JP3877919B2 - Scanning probe microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cantilever having a microprobe at the tip, a laser that irradiates the laser reflecting surface of the cantilever, an optical position detector that detects the position of the reflected light of the laser, and a sample that moves the sample. When the cantilever probe touches the sample surface, the decrease in amplitude is detected by the optical position detector so that the reduced amplitude is constant. The present invention relates to a scanning probe microscope that measures uneven shape information on the surface of a sample from an operation amount of the vertical movement by controlling the vertical movement of the sample moving means.
[0002]
[Prior art]
A conventional scanning probe microscope includes a cantilever having a microprobe at the tip, a laser that irradiates the laser reflecting surface of the cantilever, an optical position detector that detects the position of the reflected light of the laser, and a sample. When the cantilever probe touches the sample surface, the amount of decrease in the amplitude is detected by the optical position detector when the cantilever probe touches the sample surface. In the scanning probe microscope that measures the concavo-convex shape information on the sample surface from the operation amount of the vertical movement by controlling the vertical movement of the sample moving means, the dependency curve (Q of the excitation frequency and amplitude amount of the cantilever) The unevenness information on the surface of the sample is measured by setting the vicinity of the resonance point of the curve to the excitation frequency of the cantilever. It also has a phase detector that captures the signal when a time delay (phase) occurs in the vibration mode of the cantilever due to the interaction between the sample surface and the probe of the cantilever, and the excitation frequency of the cantilever is the surface roughness information The difference in physical properties of the sample surface is measured by detecting the phase in the vicinity of the resonance point of the Q curve in the same manner as in the above measurement.
[0003]
[Problems to be solved by the invention]
In the conventional scanning probe microscope, the cantilever is easy to vibrate and difficult to attenuate because the resonance frequency near the resonance point of the dependency curve (Q curve) of the excitation frequency and amplitude amount of the cantilever is used. It was. Even if the probe is interacted with the sample surface, it is difficult to attenuate and the amount of change in amplitude is not constant immediately, so the control of the sample moving means seems to be delayed, and the operation amount of the vertical movement of the sample moving means is also delayed. The surface roughness information obtained from the quantity has a drawback that it 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 change in the amplitude amount does not coincide with the vertical direction of the control. In particular, in the measurement in a vacuum, since the air resistance is lost, the cantilever is difficult to attenuate, so the amplitude amount to be changed due to the interaction with the sample is not short. There was a drawback that the control became more and more delayed and the surface roughness information could not be measured.
[0004]
Also, when measuring the difference in physical properties of the sample surface from the phase signal generated by the interaction between the probe and the sample surface (the time delay of the probe), the cantilever is difficult to attenuate, so the phase signal is also There was a drawback that it was not possible to detect the difference in physical properties correctly because it became information of a transitional process in which the vibration attenuated.
Therefore, in the present invention, the cantilever is not easily attenuated by setting the lever excitation frequency on both outer sides of the frequency band that is the half-value width of the dependency curve (Q curve) of the excitation frequency and amplitude amount of the cantilever. Distant from the vibration frequency range (near the resonance point) makes it easy to attenuate transient vibration changes after the cantilever probe contacts the sample, and enables measurement in a vacuum with no air resistance. And Furthermore, when measuring the difference in physical properties of the sample surface from the phase signal (probe time delay) generated by the interaction between the probe and the sample surface, the excitation frequency is set to a region where the cantilever is likely to attenuate. Thus, the phase signal also becomes a stable signal after attenuation, and it is an object to correctly measure the phase signal (difference and distribution of physical properties of the sample surface) resulting from the interaction between the probe and the sample surface.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention detects the position of a laser that irradiates the laser reflection surface of a cantilever and a cantilever having a minute probe at the tip and the laser, and the reflected light of the laser. It consists of an optical position detector, a sample moving means for moving the sample, and a lever excitation means for vibrating the cantilever. When the probe of the cantilever comes in contact with the sample surface, the decrease in amplitude is detected by the optical position detector. In a scanning probe microscope that measures unevenness shape information on the sample surface from the amount of operation of the vertical movement by controlling the vertical movement of the sample moving means so that the reduced amplitude amount becomes constant, the excitation frequency and amplitude of the cantilever The vibration of the cantilever is easily damped by setting the lever excitation frequency on both outer sides of the frequency band which is the half width of the quantity dependency curve (Q curve).
