stored in the memory 54 is sequentially read out, and the difference between adjacent data is obtained by calculation (first step). Next, a difference value between adjacent data of the difference value obtained in the first step is obtained by calculation (second
Process). Subsequently, the value obtained in the second step is
Is plotted as a relationship between the displacement amount (Z) and the second-order difference value (U _s ), and the characteristics shown in FIGS. 4B and 5B are created (third step). As a result, a delta function peak value is obtained at the point where the probe 2 comes into contact with the sample 6.

For example, 2 based on n digital data
Expressing the floor difference value by an expression is as follows. Here, the displacement amount of the scanner 8; Z1 to Zn, the sensor output voltage;
Assuming that Vn, the difference value Di in the first step is represented by Di = (Vi-Vi-1) / (Zi-Zi-1) (where i = 2 to n). Furthermore, the second-order difference U _{S is, U S i = (Di -Di} -1) / (Zi -Zi-1) ( except, i = 3 to n) represented by.

[0044] In approach of this modification, in order to identify the peak values to identify the second-order difference value U _B, the value probe - set as a sample contact determination reference value. Next, the CPU 20 compares the second-order difference value U _S with the probe-sample contact determination reference value U _B, and determines the displacement Z _B of the scanner 8 when a certain condition of U _S ≧ U _B is satisfied. And set this value as the approach determination start point.
Thereafter, the approach control signal output to the piezoelectric driver 24 via the D / A converter 26 from the CPU 20, it is possible to unconditionally and continuously extending the scanner 8 to approach judgment start point Z _B in the Z direction . Furthermore,
Approach determination reference value V from approach judgment start point Z _B
The scanner 8 is further extended little by little to a displacement amount ΔZ _B corresponding to _B. When the voltage value V _S from the cantilever displacement detector 12 reaches the approach determination reference value V _B , that is, when a predetermined condition of V _S ≧ V _B is satisfied, the cantilever 4 bends by a desired amount. Accordingly, it is determined that the probe 2 has approached a predetermined position of the sample 6.

According to such a modification, the point in time when the probe 2 comes into contact with the sample 6 can be specified, so that the criteria for the approach determination operation can be clarified. Note that other effects are the same as those of the above-described embodiment, and a description thereof will not be repeated.

[0046]

According to the present invention, it is possible to provide a scanning probe microscope in which a probe can accurately and accurately approach a sample in a short time.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating an approach operation of the scanning probe microscope according to the embodiment.

FIG. 3A is a diagram for explaining an approach operation based on a force curve characteristic in a static mode.
(B) is a diagram for explaining an approach operation based on a force curve characteristic of a dynamic mode, (c)
FIG. 4 is a diagram for explaining an approach operation based on a force curve characteristic in a measurement mode in which an electrostatic attractive force acts between a probe and a sample.

4A and 4B are explanatory diagrams of an approach operation according to a modification of the present invention, in which FIG. 4A shows a force curve characteristic in a static mode, and FIG. 4B shows a characteristic obtained by a second-order difference operation. FIG.

FIG. 5 is an explanatory view of an approach operation applied to a modification of the present invention, in which (a) shows a force curve characteristic in a measurement mode in which an electrostatic attractive force acts between a probe and a sample. FIG. 3B is a diagram illustrating characteristics obtained by a second-order difference operation.

6A and 6B are explanatory diagrams of an approach operation applied to a conventional scanning probe microscope, where FIG. 6A is a diagram for explaining an approach operation based on a force curve characteristic in a static mode, and FIG. FIG. 3C is a view for explaining an approach operation based on a force curve characteristic in a dynamic mode. FIG. 3C shows an approach operation based on a force curve characteristic in a measurement mode in which an electrostatic attraction is applied between the probe and the sample. FIG.

[Explanation of symbols]

 2 Probe 4 Cantilever 6 Sample 8 Scanner 10 Scanner displacement detector 12 Cantilever displacement detector

[Procedure amendment]

[Submission date] February 24, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

According to such a configuration, first, the scanner 8 is moved by the coarse movement mechanism 14 in the Z direction by a predetermined amount, and then the contact pressure between the probe 2 and the sample 6 is set by force curve measurement. Is done. Then, based on the output voltage value V _S of the photodetector 38 and the reference signal output from the CPU 20 via the D / A converter 62, the piezo driver 24 is controlled by the feedback circuit 44 so that the contact pressure is maintained. A predetermined feedback signal is applied to the scanner 8 via the scanner 8 to perform feedback control of the scanner 8 along the Z direction. While the feedback control is being performed, the piezo driver 2 is controlled based on a control signal output from the CPU 20 via the D / A converter 26.
4 applies a predetermined XY scanning signal to the scanner 8 to displace the scanner 8. At this time, the probe 2 is relatively scanned along the sample 6 in the XY directions, and the surface information of the sample 6 is measured. The measured surface information is stored in the CPU
After being input to the host computer 58 via the CPU 20 and subjected to predetermined image processing, the image is displayed on the monitor 60 as a three-dimensional image. This three-dimensional image is
It can also be stored in the memory 54.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

Next, after the cantilever 4 sets the voltage value V _B output from the cantilever displacement detector 12 when flexed by a desired amount as an approach determination reference value, the second-order difference with respect to the force curve characteristic curve Perform an operation.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

The second-order difference calculation is performed according to a calculation program input to the CPU 20 in advance.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0045

[Correction method] Change

[Correction contents]

According to such a modification, the point in time when the probe 2 comes into contact with the sample 6 can be specified, so that it is possible to clarify the criterion of the approach determination operation. Note that other effects are the same as those of the above-described embodiment, and a description thereof will not be repeated.

Claims (3)

[Claims] 1. A cantilever having a sharpened tip at a tip, a scanner which can be extended and retracted so as to change a relative distance between the probe and a sample, and a relative distance between the probe and the sample. A scanner displacement detector that detects a displacement amount of the scanner that occurs when a distance is changed; and a cantilever displacement detector that detects a displacement amount of the cantilever caused by a change in a relative distance between the probe and the sample. Determining the relationship between the amount of displacement of the scanner and the amount of displacement of the cantilever, and continuously extending the scanner to at least a position near a contact point where the probe contacts the sample based on the relationship. A scanning probe microscope comprising: a control unit; 2. The control device according to claim 1, wherein the control unit is configured to extend the scanner to the contact point or a desired nearby position of the contact point based on a relationship between a displacement amount of the scanner and a displacement amount of the cantilever. The scanning probe microscope according to claim 1, further comprising an amount setting unit. 3. The apparatus according to claim 1, wherein said control means continuously extends said scanner to said contact point.
2. A scanning probe microscope according to claim 1.