JP4098921B2 - Setting method of probe pressing force of scanning probe microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for setting the probe pressing force of a scanning probe microscope, and in particular, removes the influence of disturbances such as electrostatic force and applies only to physical quantities such as atomic force before the start of measurement. The present invention relates to a probe pressing force setting method for a scanning probe microscope that can appropriately set the probe pressing force.
[0002]
[Prior art]
A conventional typical configuration of a scanning probe microscope is shown in FIG. This scanning probe microscope is, for example, an atomic force microscope. This atomic force microscope includes a cantilever 12 having a probe 11 at a free end. The probe 11 is arranged close to the sample 13 by moving the cantilever 12 toward the sample 13 by a coarse movement mechanism (not shown). The coarse movement mechanism supports the base of the cantilever 12 and freely moves the cantilever and the probe up and down at a relatively large distance. Actually, the stationary position of the probe 11 with respect to the sample 13 is determined by the value of the probe pressing force set in the feedback control system that adjusts the distance between the probe and the sample. The position of the probe 11 is detected as an amount of displacement of the cantilever 12 by an optical displacement detection system. This optical displacement detection system is an optical lever type displacement detection system that uses the back surface of the cantilever 12 as a reflection surface. The laser light source 15 irradiates the back surface of the cantilever 12 with the laser light 14 and the back surface of the cantilever 12. And a position detector 16 for receiving the laser beam 14. The displacement signal s1 output from the position detector 16 is input to the subtracter 17. In addition, a setting signal s0 for setting the probe pressing force is input to the subtracter 17. S0 by the setting signal is a value for setting the distance between the reference probe and the sample, and is a probe pressing force against the surface of the sample 13. The setting signal s0 is given from the pressing force setting unit 18. The subtracter 17 obtains a difference between the displacement signal s1 and the set value s0 and outputs it as a deviation signal Δs. The deviation signal Δs output from the subtractor 17 is input to the control circuit 19. Based on the input deviation signal Δs, the control circuit 19 generates and outputs a control signal s2 for adjusting the distance between the probe and the sample so that the Δs becomes zero.
[0003]
The sample 13 is placed on a sample table 20. The sample stage 20 is supported by a tripod 21. The tripod 21 has a piezoelectric drive element in each of the three orthogonal axes (X, Y, Z), supports the sample stage 20 with these piezoelectric drive elements, and supports the sample in the XY axial direction and the Z-axis direction. It is a three-dimensional actuator that is moved to. The expansion / contraction operation of the Z-axis direction piezoelectric drive element 21z that determines the height position (Z-axis direction position) of the sample 13 is controlled by a control signal (voltage signal) s2 output from the control circuit 19. The operations of the two piezoelectric drive elements that move the sample 13 in the X-axis and Y-axis directions are controlled by a scanning control signal (voltage signal) s3 provided from the XY scanning circuit 22. By the scanning control signal s3, the sample stage 20 is moved in the XY directions, and the sample 13 on the sample stage 20 is also moved in the XY directions accordingly. By this operation, the probe 11 scans the surface of the sample 13 as a relative positional relationship between the sample 13 and the probe 11.
[0004]
The measurement of the surface of the sample 13 is performed by a feedback control system based on the pressing force determined by the pressing force setting signal (s0) while the probe 11 scans the surface of the sample 13 and the distance between the probe and the sample is predetermined. This is done by performing control to maintain the distance. The feedback control system including the control circuit 19 performs control so that the deflection deformation amount of the cantilever 12 always coincides with the set value s0, so that the probe 11 is pressed against the surface of the sample 13 with a constant pressing force. Retained. The control signal s2 and the scanning control signal s3 obtained during the measurement are input to the signal processing device 23. The signal processing device 23 uses the control signal s2 representing the height information of the sample surface and the scanning control signal s3 representing the measurement range of the sample surface to create data for displaying the measured unevenness information on the sample surface. . The data is sent to the display device 24, where an uneven image on the sample surface is displayed.
