JP2000329679A - Setting method for pressure force of probe in probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a setting method, for the pressure force of a probe in a scanning probe microscope, in which a measurement can be performed when an electrostatic force or the like acts between a probe and a sample or when the displacement signal of a cantilever is drifted and in which the measurement can be performed precisely at the set distance between the probe and the sample. SOLUTION: In this setting method, for the pressure force of a probe which is applied to a scanning probe microscope, before a measurement is performed, the pressure force of the probe is set in such a way that the probe 11 is subjected to a force from the surface of a sample 13, the distance between the probe and the sample is changed on the basis of the pressure force of the probe in such a way that the probe is brought close to the sample, and the standstill position of the probe with reference to the sample is decided, In addition, the method is composed of a stage at which, before the probe 11 starts to come close to the sample 13, the pressure force of the probe is set at an arbitrary pressure force larger than a set value or at a maximum value and at which the distance is changed so as to bring the probe 11 close to the sample 13. In addition, the method is composed of a stage at which, after the probe is brought close to the sample, the pressure force of the probe is set at a value to be set in advance and at which the standstill position of the probe is decided on the basis of the value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for setting a probe pressing force of a scanning probe microscope, and more particularly to a method for removing the influence of disturbances such as an electrostatic force and measuring only a physical quantity such as an atomic force at a stage before the start of measurement. The present invention relates to a method for setting a probe pressing force of a scanning probe microscope capable of appropriately setting a pressing force of a probe against a sample so as to receive an action.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional typical configuration of a scanning probe microscope. 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 cantilever 12 is moved to the sample 13 by a coarse movement mechanism (not shown).
By moving the probe 11 toward the sample 13.
It is arranged close to. The coarse movement mechanism supports the base of the cantilever 12, and moves the cantilever and the probe freely up and down over a relatively large distance. Actually, the rest 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
The displacement of the cantilever 12 is detected by an optical displacement detection system. This optical displacement detection system uses a cantilever 1
2 is a displacement detection system of an optical lever type using the back surface of the cantilever 12 as a reflection surface, and a laser light source 15 for irradiating the back surface of the cantilever 12 with a laser beam 14, and a position detector for receiving the laser beam 14 reflected on the back surface of the cantilever 12. 16. The displacement signal s1 output from the position detector 16 is input to the subtractor 17. In addition, a setting signal s0 for setting the probe pressing force is input to the subtractor 17. S0 according to the setting signal is a value for setting a distance between the probe and the sample as a reference, 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. In the subtractor 17, the displacement signal s1 and the set value s0
And outputs the result as a deviation signal Δs. Subtractor 1
The deviation signal Δs output from 7 is input to the control circuit 19. The control circuit 19 generates and outputs a control signal s2 for adjusting the distance between the probe and the sample based on the input deviation signal Δs so that the Δs becomes 0.

The sample 13 is placed on a sample stage 20. The sample stage 20 is supported by a tripod 21. The tripod 21 has three orthogonal axes (X, Y,
Z) is a three-dimensional actuator that has piezoelectric driving elements in each axis direction, supports the sample table 20 with these piezoelectric driving elements, and moves the sample in each of the XY axis directions and the Z axis direction.
The expansion / contraction operation of the Z-axis direction piezoelectric driving element 21z that determines the height position (the position in the Z-axis direction) of the sample 13 is controlled by a control signal (voltage signal) s2 output from the control circuit 19. Move the sample 13 in each direction of the X axis and the Y axis 2
The operation of the two piezoelectric driving elements is controlled by a scanning control signal (voltage signal) s3 provided from the XY scanning circuit 22. The sample stage 20 is moved in the XY directions by the scanning control signal s3, and accordingly, the sample 13 on the sample stage 20 is moved in the XY directions. With 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 surface of the sample 13 is measured by a feedback control based on the pressing force determined by the pressing force setting signal (s0) while the probe 11 scans the surface of the sample 13 while the probe 11 scans the surface of the sample 13. This is performed by controlling the system to maintain a predetermined distance. The feedback control system including the control circuit 19 performs control so that the amount of deflection of the cantilever 12 always coincides with the set value s0, whereby the probe 11 is pressed against the surface of the sample 13 with a constant pressing force. Will be retained. Control signal s2 obtained during the measurement
And the scanning control signal s3 are input to the signal processing device 23.
The signal processing device 23 includes a control signal s2 indicating height information of the sample surface and a scanning control signal s3 indicating the measurement range of the sample surface.
Is used to create data for displaying the information of the measured irregularities on the sample surface. The data is sent to the display device 24, where an uneven image of the sample surface is displayed.

