JP2000097825A - Spring characteristic measuring method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement method capable of easily measuring a spring constant of a small leaf spring-like member having a probe, such as a cantilever of a scanning probe microscope. SOLUTION: A standard sample 14 having a free-standing film 21a is used. A leaf spring shape of the cantilever 1 when the probe 1a of the cantilever 1 is brought into contact with the vicinity of the center of the free-standing film 21a to move the support 1c of the cantilever 1 relatively in a direction perpendicular to the surface of the sample 14. From the change in the displacement of the member 1b, the spring constant of the leaf spring-like member 1b is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a spring characteristic of a leaf spring-like member having a probe and supported by a support, such as a cantilever used in a scanning probe microscope or the like. is there.

[0002]

2. Description of the Related Art As a kind of scanning probe microscope, there is a scanning force microscope.

In a scanning force microscope, when the tip of a probe provided near the open end of a cantilever approaches or comes into contact with a sample from several angstroms to several hundred nanometers, the sample and the tip of the probe are brought into contact with each other. This is a microscope for measuring the physical information on the sample surface by measuring the interaction force acting between them. In particular, a device utilizing atomic force is called an atomic force microscope.

In a scanning force microscope, a force acting between the tip of a probe and a sample is generally measured using a cantilever, a very soft cantilevered leaf spring having one end fixed, and the bending thereof. This is done by detecting.

As the measurement with a scanning probe microscope becomes more precise, accurate values of the spring characteristics of the cantilever are required. For example, a force curve is acquired by a scanning probe microscope, and the physical properties such as the adsorbing force and elasticity of the sample surface are measured from the force curve. An exact value of is required. Also, in a so-called contact mode atomic force microscope, even when the pressing force of the probe against the sample surface is appropriately set in order to minimize damage to the probe and the sample surface, the spring constant of the cantilever can be accurately determined. A value is required.

In a scanning probe microscope, the cantilever is frequently replaced due to damage to the probe. Even in a cantilever obtained from one wafer, the spring characteristics vary, so it is desirable to actually measure the spring characteristics of each cantilever.

Conventionally, as a method of measuring a spring constant, which is one of the spring characteristics of a cantilever of a scanning probe microscope, an unknown spring constant is measured by pressing a cantilever having an unknown spring constant against a cantilever having a known spring constant. (CTGibson, GSWatso
n, and S Myhra, "Determination of the spring const
ants of probes for force microsocpy / spectroscopy ",
Nanotechnology 7 (1996), pp.259-262)). In this case, the spring constant of the known cantilever is estimated by calculation because the shape of the cantilever is relatively simple.

[0008]

However, in the conventional measuring method of the spring constant of the cantilever described above, since the cantilever is very small, it is difficult to align the tips of the two cantilevers, and the spring constant of the cantilever is difficult. Could not be easily measured.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and provides a measurement capable of easily measuring a spring constant of a small leaf spring-like member having a probe, such as a cantilever of a scanning probe microscope. It is an object to provide a method and an apparatus thereof.

[0010]

According to a first aspect of the present invention, there is provided a measuring method for measuring a spring constant of a leaf spring-like member having a probe and supported by a support. A method, wherein the probe is brought into contact with a standard sample having a known spring constant, and the leaf spring-shaped member is moved relatively to the standard sample in a direction substantially perpendicular to the surface of the standard sample. The spring constant of the leaf spring-like member is obtained from the change in displacement of the leaf spring-like member at that time.

As described above, the combined spring constant of the standard sample and the leaf spring-like member when the probe is brought into contact with the probe is measured from the change in the displacement of the leaf spring-like member such as a force curve, and the spring obtained by the measurement is measured. The spring constant of the leaf spring-like member was determined from the constant and the spring constant of the standard sample.

A measuring method according to a second aspect of the present invention is a measuring method for measuring a spring constant of a leaf-spring-like member having a probe and supported by a support, which is substantially uniform and different from each other. Using a standard sample having a plurality of distribution regions having a known spring constant, selecting a region closest to the spring constant of the leaf spring-like member, and bringing the probe into contact with the selected region, A spring constant of the leaf spring-like member is obtained from a change in displacement of the leaf spring-like member when the spring-like member is moved relative to the standard sample in a direction substantially perpendicular to the surface of the standard sample. Things.

According to the second aspect, the spring constant of the leaf spring-like member obtained by using the region whose spring constant is closest to the spring constant of the leaf spring-like member to be measured among the plurality of distribution regions is finally calculated. As a result, the spring constant of the leaf spring-shaped member can be measured with higher accuracy.