[0005]
With the probe 11 approaching the sample 13 to the region where the atomic force acts, the Z-axis direction piezoelectric drive element 21z of the tripod 21 is operated to change the relative distance between the probe 11 and the sample 13. When this occurs, the force acting between the probe and the sample changes, and the amount of deflection of the cantilever 12 changes. The relationship between the control signal s2 and the displacement signal s1, that is, the relationship between the probe-sample distance and the cantilever displacement (deflection amount) is as shown in FIG. The horizontal axis in FIG. 4 indicates the distance between the probe and the sample. The horizontal axis indicates the state where the probe and the sample are separated from each other. The position where the vertical axis intersects the tip of the probe and the sample is in contact with each other. The negative side shows a state where the probe is pushed into the sample. In the case of the negative side, the cantilever 12 is warped upward. The vertical axis in FIG. 4 represents the displacement amount (deflection amount) of the cantilever 12. Since the force is obtained by multiplying the displacement amount of the cantilever 12 by the spring constant of the cantilever 12, the displacement amount of the cantilever on the vertical axis is equivalent to the force (pressing force) acting between the probe and the sample. On the vertical axis, the positive side means repulsive force and the negative side means attractive force. When the vertical axis is regarded as a force acting between the probe and the sample, the slope of the straight line in the contact area corresponds to the spring constant of the cantilever and has a fixed value specific to the cantilever to be used.
[0006]
In the pressing force setting unit 18 shown in FIG. 3, conventionally, the pressing force (s0) is set as a repulsive force. This pressing force is shown by a broken line in FIG. In actual measurement, as described above, the probe that has been separated from the sample is gradually brought closer to the sample, and after the tip of the probe contacts the sample surface, the probe is further moved from the contact state. The cantilever displacement signal s1 corresponding to the pressing force of the probe and corresponding to the pressing force of the probe is brought close to the set value s0. The characteristic indicated by the thick line 25 in FIG. 4 indicates the operating characteristic that the probe gradually approaches the sample. Section a is a section from when the probe contacts the sample surface until the displacement signal s1 matches the set value s0. This characteristic diagram also shows the characteristics when the probe is brought close to the sample, then retracted again and pulled away from the sample, and there is an adsorption force (b) due to water or the like existing on the sample surface. Is shown. In the atmosphere, such an adsorption force is generally present on the sample surface, but this adsorption force is a force that acts due to the surface tension of water, and is notable when the probe is pulled away from the sample surface. It is a phenomenon that appears. Therefore, this phenomenon does not affect the conventional approach method. In FIG. 4, a section c indicates a range (driving range) in which driving by the piezoelectric driving element 21z is possible.
[0007]
[Problems to be solved by the invention]
The above-described conventional setting of the pressing force between the sample and the probe and the approaching operation theoretically assume an ideal case where only the atomic force acts between the probe and the sample when approaching the probe. In reality, however, electrostatic force often acts between the probe and the sample in addition to the interatomic force.
[0008]
FIG. 5 is a diagram showing the same characteristics as FIG. 4, and the characteristics 26 show the operating characteristics when an electrostatic force acts between the probe and the sample when the probe approaches the sample. In this characteristic diagram, the characteristic indicating the attractive force when the probe is pulled apart is not necessary for explanation, and is omitted. According to the operating characteristic 26, when the probe is brought close to the sample, an electrostatic force is first applied to the cantilever, so the stage before the probe 11 contacts the sample 13 (distance L1 between the probe and the sample). Thus, the force acting on the cantilever 12 reaches the set value s0. In such a case, the conventional atomic force microscope has a problem that the distance between the probe and the sample is controlled to L1, and thus the original atomic force microscope cannot be measured. Furthermore, there is a problem that the magnitude of the electrostatic force and the direction in which the force acts are various, and when the electrostatic force acts, it cannot be set to the originally set pressing force. In addition, the electrostatic force acts from a position far away in space compared to the atomic force. Specifically, for example, it is a distance that works sufficiently even in a state separated by several hundred μm, and therefore the distance L1 shown in FIG. 5 can be sufficiently increased to be about 100 μm. On the other hand, since the driving range c of the piezoelectric driving element 21z is about several μm to 10 μm, it has often occurred that the probe cannot be brought close to the driving range of the piezoelectric driving element 21z. In addition to the electrostatic force, a magnetic force may act, and in this case, the same problem is raised.
[0009]
Furthermore, a problem of drift of the displacement signal s1 based on environmental factors such as the air temperature and the device temperature also occurs. FIG. 6 is a view similar to FIG. 4, and a characteristic 27 shows an operation characteristic when drift occurs in the displacement signal s1 when the probe approaches the sample. That is, when a drift occurs in the displacement signal s1, it is detected as if a force exceeding the pressing force s0 is applied in a state of being separated on the positive side in the operation characteristic 27. Therefore, there arises a problem that it is impossible to measure with a conventional apparatus.
