JP3908041B2 - Method for measuring oscillation amplitude of cantilever in non-contact scanning probe microscope and scanning probe microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning probe microscope such as a scanning tunnel microscope or an atomic force microscope, and more particularly to a method for measuring an oscillation amplitude of a cantilever and a scanning probe microscope in a non-contact scanning probe microscope that scans a sample surface while oscillating the cantilever. About.
[0002]
[Prior art]
In a scanning probe microscope such as a scanning tunnel microscope or an atomic force microscope, a sample and a probe (probe) are relatively moved by a minute distance to scan a predetermined two-dimensional region of the sample. In this case, a non-contact scanning probe microscope was developed that scans the surface of the sample while oscillating a cantilever attached to the tip, and measures the interaction between the probe and the sample from changes in the oscillation frequency and amplitude. ing.
[0003]
FIG. 1 shows a non-contact scanning probe microscope based on a frequency modulation (FM) detection method using an optical lever method for detecting displacement of a cantilever. In the figure, a cantilever 2 is arranged facing the measurement sample 1. A probe 3 is attached to the end of the cantilever 2 facing the sample 1.
[0004]
A piezo element 4 is attached to the end opposite to the end where the probe of the cantilever 2 is attached. A voltage having an appropriate frequency is applied to the piezo element 4 from the oscillation control amplifier 5. As a result, the piezo element expands and contracts according to the voltage applied to the piezo element 4, and the cantilever 2 bends in the vertical direction in the drawing.
[0005]
The amount of bending of the cantilever 2 is such that the top surface of the tip of the cantilever 2 to which the probe 3 is attached is a mirror surface. The mirror surface is irradiated with laser light from a laser light source 6 and the light reflected by the mirror surface is reflected. It is measured by detecting with the divided photodiode 7. The divided photodiode 7 generates a signal corresponding to the incident position of the laser beam. That is, when the cantilever 2 is displaced, the spot position of the laser light incident on the divided photodiode is shifted. The output of the split photodiode 7 changes according to the shift of the spot position of the laser beam, and the displacement of the cantilever 2 can be detected.
[0006]
When the cantilever 2 vibrates, a sine wave is output from the split photodiode 7 correspondingly. The output of the split photodiode 7 is input to the piezo element 4 connected to the base of the cantilever 2 via the oscillation control amplifier 5. When this cantilever vibrates, the resonance frequency of the cantilever 2 is selectively amplified, and the cantilever 2 oscillates at the resonance frequency.
[0007]
The output of the split photodiode 7 is converted into a DC voltage component by a frequency modulation (FM) demodulator 9. The distance between the cantilever 2 and the sample 1 is controlled by the Z driver 10 so that the DC component is constant, that is, the resonance frequency is constant.
[0008]
Although the sample 1 is mounted on the scanner 11, the scanner 11 is not shown in detail, but the sample 3 attached to the tip of the scanner 11 can be scanned with respect to the probe 3 using a piezo element. It is configured. That is, the scanner 11 is expanded and contracted in the vertical direction (vertical direction) in the drawing in accordance with the voltage value from the Z driver 10.
[0009]
Further, the scanner 11 is curved in accordance with the voltage from the X and Y drivers 12, and is scanned two-dimensionally in the left-right direction (X direction) of the paper surface and in the direction perpendicular to the paper surface (Y direction). The two-dimensional scanning signal in the horizontal direction of the sample from the X, Y driver 12 and the vertical displacement signal from the Z driver 10 are supplied to the CPU 13.
[0010]
The CPU 13 supplies a vertical movement signal of the sample from the Z driver 10 to the cathode ray tube 14 synchronized with the two-dimensional scanning signal of the X and Y driver 12. As a result, the locus of the sample moving in the Z direction in accordance with the two-dimensional scanning of the sample is displayed on the cathode ray tube 14 as an image.