A measuring device according to a third aspect of the present invention is a measuring device for measuring a spring constant of a leaf spring-like member having a probe and having a support end supported by a support, wherein a known spring constant is measured. A standard sample having, a displacement detecting means for detecting a displacement of the leaf spring-like member, and a moving means for relatively moving the leaf spring-like member relative to the standard sample in a direction substantially perpendicular to the surface of the standard sample. Calculating means for relatively moving a supporting end of the leaf spring-like member with respect to the standard sample and obtaining a spring constant of the leaf spring-like member based on a displacement signal from the displacement detecting means. Things.

According to the third aspect, the measuring method according to the first aspect can be performed, and the same advantages as in the first aspect can be obtained. Further, if a standard sample having a plurality of distribution regions having substantially uniform and different known spring constants from each other is used as the standard sample, the measurement method according to the second aspect can be performed. The same advantages as those of the second embodiment can be obtained.

[0016] In the third aspect, an exciting means for exciting the leaf spring-like member while changing an oscillation frequency, and the exciting frequency of the exciting means and a signal from the displacement detecting means based on the excitation frequency. If means for determining at least one of the natural frequency and the Q value of the spring-like member is provided, the natural frequency and the Q value, which are spring characteristics other than the spring constant of the leaf spring-like member, can also be measured. preferable.

[0017]

Next, a description will be given of a measuring apparatus for measuring a spring constant of a cantilever used in a scanning probe microscope.

FIG. 1 is a schematic configuration diagram showing a measuring device according to a first embodiment of the present invention. For convenience of explanation, FIG.
X, Y, and Z axes orthogonal to each other are defined as shown in
It is assumed that the Y plane is parallel to the surface of the standard sample 14, and the Z direction is a direction perpendicular to the surface of the standard sample 14.

In the following description, as an example of an object whose spring constant is to be measured, a cantilever 1 generally used in a scanning probe microscope will be described, but the object of measurement of the present invention is not limited to this. For example, it may be a doubly supported leaf spring-like member having a probe at the center that can be used in a scanning probe microscope, or a minute leaf spring-like member used in other devices other than the scanning probe microscope. There may be. By the way, the cantilever 1 whose spring constant is to be measured is composed of a cantilever type leaf spring-like member 1b having a probe 1a at the tip and a support 1c supporting one end of the leaf spring-like member 1b. I have.

The measuring device according to the present embodiment includes a cantilever holder 10 for holding a support 1c of the cantilever 1.
A laser light source 12 and a PSD as displacement detecting means for detecting a displacement of the cantilever 1 due to the bending of the leaf spring-like member 1b by an optical lever method.
13, a standard sample 14 disposed immediately below the leaf spring-like member 1b, a driving device 15 such as a piezoelectric actuator on which the standard sample 14 is mounted and moves it in the Z direction, and a control device for controlling the driving device 15 16, a data processing device 17 for outputting a spring constant from the displacement of the cantilever 1 with respect to the distance between the support 1c and the standard sample 14, and a display device 18 for displaying the data output by the data processing device 17. .

Standard sample 1 used in the present embodiment
FIG. 2 shows an example of No. 4. FIG. 2A is a schematic sectional view of the standard sample 14, and FIG. 2B is a schematic plan view of the standard sample 14. This standard sample 14 is provided on a substrate 20 with free-standing films 21a, 21a.
1b is formed. The self-standing film 21 has no plastic deformation,
A uniform one is desirable. The self-supporting films 21a and 21b may be composed of a single film, or may be composed of a plurality of laminated films. Further, self-standing films 21a and 21b having different sizes were provided on the standard sample 14. The spring constant of the self-supporting film can be changed by changing the size of the self-supporting film. The standard sample in the present embodiment uses a silicon substrate as the substrate 20, a silicon nitride film as the film 21, the thickness of the film 21 is 0.2 μm, and the sizes of the windows 20a and 20b are 0.5 mm square and It can be 1 mm square.
The standard sample 14 is formed by, for example, forming a silicon nitride film 21 on the entire surface of a silicon substrate 21 and then etching the back surface of the silicon substrate 21 by anisotropic back etching to open windows 20a and 20b. , Can be manufactured.

In this standard sample 14, each self-standing film 21a,
The spring constant of 21b is substantially uniform over a fairly wide range near its center. In addition, each self-standing film 21
The spring constants of the regions near the center of a and 21b are different from each other.

The spring constants of the free-standing films 20a and 20b may be estimated in advance by calculation, or may be measured and determined in advance using a cantilever whose spring constant is known.
The self-standing films 20a and 20b for which the spring constant has been once determined can be repeatedly used for measuring the spring constant of an unknown cantilever.

Here, the measurement principle in the present embodiment will be described with reference to FIG. FIG. 4 shows a typical force curve.

