JP4165368B2 - Scanning probe microscope - Google Patents

Description

  The present invention relates to a scanning probe microscope.

  An atomic force microscope (AFM = Atomic) that measures the atomic force acting between the probe and the sample surface as a surface observation and measurement of surface roughness of metals, semiconductors, ceramics, synthetic resins, etc. Scanning probe microscopes (SPM = Scanning Probe Microscope) such as Force Microscope are widely known. This scanning probe microscope includes a cantilever that holds a sharp probe and a displacement detection means that detects the bending of the cantilever, and brings the tip of the probe close to the vicinity of the sample (a gap of several nm or less). At this time, an interatomic force (attraction or repulsion) acts between the probe and the atoms of the sample. Therefore, the probe and the sample are relatively moved along the sample surface while keeping the atomic force constant. When scanning is performed so as to move, the cantilever is displaced according to the unevenness of the surface of the sample. By detecting this amount of displacement, the surface shape of the sample can be observed.

  As a means for detecting the displacement of the cantilever, there is conventionally a means using a piezo element or the like, but in recent years, an optical detection means has been widely used (see, for example, Patent Document 1). That is, laser light is emitted from the laser irradiation optical system to the cantilever, and the reflected light is detected by a photodetector having a plurality of (usually two) light receiving surfaces in the displacement direction of the cantilever. When the cantilever is displaced, the ratio of the amount of light incident on the plurality of light receiving surfaces changes, so that the amount of displacement of the cantilever can be calculated by processing the detection signal corresponding to the plurality of received light amounts.

  In a scanning probe microscope using such optical displacement detection means, when maintenance work such as cantilever replacement is performed, the light reflected by the cantilever due to subtle misalignment etc. enters the photodetector properly. It may disappear. If measurement is performed with the probe brought close to the sample in such a state, the force acting on the cantilever cannot be measured accurately, and the probe may collide with the sample and damage the probe or the sample. Even if the collision does not occur, the scanning is performed without sufficiently extracting the performance of the probe, so that the observation image is blurred. Therefore, when an operation such as cantilever replacement is performed, it is necessary to readjust the positional relationship between the optical system of the displacement detection means and the cantilever.

  In this type of conventional microscope, for example, the spot position of the laser beam irradiated on the cantilever is observed with an optical microscope, and the adjustment as described above is performed with reference to the observation image. However, in such observation, although it is possible to determine the extent to which the laser beam hits and reflects at a certain position on the cantilever, it is possible to make a highly accurate determination as to whether all of the irradiated laser beam hits the cantilever. There wasn't. Further, even if the laser beam is irradiated to the cantilever in the best state, it is not guaranteed that the reflected light strikes the light receiving surface of the photodetector in the best state. For this reason, it has been very difficult to adjust the optical system so as to detect the displacement of the cantilever in the best state with such a conventional method.

Japanese Unexamined Patent Publication No. 2000-338027

  The present invention has been made to solve such a problem, and its main object is to provide a scanning probe microscope capable of easily and accurately adjusting an optical system for detecting displacement of a cantilever. It is to be.

The scanning probe microscope according to the present invention, which has been made to solve the above problems, irradiates light to the cantilever to which a probe for scanning a sample surface is attached and to detect the displacement of the cantilever. In a scanning probe microscope comprising: an irradiating means that includes: a light receiving means that includes a light receiving surface that is divided into a plurality of light receiving surfaces that receive reflected light with respect to the irradiated light;
a) vibration means for vibrating the cantilever at a frequency at or near its resonance point;
b) a signal corresponding to a direct current component of a difference between a plurality of received light signals detected by each light receiving surface of the light receiving means during vibration by the vibration exciting means, a signal corresponding to the amplitude of the alternating current component, and the light receiving means Signal acquisition means for obtaining a signal according to the total amount of received light by
c) In order for the operator to adjust the relative positional relationship between the displacement detection means and the cantilever, the numerical display of each signal obtained by the signal acquisition means, or the numerical value reflected or each Information presenting means for performing display or notification based on the signal;
It is characterized by having.

