JP2007033321A - Method for measuring distance between probe of scanning probe microscope and sample surface, and scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for measuring distance between a probe of a scanning probe microscope and a sample surface that prevents contact of the probe tip with the sample surface and performs approach at a high speed. <P>SOLUTION: An interatomic force microscope scans the surface of the sample 1 using the probe 6 and measures the irregularity of the surface of the sample 1 with atomic resolution. A first-step high-speed approach for shortening the distance between the probe 6 and the surface of the sample 1 and a second-step precision approach are combined. As a result, the approach time between the sample surface and the probe can be shortened as a whole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for measuring the distance between a probe and a sample surface of a scanning probe microscope, in order to reduce the distance between the probe and the sample surface until it reaches a certain arbitrary value. The present invention relates to a method and an apparatus for shortening the time to the point.

  The scanning atomic force microscope (AFM) detects the atomic force acting between the probe tip and the sample surface, and scans the sample while performing feedback so that the atomic force is constant. This is an apparatus for obtaining the surface shape of a sample. This AFM has many measurement modes, a contact mode AFM in which the tip of the probe is brought into contact, an AC mode AFM in which the probe is moved close to the sample while being vibrated and the amplitude of the probe is made constant, the probe A typical example is NC (Non Contact) mode AFM which measures without contacting the surface of the sample.

  FIG. 16 is a block diagram showing an embodiment of the AC mode AFM. In the figure, 1 is a sample, 2 is a scanner on which the sample 1 is placed, and 3 moves the sample 1 in a three-dimensional direction, and 3 is a motor that moves the scanner 2. The motor 3 can be given a driving force from a personal computer (PC) 14.

  Reference numeral 4 denotes a laser diode (LD), 5 denotes a PZT as a piezoelectric element, and 6 denotes a cantilever (hereinafter referred to as a probe) that can be given minute vibrations by the PZT 5. 7 is a photodetector (PD) that receives reflected light of the light irradiated onto the probe 6 by the laser diode 4 and converts it into an electrical signal, 8 is a preamplifier that receives the output of the photodetector 7 and amplifies the signal, and 9 This is an RMS-DC converter that receives the output of the preamplifier 8 and converts RMS (effective value) into direct current.

  An error amplifier 10 receives the output of the RMS-DC converter 9 at one input, receives a reference value at the other input, and calculates the difference by calculation, and 11 is a reference value generator for generating a reference value. A feedback circuit 12 receives the output of the error amplifier 10 to generate a feedback signal, and 13 receives a topographic signal (surface shape signal) which is an output of the feedback circuit 12 and converts an analog signal into a digital signal A The / D converter 14 is a personal computer (PC) that receives the output of the A / D converter 13 and performs predetermined arithmetic control processing. A motor drive signal is output from the personal computer PC toward the motor 3.

  An FM demodulator (D-PLL) 15 receives the output of the preamplifier 8 and performs FM demodulation. An attenuator 16 receives the output of the FM demodulator 15. The output of the FM demodulator 15 is given to the attenuator 16 and the A / D converter 13. Reference numeral 17 denotes an HV-amplifier that receives the output of the feedback circuit 12 and drives the scanner 2. The output of the FM demodulator 15 is given to the A / D converter 13 as a DC component of the phase signal. This DC component becomes the reference voltage of the A / D converter 13. Reference numeral 18 denotes a scan generator, and reference numeral 19 denotes an HV-amplifier that receives and amplifies the output of the scan generator 18. The HV-amplifier 19 drives the stage in the X and Y two-dimensional directions. The operation of the apparatus configured as described above will be described as follows.

  First, the distance in the height direction between the surface of the sample 1 and the probe (cantilever) 6 is approximately several μm using an optical microscope (not shown) and a height direction (Z-axis direction) adjusting means (not shown). The operator makes manual adjustments mechanically. Thereafter, when the automatic button is pressed, the apparatus performs position control by feedback until the distance between the surface of the sample 1 and the probe 6 becomes the most appropriate value by the following operation. The outline of the control is as follows.