[0011]
With such a configuration, the scanner 11 scans a desired region of the sample 1 two-dimensionally, and oscillates the cantilever 2 to which the probe 3 is attached. At this time, when the distance between the sample 1 and the cantilever 2 (probe) changes according to the scanning of the sample 1, the force applied to the probe 3 changes due to the interaction between the sample 1 and the probe 3. As a result, the oscillation frequency deviates from the resonance frequency.
[0012]
The Z driver 10 is controlled so that this oscillation is oscillated at the resonance frequency, that is, the DC component from the FM demodulator 9 is constant, and the distance between the sample 1 and the cantilever 2 is kept constant. . By such an action, the voltage applied from the Z driver 10 to the scanner 11 changes according to the change in the distance between the sample 1 and the probe 3 based on the scanning of the sample in the X and Y directions. As a result, when the voltage value supplied from the Z driver 10 to the scanner 11 is displayed as an image on the cathode ray tube 14 in accordance with the X and Y scans of the sample 1, an uneven image on the sample surface can be obtained.
[0013]
FIG. 2 shows a configuration of a non-contact scanning probe microscope based on a slope detection method using an optical lever method for detecting a cantilever displacement. Constituent elements that are the same as or similar to those shown in FIG. In FIG. 2, a cantilever 2 is disposed to face the measurement sample 1. A probe 3 is attached to the end of the cantilever 2 facing the sample 1.
[0014]
A piezo element 4 is attached to the end opposite to the end where the probe of the cantilever 2 is attached. A voltage having an appropriate frequency is applied to the piezo element 4 from the oscillator 5. As a result, the piezo element expands and contracts according to the voltage applied to the piezo element 4, and the cantilever 2 bends in the vertical direction in the drawing.
[0015]
The amount of bending of the cantilever 2 is such that the top surface of the tip of the cantilever 2 to which the probe 3 is attached is a mirror surface. The mirror surface is irradiated with laser light from a laser light source 6 and the light reflected by the mirror surface is reflected. It is measured by detecting with the divided photodiode 7. The divided photodiode 7 generates a signal corresponding to the incident position of the laser beam. That is, when the cantilever 2 is displaced, the spot position of the laser light incident on the divided photodiode is shifted. The output of the split photodiode 7 changes according to the shift of the spot position of the laser beam, and the displacement of the cantilever 2 can be detected.
[0016]
When the voltage from the oscillator 15 is input to the piezo element 4 connected to the base of the cantilever 2 and the cantilever 2 vibrates, a sine wave is output from the divided photodiode 7 correspondingly. The output of the divided photodiode 7 is converted into a mean square value (DC voltage component) of oscillation amplitude by the RMS converter 16. The Z driver 10 controls the distance between the cantilever 2 and the sample 1 so that this output is constant, that is, the resonance frequency is constant so that the oscillation amplitude is constant.
[0017]
Although the sample 1 is mounted on the scanner 11, the scanner 11 is not shown in detail, but is configured to be movable in the X, Y, and Z directions using piezoelectric elements. That is, the scanner 11 is moved in the vertical direction (Z direction) in the figure in accordance with the value of the voltage from the Z driver 10. Further, according to the voltage from the X and Y drivers 12, the scanner 11 is two-dimensionally scanned in the left-right direction (X direction) of the paper surface and in the direction perpendicular to the paper surface (Y direction). The two-dimensional scanning signal in the horizontal direction of the sample from the X and Y drivers 12 and the vertical displacement signal from the Z driver 10 are supplied to the CPU 13.
[0018]
The CPU 13 supplies a vertical movement signal of the sample from the Z driver 10 to the cathode ray tube 14 synchronized with the two-dimensional scanning signal of the X and Y driver 12. As a result, the locus of the sample moving in the Z direction in accordance with the two-dimensional scanning of the sample is displayed on the cathode ray tube 14 as an image.
[0019]
With such a configuration, the scanner 11 scans a desired region of the sample 1 two-dimensionally, and oscillates the cantilever 2 to which the probe 3 is attached. At this time, when the distance between the sample 1 and the cantilever 2 (probe) changes according to the scanning of the sample 1, the force applied to the probe 3 changes due to the interaction between the sample 1 and the probe 3. As a result, the oscillation amplitude deviates from a certain value.
