JP2001013155A - Measuring method for scanning probe microscope and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To scan a sample by a cantilever in a scanning probe microscope, and to accurately measure a sample surface at a high S/N ratio. SOLUTION: A multilayer piezoelectric element 22 is excited at a resonance frequency f0 of a cantilever 3 by a signal from an oscillator 9. In that state, a sample surface is scanned with bringing a probe 3a of the cantilever 3 in contact with a sample 12. An optical lever detection part 2 detects a position of the cantilever 3 at a nearly middle position of a lever body 3c. When the probe 3a comes into contact with the sample 12, the cantilever 3 vibrates at a large amplitude, while a Z-direction position of the cantilever 3 is feedback- controlled by use of a partial position having a largest amplitude detected by the optical lever detection part 2. As a result, a shape of the sample surface can be accurately measured at a high S/N ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the surface shape of a sample using a scanning probe microscope and a device therefor, and more particularly to a scanning probe microscope for measuring the surface shape of a sample by vibrating the sample. The present invention relates to a measuring method and an apparatus.

[0002]

2. Description of the Related Art As a conventional measuring method for measuring the surface shape of a sample using a scanning probe microscope, a servo system is used so that the cantilever is resonated and vibrated and the sample surface is lightly hit and the hitting condition is constant. A measurement method is known in which the position of the cantilever in the Z direction (distance between the sample and the cantilever) is feedback-controlled to obtain shape data of the sample surface. This method is generally called a tapping mode.

[0003]

However, as described above, when measuring the sample surface in the tapping mode, if the cantilever is brought close to the sample while the cantilever is tapping the sample lightly, the self-excited oscillation of the cantilever is suppressed. Therefore, the vibration amplitude of the cantilever becomes smaller as the cantilever approaches the sample. As a result, the S / S of the detection signal when the cantilever was extremely close to the sample was obtained.
There is a problem that the N ratio is remarkably reduced, the position control of the cantilever in the Z direction becomes unstable, and measurement cannot be performed accurately.

An object of the present invention is to provide a measuring method and apparatus for a scanning probe microscope, which can solve the above-mentioned problems in the prior art.

[0005]

According to the present invention, there is provided a method for measuring the shape of a surface of a sample by placing the cantilever on the surface of the sample. In the state where the sample is vibrated at the resonance frequency of or at a frequency substantially equal to the resonance frequency in the vicinity of the resonance frequency, the shape of the sample surface is measured while lightly touching the cantilever to the sample surface.

The vibration of the sample may be the whole sample, or may be local vibration of a part of the sample, that is, only a measurement portion of the sample.

When the sample is vibrated in this way, when the tip of the cantilever approaches the sample when the probe comes into contact with the sample by atomic force, the cantilever vibrates from the vibrated sample. The cantilever is vibrated. Since the frequency of the vibration is the same or substantially the same as the resonance frequency of the free vibration of the cantilever, the vibration amplitude of the cantilever gradually increases as the cantilever approaches the sample.

As a result, when the cantilever is scanned for measurement after the probe is lightly brought into contact with the surface of the sample, the vibration amplitude of the cantilever is large even if the cantilever is in contact with the sample, and the detection signal S / N ratio is improved,
High-precision measurement is possible.

Further, according to the present invention, in a scanning probe microscope in which a cantilever is placed on a surface of a sample to measure the shape of the surface of the sample, the sample is provided with a resonance frequency of free vibration of the cantilever or a substantial frequency near the resonance frequency. There is proposed a scanning probe microscope provided with a vibration means for vibrating at a frequency substantially equal to the resonance frequency.

The vibrating means may be configured to vibrate the entire sample, or may be configured to locally vibrate only a portion to be measured of the sample.

According to the present invention, in a measuring method of a scanning probe microscope in which a cantilever is applied to a surface of a sample to measure a shape of the surface of the sample, the degree of hitting of the sample by the cantilever is in a predetermined state. In order to perform feedback control of the position of the cantilever in the Z direction by a servo system, a method of detecting the position of the cantilever at a position between the fixed end of the cantilever and the probe is proposed.

It is preferable that the position for detecting the position on the cantilever is a substantially intermediate position between the fixed end of the cantilever and the probe.