  In the scanning probe microscope according to the present invention, the vibration means is, for example, a vibrator. When the cantilever is irradiated with laser light by the irradiating means while the cantilever vibrates at a frequency at or near the resonance point, the light receiving means straddles a plurality of light receiving surfaces according to the vibration of the cantilever. The position of the incident light beam changes. Therefore, when the difference between a plurality of light receiving signals detected by the respective light receiving surfaces of the light receiving means is taken, the AC component of the difference signal has a frequency corresponding to this vibration, and the amplitude of the light irradiation position is at the tip of the cantilever. It gets bigger. Further, the direct current component of the difference signal reflects the initial positional deviation of the incident light beam with respect to the plurality of light receiving surfaces (that is, the same as the cantilever stationary state). Further, the total amount of light received by the light receiving means can be an index for determining whether the irradiation light is sufficiently applied to the cantilever and whether the reflected light from the cantilever is applied without protruding from the light receiving surface.

  In the scanning probe microscope according to the present invention, each signal as described above is acquired by the signal acquisition means, and a numerical value indicating the magnitude of the signal, a level display reflecting the numerical value, and the like are performed by the information presentation means, for example. . Therefore, before actually performing the measurement operation, the operator (operator) observes this display, for example, the total received light amount is as large as possible, the direct current component of the differential signal is as small as possible, and the alternating current component of the differential signal is as large as possible. The relative positional relationship between the cantilever and the displacement detecting means (specifically, the irradiating means and the light receiving means) can be adjusted to a state assumed to be optimal for detecting the displacement. Accordingly, the measurement is not started in a state where adjustment is insufficient, and the cantilever and the sample can be prevented from colliding and being damaged during the measurement.

  As described above, the simplest aspect of the information presenting means is the numerical display or level display of the signal. In addition, the information presenting means uses at least one signal obtained by the signal obtaining means as a predetermined criterion. A determination means for comparing with the value may be included, and the adjustment state of the relative positional relationship may be determined based on the determination result. Specifically, the result of the determination unit may be notified to the operator by display or sound.

  In this configuration, as long as the determination reference value is appropriately determined, it is possible to make an accurate determination as compared to the case where the operator determines the appropriateness while observing the digitized signal value or level. The burden on the operator is also reduced. Note that the appropriate determination reference value depends on, for example, factors such as the reflectance of the reflecting surface of the cantilever, the vibration amplitude determining factor such as the elastic constant, or the shape. Therefore, a storage unit that stores a determination reference value according to the type of cantilever that may be used in advance is prepared, and a determination reference value according to the type of cantilever actually attached to the microscope is stored from the storage unit. It is preferable to read and use. According to this, even if any cantilever is used, adjustment can be performed so that the displacement of the cantilever can be detected in the best state or close to it.

  Further, in the scanning probe microscope according to the present invention, when the determination unit determines that the adjustment of the relative positional relationship is insufficient, the control unit prohibits an operation in which the cantilever and the sample approach each other. It is more preferable that the configuration is provided.

  According to this configuration, in the case where adjustment is insufficient and there is a possibility of collision between the sample and the cantilever when the sample and the cantilever are brought close to each other, the operation for such proximity is not performed. . Therefore, even if the adjustment by the operator is insufficient or the adjustment is forgotten, it is possible to reliably prevent an accident in which one of the sample and the cantilever collides and one of them is damaged.

  Furthermore, in the scanning probe microscope according to the present invention, when the cantilever and the sample are in the middle of measurement for measurement, or when the cantilever and the sample are in close measurement, The determination means compares a signal according to the total received light amount by the light receiving means with a determination reference value, and when the control means determines that the total received light amount is insufficient according to the determination result, the cantilever and the sample It is more preferable that the operation of stopping the approaching or the operation of separating the cantilever and the sample is executed.

  According to this configuration, when the cantilever and the sample are being brought close to each other for measurement, or when the measurement is in progress (scanning), for example, the cantilever may be damaged or irradiated light Even when the amount of light suddenly decreases, such a defect can be detected quickly, and the distance between the cantilever and the sample can be increased. As a result, breakage and damage to the sample and the microscope can be minimized. In addition, useless measurement is not performed in a situation where appropriate measurement cannot be performed.

  As described above, according to the scanning probe microscope according to the present invention, the operator can easily and clearly confirm whether or not the adjustment of the optical system for detecting the displacement is appropriate before actually performing the measurement operation. Therefore, it can be avoided that the measurement is started with insufficient adjustment of the optical system, and the cantilever and the sample collide at the time of measurement, and the cantilever is damaged or the sample itself is damaged. It can be prevented beforehand. In addition, if the optical system is not fully adjusted, the operator can easily adjust it, so that the displacement of the cantilever can be accurately detected during scanning, thereby obtaining a clear surface observation image. Can do. In addition, it is less dependent on the skill and experience of the operator for such adjustment, and even a less experienced person can obtain a good surface observation image.