[0010]
An object of the present invention is to solve the above-described problem. Even when an electrostatic force other than an atomic force acts between the probe and the sample, or when the displacement signal of the cantilever drifts, the probe It is an object to provide a probe pressing force setting method for a scanning probe microscope that can be made to approach a desired position and can accurately perform measurement at a set probe-sample distance.
[0011]
[Means and Actions for Solving the Problems]
The probe pressing force setting method for a scanning probe microscope according to the present invention includes the following steps to achieve the above object.
[0012]
In the first probe pressing force setting method, the probe pressing force is set so that the probe receives a force from the surface of the sample before the measurement is performed, and the probe is pressed between the probe and the sample based on the probe pressing force. This method is applied to a scanning probe microscope in which the distance between the probe and the sample is changed so that the probe and the sample approach each other and the stationary position of the probe with respect to the sample is determined. In addition, by setting the probe pressing force to an arbitrary value or a maximum value that is larger than the previously set probe pressing force, the above-mentioned distance between the probe and the sample is changed, and the probe is applied to the sample. a step of approaching after finishing the operation of the approach, the probe pressing force is set to a preset value, the steps of determining the stationary position of the probe on the basis of the preset value, in a process comprising is there.
[0013]
The second probe pressing force setting method is a probe pressing force setting method applied to the scanning probe microscope as described above, and the probe pressing force is applied before the probe and the sample start approaching. , The step of bringing the probe closer to the sample by changing the distance between the probe and the sample by setting to an arbitrary value or maximum value larger than the set probe pressing force, and the approach operation and measuring the amount of the disturbance by the force curve measured after the completion of the, the tip pressing force, based on the amount of the measured disturbance, is corrected to a value such that the influence of the disturbance is removed, the A step of determining a stationary position of the probe based on the corrected value .
[0014]
First, the probe's pressing force is almost maximized after it contacts the sample surface, and then the original pressing force is set to eliminate the influence of electrostatic force and other suitable distances that enable measurement. It is possible to set the interval between the probe and the sample.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
[0016]
The present invention relates to a contact mode scanning probe microscope, such as an atomic force microscope, in which the probe is brought close to the sample and the distance between the sample and the probe is set to a required distance before the measurement is started. This is a method of appropriately setting the pressing force of the probe when pressing against the sample. In the description of this embodiment, the atomic force microscope of FIG. 3 used in the description of the prior art is used as the configuration of the scanning probe microscope in which the probe pressing force setting method according to the present invention is implemented. In the configuration shown in FIG. 3, the characteristic configuration of the present embodiment is that a setting value is set by the pressing force setting unit 18 that gives a setting value (pressing force setting signal) s0 as a reference value to the subtractor 17. Is in the way. Other configurations and operations in the scanning probe microscope are the same as those described above. In the description of this embodiment, a characteristic configuration will be described in detail.
[0017]
In FIG. 3, the pressing force setting unit 18 is configured so that the set value set there can be arbitrarily changed by the operator's operation. In the atomic force microscope, a pressing force is set in advance before starting measurement. Then, the probe 11 at a position away from the sample 13 (cantilever 12 having the probe 11 at the tip) is moved closer to the sample 13, and the above-described preset pressing force setting value (with respect to the surface of the sample 13 ( When the position of the probe 11 is set by the distance), the displacement amount (deflection deformation amount) of the cantilever, that is, the pressing force of the probe 11 is first set to an arbitrary value (including the maximum value) larger than the set value. Is set until the value is detected, and then the pressing force of the probe 11 is reset to the preset pressing force setting value.
[0018]
A characteristic 32 shown in FIG. 1 is an operation characteristic indicating a method of approaching the probe 11 to the sample 13 based on the first embodiment, that is, a pressing force setting method. This shows the case where the electrostatic force acts as a disturbance. In the operating characteristic 32, the probe 11 is initially present at a position L 2 away from the sample 13. Further, as a measurer, s0 is determined as a preset pressing force setting value. In FIG. 1, elements that are substantially the same as, for example, the elements described in FIG. 4, such as the pressing force setting value s 0 and the interval c, are denoted by the same reference numerals. In FIG. 1, in the operation characteristic 32, the positional relationship and the dimensional relationship on the horizontal axis and the vertical axis are drawn slightly exaggerated so that the characteristic relationship of the present invention can be understood. The same applies to other drawings.