  The probe 6 is vibrated at a constant output by the PZT 5 and adjusted so that the laser spot comes to the tip of the probe 6. At this time, the reflected laser beam is detected as an optical signal by the photodetector 7, amplified by the preamble 8, and then detected by the RMS-DC converter 9 to detect the amplitude of the probe 6. At this time, since a phase difference is generated between the waveform applied to the probe 6 and the waveform detected by the photodetector 7, the voltage value output from the RMS-DC converter 9 is maximized. The phase is adjusted in the FM demodulator (D-PLL) 15. Next, the stage is brought closer to the probe 6 using the motor 3 until the RMS-DC value becomes the same as the reference value (approach). In the state where the approach is completed, a scanning voltage is applied to the scanner 2 and the feedback circuit is operated so that the output from the error amplifier 10 becomes 0, thereby controlling the distance between the sample surface and the probe.

As a conventional device of this type, a piezoelectric body having a probe at its free end is supported at one end, and the amount of displacement of the probe due to the atomic force between the probe and the sample is optically measured. An apparatus is known that detects and automatically controls the movement of the piezoelectric body in the Z-axis direction based on the detected change in the amount of probe displacement (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-101317 (paragraphs 0033 to 0045, FIG. 1)

  FIG. 17 is a diagram showing an RMS-DC output signal when an AC-AFM approach is performed. The vertical axis represents voltage (RMS-DC signal), and the horizontal axis represents time. As is apparent from the figure, the RMS-DC value gradually changes after the approach is started, but when approaching the reference value, the RMS-DC value changes abruptly. Such a rapid change may cause the probe to contact the sample surface, and is a phenomenon that should be avoided in order to protect the tip of the probe and the sample surface.

  The atomic force microscope (probe microscope) can scan the surface of the sample 1 using the probe 6 and measure the unevenness of the surface of the sample 1 with atomic resolution. As a preparation stage for measurement, laser adjustment to the probe and oscillation adjustment of the probe 6 are performed. As a first step, the distance between the sample stage and the probe 6 is adjusted using an optical microscope in order to make the distance between the probe and the sample surface as close as possible. Finally, the distance between the tip of the probe and the sample surface is made close by using a DC motor or a stepping motor so that a predetermined distance is obtained. After these preparations are complete, measurements can be made.

  The atomic force microscope uses a motor to bring the distance between the probe tip and the sample surface close to a certain set distance (approach). The speed is set to a slow value (for example, 1 μm / sec or less) so that the probe does not collide with the sample surface. Therefore, a waiting time of about 2 minutes is required to approach a distance of 100 μm. If the approach speed is increased, the current control method has a high risk of the tip of the probe contacting the sample surface, and the speed cannot be increased.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a method and an apparatus for measuring the distance between a probe and a sample surface of a scanning probe microscope, in which the tip of the probe and the sample surface are not in contact and are approached at high speed The purpose is to provide.

  (1) The invention according to claim 1 is a scanning probe microscope that scans the surface of a sample using a probe and measures the unevenness of the sample surface with atomic resolution. While detecting the phase difference between the oscillation signal and the signal from the probe detected by the photodetector and performing feedback control until a predetermined change in the phase difference signal is detected, then in the second stage, The distance between the probe and the sample surface is controlled by performing feedback control using a sample surface observation feedback signal which is an output of the photodetector.

(2) The invention described in claim 2 is characterized in that an amplitude signal or an FMD value is used as the sample surface observation feedback signal.
(3) The invention according to claim 3 is characterized in that the control in the first stage is performed using a motor, and the control in the second stage is performed using expansion and contraction of a piezo element and a motor.

  (4) The invention according to claim 4 is a scanning probe microscope that scans the surface of a sample using a probe and measures the unevenness of the sample surface with atomic resolution. A first control means for calculating a phase difference between a vibration signal and a signal from a probe detected by a photodetector and performing feedback control until a predetermined change in the phase difference signal is detected; And a second control means for controlling the distance between the probe and the sample surface by performing feedback control using a sample surface observation feedback signal which is an output of the tester.