The position detection of the cantilever may be performed by directly attaching a sensor such as a strain gauge on the cantilever, or a spot of the laser beam is applied to a predetermined spot on the cantilever, and the reflected laser beam generated thereby is divided by a split type. A configuration in which light is received by a photodiode and detected is also possible.

During the measurement, the cantilever vibrates so that the fixed end and the probe become a node, and the portion between them becomes an antinode of vibration, and the vibration amplitude there increases. Therefore, according to the above method, the detection sensitivity can be increased.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the scanning probe microscope according to the present invention. In this scanning probe microscope, as shown in the figure, a displacement detecting unit 2 (hereinafter, referred to as an optical lever detecting unit) of a cantilever 3 is attached to a lower end of a piezo scanner 1 having an upper end fixed. The optical lever detection unit 2 has a known configuration using a laser beam.
Output signal from the RMS-DC circuit (Root mean square)
-DC circuit, that is, a root-mean-square circuit 4, where it is detected and converted into a DC signal having a level corresponding to the displacement of the cantilever 3. The DC output signal from the RMS-DC circuit 4 is input to the comparator 5 and the target value setting unit 6
Is compared with the target value set in. An output indicating the result of the magnitude comparison in the comparator 5 is input to a proportional-integral (PI) control unit 7.

The output signal of the proportional-integral control unit 7 is
The signal is sent to the amplifier 8. The output of the amplifier 8 is applied to the Z-direction of the piezo scanner 1, that is, to the axial drive electrode 1a of the piezo scanner 1. The scanning signal output of the XY scanning signal generator 10 is applied to the X and Y direction driving electrodes 1b and 1c, respectively. The comparator 5, the target value setting unit 6, and the PI control unit 7 control the distance between the probe 3a of the cantilever 3 and the sample 12 to a value set by the target value setting unit 6. The Z servo system 11 is configured. Therefore, the output signal of the proportional-integral control unit 7 represents the shape of the surface of the sample 12, and is sent as an image signal a to an image display device (not shown).

Reference numeral 9 denotes 1 to 400 kHz
, And an output signal from the oscillator 9 is applied to the multilayer piezo 22. As is well known, the multi-layer piezo 22 is formed by stacking a plurality of piezo plates having the same polarity in the same direction. The multi-layer piezo 22 is provided on a fixed base 23, and the sample 12 is placed on the multi-layer piezo 22. I have. When the output signal from the oscillator 9 is applied to the multilayer piezo 22, the displacement amounts of the individual piezos are added and a large displacement can be obtained. With the above configuration, the sample 12 can be forcibly vibrated by the multilayer piezo 22 at the same frequency as the frequency of the output signal from the oscillator 9.

In the scanning probe microscope shown in FIG. 1, the vibrating device constituted by the oscillator 9 and the multi-layer piezo 22 converts the sample 12 into the same frequency as the resonance frequency f0 of the free vibration of the cantilever 3. It is constituted so that it can be vibrated. That is, by setting the frequency of the output voltage from the oscillator 9 to f0,
Vibrates at the frequency f0, which causes the sample 12 to
Excited entirely at 0.

Next, the operation of the scanning probe microscope shown in FIG. 1 will be specifically described with reference to FIGS.
Here, FIG. 2 shows the distance d (horizontal axis) between the probe 3a provided at the tip of the cantilever 3 and the sample 12, and the R
The relation with the level (vertical axis) of the output signal of the MS-DC circuit is shown.

First, the distance d between the probe 3a and the sample 12
The sample 12 is vibrated in the vertical (Z) direction by operating the oscillator 9 in a state where the two are separated from each other by a predetermined distance so that they do not come into contact with each other, and applying the output signal of the oscillator 9 to the multilayer piezo 22. At this time, the frequency of the oscillator 9 is adjusted so that the frequency of the sample 12 becomes the resonance frequency f0 of the free vibration of the cantilever 3.

As described above, when the sample 12 is vibrated in the vertical (Z) direction by the multilayer piezo 22, the whole of the sample 12 is forcibly vibrated with a predetermined constant amplitude. At this time, since the probe 3a is far away from the sample 12, and the amplitude of the sample 12 is smaller than the distance d between the probe 3a and the sample, the probe 3a does not contact the sample surface, and the RMS-DC The output signal value of the circuit is zero.