  Hereinafter, a scanning probe microscope according to an embodiment of the present invention will be specifically described with reference to the drawings. 1 is an overall configuration diagram of a scanning probe microscope according to the present embodiment, FIG. 2 is a top view of a cantilever, FIG. 3 is a diagram showing an example of a light spot state on a light receiving surface of a photodetector, and FIG. 4 is a photodetector. It is a figure which shows an example of the waveform which processed the detection signal by.

  The scanner 2 holds the sample 1 on its upper surface, and scans the sample 1 in the x- and y-axis directions and finely moves it in the z-axis direction. The motor 3 performs coarse movement so that the sample 1 and the scanner 2 are integrated and brought close to or away from the cantilever 4 described later. A cantilever 4 having a probe 5 at its tip is disposed above the sample 1, and a vibrator 7 as a vibrating means is attached to the end of the cantilever 4. In order to detect the displacement of the cantilever 4, the following optical system is provided. That is, the light emitted from the laser light source 8 held by the laser light source holder 9 is condensed at a predetermined position on the top surface of the tip of the cantilever 4 by the mirror 12 to form the laser spot 6. The position of the emitted light from the laser light source 8 can be adjusted in the yz plane by appropriately adjusting the position adjusting screws 10 and 11 provided in the laser light source holder 9. The light reflected from the cantilever 4 at the laser spot 6 enters the photodetector 13 held by the photodetector holder 14. By appropriately adjusting the position adjusting screws 15 and 16 provided in the photodetector holder 14, the position of the light receiving surface of the photodetector 13 with respect to incident light can be adjusted in the yz plane.

  The photodetector 13 has a configuration in which the light receiving surface is divided into two parts in the vertical direction (z-axis direction) as shown in FIG. 3A, and the amount of light received by the upper light receiving surface 13U and the lower light receiving surface 13L. The corresponding detection signal is output to the computing unit 17 independently. Based on both detection signals, the arithmetic unit 17 receives the first signal S1 corresponding to the total amount of light received by the photodetector 13 (the sum of the amounts of light received by both the light receiving surfaces 13U and 13L), the upper light receiving surface 13U and the lower light receiving. A second signal S2 corresponding to the direct current component of the light amount difference from the surface 13L and a third signal S3 corresponding to the amplitude of the alternating current component of the light amount difference between the upper light receiving surface 13U and the lower light receiving surface 13L are calculated. The three signals S1, S2, and S3 are input to the control / processing unit 18 and the display 21. The display 21 displays the levels of the three signals S1, S2, and S3 by the level indicator 21a. In addition, in order to make the display on the level indicator 21a easy to see, a peak hold display in which an appropriate hold time is set may be used. Alternatively, the numerical value may be simply displayed digitally.

  The control / processing unit 18 is mainly composed of a microcomputer, and an input unit 19 and a storage unit 20 are connected to control operations of the vibrator 7, the motor 3, and the scanner 2 according to a predetermined algorithm. The input unit 19 is a key operation switch, a keyboard, or the like, and an operator gives a predetermined instruction to the control / processing unit 18. On the other hand, in the storage unit 20, determination reference values corresponding to the types of various cantilevers to be used are stored in advance. This is because, for example, the reflectivity, elastic modulus (spring constant), shape, etc. of the reflecting surface differ depending on the type of cantilever, so that accurate determination independent of the type of cantilever can be made in consideration of these factors. is there.

  In the scanning probe microscope according to the present embodiment, an operator manually uses an optical system, that is, a laser light source, using a display based on signals S1, S2, and S3 calculated by the calculator 17 based on a detection signal from the photodetector 13. 8 and the position of the photodetector 13 can be adjusted. Next, the relationship between the adjustment state of the optical system and the signals S1, S2, and S3 calculated by the computing unit 17 will be described in relation to such adjustment.