When the probe 11 is brought close to the region where the atomic force acts on the sample 13, the piezoelectric actuator 21 z in the Z-axis direction of the tripod 21 is operated, and the relative distance between the probe 11 and the sample 13 is increased. Is changed, 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 at that time,
That is, the relationship between the distance between the probe and the sample and the displacement (deflection amount) of the cantilever is as shown in FIG. The horizontal axis in FIG. 4 indicates the distance between the probe and the sample, and the horizontal axis indicates the state in which the probe and the sample are separated from each other. The negative side indicates a state where the probe is pushed into the sample. On the negative side, the cantilever 12 is warped upward. The vertical axis in FIG. 4 indicates the displacement amount (deflection amount) of the cantilever 12. Since the force is obtained by multiplying the displacement of the cantilever 12 by the spring constant of the cantilever, the displacement 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 repulsion, and the negative side means attraction. When the vertical axis is regarded as the force acting between the probe and the sample, the inclination of the straight line in the contact area corresponds to the spring constant of the cantilever, and has a fixed value unique to the cantilever to be used.

In the pressing force setting section 18 shown in FIG. 3, the pressing force (s0) is conventionally set as a repulsive force. This pressing force is shown by a broken line in FIG. In actual measurement, conventionally, as described above, a probe far from the sample is gradually approached to the sample, and after the tip of the probe contacts the sample surface, the probe is further moved from the contact state. The probe is pressed against the sample surface and approached until the displacement signal s1 of the cantilever corresponding to the pressing force of the probe matches the set value s0. The characteristic shown by the thick line 25 in FIG. 4 indicates the operation characteristic that the probe gradually approaches the sample. The section a is a section from when the probe contacts the sample surface until the displacement signal s1 matches the set value s0. Also,
This characteristic diagram also shows the characteristics when the probe is moved closer to the sample, then retracted again and separated from the sample, and shows the case where the adsorption force (b) due to water or the like present on the sample surface exists. ing. In the atmosphere, such an adsorbing force generally exists on the sample surface, but this adsorbing force is a force acting due to the surface tension of water, and is noticeable when the probe is separated from the sample surface. It is a phenomenon that appears.
Therefore, the phenomenon does not affect the conventional approach. In FIG. 4, a section c indicates a range (drive range) in which driving by the piezoelectric driving element 21z is possible.

[0007]

SUMMARY OF THE INVENTION The conventional sample described above
The setting of the pressing force between the probes and the approaching operation theoretically assume an ideal case in which only the atomic force acts between the probe and the sample when the probe approaches. However, actually, an electrostatic force acts between the probe and the sample in addition to the atomic force in many cases.

FIG. 5 is a diagram showing characteristics similar to those of FIG.
A characteristic 26 indicates an operation characteristic 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 attraction force when the probe is separated is unnecessary for explanation, and thus is omitted. Operating characteristics 26
According to the method, when the probe approaches the sample, an electrostatic force acts on the cantilever first.
At a stage (distance L1 between the probe and the sample) before contact with No. 3, the force acting on the cantilever 12 reaches the set value s0. In such a case, in the conventional atomic force microscope, since the distance between the probe and the sample is controlled to L1, there is a problem that the measurement of the original atomic force microscope cannot be performed. Furthermore, the magnitude of the electrostatic force and the direction in which the force acts vary, and there is a problem that if the electrostatic force acts, it is not possible to set the originally set pressing force. Further, the electrostatic force acts from a position far apart spatially as compared with the atomic force. To give a specific numerical value, for example, it is a distance that works sufficiently even at a distance of about several hundred μm,
Therefore, it is sufficiently possible that the distance L1 shown in FIG. 5 becomes about 100 μm. On the other hand, the piezoelectric drive element 2
Since the driving range c of 1z is about several μm to 10 μm,
Conventionally, it has often happened that the probe cannot be brought close to the driving range of the piezoelectric driving element 21z. In addition, a magnetic force may act in addition to the electrostatic force, and the same problem is raised in this case.