The force curve is obtained by moving the support 1c of the cantilever 1 relative to the standard sample 14 in a direction substantially perpendicular to the surface of the standard sample 14,
The distance z between the support end of the standard sample and the surface of the standard sample 14,
This is a locus that appears when the displacement l of the cantilever 1 at that time is measured and the relationship between the distance z and the displacement l is shown in a graph. The path A → B → C → D in FIG. 4 is a force curve obtained when the probe 1a is brought close to and brought into contact with the surface of the standard sample 14 (the surface of the free-standing film 21a or 21b), and the path D → E → F → G is a force curve obtained when the probe 1 a is moved away from a state where the probe 1 a is in contact with the surface of the standard sample 14.

Since the free-standing film in contact with the probe 1a has elasticity, the inclination of the straight line between H and D indicates the spring constant K of the entire system including the cantilever 1 and the free-standing film. Since the spring constant K of the entire system is a series connection of the spring constant k1 of the self-supporting membrane and the spring constant k2 of the cantilever 1, the composite spring constant of the self-supporting membrane and the cantilever 1 is expressed by Expression (1). Is done. Then, when equation (1) is solved for k2, equation (2) is obtained. Therefore, if the spring constant k1 of the self-supporting membrane is known, the spring constant K of the entire system is
That is, by measuring the inclination of the straight line between HD and D, the spring constant k2 of the cantilever is obtained.

[0027]

K = k1 · k2 / (k1 + k2) (1)

[0028]

## EQU00002 ## k2 = K.multidot.k1 / (k1-K) (2)

It should be noted that only the portion necessary for obtaining the slope of the straight line between HD and D (or the slope of a straight line having the same slope) need be measured.

When the displacement of the leaf spring-like member 1b is detected based on the signal from the PSD 13, the data processing device 17 outputs a value z01 (corresponding to the Z-direction drive signal from the control device 16 to the drive device 15). Support 1 for standard sample 14
c (corresponding to the relative position in the Z direction) and a value l01 (corresponding to the displacement (deflection) of the leaf spring-like member 1b) corresponding to the signal from the PSD 13 are taken in as data (z01, 101). This data corresponds to the data at point H in FIG. Further, the control device 16 controls the driving device 15 so that the support 1c is brought closer to the standard sample 14. At this time, the data processing device 18 outputs a value z02 and a PS value corresponding to the Z-direction drive signal from the control device 16 to the drive device 15.
The value 102 corresponding to the signal from D13 is stored in the data (z0
2, 102). This data corresponds to the data at point D in FIG. The data processing device 17
From these data, the spring constant K of the entire system corresponding to the slope of the straight line between H and D in FIG. 4 is obtained according to the equation (3).

[0031]

K = (102-101) / (z01-z02) (3)

Thereafter, the data processing device 17 calculates the value of K and the known spring constant k1 of the self-standing film of the standard sample 14 contacted with the probe 1a according to the above-described equation (2).
The spring constant k2 of the leaf spring-like member 1b of the cantilever 1 is obtained.

The display device 18 displays the spring constant k2 of the leaf spring-like member 1b of the cantilever 1 obtained by the data processing device 17.

The above operation may be repeated a plurality of times in order to increase the measurement accuracy.

Next, an example of a procedure for measuring the spring constant k2 of the leaf spring-like member 1b of the cantilever 1 using the measuring device according to the present embodiment will be described. First, the observer observes, for example, with an optical microscope (not shown) and adjusts the XY position of the probe 1a to the free-standing films 21a and 21b of the standard sample 14.
The cantilever 1 and the standard sample 14 are aligned so as to be near the center of one of them (here, the self-supporting film 21a). As described above, the self-standing films 21a, 21a
Since the spring constant of 1b is constant in a substantially wide range near the center thereof, it is not necessary to perform positioning of the cantilever 1 and the standard sample 14 with high accuracy, and this positioning is extremely easy.

When the positioning is completed, the measurer gives a measurement start command to the present measuring device using an operating device or the like (not shown). As a result, the above-described operations of the respective parts are automatically performed, and the leaf spring-like member 1b of the cantilever 1 is displayed on the display device 18.
Is displayed. The displayed spring constant k2 may be used as a final measurement result. However,
For the measurement of the spring constant of the cantilever 1, it is better to use a self-standing film having a spring constant k1 that is substantially equal to the spring constant k2 to be measured. Therefore, for example, it is preferable to perform measurement using a self-supporting film having a soft spring constant, and gradually replace the rigid self-supporting film with a rigid spring constant, and accurately measure with a self-supporting film having an appropriate spring constant. Because, as can be seen from the above equation (2), as the spring constant k1 of the standard sample is closer to the spring constant k2 of the leaf spring-like member 1b, the spring constant K ( H- in FIG.
(Corresponding to the inclination of the straight line between D) increases, thereby improving the measurement accuracy of the spring constant k2 of the leaf spring-like member 1b. Therefore, when there are a plurality of self-supporting films, when measuring the leaf spring-like member 1b, measurement is performed using a self-supporting film having a spring constant closest to the leaf spring-like member 1b. It is preferable to display k2 as a measurement result. Such an operation is based on the XY described above.
By providing a drive unit and a processing unit that determines the relationship between the obtained spring constant k2 and the spring constant of a known free-standing film having a different spring constant, complete automation can be achieved.