  When the laser light emitted from the laser light source 8 strikes the cantilever 4 and the reflected light enters the photodetector 13, a light spot SP is formed on the light receiving surfaces 13U and 13L. When the cantilever 4 is stationary and the light spot SP hits an intermediate position between the two-divided light receiving surfaces 13U and 13L (the state shown in FIG. 3A), the amount of light received by both the light receiving surfaces 13U and 13L becomes equal. The difference signal calculated by the device 17 becomes almost zero. In the photodetector 13, in principle, this state is the best position for the optical system. When the light spot SP is at a position shifted above or below the two-divided light receiving surfaces 13U and 13L (the states shown in FIGS. 3B and 3C), a steady difference signal is generated. This is the DC component of the difference signal, that is, the offset.

  3 (a) to 3 (c), for example, as shown in FIG. 2 (a) or (b), the laser spot 6 formed by irradiation light does not deviate from the cantilever 4, and the reflected light is detected by light. This is an example in the case where it strikes the light receiving surface of the vessel 13 with certainty. However, for example, when a part of the laser spot 6 comes off the cantilever 4 as shown in FIG. 2 (c), the light spot SP on the light receiving surfaces 13U and 13L as shown in FIG. 3 (d). Some are missing. In addition, even when the laser spot 6 cannot be removed from the cantilever 4, if the position of the photodetector 13 is not appropriate and a part of the reflected light deviates from the photodetector 13, FIG. ), A part of the light spot SP protrudes from the light receiving surfaces 13U and 13L. In either case, the amount of light received by the light receiving surfaces 13U and 13L decreases, so the S / N ratio of the received light signal decreases. Therefore, in principle (except for special cases to be described later), it is desirable that the first signal S1 corresponding to the total amount of received light is as large as possible.

  Next, consider the case where the vibrator 7 is driven to vibrate the cantilever 4 in the z direction at a predetermined frequency f at or near the resonance point. For example, when the cantilever 4 is stationary and the light spot SP is in the state shown in FIG. 3A, when the cantilever 4 vibrates, the light spot SP vibrates in the z direction according to the vibration displacement of the cantilever 4. . That is, since the position of the light spot SP vibrates between, for example, the states shown in FIGS. 3B and 3C, the difference signal causes, for example, a sinusoidal change corresponding to the vibration. However, if the light spot SP vibrates so that it completely enters one of the light receiving surfaces 13U and 13L, even if the vibration further increases, the change in the difference signal does not increase. Therefore, the change range of the difference signal is limited in both the positive and negative directions, and this is a detectable range as shown in FIG.

  The change in the sinusoidal difference signal is an AC component of the difference signal. As described above, when the difference signal initially has a DC component, the difference signal is in a state where the AC component is added to the DC component (see FIG. 4 waveform reference). Although the detection accuracy improves as the AC component increases, it is difficult to increase the AC component because the possibility that the detection range is limited increases when the DC component is large. Therefore, it is desirable that the direct current component is close to zero, and it is desirable to make the alternating current component as large as possible in that state. That is, it is desirable that the second signal S2 that is the DC component of the difference signal is as small as possible, and the third signal S3 that is the amplitude of the AC component of the difference signal is as large as possible.

  When viewed from the laser spot 6 of the cantilever 4, the displacement amount of the cantilever 4 increases toward the tip. That is, for example, as shown in FIG. 2A, the laser spot 6 is near the tip of the narrow part (substantial vibration region) of the cantilever 4, and as shown in FIG. Comparing with the case of the vicinity of the base of the narrow part of the cantilever 4, the former has a larger displacement than the latter with respect to the same displacement of the probe 5, and as a result, the fluctuation amplitude of the difference signal also becomes larger. Accordingly, the position of the laser light source 8 is adjusted so that the laser spot 6 is as far as possible from the tip of the vibration region without detaching from the cantilever 4, and the light spot SP by reflected light in a state where the cantilever 4 is stationary is illustrated. The best state can be achieved by adjusting the position of the photodetector 13 so that the state shown in FIG. In other words, in this example, the positions of the laser light source 8 and the photodetector 13 may be adjusted so that the first signal S1 and the third signal S3 are as large as possible and the second signal S2 is as small as possible.

  Next, the procedure and operation for checking the adjustment of the optical system at the time of non-measurement (when the sample 1 is not brought close to the cantilever 4) will be described. Such an operation is mainly performed after the cantilever 4 is replaced.