  (1) According to the invention of claim 1, until the phase signal becomes a predetermined value by feedback control using the phase difference signal between the excitation signal to the probe and the light detection signal in the first stage, By adjusting the distance between the sample surface and the probe, and then performing sample surface observation feedback control so that the distance between the sample surface and the probe becomes an optimum distance in the second step, at least the first sample surface and Since the sequence for controlling the distance between the probes is performed until the phase signal reaches a predetermined value so that the sample surface does not come into contact with the probe, the time required for the first stage can be increased. The probe and the sample surface are not in contact with each other and can be approached at high speed.

  (2) According to the second aspect of the present invention, the RMS-DC signal or the FMD value can be used as the sample surface observation feedback signal, and good feedback control can be performed.

  (3) According to the invention described in claim 3, the motor is used as means for adjusting the distance between the sample surface and the probe in the first stage, and the control in the second stage is control of the distance between the sample surface and the probe. In addition, since the control using the expansion and contraction of the motor and the piezo element is performed, the time required for the distance between the probe and the front of the sample to become an optimum value as a whole can be increased.

  (4) According to the invention described in claim 4, in the first stage, based on the phase difference between the excitation signal to the probe and the signal detected by the photodetector from the probe signal, the sample surface and the probe Since the distance between the sample surface and the probe is controlled so that the distance between the sample surface and the probe becomes the optimum value in the second stage, the distance between the sample surface and the probe is controlled. As a whole, it is possible to approach at a high speed with respect to the distance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
FIG. 1 is a diagram illustrating a relationship between an RMS-DC value and a phase difference signal from the start of an approach to the stop of the approach in the AC-AFM. Here, the phase difference signal is defined by a phase difference between an excitation signal to the probe and a signal obtained by detecting the signal from the probe with a photodetector (the same applies hereinafter). The vertical axis is voltage, and the horizontal axis is time. f1 represents a phase difference signal, and f2 represents an RMS-DC value that is a sample surface observation feedback signal proportional to the amplitude of the signal detected by the photodetector with the signal from the probe. As can be seen from the figure, when both signals are compared at a certain time T1, the amount of change in the signal from the start of the approach is greater for the phase difference signal. In addition, the phase difference signal also appears earlier when the change appears in the signal. This is because the phase difference signal depends on sensitively detecting changes in the distance between the probe and the sample.

  Therefore, if it is possible to stop the approach by detecting the phase difference signal immediately before stopping the approach with the reference value obtained from the phase difference signal, the tip of the probe does not touch the sample surface. Can be stopped.

  Therefore, the new approach method is a combination of approaches of two steps. In the first stage, the distance between the sample surface and the probe is stopped at a predetermined position using the set minimum change amount of the phase difference value. Here, the distance between the sample surface and the probe in the first stage is set to a value that ensures that the sample surface and the probe do not contact each other. Accordingly, in this approach, the distance between the sample and the tip of the probe is long, so that the approach is performed using a motor while performing feedback control. Here, the motor approach allows the motor speed to be set arbitrarily. Next, the second-stage approach operates by combining the expansion and contraction of the Z-axis (height direction) of the scanner and the movement of the stage. In this second stage, the RMS-DC value is used as the control signal. Of course, an amplitude value obtained by peak hold of the signal detected by the photodetector may be used. By this moving method, it is possible to approach safely until the RMS-DC value becomes the reference without the tip of the probe contacting the sample surface.

FIG. 2 is a flowchart showing a new approach algorithm (AC-AFM). In the following description, the same identification numbers as those in FIG.
S1: The probe is set to vibrate with AC-AFM.

At this time, tuning (adjustment) of the probe 6 necessary for AC-AFM measurement is performed.
S2: Reference value calculation and phase adjustment are performed.
The phase difference between the excitation signal of the probe 6 and the signal detected by the photodetector 7 is adjusted so that the RMS-DC value becomes maximum. Next, the reference value of the approach condition is calculated. The operations of S1 and S2 are operations normally performed when the sample surface is observed in the AC-AFM mode.
S3: The minimum change amount of the phase difference and the approach speed are set.

