JP2001108602A - Scanning-type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the difference in the physical properties of a sample surface from the uneven shape of the sample surface and time delay (phase) when a cantilever leaves by attenuating the cantilever easily for following the uneven sample surface easily. SOLUTION: By setting the vibration frequency of a cantilever to both the outsides of the frequency band of the half-value width of a Q curve, the lever is allowed to attenuate easily, thus improving a following property for the sample surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cantilever having a fine probe at its tip, a laser for irradiating a laser reflecting surface of a cantilever, and a light position detecting device for detecting a position of reflected light of the laser. It consists of a sample moving means for moving the sample and the sample, and a lever vibration means for oscillating the cantilever. When the probe of the cantilever comes into contact with the surface of the sample, the amount of decrease in the amplitude is detected by the optical position detector, and the reduced amplitude is used. The present invention relates to a scanning probe microscope that controls the vertical movement of a sample moving unit so that the amount becomes constant, thereby measuring information on the unevenness of the sample surface from the operation amount of the vertical movement.

[0002]

2. Description of the Related Art A conventional scanning probe microscope employs a cantilever and a cantilever having a fine probe at the tip.
A cantilever comprising a laser for irradiating the laser reflecting surface, an optical position detector for detecting the position of the reflected light from the laser, a sample moving means for moving the sample, and a lever vibrating means for vibrating the cantilever. When the needle touches the sample surface, the amount of decrease in the amplitude is captured by the optical position detector, and the vertical movement of the sample moving means is controlled so that the reduced amplitude is constant. In the scanning probe microscope for measuring the unevenness information of the sample, the resonance frequency of the curve (Q curve) of the oscillation frequency and the amplitude of the cantilever is set as the oscillation frequency of the cantilever. Information is being measured. The cantilever has a phase detector that captures a signal when a time delay (phase) occurs in the vibration form of the cantilever due to the interaction between the sample surface and the probe of the cantilever. As in the case of the measurement, the difference in the physical properties of the sample surface is measured by detecting the phase near the resonance point of the Q curve.

[0003]

In the conventional scanning probe microscope, the vicinity of the resonance point of the curve (Q curve) of the oscillation frequency and the amplitude of the cantilever is used as the lever oscillation frequency. There was a disadvantage that it was easy to vibrate and was not easily damped. Even if the tip interacts with the sample surface, it is difficult to attenuate and the change in the amplitude does not become constant immediately, so the control of the sample moving means tends to be delayed, and the operation amount of the vertical movement of the sample moving means tends to be delayed. There is a disadvantage that the surface unevenness information obtained from the quantity cannot be measured correctly. There is also a method of increasing the control speed of the vertical movement of the sample moving means, but there is a drawback that an oscillation phenomenon occurs in which the direction of the change in the amplitude amount does not coincide with the vertical direction of the control. In particular, in a measurement in a vacuum, the cantilever is hardly attenuated because air resistance is lost, so that the amplitude amount to be changed due to the interaction with the sample is not good. There was a disadvantage that the control became more and more delayed and the surface unevenness information could not be measured.

Also, when measuring the difference in physical properties of the sample surface from the phase signal (time delay of the probe) generated by the interaction between the probe and the sample surface, the phase signal is also difficult because the cantilever is hardly attenuated. There was a drawback that the difference in physical properties could not be detected correctly because the information of the transient process in which the vibration of the cantilever was attenuated. In view of this, the present invention provides a cantilever that is hardly attenuated by setting lever outside frequencies on both sides of a frequency band having a half-value width of a dependency curve (Q curve) of the oscillation frequency and amplitude of the cantilever. The problem is to make it easy to attenuate the transient vibration change after the probe of the cantilever comes into contact with the sample by moving it away from the vibration frequency region (near the resonance point), and to make it possible to perform measurement especially in a vacuum without air resistance. And Furthermore, when measuring the difference in the physical properties of the sample surface from the phase signal (the time delay of the probe) generated by the interaction between the probe and the sample surface, the excitation frequency is set to a region where the cantilever is easily attenuated. Accordingly, it is an object of the present invention to correctly measure a phase signal (difference and distribution of physical properties of the sample surface) resulting from the interaction between the probe and the sample surface, which also becomes a stable signal after the attenuation.