  When the operator gives an instruction to start the adjustment operation from the input unit 19, the control / processing unit 18 turns on the laser light source 8 and irradiates the cantilever 4 with the laser light. Further, the vibrator 7 is driven to vibrate the cantilever 4 at a predetermined frequency f at or near the resonance point. A detection signal is output from the photodetector 13 by the reflected light from the cantilever 4, and the arithmetic unit 17 performs the above calculation. As a result, the level indicator 21a of the display 21 displays the levels of the first signal S1, the second signal S2, and the third signal S3. While checking the levels of these signals S1, S2, and S3, the operator appropriately adjusts the position adjusting screws 10 and 11 so that the first signal S1 and the third signal S3 are as large as possible and the second signal S2 is as small as possible. The position of the laser light source 8 is adjusted by turning and the position adjusting screws 15 and 16 are appropriately turned to adjust the position of the photodetector 13.

  Note that other means such as an optical microscope may be used in combination in order to initially perform approximate positioning (for example, positioning so that a part of the laser spot 6 hits the vibration region of the cantilever 4). In any case, it can be confirmed by the display on the display 21 whether or not the state finally becomes the best or close to it.

  Even if the operator manually adjusts while looking at the level indicator 21a and the numerical value display as described above, it is possible to achieve satisfactory adjustment much more easily and reliably than the conventional method. However, the scanning probe microscope of this embodiment is provided with means for assisting the manual adjustment as described above. That is, the control / processing unit 18 that has received the first to third signals S1, S2, and S3 compares the signals S1, S2, and S3 with the determination reference values read from the storage unit 20, and determines the magnitude relationship. As described above, since the judgment reference value differs for each type of cantilever, the operator first designates the type of cantilever to be used by the input unit 19, and the judgment standard value corresponding to the designation is read from the storage unit 20. It is.

  If the first signal S1 and the third signal S3 are larger than the respective determination reference values, it can be determined that they are within the allowable range. On the other hand, when the second signal S2 is smaller than the determination reference value, it can be determined that the second signal S2 has entered the allowable range. Therefore, when it is determined that the control / processing unit 18 has entered the permissible range for each signal, the display lamp (for example, LED) 21b of the display 21 is turned on. As a result, the operator grasps the adjustment state by turning on or off the indicator lamp 21b, and adjusts the positions of the laser light source 8 and the photodetector 13 so that all the indicator lamps 21b are lit. It can be.

  The control / processing unit 18 permits the operation of driving the motor 3 to bring the sample 1 close to the cantilever 4 only when the three signals S1, S2, and S3 are all within the allowable range. That is, even when the input unit 19 instructs the operator to start measurement in a state where any of the first, second and third signals S1, S2, S3 is not within the allowable range, the control / processing unit 18 does not accept this, and does not send to the motor 3 a control signal for operating the scanner 2 and the sample 1 in a direction to bring them closer to the cantilever 4. Preferably, the operator should be informed that measurement is impossible by a warning display or warning sound. Therefore, since the sample 1 does not approach the cantilever 4 when the optical system for detecting the displacement is insufficient, the probe 5 (or the cantilever 4 main body) and the sample 1 are prevented from colliding with each other. be able to. Further, if the adjustment of the optical system is insufficient, there is a possibility that the force acting on the cantilever 4 cannot be measured accurately even if a collision does not occur. However, it is possible to avoid performing the measurement itself in such a state.

  Furthermore, in the scanning probe microscope of the present embodiment, not only during non-measurement as described above, but also when the motor 3 is operated to bring the sample 1 close to the cantilever 4 as a pre-measurement work, Even during measurement in which the scanner 2 scans the sample 1 in a state in which they are in close proximity to each other, the control / processing unit 18 can detect a malfunction in the operation based on the signal obtained from the computing unit 17. . For example, the probe 5 may come into contact with the sample 1 during the pre-measurement work or during the measurement, and the probe 5 may be damaged. In addition, the output power of the laser light source 8 may suddenly decrease due to a malfunction of the laser light source 8. In such a case, the force acting on the cantilever 4 cannot be measured, and if it is determined that there is no or weak force, control is performed to bring the sample 1 closer to the cantilever 4. As a result, the sample 1 is strongly pressed against the main body of the cantilever 4, and the sample 1 may be severely damaged or may damage equipment parts other than the cantilever 4.

  Therefore, the control / processing unit 18 compares the first signal S1 corresponding to the total amount of received light during the pre-measurement work and during the measurement with a determination reference value, and when the first signal S1 falls below the determination reference value, the cantilever 4 It is determined that some trouble has occurred. If the measurement is in progress, the measurement is stopped, and the motor 3 is operated in a direction to move the sample 1 away from the cantilever 4. Thereby, the breakage of the sample 1 and the serious damage of the apparatus can be minimized.