  In order to stop the motor approach by detecting the phase difference signal, a minimum change amount is set. The minimum amount of change to be set is set by an angle, usually around 2 degrees, but the angle to be set varies depending on the state of the sample and the environment (air, vacuum, liquid, etc.), so set it according to the situation. . Moreover, although the minimum change amount is set in angle, the unit can also be set in radians, for example, if angle conversion is performed.

Since the phase difference adjustment is calculated by the voltage value in the electric circuit, it can be set by the voltage. Next, the speed of the motor approach used in the first stage approach is set. The motor speed is 50 μm / sec at the maximum, but it varies depending on the stage structure and the motor used, so that it can be arbitrarily changed.
S4: The motor approach is started at the speed set in step S3.

The state of the scanner in the Z-axis direction at this time is a state in which the feedback circuit 12 is operated and extended as shown in FIG. FIG. 3 is a diagram illustrating a state of the scanner. (A) shows a retracted state, and (b) shows a state extending to the maximum swing width.
S5: The designated phase difference value is compared with the current phase difference value. During the motor approach in step S4, the phase difference is observed. The phase difference immediately before the approach is compared with the phase difference during the approach, and it is observed whether the phase value is changed by the minimum change amount set in step S3. The phase difference immediately before the approach is compared with the phase difference during the approach, and it is observed whether the phase value is changed by the minimum change amount set in step S3. If the phase difference has not changed by the minimum change amount, the motor approach is continued.
S6: Stopping the motor approach When the phase difference changes by the minimum change amount set in step S3 during the approach of step S4, the motor approach is stopped. The operation from step S1 to step S6 is taken as a first stage approach. The following is the second stage approach.
S7: Put the scanner in the retract state. The scanner 2 is once put in the retract state. The state at that time is set to the most contracted state as shown in FIG.
S8: The stage is moved in a direction in which the distance between the surface of the sample 1 and the probe 6 is reduced by a distance corresponding to half the maximum swing width of the scanner, as shown in (a) and (b) of FIG. A distance that is half the maximum swing width is calculated from the stretched state and the shrunken state. Only the calculated distance is moved in the direction in which the distance between the surface of the sample 1 and the probe 6 is reduced using the scanner 2.
S9: Bring the scanner 2 into the approach state While operating the feedback circuit 12, the retract state of the scanner 2 is released.
S10: In the state of step S9, the error amplifier 10 compares whether the RMS-DC value is the reference value calculated in step 2.

If the RMS-DC value is not the reference value with the scanner 2 extended to the maximum swing width as shown in FIG. 3B, the operations in steps S7 to S10 are repeated.
S11: When the RMS-DC value becomes the reference value, the approach is terminated.

  If the RMS-DC value becomes the same as the reference value in the state of step S10, the approach is terminated. If the phase difference has changed by the minimum change amount set in step S3 at the time of starting the motor approach, the first-stage approach has already been completed. The approach is omitted, and the second step approach S7 is performed.

  As described above, according to the embodiment of the present invention, the first-stage approach using the phase difference signal for controlling the distance between the sample surface and the probe to a predetermined value, the sample surface and the probe, By performing the second-stage approach using the RMS-DC signal so that the distance between the two becomes an optimum value, the distance between the sample surface and the probe as a whole is controlled to be optimum. A fast approach is possible.

(Embodiment 2)
FIG. 4 is a diagram showing the approach state of the scanner, and shows the approach in the second stage. During the second stage of steps S7 to S11 in FIG. 2, a diagram of the scanner 2 when the scanner 2 is in the extended state and the approach state when the scanner 2 is contracted. A diagram of the scanner at the time is shown. Normally, the approach state is preferably a state where the scanner extends and contracts like the approach state at the intermediate position in FIG. 5C, that is, a state where the applied voltage is 0V.

  However, depending on the distance between the tip of the probe 6 and the sample 1 and the maximum amplitude of the scanner 2, the scanner 2 may be in a state as shown in FIGS. Therefore, an algorithm is incorporated so that the approach state of the scanner 2 comes to an intermediate position during the operations in steps S7 to S11 in FIG. 2 in the first embodiment.