[0005]

In order to solve the above-mentioned problems, the present invention provides a cantilever having a fine probe at its tip and a laser for irradiating a laser reflecting surface of a cantilever with a laser. It consists of an optical position detector for detecting the position of the reflected light of the laser, a sample moving means for moving the sample, and a lever vibrating means for oscillating the cantilever. The amplitude decreases when the probe of the cantilever comes into contact with the sample surface. In the scanning probe microscope, the vertical position of the sample moving means is controlled by controlling the vertical movement of the sample moving means so that the reduced amount of amplitude is kept constant by capturing the minute by the optical position detector. , Cantilever excitation frequency and amplitude dependence curve (Q
The vibration of the cantilever can be easily attenuated by setting the lever excitation frequencies on both sides of the frequency band having the half width of the curve.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a cantilever having a fine probe at the tip, a laser for irradiating a laser reflecting surface of a cantilever, and a light for detecting the position of reflected light from the laser. It consists of a position detector, a sample moving means for moving the sample, and a lever vibrating means for oscillating the cantilever. When the probe of the cantilever comes into contact with the surface of the sample, the amount of decrease in the amplitude is detected. By controlling the vertical movement of the sample moving means so that the reduced amplitude becomes constant,
In a scanning probe microscope that measures the unevenness information of the sample surface from the operation amount of the up and down movement, the outer and outer sides of the frequency band that is the half width of the dependency curve (Q curve) of the vibration frequency and amplitude of the cantilever are measured. By setting the lever excitation frequency, the cantilever is easily attenuated, and the unevenness information and the phase (physical properties) of the sample surface are stably measured.
In particular, it enables measurement in a vacuum without air resistance.

[0007]

Embodiments will be described with reference to the drawings.
1 (a), 1 (b) and 1 (c) are schematic diagrams of the method of the present invention in measurement with a scanning probe microscope. FIG. 1A illustrates a case where the information to be measured is a surface unevenness. The cantilever 2 having the probe 1 is attached to the lever vibrating means 3. Laser reflection surface 4
The light 5 is irradiated and the reflected light 7 is detected as the position of the light position detector 8. The cantilever 2 is vibrated by the lever vibration means 3 so that the probe 1 moves up and down. Tip 1
The laser reflected light reaches the position D of the optical position detector when it comes into contact with the concave portion on the surface of the sample 9. When the probe separates from the concave portion of the sample and reaches the upper limit of vibration, the laser reflected light reaches the position B of the optical position detector. When the probe vibrates in contact with or away from the concave portion of the sample, the amplitude of the cantilever is obtained as the difference between the position D and the position B. Next, sample moving means 1
When the probe is moved to the left by the scanning operation 11 of 0, the probe hits or separates from the convex portion of the sample. When the probe hits the convex portion, the laser reflected light reaches the position C of the optical position detector. When the probe separates from the projection and reaches the upper limit of the vibration, the laser reflected light reaches the position B of the optical position detector.

When the probe vibrates so as to hit or separate from the convex portion of the sample, the amplitude of the cantilever is obtained as the difference between the position C and the position B. By detecting the difference between the positions where the laser reflected light reaches the optical position detector, the unevenness information of the sample can be measured. Further, the vertical movement 12 of the sample moving means 10 may be controlled so that the difference between the arrival positions of the laser reflected light to the optical position detector becomes constant, and the unevenness information of the sample may be obtained from the operation amount of the vertical movement. The latter method is usually employed because the smaller the contact of the probe with the sample (the degree of pressing), the more difficult it is to damage the probe and the surface of the sample.

Next, FIG. 1B is a schematic diagram when the cantilever is vibrating. The cantilever-2 is attached to the lever vibration means 3. The lever vibration means 3 uses a piezoelectric element, and a certain voltage is applied to the piezoelectric element at a certain period. The piezoelectric element causes a vertical vibration 13 to vibrate the cantilever-2. The cantilever vibrates with a certain amplitude A. The amplitude A depends on the voltage applied to the piezoelectric element in the lever vibration means 3 and the vibration frequency. Even if the applied voltage is set to a constant value, it greatly depends on the frequency to be excited.