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a cantilever having a minute probe at the tip, a laser that irradiates the laser reflecting surface of the cantilever, an optical position detector that detects the position of the reflected light of the laser, and a sample. It consists of a sample moving means that moves and a lever excitation means that vibrates the cantilever. When the probe of the cantilever touches the sample surface, the decrease in amplitude is detected by the optical position detector. By controlling the vertical movement of the sample moving means so that the amplitude amount is constant, in the scanning probe microscope that measures the concavo-convex shape information on the sample surface from the operation amount of the vertical movement, the excitation frequency and amplitude amount of the cantilever By using the lever excitation frequency on both outer sides of the frequency band that is the half-width of the dependence curve (Q curve), the cantilever is easily attenuated, and the irregularity information and phase (physical properties) of the sample surface are stabilized. To measure It was so. In particular, measurement in a vacuum without air resistance is possible.
[0007]
【Example】
The embodiment will be described with reference to the drawings. FIGS. 1A, 1B, and 1C are schematic views of the method of the present invention in measurement with a scanning probe microscope.
The case of surface irregularities as information to be measured will be described with reference to FIG. The cantilever-2 having the probe 1 is attached to the lever excitation means 3. The laser reflecting surface 4 is irradiated with a laser 5 and the reflected light 7 is detected as the position of the optical position detector 8. The cantilever-2 is vibrated by the lever vibration means 3 so that the probe 1 moves up and down. When the probe 1 comes into contact with the concave portion of the surface of the sample 9, the laser reflected light reaches the position D of the optical position detector. When the probe moves away 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 and out of the sample recess, the amplitude of the cantilever is obtained as the difference between the position D and the position B. Next, when the sample moving means 10 is moved to the left by the scanning operation 11, the probe hits or leaves on 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. The laser reflected light reaches the position B of the optical position detector when the probe moves away from the convex portion and reaches the upper limit of vibration.
[0008]
When the probe oscillates against or away from the convex portion of the sample, the amplitude of the cantilever is obtained as the difference between position C and position B. If the difference in the arrival position of the laser reflected light to the optical position detector is detected, 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 in the arrival position of the laser reflected light to the optical position detector is constant, and the unevenness information of the sample may be obtained from the operation amount of the vertical movement. The latter method is usually used because the way the probe touches the sample (pressing condition) is small and constant, so that damage to the probe and the sample surface is less likely.
[0009]
Next, FIG. 1B shows a schematic diagram when the cantilever is vibrating. The cantilever-2 is attached with lever excitation means 3. The lever excitation means 3 uses a piezoelectric element, and is applied at a certain period with a certain voltage applied to the piezoelectric element. The piezoelectric element causes vertical vibration 13 to vibrate cantilever-2. The cantilever vibrates with a certain amplitude amount A. The amplitude A depends on the voltage applied to the piezoelectric element in the lever excitation means 3 and the vibration frequency. Even if the applied voltage is determined to be a constant value, it depends greatly on the frequency to be vibrated.