Next, the operation of FIG. 4 will be described. In the following description, the same component identification symbols as those in FIG. 16 are given the same reference numerals.
S1: The amount of amplitude per unit voltage is obtained from the voltage applied to the scanner 2 and the voltage-width characteristic calculated from the amount of amplitude in the Z-axis direction.
S2: In the cases of (d) and (e), the applied voltage is converted into a distance from the voltage-width characteristic of S1.
S3: In the case of (d), the scanner 2 is once retracted, and is moved by the motor for the distance determined in S2 in a direction in which the distance between the surface of the sample 1 and the tip of the probe 6 is reduced.
S4: After the movement is completed, the retract state of the scanner 2 is canceled and the approach state is set.
S5: In the case of (c), the scanner 2 is once retracted, and is moved by the motor for the distance obtained in step S2 in the direction in which the distance between the surface of the sample 1 and the tip of the probe extends.
S6: After the movement is completed, the retract state of the scanner is canceled and the approach state is set.

(Embodiment 3)
The following embodiment will be described. FIG. 5 is a diagram showing the relationship between the RMS-DC value of AC-AFM and the phase difference signal. In the figure, f1 indicates a phase difference (Phase), and f2 indicates an RMS-DC characteristic. The vertical axis is voltage, and the horizontal axis is time. Unlike the phase signal shown in FIG. 1, depending on the material of the probe 6, the position of laser irradiation, the natural frequency of the probe 6, etc., a phase difference signal may be detected as shown in FIG.

  Therefore, in both cases of FIGS. 1 and 5, if the approach can be stopped by detecting the phase difference signal, the tip of the probe 6 does not contact the surface of the sample 1 and the approach is stopped. It becomes possible.

  In this case, the algorithm is the same as the operation in step S2 in FIG. 2, but in the operation of “compare the designated phase difference value with the current phase difference value” in step S5, Adds or subtracts the specified minimum displacement value to or from the phase difference value. At that time, the obtained phase difference value is compared with the value being approached. This method makes it possible to stop the first-stage approach even for the phase difference signals of FIGS.

(Embodiment 4)
In the first embodiment described above, the retract of the scanner 2 is released by applying a step-like voltage as shown in FIG. 6A to control the gain filter or PID of the feedback circuit, and the scanner. 2 control is performed. Such an instantaneous reaction includes a risk that the tip of the probe 6 contacts the surface of the sample 1. Therefore, it is preferable to adjust the voltage applied during the approach.

  FIG. 6 is a diagram showing the applied voltage in the Z-axis direction of the scanner. (A) shows a step response and (b) shows a ramp response. The vertical axis represents applied voltage, and the horizontal axis represents time. As shown in (b), the applied voltage is applied like a ramp response. As a result, the response of the scanner becomes gentle and the collision of the probe can be avoided more. Also, the ramp response output method can be achieved by controlling the voltage applied in the Z-axis direction of the scanner in a time-series manner like the ramp response, or by adjusting the gain filter or PID control of the feedback circuit. Become.

(Embodiment 5)
In the drawing shown in FIG. 3, the probe 6 is fixed, and a motor approach is performed using the motor 3 for the scanner 2. In this embodiment, the relationship between the scanner 2, the probe 6, and the stage is shown. In the system configured as described above, the relationship between the scanner 2, the probe 6, and the stage can be freely set structurally and is not fixed as shown in FIG. FIG. 7 is a diagram showing the relationship between the probe, the sample, and the stage. The scanner 2 can be moved, and the cantilever 6 can be moved.

(Embodiment 6)
In this embodiment, the principle of the electrostatic force microscope (EFM) can be used when the distance between the sample surface and the tip of the probe is to be stopped at a far place by the first stage approach. The electrostatic force microscope is a measurement method in which a bias is applied between a sample and a probe to generate an electrostatic force and a change in the force due to the electrostatic force is detected. The electrostatic force can be detected at a location farther than the attractive region.

  Therefore, a bias can be applied between the sample 1 and the probe 6 during the first stage approach. At this time, due to the generated electrostatic force, the probe can detect the force at a farther place, and the change of the phase difference value can also be detected at a farther position.