[0020]
The Z driver 10 is controlled so that the oscillation amplitude is constant, that is, the output value from the RMS converter 16 is constant, and the distance between the sample 1 and the cantilever 2 is kept constant. By such an action, the voltage applied from the Z driver 10 to the scanner 11 changes according to the change in the distance between the sample 1 and the probe 3 based on the scanning of the sample in the X and Y directions. As a result, when the voltage value supplied from the Z driver 10 to the scanner 8 is displayed as an image on the cathode ray tube 14 in accordance with the X and Y scans of the sample 1, an uneven image on the sample surface can be obtained.
[0021]
[Problems to be solved by the invention]
Since the non-contact scanning probe microscope shown in FIGS. 1 and 2 can be observed without bringing the sample and the cantilever (probe) into contact with each other, it is used for analyzing the interaction between the sample and the probe. For this analysis, it is necessary to accurately know the distance between the probe and the sample. Therefore, it is necessary to obtain the oscillation amplitude of the cantilever.
[0022]
When the cantilever is oscillated, the output of the split photodiode becomes a sine wave. Although the amplitude of the sine wave and the oscillation amplitude of the cantilever (probe) are in a proportional relationship, they cannot be directly converted into the absolute value of the oscillation amplitude. Further, since the oscillation amplitude of the cantilever (probe) is not constant due to individual differences in the cantilever, laser beam alignment, and the like, it is necessary to recalculate the oscillation amplitude when the cantilever is replaced or the alignment is adjusted.
[0023]
The present invention has been made in view of the above points, and an object of the present invention is to provide a method for measuring oscillation amplitude of a cantilever and a scanning probe in a non-contact scanning probe microscope capable of easily obtaining a transmission amplitude of a cantilever (probe). To realize a microscope.
[0024]
[Means for Solving the Problems]
In the method for measuring the oscillation amplitude of a cantilever in a non-contact scanning probe microscope and the scanning probe microscope according to the present invention, the sample is scanned two-dimensionally relative to the probe, and the distance between the sample and the probe. A cantilever having a probe attached to the tip, a displacement detection means for detecting the displacement of the cantilever tip, and a means for oscillating the cantilever, based on a signal from the displacement detection means at the tip of the cantilever In a non-contact scanning probe microscope in which the distance between the probe and the sample is controlled, the relative scanning range of the sample and the probe can be set in a small range or at the same position that is not affected by the unevenness of the sample surface. , the oscillation amplitude of the cantilever is changed in at least two stages, the distance between the oscillation center of the sample surface and the probe at that time From the change, and it characterized in that so as to measure the oscillation amplitude of the cantilever tip.
[0025]
That is, in the present invention, the oscillation amplitude of the cantilever is changed in a state where the relative scanning range of the sample and the probe is a small range that is not affected by the unevenness of the sample surface or the same position. The oscillation amplitude of the cantilever is simply obtained from the change in height of the corresponding uneven image, that is, the amount of movement of the cantilever in the Z direction.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 2, when the cantilever 2 oscillates, the output of the split photodiode 7 oscillates accordingly. The oscillation amplitude of the cantilever 2 and the amplitude of the oscillation signal output from the divided photodiode 7 are in a proportional relationship. The oscillation amplitude of the output of the divided photodiode can be observed directly with an oscilloscope or the like, or can be observed using the root mean square (RMS) voltage.
[0027]
FIG. 3 is an explanatory diagram of a method for measuring a cantilever oscillation amplitude based on the present invention. When the oscillation amplitude of the output of the divided photodiode is set to Z as shown in FIG. 3A by adjusting the output of the oscillation control amplifier 5 in the configuration of FIG. 1 or the output of the oscillator 15 in the configuration of FIG. Furthermore, the oscillation amplitude of the cantilever 2 is A = B × Z (B is a proportional coefficient) proportional to Z, as shown in FIG.