[0010]
FIG. 1C shows an excitation frequency region of the lever of the present invention as a difference from the conventional one. The vertical axis represents the amplitude amount A of the cantilever, and the horizontal axis represents the excitation frequency of the lever. When the excitation frequency f is increased from a lower frequency, the amplitude amount A of the cantilever becomes a maximum value Amax at a certain frequency. When the excitation frequency f is further increased, the amplitude amount A decreases. Which frequency is maximized is determined by the material, length, thickness and width of the cantilever. A dependency curve of the excitation frequency of the amplitude A as shown in the figure is called a Q curve. The peak of the Q curve is the resonance point 14. The excitation frequency at the resonance point is called the resonance frequency. If the lever is vibrated in the vicinity of the resonance frequency, it becomes easy to vibrate and is difficult to attenuate. If vibration is applied in the vicinity of the resonating frequency (in the vicinity of the resonance point 14), the cantilever has a large amplitude amount A even with the same applied voltage, and is likely to vibrate and hardly attenuates. Even if the probe is affected by the sample, it is difficult to attenuate, so the amplitude to be changed is not short. Conventionally, the excitation frequency of the cantilever has been set to the vicinity of the resonance point by giving priority to the point that easily vibrates.
[0011]
If the height (amplitude amount) of the resonance point 14 is Amax, and the frequency of the point on the Q curve having a height of ½ of Amax is f1 and f2, the frequency band between f1 and f2 is a half-width band. To do. In the half-band frequency band, the closer to the resonance point 14, the more easily the lever vibrates and is less likely to attenuate. In the present invention, the excitation frequency of the lever is set on both outer sides of the half-value width frequency band. The lever is less likely to vibrate on both outer sides of the half-bandwidth frequency band, and tends to attenuate. By setting the excitation frequency region of the lever to be easily attenuated, the amplitude amount of the lever is easily attenuated even if there is a change according to the uneven shape of the sample. Since the amount can be determined immediately and the vertical movement of the sample moving means can be followed according to the unevenness of the sample surface, the information obtained from the operation amount of the vertical movement becomes the uneven shape of the sample surface. Correct unevenness information on the sample surface can be measured.
[0012]
FIG. 2A is a schematic diagram showing the relationship between the amount of vibration of the cantilever and the sample surface when the concavo-convex shape of the sample is measured in a vacuum so that the amplitude of the cantilever is constant. When the probe is not in contact with the sample surface, the cantilever vibrates with an amplitude amount A0. It is assumed that 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 amount of the cantilever becomes A1. A1 is smaller than A0. It is assumed that control is started from this point for explanation.
[0013]
The vertical movement 12 of the sample moving means 10 is controlled so that the amplitude of the cantilever becomes constant with A1 while scanning. As described above, the concavo-convex 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 the surface of the same height as the instantaneous convex portion where the probe is further to the right of the right corner of the convex portion 21 disappears suddenly, so the amplitude amount of the cantilever changes from A1. However, the lever is not easily attenuated because it is difficult to attenuate. At this time, if the amount of amplitude becomes constant immediately, the amount of operation of the vertical movement of the sample moving means can be determined, and if the sample is brought close to the probe by the sample moving means until the amount of amplitude becomes A1, the amount of operation of the vertical movement is The height of the part can be determined. However, when the probe deviates from the right corner of the convex portion, the contact with 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, and the amount of amplitude cannot be determined immediately. The actual amount of amplitude becomes a constant value after the probe hits the concave portion of the sample surface after a certain period of time and settles at A2.
[0014]
The amount of operation of the up and down movement of the sample moving means is determined for the first time so that A2 which is a constant value is compared with A1 which is the target value and the amplitude A2 is the same as A1. However, in actuality, since the control for determining the operation amount of the vertical movement of the sample moving means is always performed, the operation amount is determined by information in the middle of the amplitude amount becoming A2. That is, the operation amount of the up / down movement is determined even though the probe is not in contact with the sample surface. The sample surface unevenness information measured from the transient amplitude amount of the cantilever is not the original shape of the sample surface but the difficulty of attenuation of the cantilever. For example, the amplitude of the cantilever is measured at the falling and rising parts of the unevenness of the sample, because the amount of up / down movement is determined in a way that it cannot follow the unevenness of the sample surface due to the difficulty of attenuation and is transiently delayed. As shown in FIG. 2B, the (obtained) unevenness information differs between the unevenness information of the sample and the measured unevenness information.