  Next, another type of invention will be described. FIG. 8 is a diagram showing the amplitude-frequency characteristics of the probe. The vertical axis represents amplitude, and the horizontal axis represents frequency. In NC (Non Contact) -AFM, as shown in FIG. 8, a change in force received from a sample is detected as a resonance frequency shift (ΔF) of the probe and an amplitude change (ΔA). There is a method. Since a method for detecting a frequency shift can detect a weak probe-sample force in the attractive region, a method for detecting a frequency shift (FM-AFM) has recently been adopted. .

FIG. 9 is a block diagram illustrating an embodiment of the NC mode AFM. The same components as those in FIG. 16 are denoted by the same reference numerals. This figure shows the signal flow when FM-AFM is used in Non Contact Mode AFM (NC-AFM). Laser light from the tip of the probe 6 oscillating at the resonance frequency Fo is detected and input to the FM demodulator 15a. In the D-PLL in the FM demodulator 15a, the phase and amplitude are adjusted so that the oscillation of the probe 6 is constant. The approach is performed with the motor 3 until the frequency reaches the specified reference (F _{1 in} FIG. 8). In the state where the approach is completed, a scanning voltage is applied to the scanner, and the feedback circuit is operated so that the output from the error amplifier 10 (Z direction signal) becomes zero, and measurement is performed. A frequency demodulated signal (FMD) that is an output of the FM demodulator 15 a is input to one input of the error amplifier 10. The reference value from the reference value generator 11 is input to the other input of the error amplifier 10. Other configurations are the same as those shown in FIG.

(Embodiment 7)
FIG. 10 is a diagram showing the relationship between the FMD value of NC-AFM and the phase difference signal. The vertical axis is voltage, and the horizontal axis is time. This figure shows the relationship between the FMD value and the phase difference signal from the start of the approach to the stop of the approach in NC-AFM. Since the FMD value is output using the phase difference signal, the signal waveform has the same shape. f5 indicates a phase difference signal, and f6 indicates an FMD signal. However, as can be seen from the figure, when both signals are compared at a certain time T1, the amount of change in the signal from the start of the approach is greater for the phase difference signal.

  Also, the phase difference signal is earlier in the time when the change appears in the signal. This is because the phase difference signal depends on sensitively detecting a change in the distance between the sample 1 and the probe 6. From this, it is possible to detect the phase difference signal and stop the approach immediately before stopping the approach with the reference value obtained from the FMD value.

Therefore, the new approach method is a combination of approaches in two stages. In the first stage, the operation is stopped at the minimum change amount of the set minimum phase difference value.
Since the distance between the sample 1 and the tip of the probe is large, the motor approach so far allows the motor speed to be set arbitrarily. Next, the second-stage approach operates by combining the Z-axis expansion and contraction of the scanner and the movement of the stage. By this moving method, the tip of the probe does not contact the sample surface, and it is possible to approach safely until the FMD value becomes the reference value. Next, the operation of the present invention will be described.

FIG. 11 is a flowchart showing another example of the algorithm (NC-AFM) of the new approach of the present invention. As the identification numbers of the constituent elements in the following description, those shown in FIG. 9 are used. The present invention will be described below with reference to this flowchart.
S1: The probe is set to vibrate with NC-AFM.

Tune the probe that is necessary for NC-AFM measurement.
S2: Calculation of reference value The FMD value is adjusted, and the reference value of the approach condition is calculated. The operations in steps S1 and S2 are operations normally performed when the sample surface is observed in the NC-AFM mode.
S3: The minimum change amount of the phase difference, the frequency displacement amount, and the approach speed are set.

In order to stop the motor approach by detecting the phase difference signal, a minimum change amount is set. The minimum change amount to be set is the same as that of the AC-AFM described above. However, as described above, the frequency displacement amount can be set so that it can be selected. Next, the speed of the motor approach used in the first stage approach is set. The setting method is the same as AC-AFM.
S4: Start the motor approach.

  The motor approach is started at the speed set in step S3. At this time, the state of the scanner 2 in the Z-axis direction is such that the feedback circuit 12 is operated and extended as shown in FIG.