Further, there is a problem of drift of the displacement signal s1 based on environmental factors such as air temperature and apparatus temperature. FIG. 6 shows FIG.
The characteristic 27 shows the operation characteristic when a 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 acts in a state of being separated on the positive side in the operation characteristic 27. For this reason, there is a problem that the measurement cannot be performed with the conventional device.

An object of the present invention is to solve the above-mentioned problems, and it is possible to prevent a case where an electrostatic force other than an atomic force acts between a probe and a sample or a case where a displacement signal of a cantilever drifts. In order to provide a method for setting a probe pressing force of a scanning probe microscope, a probe can be brought close to a desired position, and accurate measurement can be performed at a set probe-sample distance. is there.

[0011]

A method for setting a probe pressing force of a scanning probe microscope according to the present invention comprises the following steps to achieve the above object.

In a first method for setting a probe pressing force, a probe pressing force is set so that the probe receives a force from the surface of the sample before measurement, and the probe pressing force is set based on the probe pressing force. This method is applied to a scanning probe microscope that changes the distance between the sample and the probe so that the probe approaches the sample, and determines the rest position of the probe with respect to the sample. Changing the distance by bringing the probe pressing force closer to the sample by setting the probe pressing force to an arbitrary value or a maximum value larger than the set probe pressing force described above, After the above operation is completed, the probe pressing force is set to a value to be set in advance, and the rest position of the probe is determined based on the value.

The second method for setting the pressing force of the probe is a method for setting the pressing force of the probe applied to the above-described scanning probe microscope in the same manner as described above.
The step of bringing the probe closer to the sample by changing the distance by setting the probe pressing force to an arbitrary value or a maximum value larger than the set probe pressing force described above, and terminating the approach operation. After the step of measuring the amount related to the disturbance, the probe pressing force is set to a value that should be set in advance so that the influence of the disturbance is removed by taking the amount related to the disturbance into consideration, and based on this, the probe is pressed. Determining a rest position of the camera.

First, after the probe is brought into contact with the surface of the sample, the pressing force of the probe is almost maximized, and then the original pressing force is set, thereby eliminating the influence of electrostatic force and the like, thereby enabling measurement. It is possible to set the distance between the probe and the sample at an appropriate distance.

[0015]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

According to the present invention, in a contact type scanning probe microscope such as an atomic force microscope, a probe is brought close to a sample at a stage before the measurement is started to set a required distance between the sample and the probe. This is a method of appropriately setting the pressing force of the probe when pressing the probe against the sample. In the description of this embodiment, the atomic force microscope of FIG. 3 used in the description of the related art is used as the configuration of the scanning probe microscope in which the method for setting the probe pressing force according to the present invention is performed. In the configuration shown in FIG. 3, the characteristic configuration of the present embodiment is that the setting of the set value in the pressing force setting unit 18 that gives the set value (pressing force setting signal) s0 as the reference value to the subtractor 17 In the way. Other configurations and operations of 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.

In FIG. 3, the pressing force setting section 18 is configured so that the set value set there can be arbitrarily changed by an operation of a measurer. In an atomic force microscope, a pressing force is set in advance before starting measurement.
Then, the probe 11 (the cantilever 12 having the probe 11 at the tip) located at a position away from the sample 13 is made to approach the sample 13, and the above-described preset pressing force setting value ( When the position of the probe 11 is set at (or distance), the displacement (flexure) 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 above set value. , And the approach is performed until the value is detected. Thereafter, the pressing force of the probe 11 is reset to the above-described pressing force set value.

A characteristic 32 shown in FIG. 1 is an operation characteristic indicating a method of approaching the probe 11 to the sample 13, that is, a method of setting a pressing force, based on the first embodiment. This shows a case where the electrostatic force acts as a disturbance. Operating characteristics 32
At first, the probe 11 is at a position L away from the sample 13.
There are two places. As a measurer, s0 is determined as a preset pressing force set value. In FIG. 1, substantially the same elements as those described with reference to FIG. 4, such as the pressing force set value s0 and the section c, are denoted by the same reference numerals. Further, in the operating characteristics 32 in FIG.
The positional relationship and the dimensional relationship on the horizontal axis and the vertical axis are slightly exaggerated so that the characteristic relationship of the present invention can be understood. This is the same in other drawings.