[0019]
When the probe 11, that is, the cantilever 12 is moved toward the sample 13 by the moving mechanism (coarse movement mechanism not shown), the value set by the pressing force setting unit 18 is set to an arbitrary value or a maximum value larger than the pressing force setting value s 0. Set to pressing force (s _max ). In the following description, an example in which the value set by the pressing force setting unit 18 is the maximum pressing force s _max will be described. The set value s _max of the maximum pressing force is a value determined by the configuration of a detection circuit or the like that detects the displacement signal s1 of the cantilever 12. Thus, when the approach of the probe 11 is started, the set value given to the subtracter 17 by the pressing force setting unit 18 is the set value s _max of the maximum pressing force, and therefore the probe from the position L2 is set. Changes as the operating characteristic 32. After the probe 11 comes into contact with the sample surface, the probe 11 is further pressed against the sample surface based on the set value s _max of the maximum pressing force set by the pressing force setting unit 18. Then, the distance between the probe and the sample is controlled so as displacement signal s1 is equal to the set value s _max. In the operation characteristic 32, the control finally ends at the position L3. Thereafter, the setting value set in the pressing force setting unit 18 is returned from the setting value s _max of the maximum pressing force to the pressing force setting value s0 determined in advance by the measurer as indicated by the arrow 33. In this case, since the probe is moved away from the sample surface, the above-described characteristics of the attractive force appear, and the pressing force set value s0 becomes a value corresponding to the position L4 shown in FIG. Controlled. According to such a pressing force setting method, the maximum pressing force is temporarily set initially and then set to the original appropriate pressing force setting value. Also, the probe can be brought close to the driving range c of the piezoelectric driving element 21z. In some cases, the attracting force does not act. At this time, the piezoelectric drive element 21z is stopped at the position L5 at the end of the drive range by the set value changing operation (the operation indicated by the arrow 33). The region where the sample surface exists can be approached. In this embodiment, the pressing force set value s0 is set as a repulsive force, but it is of course possible to set it as an attractive force.
[0020]
A characteristic 34 shown in FIG. 2 is an operation characteristic indicating the approach method (pressing force setting method) of the probe 11 to the sample 13 according to the second embodiment. Also in the operating characteristic 34, the probe 11 is initially present at a position L2 away from the sample 13. In this embodiment, it is assumed that an electrostatic force s00 acts as a repulsive force between the probe 11 and the sample 13 in addition to the atomic force. As described above, as a measurer, s0 is determined as an original pressing force setting value set in advance. The pressing force setting value s0 in this case is strictly an ideal setting value, and does not take into account the estimated electrostatic force or drift. Further, the maximum pressing force s _max set by the pressing force setting unit 18 is the same as in the first embodiment, and the set value is not limited to the maximum pressing force s _max and is larger than the pressing force setting value s0. Any value can be set.
[0021]
Also in this embodiment, first, the maximum pressing force setting value s _max is set in the pressing force setting unit 18. The set value of the maximum pressing force is determined by the configuration of a detection circuit or the like that detects the displacement signal s1 of the cantilever 12. When the probe 11, that is, the cantilever 12 is moved toward the sample 13 by the moving mechanism (coarse movement mechanism not shown), the pressing force setting unit 18 sets the set value s _max of the maximum pressing force. In the case of this embodiment, when the approach of the probe 11 is started, the setting value given to the subtracter 17 by the pressing force setting unit 18 is the setting value s _max of the maximum pressing force, so from the position L2. When the probe is brought close, the operating characteristic 34 changes. Since an electrostatic force acts between the probe and the sample, the probe 11 tilts to the left and remains on the probe 11 until the probe 11 is in contact with the surface of the sample 13. After the probe 11 comes into contact with the sample surface, the probe 11 is further pressed against the sample surface based on the set value s _max of the maximum pressing force set by the pressing force setting unit 18. Then, the distance between the probe and the sample is controlled so as displacement signal s1 is equal to the set value s _max. In the operation characteristic 34, the control finally ends at the position L3.