[0028]
In this state, normal image observation is performed. At this time, the scanning range of the sample 1 is made small or zero so as not to be affected by the unevenness of the surface of the sample 1. When the scanning screen reaches about 1/3 of the entire screen (timing 1), as shown in FIG. 3C, the oscillation amplitude of the output of the divided photodiode 7 is set to Z / 2. Then, correspondingly, the oscillation amplitude of the cantilever 2 becomes A / 2 as shown in FIG.
[0029]
In such a state, the distance between the cantilever 2 and the surface of the sample 1 approaches A / 4. Then, as shown in FIG. 3E, when the scanning screen D reaches about 2/3 of the entire screen (timing 2), the oscillation amplitude of the output of the divided photodiode 7 is returned to Z. Then, the oscillation amplitude of the cantilever 2 also returns to A as shown in FIG. 3 (b), the distance between the cantilever 2 and the sample 1 is also returned to the original. As shown in FIG. 3F obtained by such an operation, A / 4 can be accurately measured from the cross-sectional profile in the vertical direction of the image, and the oscillation amplitude A of the cantilever 2 (probe 3). Can be requested.
[0030]
FIG. 4 shows a configuration for automatically measuring the oscillation amplitude A of the cantilever described above. In the configuration of FIG. 4, the CPU 20 is provided, and the oscillation control amplifier 8 is controlled by an instruction from the CPU 20, and the output of the amplifier 8 is set to Z. By setting the output Z, the oscillation amplitude of the cantilever 2 becomes A = B × Z (B is a proportional coefficient) proportional to Z.
[0031]
In this state, the X and Y drivers scan the sample 1 under the control of the CPU 20. At this time, the scanning range of the sample 1 is made small or zero so as not to be affected by the unevenness of the surface of the sample 1. When the scanning screen reaches about 1/3 of the entire screen (timing 1), the CPU 20 controls the oscillation control amplifier 8 so that the oscillation amplitude of the output of the divided photodiode 7 becomes Z / 2. Set the output voltage. Then, the oscillation amplitude of the cantilever 2 also becomes A / 2 correspondingly.
[0032]
In such a state, the distance between the cantilever 2 and the surface of the sample 1 approaches A / 4. Then, as shown in FIG. 3E, when the scanning screen reaches about 2/3 of the entire screen (timing 2), the CPU 20 controls the oscillation control amplifier 8 to oscillate the output of the divided photodiode 7. Return the amplitude to Z. Then, the oscillation amplitude of the cantilever 2 also returns to A, and the distance between the cantilever 2 and the sample 1 also returns. The signal of the cross-sectional profile in the vertical direction of the image as shown in FIG. 3 (f) obtained by such an operation is stored in the CPU 20. The CPU 20 can automatically and accurately determine the value of A / 4 based on the stored cross-sectional profile signal, and can determine the oscillation amplitude A of the cantilever 2 (probe 3).
[0033]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the oscillation amplitude of the cantilever is first set to Z, then set to Z / 2, and then returned to Z again. However, the oscillation amplitude of the cantilever may be two steps. In that case, cross-section profile showing a displacement in the height direction of the sample is as shown in FIG.
[0034]
【The invention's effect】
As described above, in the method for measuring the oscillation amplitude of the cantilever in the non-contact scanning probe microscope and the scanning probe microscope according to the present invention, the sample is scanned two-dimensionally relative to the probe, and the sample and the probe are scanned. A cantilever having a tip attached to the tip, a displacement detecting means for detecting the displacement of the cantilever tip, and a means for oscillating the cantilever, and a displacement detecting means for the tip of the cantilever In the non-contact scanning probe microscope in which the distance between the probe and the sample is controlled based on the signal from the probe, the relative scanning range of the sample and the probe is small enough not to be affected by the unevenness of the sample surface range or in the same position, the oscillation amplitude of the cantilever is changed in at least two stages, the sample surface and the probe at that time From a change in distance between the moving center it is characterized in that so as to measure the oscillation amplitude of the cantilever tip.