FIG. 12 is a diagram illustrating the state of the scanner 2. (A) shows a retracted state, and (b) shows a state extending to the maximum swing width.
S5: The designated phase value or designated frequency displacement amount is compared with the current phase value. During the motor approach in step S4, the phase difference value is observed. The phase difference value or FMD immediately before the approach is compared with the phase difference value during the approach, and it is monitored whether the phase difference corresponding to the minimum change amount set in step S3 or only the frequency displacement amount is changed. If the phase difference value or frequency displacement has not changed by the specified value, the motor approach is continued.
S6: The motor approach is stopped.

During the approach of step S4, when the phase difference or the amount of frequency displacement changes by the minimum change amount set in step S3, or when only the amount of frequency displacement changes, the approach is stopped.
Here, the operation from step S1 to step S6 is a first-stage approach.

The following is the second stage approach.
S7: Put the scanner in the retract state. The scanner 2 is once put in the retract state. The state at that time is set to the most contracted state as shown in FIG.
S8: The stage is moved in a direction in which the distance between the surface of the sample 1 and the probe 6 is reduced by half the distance of the maximum swing width of the scanner 2, as shown in FIG. 12, the scanner 2 is extended in the Z-axis direction. A half distance of the maximum swing width is calculated from the state and the contracted state. Only the calculated distance is moved in the direction in which the distance between the probe 6 and the scanner 2 is reduced using the motor 3.
S9: The scanner is brought into the approach state.

The retract state of the scanner 2 is canceled while operating the feedback circuit 12.
S10: Check whether the FMD value is a reference value In the state of step S9, a comparison is made to determine whether the FMD value is the reference value calculated in step S2. If the FMD value is not the reference value, the operations from step S7 to S10 are repeated.
S11: When the FMD value is the reference value, the approach is terminated.

  Further, when the phase difference value or the FMD value is changed by the minimum change amount or the frequency displacement amount set in step S3 at the time of starting the motor approach, the first step approach is omitted, Try to move to a two-step approach.

  As described above, according to this embodiment, the first-stage approach using the phase difference signal or the frequency displacement signal that is controlled until the distance between the sample surface and the probe reaches a predetermined value; By performing the second-stage approach using the FMD signal so that the distance between the sample surface and the probe becomes an optimum value, the overall distance between the sample surface and the probe is controlled optimally. Doing so enables a fast approach.

(Embodiment 8)
FIG. 13 is a flowchart showing an algorithm of a high-speed collision prevention approach of NC-AFM using an AC-AFM phase difference signal.

(First stage approach)
First, probe excitation is set by AC-AFM (S1). Next, a reference value is calculated and the phase difference is adjusted (S2). Next, the minimum change amount of the phase difference and the approach speed are set (S3). Next, the motor approach is started (S4). Then, it is determined whether or not the specified phase difference value has been reached (S5). When the designated phase difference value is reached, the motor approach is stopped (S6).

(Second stage approach)
When the motor approach is stopped in step S6, the scanner is brought into a retracted state (S7). Next, automatic adjustment for NC-AFM is performed to calculate a reference value (S8). Next, the stage is moved in a direction in which the distance between the probe and the sample surface is reduced by a distance corresponding to half the maximum swing width of the scanner (S9). Next, the scanner is brought into the approach state (S10). Next, it is checked whether the FMD value is a reference value (S11). If the FMD value is not the reference value, steps S7 to S11 are repeated. If the FMD value is the reference value, the approach is terminated (S12).

(Embodiment 9)
FIG. 14 is a flowchart illustrating another example of the NC-AFM anti-collision fast approach algorithm using the AC-AFM phase difference signal. In this embodiment, the first stage is performed in the AC-AFM mode, and the second stage is performed in the NC-AFM mode.

(First stage approach)
The probe excitation setting is performed by the NC-AFM, and the adjusted phase difference signal necessary for the AC-AFM is stored (S1). Next, the mode is switched to the AC-AFM mode (S2). Next, a setting approach speed for setting a minimum change amount of the phase difference is set (S3). Then, the motor approach is started based on the set value (S4). Next, it is checked whether or not the designated phase difference value has been reached (S5). When the designated phase difference value is reached, the motor approach is stopped (S6).