The probe 11, ie, the cantilever 12, is moved.
Move toward sample 13 by mechanism (coarse movement mechanism not shown)
When pressing, the value set in the pressing force setting unit 18 is
Any value greater than the setting value s0 or the maximum pressing
Force (s_max). In the following description,
The value set in the setting part 18 is the maximum pressing force s_maxPlace
An example of the case will be described. Set value of maximum pressing force s_max
Is a detection circuit for detecting the displacement signal s1 of the cantilever 12.
It is a value determined by the configuration of the road and the like. Thus, the probe
When the approach of 11 is started, the pressing force setting unit 18
The setting value given to the subtractor 17 is the maximum pressing
Set value of force_maxTherefore, connect the probe from the position L2.
When approaching, it changes like the operation characteristic 32. Probe 11
After the contact with the sample surface,
Set value s of the specified maximum pressing force _maxBased on
Then, the probe 11 is pressed against the sample surface. After that,
The position signal s1 is equal to the set value s_maxProbe / sample to match
The distance between them is controlled. Finally, in the operating characteristic 32
The control ends at the position L3. After that, the pressing force setting unit 1
The setting value set to 8 is changed as shown by an arrow 33,
Set value of maximum pressing force s_maxFrom the pusher
Return to the setting value s0. In this case, place the probe on the sample surface
Because it is an operation of separating from the above, the characteristics of the attraction force described above
Appears, and the pressing force set value s0 is shown in FIG.
Is controlled so as to have a value corresponding to the position L4. this
According to such a pressing force setting method, temporary
Set the maximum pressing force to
Force set value, so electrostatic force acts
Also within the driving range c of the piezoelectric driving element 21z.
The probe can be moved closer. Also, the suction force does not work.
At that time, the setting value change operation (arrow 3)
3) drives the piezoelectric drive element 21z.
Although it stops at the position L5 at the end of the range, the drive range
The region where the sample surface exists in the box c can be approached.
In this embodiment, the pressing force set value s0 is used as a repulsive force.
It is set, but it can be set as gravity.
It is.

A characteristic 34 shown in FIG. 2 is an operating characteristic showing a method of approaching the probe 11 to the sample 13 (a method of setting a pressing force) based on the second embodiment. In the operating characteristics 34 as well, the probe 11 is present at a position L2 that is initially separated from the sample 13. In this embodiment, the probe 11 and the sample 1
It is assumed that the electrostatic force s00 acts as a repulsive force in addition to the atomic force during the period 3. As mentioned above, as a measurer,
It is assumed that s0 is determined as a preset original pressing force set value. The pressing force set value s0 in this case is a strictly ideal set value, and does not take into account the estimated electrostatic force, drift, and the like. 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 but is larger than the pressing force set value s0. Any value can be set.

Also in this embodiment, first, a maximum pressing force set 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 for detecting the displacement signal s1 of the cantilever 12, and the like. When the probe 11, that is, the cantilever 12 is moved toward the sample 13 by a moving mechanism (coarse movement mechanism not shown), the pressing force setting unit 18 sets a 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 set value given to the subtractor 17 by the pressing force setting unit 18 is the set value s of the maximum pressing force.
_Since it is _max , when the probe approaches the position L2, it changes like the operation characteristic. Since an electrostatic force is acting between the probe and the sample, the probe 1 is tilted upward and left away from the probe 11 until it comes into contact with the surface of the sample 13.
Force acts on 1. 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. After that, the displacement signal s1 becomes the set value s _max
The distance between the probe and the sample is controlled so as to match In the operation characteristic 34, the control is finally ended at the position L3.