FIG. 1C shows the vibration frequency range of the lever of the present invention as compared with the conventional one. The vertical axis represents the amplitude A of the cantilever, and the horizontal axis represents the vibration frequency of the lever. When the excitation frequency f is increased from a low frequency, the amplitude A of the cantilever reaches a maximum value Amax at a certain frequency. When the excitation frequency f is further increased, the amplitude amount A decreases. The maximum frequency is determined by the material, length, thickness and width of the cantilever. The dependency curve of the amplitude A on the excitation frequency as shown in the figure is called a Q curve. The peak of the Q curve becomes the resonance point 14. The excitation frequency at the resonance point is called a resonance frequency. If the lever is vibrated in the vicinity of the resonance frequency, the lever is easily vibrated and hardly attenuated. If the vibrator is vibrated in the vicinity of the resonating frequency (near the resonance point 14), the cantilever has a large amplitude A even with the same applied voltage, and is easily vibrated and hardly attenuated. Even when the probe is acted on by the sample, it is hard to attenuate. Conventionally, the vibration frequency of the cantilever has been set near the resonance point by giving priority to the point that the vibration is easy.

If the height (amplitude) of the resonance point 14 is Amax, and the frequencies of the points on the Q curve having a height of 1/2 of Amax are f1 and f2, the half width between f1 and f2 is Frequency band. In the half-width frequency band, the resonance point 14
, The lever is more likely to vibrate and hardly attenuate. In the present invention, the excitation frequency of the lever is set on both sides of the half-width frequency band. The lever is located outside the half-width frequency band.
Is less likely to vibrate and tends to attenuate. By setting the range of the excitation frequency where the lever is easily attenuated, the amplitude of the lever is easily attenuated even if it changes according to the uneven shape of the sample, and tends to become a constant value. Since the amount can be determined immediately and the vertical movement of the sample moving means can be followed in accordance with the unevenness of the sample surface, the information obtained from the operation amount of the vertical movement is the uneven shape of the sample surface. It is possible to measure correct irregularity information on the sample surface.

FIG. 2A is a schematic diagram showing the relationship between the amount of vibration of the cantilever and the surface of the sample when measuring the unevenness of the sample in a vacuum so that the amplitude of the cantilever becomes constant. Cantilever when the probe does not touch the sample surface
Vibrates with the amplitude A0. When the sample moves leftward by the scanning operation 11 of the sample moving means 10, the probe hits the convex surface 21 of the sample and the amplitude of the cantilever is A1.
Let's say A1 is smaller than A0. At this point, control is assumed to be started for the sake of explanation.

The vertical movement 1 of the sample moving means 10 so that the amplitude of the cantilever becomes constant at A1 while scanning.
2 is controlled. As described above, the uneven shape of the sample surface is measured from the operation amount of the vertical movement. As the scanning operation proceeds, the sample moves further to the left, and when the probe comes to the further right of the right corner of the protrusion 21, the surface having the same height as the protrusion suddenly disappears, so that the amplitude of the cantilever changes from A1. However, since the lever is hardly attenuated, it is not immediately stable. At this time, if the amplitude amount becomes constant immediately, the operation amount of the vertical movement of the sample moving means can be determined. If the sample is brought closer to the probe by the sample moving means until the amplitude amount becomes A1, the operation amount of the vertical movement is raised. The height of the part can be determined. However, when the probe deviates from the right corner of the projection, the object hit by the probe suddenly disappears and the cantilever starts to swing with another amplitude. However, since there is no air resistance around the cantilever, it is difficult to attenuate, so that the amplitude amount is not immediately fixed. The actual amplitude amount becomes a constant value after the probe hits a concave portion on the surface of the sample after a certain time elapses, and calms down to A2.

A2, which has become a constant value, is compared with A1, which is a target value, and the operation amount of the vertical movement of the sample moving means is determined for the first time so that the amplitude A2 becomes the same as A1. However, in practice, control for determining the operation amount of the vertical movement of the sample moving means is always performed, so that the operation amount is determined by the information in the course of the amplitude amount becoming A2. That is, the operation amount of the vertical movement is determined even when the probe does not touch the sample surface. The sample surface unevenness information measured from the transient amplitude of the cantilever does not have the original shape of the sample surface, but is hard to attenuate the cantilever. For example, the amplitude of the cantilever is measured at the falling portion and the rising portion of the unevenness of the sample because the operation amount of the vertical movement is determined in such a manner that the amplitude of the cantilever cannot follow the unevenness of the sample surface due to the difficulty of attenuation and is transiently delayed. As shown in FIG. 2B, the unevenness information (obtained) has a difference between the unevenness information of the sample and the measured unevenness information.