[0022]
In this embodiment, when the probe 11 is brought close to and in contact with the sample 13, the approach / contact operation is performed so that the operation characteristic 34 shown in FIG. Strictly speaking, a force curve is measured in the middle to measure electrostatic force or drift amount. That is, the force curve measurement is performed immediately after the probe 11 comes into contact with the sample 13. In this case, the force curve measurement means that after the tip of the probe contacts the sample and is adsorbed by the adsorption layer on the sample surface, the two are separated again, and the operating characteristics obtained at that time act on the probe from the sample. This is a measurement for detecting a force (such as an adsorption force or an electrostatic force). In the operation characteristic 34 shown in FIG. 2, illustration of fine operation characteristics related to force curve measurement is omitted. The movement related to the approach and contact of the probe to the sample is performed by a coarse movement mechanism, and the fine movement between the sample and the probe for performing the force curve measurement is performed by a fine movement mechanism (piezoelectric drive in the Z-axis direction of the tripod 21) By element 21z). As described above, the force curve measurement is performed immediately after the probe contact, whereby the electrostatic force or the drift amount is measured. Here, the electrostatic force obtained by the force curve measurement is s00. Next, a value obtained by adding the preset original pressing force setting value s0 and the electrostatic force s00 is determined as the pressing force setting value to be set. Thereafter, the probe is pressed against the sample until the maximum pressing force is reached as indicated by the operating characteristic 34 in FIG. 2, and thereafter, the set value set in the pressing force setting unit 18 is set to the maximum as shown by the arrow 35. The setting value s _{max of} the pressing force is returned to the pressing force setting value s0 + s00 set by the measurer as described above, and resetting is performed. According to such a pressing force setting method, for example, when an electrostatic force is applied as a force other than an interatomic force, the initial pressing force is temporarily set at the initial stage, and the electrostatic force is measured in the middle. Then, since the pressing force setting value obtained by adding the original appropriate pressing force setting value and the electrostatic force is set, the probe 11 and the cantilever 12 are measured against the surface to be measured of the sample 13. Can be set to an appropriate pressing force. In this embodiment, it is needless to say that the pressing force set value attractive force can be set.
[0023]
As described above, the maximum value of the probe pressing force is a value determined by the configuration of the cantilever displacement detection circuit and the like, and is unique to the scanning probe microscope. Therefore, it is possible to automate the setting of the pressing force for approaching the probe before measurement by storing it in the pressing force setting unit 18 in advance.
[0024]
【The invention's effect】
As is apparent from the above description, according to the present invention, when setting a reference pressing force setting value between a probe and a sample in a scanning probe microscope having an optical lever type optical position detection system. Since the original set value is set after first setting an arbitrary pressing force or maximum pressing force larger than the set value, extra electrostatic force other than atomic force acts between the probe and the sample. Even when the displacement signal detected from the cantilever drifts, it can be appropriately set in a measurable state and can be measured with the original optimum set value.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a first embodiment of a probe pressing force setting method according to the present invention.
FIG. 2 is a view for explaining a second embodiment of the probe pressing force setting method according to the present invention.
FIG. 3 is a configuration diagram showing a typical configuration of a scanning probe microscope.
FIG. 4 is a diagram for explaining a conventional probe pressing force setting method;
FIG. 5 is a diagram for explaining a problem of a conventional probe pressing force setting method.
FIG. 6 is a diagram for explaining another problem of the conventional probe pressing force setting method.
[Explanation of symbols]
11 Probe 12 Cantilever 13 Sample 14 Laser Light 15 Laser Light Source 16 Position Detector 17 Subtractor 21 Tripods 32 and 34 Operating Characteristics

Claims (2)

Prior to the measurement, the probe pressing force is set so that the probe receives a force from the surface of the sample, and the distance between the probe and the sample is determined based on the probe pressing force with the probe. The probe pressing force setting method of the scanning probe microscope, wherein the sample is changed so as to approach and the stationary position of the probe with respect to the sample is determined,
Between before the said probe and the sample begins to approach, the probe pressing force, the sample and the probe by setting the set pressing any value or maximum value greater than the force the method comprising the distance by changing the to approach the probe to the sample,
After completing the operation of the approach, the probe pressing force, the method comprising: setting a preset value, determining the rest position of the probe on the basis of the preset value,
A probe pressing force setting method for a scanning probe microscope. Prior to the measurement, the probe pressing force is set so that the probe receives a force from the surface of the sample, and the distance between the probe and the sample is determined based on the probe pressing force with the probe. The probe pressing force setting method of the scanning probe microscope, wherein the sample is changed so as to approach and the stationary position of the probe with respect to the sample is determined,
Between before the said probe and the sample begins to approach, the probe pressing force, the sample and the probe by setting the set pressing any value or maximum value greater than the force the method comprising the distance by changing the to approach the probe to the sample,
Measuring the amount of disturbance by force curve measurement after finishing the approaching operation;
The step of the probe pressing force, based on the amount of the said measured disturbance, is corrected to a value such that the influence of the disturbance is removed, defining said rest position of the probe on the basis of the corrected value When,
A probe pressing force setting method for a scanning probe microscope.

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