In this embodiment, when the probe 11 is brought close to and brought into contact with the sample 13, the approach and the movement are performed so that the operation characteristic 34 shown in FIG.
The contact operation is performed. More precisely, a force curve measurement is performed in the middle to measure the electrostatic force or the drift amount. That is, the force curve measurement is performed immediately after the probe 11 comes into contact with the sample 13. Force curve measurement in this case means that after the tip of the probe comes into contact with the sample and is adsorbed on the adsorption layer on the surface of the sample, 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 adsorbing force or an electrostatic force). In the operating characteristics 34 shown in FIG. 2, illustration of fine operating characteristics related to the force curve measurement is omitted. The movement related to the approach and contact of the probe with the sample is performed by the coarse movement mechanism, and the fine movement between the sample and the probe for performing the force curve measurement is performed by the fine movement mechanism (the Z-axis piezoelectric drive of the tripod 21). This is performed by the element 21z). As described above, the force curve measurement is performed immediately after the contact with the probe, whereby the electrostatic force or the drift amount is measured. Here, let the electrostatic force obtained by the force curve measurement be s00. Next, a value obtained by adding a preset original pressing force set value s0 and an electrostatic force s00 is determined as a pressing force set value to be set. Thereafter, the probe is pressed against the sample until the pressing force reaches the maximum pressing force as shown in the operating characteristic 34 of FIG. 2, and thereafter, the set value set in the pressing force setting unit 18 is changed to the maximum as shown by the arrow 35. The set value of the pressing force s _max is returned to the set value of the pressing force s0 + s00 set by the measurer as described above, and resetting is performed. According to such a pressing force setting method, when, for example, an electrostatic force is acting as a force other than the atomic force, the maximum pressing force is temporarily set initially, and the electrostatic force is measured during the process. Thereafter, a pressing force set value obtained by adding the originally appropriate pressing force set value and the electrostatic force is set.
Probe 11 and cantilever 12 with respect to the surface to be measured
Can be set to an appropriate pressing force that enables measurement. In this embodiment, it is needless to say that the pressing force set value can be set as the attractive force.

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 store the pressing force in the pressing force setting unit 18 in advance and automate the setting of the pressing force for approaching the probe before the measurement.

[0024]

As is apparent from the above description, according to the present invention, in a scanning probe microscope equipped with an optical lever type optical position detecting system, a reference pressing force set value between a probe and a sample is used as a reference. When setting the force, first set an arbitrary pressing force or the maximum pressing force larger than the set value, and then set the original set value, so that extra static electricity other than the atomic force etc. between the probe and the sample is set. Even when a force or the like acts or a displacement signal detected from the cantilever drifts, it is possible to appropriately set a measurable state, and it is possible to perform measurement with an originally optimum set value.

[Brief description of the drawings]

FIG. 1 is a view for explaining a first embodiment of a method for setting a probe pressing force according to the present invention.

FIG. 2 is a diagram for explaining a probe pressing force setting method according to a second embodiment of 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 view for explaining another problem of a conventional method for setting a probe pressing force.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Probe 12 Cantilever 13 Sample 14 Laser beam 15 Laser light source 16 Position detector 17 Subtractor 21 Tripod 32,34 Operating characteristics

Claims (2)

[Claims] Before performing measurement, a probe pressing force is set so that the probe receives a force from the surface of the sample, and a distance between the probe and the sample is set based on the probe pressing force. A method for setting a probe pressing force of a scanning probe microscope in which the probe and the sample are changed so as to approach each other and a rest position of the probe with respect to the sample is determined, wherein the probe and the sample approach each other. Before starting, changing the distance by setting the probe pressing force to an arbitrary value or a maximum value larger than the set pressing force to bring the probe closer to the sample. After the approach operation is completed, the probe pressing force is
Setting a value to be set in advance and determining the rest position of the probe based on the value. A method for setting a probe pressing force of a scanning probe microscope, comprising: 2. A probe pressing force is set so that a probe receives a force from a surface of a sample before measurement, and a distance between the probe and the sample is set based on the probe pressing force. A method for setting a probe pressing force of a scanning probe microscope in which the probe and the sample are changed so as to approach each other and a rest position of the probe with respect to the sample is determined, wherein the probe and the sample approach each other. Before starting, changing the distance by setting the probe pressing force to an arbitrary value or a maximum value larger than the set pressing force to bring the probe closer to the sample. Measuring the amount of disturbance after the approaching operation is completed; and setting the probe pressing force such that the influence of the disturbance is removed by taking the amount of the disturbance into consideration. To the power value, and based on this Determining the rest position of the probe, and a method for setting the probe pressing force of the scanning probe microscope.