According to the present invention, even in a vacuum, the vibration of the cantilever is attenuated by setting the excitation frequency of the cantilever to both outsides of the half bandwidth of the Q curve as shown in FIG. 1 (c). Especially, in a vacuum, the air around the cantilever is eliminated, so that the cantilever does not receive the air resistance when vibrating, and is more likely to vibrate than in the atmosphere, and hardly attenuates once it starts to vibrate. By setting the excitation frequency of the cantilever to both outsides of the frequency band of the half width of the Q curve, it is possible to measure the correct unevenness information on the sample surface as in the atmosphere.

FIG. 3 shows the time relationship between the voltage waveform applied to the lever vibration means and the optical position output signal detected by the optical position detector. If the probe and the sample surface do not interact with each other, the applied voltage waveform and the optical position output waveform are the same without a time delay. The probe and the sample surface are separated from each other with a time delay even if the probe is separated from the sample surface due to adhesive force, electrostatic force, magnetic force, or the like. The applied voltage when the probe is moving away from the sample surface is V1 and the applied voltage when the probe is in contact with the sample surface is -V1. When the probe is in contact with the sample surface, the optical position output signal is W1, and when the probe is away from the sample surface, the optical position output signal is W2. The applied voltage waveform is V due to the above interaction between the probe and the sample surface.
Even if it becomes 1, the optical position output signal becomes W2 after time T seconds. That is, if there is an acting force due to physical properties on the sample surface, a time delay (phase) occurs when the probe leaves the sample surface. At this time, the magnitude of the physical property of the sample surface can be compared by detecting the magnitude of the delay time T. Here, in order to obtain a correct phase signal, the probe must surely hit or separate from the sample surface. When measuring the phase, the vibration of the lever is easily attenuated by changing the lever excitation frequency to both sides of the frequency band that is the half width of the Q curve, and the change in the amplitude of the lever is quickly performed. The probe reliably follows the irregularities on the surface, and the phase signal can be measured correctly.

FIG. 4 shows an embodiment in a vacuum. Ray
The laser 5 from the generator 61 passes through the window 62 and is introduced into the vacuum vessel 63. The vacuum container and the window are kept airtight, and the vacuum container is
A vacuum state is thereby achieved. In the vacuum vessel, a cantilever 2, a lever vibrating means 3, a sample 9, and a sample table 65 on which the sample is heated or cooled or placed at room temperature are provided. The sample stage can be scanned and moved up and down by the sample stage moving means 69. The laser introduced into the vacuum vessel through the window is applied to the laser reflecting surface of the cantilever-2, and the reflected light 7 of the laser is transmitted through the window to an optical position detector 8 installed outside the vacuum vessel. To reach. The amount of amplitude of the cantilever can be obtained depending on the position of the optical position detector. When the probe hits the surface of the sample, the amplitude decreases. However, if the operation amount is determined by the vertical movement according to the scanning operation of the sample moving means so as to maintain the reduced amplitude, the sample unevenness information can be obtained. At this time, by setting the lever vibration frequency to both sides of the frequency band of the half width of the Q curve, the lever is easily attenuated and easily follows the unevenness of the sample, so that the unevenness shape information of the sample can be measured. . Also, by measuring the voltage waveform applied to the lever vibrating means 3 and the output signal of the optical position detector 8, a time delay (phase) when the probe separates can be obtained. Since the physical property value becomes large or small, the physical property distribution can be measured.

The measurement may be performed not only in a vacuum but also under an atmospheric pressure by evacuating by a vacuum exhaust means and then introducing gas 68 into a vacuum vessel. Further, when performing gas replacement, a gas containing humidity may be introduced for measurement. Alternatively, the measurement may be performed at a pressure of 1 atm by continuously flowing a gas or a gas including humidity into the vacuum vessel without evacuating. Alternatively, the sample may be set in a cell in which a solution can be placed, placed on a sample moving means, and measured in the solution.

By setting the lever excitation frequency to both sides of a frequency band which is a half width of a dependency curve (Q curve) of the lever amplitude and the excitation frequency, the lever can be easily attenuated. Not only in the atmosphere but also in a vacuum, a gas, and a solution, the irregularity of the sample can be followed to accurately measure not only the irregularity of the sample surface but also the time delay (phase) when the probe leaves the sample surface.