According to the present embodiment, since the positioning of the cantilever 1 and the standard sample 14 is extremely easy as described above, the spring constant k2 of the leaf spring-like member 1b of the cantilever 1 can be easily measured. Can be.

FIG. 3 is a schematic configuration diagram showing a measuring device according to a second embodiment of the present invention. In FIG. 3, FIG.
Elements that are the same as or correspond to the elements in them are given the same reference numerals, and duplicate descriptions thereof are omitted.

This embodiment is different from the above-described embodiment in that a leaf spring-like member 1 is provided between the holder 1 and the support portion 11.
b, a vibrator 30 such as a piezoelectric member for exciting b, a control device 31 for providing a vibrator 30 with a drive signal for vibrating the piezoelectric member 10 while changing the vibration frequency,
The only difference is that a processing unit 32 for obtaining the natural frequency and the Q value of the leaf spring-like member 1b of the cantilever 1 based on the drive signal from the first to the vibrator 30 and the signal from the PSD 13 is added. The processing unit 32 obtains the natural frequency and the Q value from the frequency dependence of the vibration amplitude of the cantilever. The natural frequency and Q value of the leaf spring-like member 1b obtained by the processing unit 32 are displayed on the display device 18.

In this embodiment, when the spring constant k2 of the leaf spring-like member 1b is measured, the operations of the piezoelectric member 30, the control device 31, and the processing unit 32 are stopped, and the operation is exactly the same as in the above-described embodiment. Thus, the measurement of the spring constant k2 is performed.

On the other hand, when the natural frequency and the Q value of the leaf spring-like member 1b are measured, the piezoelectric member is set in a state where the standard sample 14 is removed or in a state where the probe 1a is sufficiently separated from the standard sample 14. 30, control device 31, and processing unit 32
Is operated, and the natural frequency and the Q value of the leaf spring-like member 1b are displayed on the display device 18.

According to this embodiment, not only can the spring constant k2 of the leaf spring-like member 1b of the cantilever 1 be measured, but also the natural frequency and the Q value of the leaf spring-like member 1b can be measured. Thus, the spring characteristics of the leaf spring-like member 1b can be comprehensively measured.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

For example, each of the above-described embodiments is an example in which a dedicated measuring device is configured separately from the scanning probe microscope. However, the measuring device according to the present invention can be incorporated in a scanning probe microscope. .

[0045]

As described above, the spring constant of a small leaf spring-like member having a probe, such as a cantilever of a scanning probe microscope, can be easily measured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a measuring device according to a first embodiment of the present invention.

FIG. 2 is a view showing an example of a standard sample. FIG. 2 (a) is a schematic sectional view, and FIG. 2 (b) is a schematic plan view.

FIG. 3 is a schematic configuration diagram illustrating a measuring device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a typical force curve.

[Explanation of symbols]

 Reference Signs List 1 cantilever 1a probe 1b leaf spring-like member 1c support body 10 cantilever holder 11 support portion 12 laser light source 13 PSD 14 standard sample 15 drive device 16 control device 17 data processing device 18 display device 21 substrate 20a, 20b window 21a, 22b self-supporting Film 30 vibrator 31 controller 32 processing unit

Claims (3)

[Claims] 1. A measuring method for measuring a spring constant of a leaf spring-like member having a probe and supported by a support, comprising: contacting the probe with a standard sample having a known spring constant; When the leaf spring-shaped member is moved relative to the standard sample in a direction substantially perpendicular to the standard sample surface,
A measurement method comprising: obtaining a spring constant of the leaf spring-like member from a change in displacement of the leaf spring-like member. 2. A method for measuring a spring constant of a leaf spring-like member having a probe and supported by a support, comprising: a plurality of distributions having substantially uniform and different known spring constants. Using a standard sample having a region, selecting the region closest to the spring constant of the leaf spring-like member and bringing the probe into contact with the selected region, the leaf spring-like member is substantially flush with the standard sample surface. A measurement method comprising: obtaining a spring constant of the leaf spring-like member from a change in displacement of the leaf spring-like member when the leaf spring-like member is moved relatively to the standard sample in a vertical direction. 3. A measuring device for measuring a spring constant of a leaf spring-like member having a probe and having a support end supported by a support, comprising: a standard sample having a known spring constant; Displacement detecting means for detecting the displacement of the standard spring; moving means for relatively moving the leaf spring-shaped member with respect to the standard sample in a direction substantially perpendicular to the surface of the standard sample; A measuring means for relatively moving a supporting end of the plate-shaped member and obtaining a spring constant of the leaf spring-shaped member based on a displacement signal from the displacement detecting means.