[0015]
Even in a vacuum, in the present invention, as shown in FIG. 1C, the vibration of the cantilever can be easily damped by setting the excitation frequency of the cantilever outside both frequency bands of the half width of the Q curve. In the vacuum, the air around the cantilever disappears, so when the cantilever vibrates, it does not receive air resistance, and is more likely to vibrate than in the atmosphere. By setting the excitation frequency of the cantilever outside both frequency bands 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.
[0016]
FIG. 3 shows the temporal relationship between the applied voltage waveform of the lever excitation means and the optical position output signal detected by the optical position detector. If the probe and the sample surface are not interacted, the applied voltage waveform and the optical position output waveform are the same with no time delay. Even if an attempt is made to separate the probe from the sample surface due to adhesive force, electrostatic force, magnetic force, or the like, the probe and the sample surface are separated with a time delay. The applied voltage when the probe is about to move away from the sample surface is V1, and the applied voltage when the probe is in contact with the sample surface is -V1. The optical position output signal is W1 when the probe is in contact with the sample surface, and the optical position output signal is W2 when the probe is separated from the sample surface. Even if the voltage waveform applied to the probe and the sample surface is V1 due to the aforementioned interaction, the optical position output signal becomes W2 after time T seconds. That is, if the sample surface has an action force due to physical properties, a time delay (phase) occurs when the probe moves away from the sample surface. At this time, the magnitude of the physical properties 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 touch or leave the sample surface. When measuring the phase, the lever excitation frequency is set on both sides of the frequency band that has the half width of the Q curve, making it easy to attenuate the vibration of the lever and changing the amplitude of the lever quickly. The probe reliably follows the surface irregularities and the phase signal can be measured correctly.
[0017]
Next, FIG. 4 shows an embodiment in a vacuum. The laser 5 from the laser generator 61 is introduced into the vacuum vessel 63 through the window 62. The vacuum container and the window are hermetically sealed, and the vacuum state of the vacuum container is achieved by the vacuum exhaust means 64. In the vacuum vessel, a cantilever-2, lever-exciting means 3, a sample 9, and a sample stage 65 on which the sample is heated or cooled or placed at room temperature are installed. 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 irradiated onto the laser reflecting surface of the cantilever-2, and the reflected light 7 of the laser is detected by the optical position detector 8 installed outside the vacuum vessel through the window. To reach. The amount of amplitude of the cantilever is obtained by the position of the optical position detector. Although the amount of amplitude decreases when the probe hits the sample surface, the sample unevenness information can be obtained by determining the operation amount by the up and down operation according to the scanning operation of the sample moving means so as to maintain the decreased amount of amplitude. At this time, by setting the lever excitation vibration frequency to the outside of the half band width of the Q curve, the lever is easily attenuated and can easily follow the sample unevenness, and the uneven shape information of the sample can be measured. . Further, by measuring the voltage waveform applied to the lever excitation means 3 and the output signal of the optical position detector 8, a time delay (phase) when the probe leaves can be obtained. The physical property distribution can be measured because the physical property value is large or small.
[0018]
Further, the measurement may be performed not only in a vacuum but also in an atmospheric pressure by introducing a gas 68 into a vacuum vessel after evacuating by a vacuum exhaust means. Further, measurement may be performed by introducing a gas containing humidity when replacing the gas. Further, measurement may be performed at 1 atm by continuously flowing gas or humidity including gas into the vacuum vessel without evacuation.
Alternatively, the sample may be set in a cell in which the solution can be placed and placed on the sample moving means for measurement in the solution.
[0019]
By making the lever excitation frequency outside the frequency band that is the half-value width of the amplitude curve of the lever and the dependency curve (Q curve) of the excitation frequency, the lever can be easily attenuated, and only in the atmosphere In addition, the time delay (phase) when the probe leaves the sample surface as well as the sample surface unevenness information can be correctly measured by following the unevenness of the sample in vacuum, gas, and solution.
[0020]
【The invention's effect】
The present invention is implemented in the form as described above, and has the following effects.