(Second stage approach)
When the motor approach is stopped in step S6, the scanner is brought into a retracted state (S7). Then, the mode is switched to the NC-AFM mode, and a reference value is set (S8). Next, the stage is moved in a direction in which the distance between the probe and the sample surface is reduced by a distance corresponding to half the maximum swing width of the scanner (S9). Then, the scanner is brought into the approach state (S10). Then, it is checked whether or not the FMD value is a reference value (S11). If the FMD value is not the reference value, the processes in steps S7 to S11 are repeated. If the FMD value is the reference value, the approach process is terminated (S12).

  FIG. 15 is an explanatory diagram of a damageless high-speed approach. In the figure, 1 is a sample and 6 is a probe. The figure shows that it consists of a high-speed approach area using a motor and a precision approach area using a scanner. A weak attractive force acting as a long distance force can be detected from a distance. Therefore, the approach is performed at a high speed (50 μm / sec) until this force is detected, and thereafter the precise approach is performed. Since the approach is short, it is possible to approach without worrying about the distance between the sample surface and the probe.

It is a figure which shows the relationship between the RMS-DC value of AC-AFM, and a phase difference signal. It is a flowchart which shows the algorithm (AC-AFM) of a new approach. It is a figure which shows the state of a scanner. It is a figure which shows the approach state of a scanner. It is a figure which shows the relationship between the RMS-DC value of AC-AFM, and a phase difference signal. It is a figure which shows the applied voltage to the Z-axis direction of a scanner. It is a figure which shows the relationship between a probe, a sample, and a stage. It is a figure which shows the amplitude-frequency characteristic of a probe. It is a block diagram which shows the example of embodiment of NC mode AFM. It is a figure which shows the relationship between the FMD value of NC-AFM, and a phase difference signal. It is a flowchart which shows the algorithm (NC-AFM) of a new approach. It is a figure which shows the state of a scanner. It is a flowchart which shows the algorithm of the collision prevention high-speed approach of NC-AFM using the phase difference signal of AC-AFM. It is a flowchart which shows the other example of the algorithm of the collision prevention high-speed approach of NC-AFM using the phase difference signal of AC-AFM. It is explanatory drawing of the damageless high-speed approach of this invention. It is a block diagram which shows the embodiment of AC mode AFM. It is a figure which shows the RMS-DC output signal in the case of AC-AFM.

Explanation of symbols

1 Sample 2 Scanner 3 Motor 4 Laser Diode 5 Piezoelectric Element (PZT)
6 Probe 7 Photo detector (PD)
8 Preamplifier 10 Error amplifier 11 Reference value 12 Feedback circuit 13 A / D converter 14 Personal computer (PC)
15aFM demodulator 16 Attenuator 17 HV-Amplifier 18 Span generator 19 HV-Amplifier

Claims (4)

In a scanning probe microscope that scans the sample surface using a probe and measures the unevenness of the sample surface with atomic resolution,
In the first stage, the phase difference between the excitation signal to the probe and the signal detected by the photodetector from the probe is calculated, and feedback control is performed until a predetermined change in the phase difference signal is detected. ,
Next, in the second stage, the distance between the probe and the sample surface is controlled by performing feedback control using the sample surface observation feedback signal which is the output of the photodetector, and the scanning probe microscope For controlling the distance between the probe and the sample surface.   2. The distance control method between a probe of a scanning probe microscope and a sample surface according to claim 1, wherein an amplitude signal or an FMD value is used as the sample surface observation feedback signal.   2. The probe and sample of a scanning probe microscope according to claim 1, wherein the control in the first stage is performed using a motor, and the control in the second stage is performed using a piezoelectric element expansion and contraction and a motor. Distance control method between surfaces. In a scanning probe microscope that scans the sample surface using a probe and measures the unevenness of the sample surface with atomic resolution,
In the first stage, the phase difference between the excitation signal to the probe and the signal detected by the photodetector from the probe is calculated, and feedback control is performed until a predetermined change in the phase difference signal is detected. First control means;
A second control means for controlling the distance between the probe and the sample surface by performing feedback control using a sample surface observation feedback signal which is an output of the photodetector;
A scanning probe microscope comprising:

Images