Thereafter, the Z-servo system 11 is operated, and a gradually larger voltage is applied to the Z-direction drive electrode 1a of the piezo scanner 1, so that the optical lever detecting unit 2 is lowered, and the probe 3a and the sample 12 are moved. Is gradually reduced. Finally, the probe tip 3a comes into contact with the vibrating surface of the sample 12. Then, the cantilever 3 becomes the sample 12
Vibrates at the same vibration frequency as the sample 12, that is, the resonance frequency f0 of the cantilever 3 itself.

The displacement caused by the contact of the probe 3a with the sample 12 is optically detected by the optical lever detector 2, whereby the cantilever 3 contacts the sample 12 as shown in FIG. After d1), the vibration amplitude of the cantilever 3 increases as the cantilever 3 is brought closer to the sample 12. In the present embodiment, since the target value is set to ΔA in FIG. 2, the probe 3a enters (d1 -d0) from its surface position (d = d1) at the maximum stroke of the forced vibration of the sample 12. At this point, the Z coarse movement ends. afterwards,
The XY scanning signal generator 10 is operated to scan the cantilever 3 on the surface of the sample 12, and observation of the sample 12 is started. As a result, when the measurement is performed in the state of (d = d0), the vibration amplitude of the cantilever 3 increases, the S / N ratio of the detection signal from the optical lever detection unit 2 increases, and accurate measurement is possible. Becomes

As described above, since the cantilever 3 vibrates at its own resonance frequency f0 in response to the vibration of the sample 12, the vibration amplitude of the cantilever 3 tends to further increase as the distance between the probe 3a and the sample 12 decreases. Having. In this case, as shown in FIG. 3, the probe 3a of the cantilever 3
The base (fixed portion) 3b and the base (fixed portion) 3b serve as nodes of vibration, and the middle part of the lever body 3c of the cantilever 3 becomes a vibration antinode and vibrates greatly. In the optical lever detection unit 2, a laser beam is applied to a position where the vibration amplitude of the intermediate portion of the lever body 3 is the largest, and the reflected laser light generated thereby is converted into an electric signal, and the RMS-DC circuit 4 converts the reflected laser light into a DC signal. It is changed and compared with the target value in the comparator 5. As described above, the position detection is performed by using the portion where the vibration amplitude of the cantilever 3 is largest, and the S / N ratio of the detection signal is increased by performing the position detection by using the portion where the detection signal is large. Therefore, more accurate measurement can be performed.

In the scanning probe microscope shown in FIG.
As described above, the sample 12 is forcibly vibrated by the signal output of the oscillator 9 by using the multilayer piezo 22. At this time, the frequency of the signal output of the oscillator 9 is made the same as the resonance frequency f0 of the free vibration of the cantilever 3, thereby After the cantilever 3 comes into contact with the sample 12 as shown in FIG.
Is not reduced but rather increased. As a result, the S / N ratio of the detection signal from the optical lever detection unit 2 is increased, and accurate measurement can be performed.
Here, the resonance frequency f0 of the cantilever 3 needs to be sufficiently higher than the operation band of the Z servo system.

More specifically, since the resonance frequency f0 of the cantilever 3 is usually 100 to 300 kHz, it is preferable that the operating band fservo of the Z servo system be about 1 kHz.

According to the present embodiment, the initial adjustment is finished when the probe 3a comes into contact with the surface of the sample 12 at a predetermined contact pressure due to the Z coarse movement, and thereafter, the sample 12 is moved to the cantilever 3 position.
Since the observation of the surface of the sample 12 is started at the resonance frequency f0, when the measurement is performed while hitting the surface of the sample 12 with the tip of the cantilever 3, the vibration amplitude of the cantilever 3 makes the cantilever 3 approach the sample 12. (See FIG. 2). Therefore, it is possible to increase the detection sensitivity. Further, since the vibration amplitude when the probe 3a comes very close to the sample 12 becomes maximum, the S / N ratio of the detection signal when the probe 3a comes very close to the sample 12 is improved, and the detection characteristics are stabilized. Therefore, stable detection data on the sample surface can be obtained.