[0020]

The present invention is embodied in the form described above and has the following effects. Cantilever and cantilever with micro tip at tip
A cantilever comprising a laser for irradiating the laser reflecting surface, an optical position detector for detecting the position of the reflected light from the laser, a sample moving means for moving the sample, and a lever vibrating means for vibrating the cantilever. When the needle touches the sample surface, the amount of decrease in the amplitude is captured by the optical position detector, and the vertical movement of the sample moving means is controlled so that the reduced amplitude is constant. In the scanning probe microscope for measuring the uneven shape information of the above, both outer sides of the frequency band corresponding to the half width of the dependency curve (Q curve) of the vibration frequency and the amplitude of the cantilever are used as the lever vibration frequency. As a result, the cantilever is easily attenuated, and the unevenness information and phase (physical properties) of the sample surface are stably measured. In particular, there is an effect of enabling measurement in a vacuum having no air resistance.

[Brief description of the drawings]

FIG. 1A is a schematic diagram of a method for measuring surface unevenness distribution by a scanning probe microscope, FIG. 1B is a schematic diagram for explaining vibration of a cantilever, and FIG. 1C is a schematic diagram of a cantilever. FIG. 4 is an explanatory diagram of a dependency curve of an amplitude amount and an excitation frequency and an excitation frequency region of the present invention.

FIG. 2A is an explanatory diagram showing a relationship between a probe and a sample surface when measuring surface unevenness distribution with a scanning probe microscope;
(B) is an explanatory diagram of the unevenness information measured when the cantilever is hardly attenuated when measuring the surface unevenness distribution with a scanning probe microscope.

FIG. 3 is an explanatory view showing a time delay (phase) of a probe tip moving away from a sample surface when measuring a physical property distribution with a scanning probe microscope.

FIG. 4 is a schematic diagram showing an example when measuring sample surface unevenness information and physical property distribution with a scanning probe microscope.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Probe 2 Cantilever 3 Lever vibrating means 4 Laser reflecting surface 5 Laser 7 Reflected light 8 Optical position detector 9 Sample 10 Sample moving means 11 Scanning operation 12 Vertical operation 13 Vibration 14 Resonance point 21 Sample convex Part 61 Laser generator 62 Window 63 Vacuum container 64 Vacuum exhaust means 65 Sample table 66 Laser moving means 67 Optical position detector moving means 68 Gas introduction 69 Sample table moving means B, C, D Laser reflected light A, A0, A1, A2 The amplitude of the cantilever Amax The amplitude of the resonance point of the Q curve f1, f2 The frequency that is half the amplitude of the resonance point of the Q curve V1 , -V1 Voltage applied to lever-vibration means W1, W2 Optical position output signal from optical position detector

Claims (7)

[Claims] A cantilever having a minute probe at its tip and a laser for irradiating a laser reflecting surface of a cantilever with a laser.
An optical position detector for detecting the position of the reflected light of the laser, a sample moving means for moving the sample, and a lever vibration means for oscillating the cantilever with a desired amplitude at a constant period, the probe of the cantilever is provided on the surface of the sample. The vertical position of the sample moving means is controlled by controlling the vertical movement of the sample moving means so that the reduced amount of amplitude is captured by the optical position detector when it comes into contact with In the scanning probe microscope for measuring the vibration frequency of the cantilever, both outer sides of the frequency band which is the half width of the dependency curve (Q curve) of the vibration frequency and the amplitude of the cantilever are set as the lever vibration frequency. Scanning probe microscope. 2. A phase detector for capturing a signal when a time delay (phase) occurs in the vibration form of the cantilever due to the interaction between the sample surface and the probe of the cantilever, and detecting the phase by detecting the phase. 2. The scanning probe microscope according to claim 1, wherein a difference in physical properties of the sample surface is measured. 3. The method according to claim 1, wherein the measurement is performed in the atmosphere.
Or the scanning probe microscope according to claim 2. 4. The scanning probe microscope according to claim 1, further comprising a cell for storing the solution, wherein the sample is placed in the solution and measured in the solution. 5. The scanning probe microscope according to claim 1, wherein the measurement is performed in a vacuum environment having a vacuum vessel and an exhaust means. 6. The scanning probe microscope according to claim 5, wherein the vacuum vessel is once evacuated and then replaced with gas so that measurement can be performed in a gas atmosphere. 7. The scanning probe microscope according to claim 6, wherein when replacing the gas, humidity is included in the gas.