A cantilever having a microprobe at the tip, a laser irradiated on the laser reflecting surface of the cantilever, 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 cantilever When the cantilever probe touches the sample surface, the amount of decrease in the amplitude is detected by the optical position detector so that the reduced amplitude is constant. In the scanning probe microscope that measures the concavo-convex shape information on the sample surface from the operation amount of the vertical motion by controlling the vertical motion, the half-value width of the dependency curve (Q curve) of the excitation frequency and amplitude amount of the cantilever The cantilever is easily attenuated by setting the lever excitation frequencies on both outer sides of the frequency band, and the unevenness information and phase (physical properties) of the sample surface are stably measured. In particular, there is an effect that enables measurement in a vacuum without air resistance.
[Brief description of the drawings]
FIG. 1A is a schematic diagram of a method for measuring surface unevenness distribution with a scanning probe microscope, FIG. 1B is a schematic diagram illustrating vibration of a cantilever, and FIG. 1C is a cantilever. It is explanatory drawing of the dependence curve of the amplitude amount and excitation frequency of this, and the excitation frequency area | region of this invention.
FIG. 2A is an explanatory diagram showing the relationship between a probe surface and a sample surface when measuring the surface unevenness distribution with a scanning probe microscope, and FIG. 2B shows the surface unevenness distribution with a scanning probe microscope. It is explanatory drawing of the uneven | corrugated information measured when the cantilever at the time of measuring is hard to attenuate | damp.
FIG. 3 is an explanatory diagram showing a time lag (phase) away from the sample surface of a probe when measuring a physical property distribution with a scanning probe microscope.
FIG. 4 is a schematic diagram showing an example in measuring sample surface unevenness information and physical property distribution with a scanning probe microscope.
[Explanation of symbols]
1 Probe 2 Cantilever
3 Laser excitation means 4 Laser reflecting surface 5 Laser 7 Reflected light 8 Optical position detector 9 Sample 10 Sample moving means 11 Scan action 12 Vertical action 13 Vibration 14 Resonant point 21 Sample convex part 61 Laser generation 62 Window 63 Vacuum container 64 Vacuum exhaust means 65 Sample stage 66 Laser moving means 67 Optical position detector moving means 68 Gas introduction 69 Sample stage moving means B, C, D To the optical position detector of the laser reflected light A, A0, A1, A2 where the wave reaches Acanal lever amplitude Amax Q curve resonance point amplitude f1, f2 Q curve resonance point frequency V1, -V1 lever addition Applied voltage W1, W2 Optical position output signal at optical position detector

Claims (7)

A cantilever with a small probe at the tip;
A laser for irradiating the The reflecting surface, - les of the cantilever
A light position detector for detecting the position of The reflected light, - said Les
Sample moving means for moving the sample;
And a lever vibrating means for vibrating at a desired amplitude of the cantilever at a constant period,
In a scanning probe microscope that measures uneven shape information on the sample surface by controlling the vertical movement of the sample moving means so that the amplitude of the cantilever is constant ,
2. A scanning probe microscope characterized in that the excitation frequency of the cantilever is outside both frequency bands of the half-width of the Q curve of the primary resonance frequency . Caused by the interaction between the sample surface and the probe, and measuring the difference in physical properties of the sample surface by detecting the phase of the signal in the vibration state and the light position detector of the cantilever according Item 2. A scanning probe microscope according to Item 1.   3. The scanning probe microscope according to claim 1, wherein measurement is performed in the atmosphere. The scanning probe microscope according to claim 1 , further comprising a cell in which the solution is placed on the sample moving means, and measuring in the solution in the cell . The scanning probe microscope according to claim 1 , further comprising a vacuum container and an exhaust unit, wherein the cantilever and the sample are arranged in the vacuum container and measured in a vacuum environment. 6. The scanning probe microscope according to claim 5, wherein after the vacuum vessel is evacuated, the inside of the vacuum vessel is replaced with gas and measurement is performed in a gas atmosphere. The scanning probe microscope according to claim 6, wherein humidity is included in the gas replacement .

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