  In the shape of the cantilever as shown in FIG. 2, the largest state with respect to the total amount of received light is the best state, but depending on the type of cantilever, this may not always be the case. For example, in the case of the cantilever 4 having the upper surface shape shown in FIG. 5, the vibration region becomes narrower toward the tip, and a part of the laser spot 6 inevitably protrudes from the cantilever 4. For this reason, when the laser spot 6 is moved toward the tip of the vibration region, the total amount of received light decreases after a certain position. In such a case, it is not easy to determine an appropriate position while viewing the level indicator display and numerical display as described above. However, even in such a case, if the determination reference value is appropriately determined as described above, a position where the light transmission / reception light amount is appropriately large and the vibration amplitude with respect to the displacement amount is sufficiently large can be found quickly. be able to.

  In the above embodiment, the operator adjusts the positions of the laser light source 8 and the light detector 13 by turning the position adjusting screws 10, 11, 15, and 16. However, the laser light source holder 9 and the light detector are used. Drive means for moving the holder 14 in the yz plane is provided, and the control / processing unit 18 feedback-controls the operation of the drive means based on signals S1, S2, and S3 input from the computing unit 17. Thus, the optical system may be automatically adjusted to a state close to the best.

  Moreover, since the said embodiment is an example of this invention, even if it corrects, changes, an addition etc. suitably in the range of the meaning of this invention also in the point other than having described above, it is included by this invention. Is clear.

1 is an overall configuration diagram of a scanning probe microscope according to an embodiment of the present invention. The top view of a cantilever. The figure which shows an example of the light spot state on the light-receiving surface of a photodetector. The figure which shows an example of the waveform which processed the detection signal by the photodetector. The top view of the cantilever which has another shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sample 2 ... Scanner 3 ... Motor 4 ... Cantilever 5 ... Probe 6 ... Laser spot 7 ... Vibrator 8 ... Laser light source 9 ... Laser light source holder 10, 11 ... Position adjusting screw 12 ... Mirror 13 ... Photo detector 13U ... Upper light receiving surface 13L ... Lower light receiving surface 14 ... Photodetector holders 15, 16 ... Position adjusting screw 17 ... Calculator 18 ... Control / processing unit 19 ... Input unit 20 ... Storage unit 21 ... Display 21a ... Level indicator 21b ... Indicator light

Claims (4)

A cantilever equipped with a probe for scanning the sample surface, an irradiation means for irradiating the cantilever with light to detect displacement of the cantilever, and a plurality of divided light receiving portions for receiving reflected light from the irradiated light In a scanning probe microscope comprising a displacement detection means including a light receiving means having a surface,
a) vibration means for vibrating the cantilever at a frequency at or near its resonance point;
b) a signal corresponding to a direct current component of a difference between a plurality of received light signals detected by each light receiving surface of the light receiving means during vibration by the vibration exciting means, a signal corresponding to the amplitude of the alternating current component, and the light receiving means Signal acquisition means for obtaining a signal according to the total amount of received light by
c) In order for the operator to adjust the relative positional relationship between the displacement detection means and the cantilever, the numerical display of each signal obtained by the signal acquisition means, or the numerical value reflected or each Information presenting means for performing display or notification based on the signal;
A scanning probe microscope comprising:   The information presentation unit includes a determination unit that compares at least one of the signals obtained by the signal acquisition unit with a predetermined determination reference value, and determines the adjustment state of the relative positional relationship based on the determination result. The scanning probe microscope according to claim 1.   3. The scanning according to claim 2, further comprising a control unit that prohibits an operation in which the cantilever and the sample approach each other when the determination unit determines that the adjustment of the relative positional relationship is insufficient. Type probe microscope.   When the cantilever and the sample are in the process of being brought close to each other for measurement, or when the cantilever and the sample are in a state of being measured close to each other, the determination means responds to the total amount of light received by the light receiving means. The control unit compares the signal with the determination reference value, and when the determination result determines that the total amount of received light is insufficient, the control unit stops the operation in which the cantilever and the sample approach each other, or separates the cantilever and the sample. The scanning probe microscope according to claim 3, wherein an operation is executed.

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