In the above, the resonance frequency f of the cantilever 3
The embodiment in which the sample 12 is vibrated at the same frequency as 0 has been described. However, the excitation frequency of the sample 12 does not have to be the same as the resonance frequency f0, but may be any frequency that can be considered substantially the same. Here, "substantially the same" refers to a frequency range centered on the resonance frequency f0 within a range where the characteristics shown in FIG. 2 can be obtained.

It is not necessary to vibrate the sample 12 as a whole, but it is sufficient if the measurement area of the sample 12 is vibrated.

Therefore, the multilayer piezo 22 shown in FIG.
Instead, as shown in FIG. 4, a configuration in which only a required part of the sample 12 is excited by using a smaller multilayer piezo 24 can be adopted.

Further, in the embodiment of FIG. 1, a configuration has been described in which the position of the cantilever 3 is optically detected using laser light. However, the position detection of the cantilever 3 is not limited to this configuration.

For example, as shown in FIG. 5, a strain gauge DG is attached to the lever body 3c of the cantilever 3, whereby the amount of distortion of the lever body 3c is detected, and d shown in FIG.
A so-called self-detection type cantilever that electrically detects the value of can also be used. Also in this case, it is preferable that the mounting position of the strain gauge DG is near the center of the lever main body 3c where the amount of distortion is the largest.

FIG. 6 is a block diagram showing another embodiment of the scanning probe microscope according to the present invention. The scanning probe microscope shown in FIG. 6 is characterized by being realized by a scanning probe microscope 30 using a voice coil motor. 6, the same reference numerals as those in FIG. 1 indicate the same or equivalent.

When the scanning probe microscope 30 applies a current from the current source 31 to the coil 33 of the voice coil motor 32 in the Z direction in response to the output from the PI control unit 7, the movable element 34 moves downward in the figure. When driven, the cantilever 3 attached to the optical lever detection unit 2 at the end of the spindle 35 roughly moves in the Z direction. Therefore, in the present embodiment, the oscillator 9 is operated, the Z servo system is operated while the sample 12 is forcibly vibrated by the multilayer piezo 22, and Z coarse movement is performed. Then, when the contact pressure of the cantilever 3 with respect to the sample 12 becomes ΔA in FIG. 2, the Z coarse movement ends. The vibration frequency of the sample 12 at this time is set to the resonance frequency f0 of the free vibration of the cantilever 3.

Subsequently, the voice coil motor 40 in the X direction
An XY scanning signal is applied to a Y-direction voice coil motor (not shown). Then, the shape data of the surface of the sample 12 can be obtained from the optical lever detection unit 2 in the same manner as in the conventional tapping mode. Depending on the configuration of the scanning probe microscope 30, FIG.
The same effect as that of the embodiment shown in FIG.

The embodiments of the present invention described above are merely examples of the present invention, and the present invention is, of course, not limited to the configurations of these embodiments.

[0038]

According to the present invention, as described above, the sample is vibrated at the resonance frequency of the free oscillation of the cantilever.
In addition to increasing the sensitivity of the measurement, the vibration amplitude can be varied greatly depending on whether the cantilever and the sample are in contact or not, so that it is possible to detect whether the cantilever has contacted the sample with extremely high accuracy. Can be used to improve performance. Further, since the sample is vibrated at the resonance frequency of the free vibration of the cantilever and the cantilever is brought into contact with the sample, the vibration amplitude of the cantilever tends to increase as the cantilever approaches the sample. Therefore, the vibration amplitude of the cantilever can be kept large during the measurement, and the detection sensitivity can be increased. As described above, since the detection method maximizes the vibration amplitude when the probe comes very close to the sample, the S / N ratio of the detection signal when the probe comes very close to the sample is improved, and the detection characteristics are improved. Stabilize.

When the probe of the cantilever is brought into contact with the vibrating sample to scan the sample by vibrating the cantilever and measure the surface shape of the sample, the vibration amplitude at the intermediate portion of the lever body of the cantilever is measured. According to the method of detecting the position of the cantilever by picking up the cantilever, the detection signal S / N can be increased, so that extremely high-sensitivity detection can be performed and highly accurate measurement can be performed.

[0040]

[Brief description of the drawings]

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

FIG. 2 shows a scanning probe microscope shown in FIG.
FIG. 4 is a diagram illustrating a relationship between a probe-sample distance and an RMS-DC circuit output level.

FIG. 3 is an explanatory diagram for explaining a method of detecting the position of a cantilever in the scanning probe microscope shown in FIG.