[0035]
That is, in the present invention, the oscillation amplitude of the cantilever is changed in a state where the relative scanning range of the sample and the probe is a small range that is not affected by the unevenness of the sample surface or the same position. The oscillation amplitude of the cantilever can be easily obtained from the corresponding change in height of the uneven image, that is, the amount of movement of the cantilever in the Z direction.
[Brief description of the drawings]
FIG. 1 is a diagram showing a non-contact scanning probe microscope in which a resonant frequency of a cantilever is converted into a DC voltage component by a frequency modulation demodulator.
FIG. 2 is a diagram showing a non-contact scanning probe microscope in which the oscillation amplitude of a cantilever is converted into a mean square value.
FIG. 3 is a diagram for explaining the operation of the present invention.
FIG. 4 is a diagram showing a non-contact scanning probe microscope in which the oscillation amplitude of a cantilever is automatically obtained.
[Explanation of symbols]
1 Sample 2 Cantilever 3 Probe 4 Piezoelectric Element 5 Oscillation Control Amplifier 6 Light Source 7 Split Photodiode 9 FM Demodulator 10 Z Driver 11 Scanner 12 X, Y Drivers 13, 20 CPU
14 Cathode ray tube 15 Oscillator 16 RMS converter

Claims (6)

The sample is scanned two-dimensionally relative to the probe, and the scanner changes the distance between the sample and the probe, the cantilever with the probe attached to the tip, and the displacement of the cantilever tip In a non-contact scanning probe microscope provided with a displacement detecting means for detecting and a means for oscillating a cantilever, and controlling the distance between the probe and the sample based on a signal from the displacement detecting means at the tip of the cantilever, The oscillation range of the cantilever is changed in at least two steps within a small range that is not affected by the unevenness of the sample surface or the same position relative to the probe, and the sample surface and the probe vibrate at that time. from a change in distance between the center of the cantilever in the noncontact scanning probe microscope so as to measure the oscillation amplitude of the cantilever tip originating Amplitude measurement method. 2. The method for measuring oscillation amplitude of a cantilever in a non-contact scanning probe microscope according to claim 1, wherein the tip of the cantilever is irradiated with laser light to detect the displacement of the light reflected by the cantilever. The cantilever is oscillated, the signal from the displacement detection means at the tip of the cantilever is converted into a DC voltage component by a frequency modulation demodulator, and the distance between the cantilever and the sample is controlled so that this DC component is constant Item 3. A method for measuring oscillation amplitude of a cantilever in the non-contact scanning probe microscope according to Item 1 or 2. The cantilever was oscillated, the signal from the displacement detection means at the tip of the cantilever was converted to the mean square value of the oscillation amplitude, and the distance between the cantilever and the sample was controlled so that the converted signal value was constant. A method for measuring the oscillation amplitude of a cantilever in the non-contact scanning probe microscope according to claim 1. The relative scanning range of the sample and the probe is a small range that is not affected by the unevenness of the sample surface, or the same position, and the oscillation amplitude of the cantilever at the start of scanning is set to the first value, and constant after the start of scanning. The oscillation amplitude of the cantilever is set to the second value at the first timing after the elapse of time, and the oscillation amplitude of the cantilever is returned to the first value at the second timing after the elapse of a certain time after the first timing. A method for measuring an oscillation amplitude of a cantilever in the non-contact scanning probe microscope according to claim 1. The sample is scanned two-dimensionally relative to the probe, and the scanner changes the distance between the sample and the probe, the cantilever with the probe attached to the tip, and the displacement of the cantilever tip Displacement detecting means for detecting; means for oscillating the cantilever; means for controlling the distance between the probe and the sample based on a signal from the displacement detecting means at the tip of the cantilever; and changing the oscillation amplitude of the cantilever in at least two stages. A non-contact scanning probe microscope which measures the oscillation amplitude at the tip of the cantilever from the change in the distance between the sample surface and the vibration center of the probe at different oscillation amplitudes.

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