FIG. 4 is an explanatory diagram for explaining another method of exciting the sample in the scanning probe microscope of FIG. 1;

FIG. 5 is an explanatory diagram for describing another position detection method of the cantilever.

FIG. 6 is a block diagram showing another embodiment of the scanning probe microscope according to the present invention.

[Explanation of symbols]

 2 Optical lever detection unit 3 Cantilever 3a Probe 3b Base (fixed part) 3c Lever body 9 Oscillator 11 Z servo system 12 Sample 12 22 Multilayer piezo DG Strain gauge

Continued on the front page (72) Inventor Akihiko Homma 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba Inside Seiko Instruments Inc. (72) Inventor Akira Inoue 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. In-house F term (reference) 2F069 AA60 AA66 CC06 DD30 GG01 GG06 GG07 GG62 HH05 JJ08 LL03 MM32 MM34

Claims (13)

[Claims] 1. A method for measuring the shape of a surface of a sample by applying a cantilever to the surface of the sample, the method comprising: measuring a resonance frequency of free vibration of the cantilever or substantially the resonance frequency in the vicinity thereof. A measurement method for a scanning probe microscope, wherein the shape of the surface of the sample is measured while lightly contacting the cantilever with the surface of the sample while the sample is vibrated at the same frequency. 2. The method for measuring a scanning probe microscope according to claim 1, wherein the entire sample is vibrated. 3. The method for measuring a scanning probe microscope according to claim 1, wherein only a necessary portion required for measurement of said sample is vibrated. 4. A scanning probe microscope in which a cantilever is placed on a surface of a sample to measure the shape of the surface of the sample, wherein the sample has a resonance frequency of free vibration of the cantilever or
A scanning probe microscope comprising a vibration means for vibrating at a frequency substantially equal to the resonance frequency in the vicinity of the vibration frequency. 5. The scanning probe microscope according to claim 4, wherein said vibrating means is configured to vibrate the entire sample. 6. A scanning probe microscope according to claim 4, wherein said vibrating means is configured to vibrate only a required portion required for measuring said sample. 7. A measuring method of a scanning probe microscope in which a cantilever is applied to a surface of a sample to measure a shape of the surface of the sample, wherein a servo is applied so that a degree of hitting of the sample by the cantilever is in a predetermined state. A feedback system for controlling the position of the cantilever in the Z direction by a system, wherein the position of the cantilever is detected at a position between a fixed end of the cantilever and a probe. Method. 8. The measuring method of a scanning probe microscope according to claim 7, wherein the position detection of the cantilever is performed at an antinode of vibration of the lever main body. 9. The measuring method for a scanning probe microscope according to claim 8, wherein the position of said cantilever is detected at a central portion of said lever main body. 10. The position detecting means of the cantilever,
The measuring method of a scanning probe microscope according to claim 7, 8 or 9, which is an optical lever detecting means. 11. The cantilever position detecting means,
The measuring method for a scanning probe microscope according to claim 7, 8 or 9, wherein the measuring method is a strain gauge attached to the cantilever. 12. A measuring method of a scanning probe microscope in which a cantilever is applied to a surface of a sample to measure the shape of the surface of the sample, wherein the resonance frequency of free vibration of the cantilever or the resonance frequency substantially in the vicinity of the resonance frequency. In a state where the sample is vibrated at the same frequency, the surface of the sample is scanned while lightly touching the cantilever with the surface of the sample, and the position of the cantilever in the Z direction is servo-controlled by the servo system so that the cantilever hits the sample in a predetermined state. Wherein the position of the cantilever is detected at a position between a fixed end of the cantilever and a probe in order to perform feedback control of the scanning probe microscope. 13. A scanning probe microscope in which a cantilever is placed on a surface of a sample to measure the shape of the surface of the sample, wherein the sample is provided with a resonance frequency of free vibration of the cantilever or
Vibrating means for vibrating at the frequency substantially equal to the resonance frequency in the vicinity thereof, and feeding back the position of the cantilever in the Z direction by a servo system so that the degree of hitting of the sample by the cantilever is in a predetermined state. A scanning probe microscope, comprising: a detecting means for detecting a position of the cantilever at a position between a fixed end of the cantilever and a probe for control.