JPH11271343A - Scanning type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve lateral resolution, by detecting the displacement of a scanner in X and Y directions caused by a voltage impressed on Z-direction response and feeding back the displacement signal, and suppressing oscillations in the X and Y directions. SOLUTION: As oscillations in X and Y (two dimensional) directions are determined according to the mechanical natural frequency of a cylindrical scanner and is approximately constant, the detection signals of a lateral sensor only in the vicinity of the mechanical natural frequency are extracted by a band pass filter. Next, the difference between the oscillations in the X and Y directions and the target location of lateral scanning is amplified by an integrating amplifier K3 /S to obtain the amount of displacement E2 from the target location of scanning in the X and Y directions due to the oscillations in the X and Y directions. Then the amount E2 of displacement is subtracted from the first Z (vertical) direction movement instructing voltage E1 to obtain the final Z direction movement instructing voltage E3 . As the response of a servo in the Z direction is lowered, and the oscillations in the X and Y directions caused by the movement in the Z direction are reduced by this control, it is possible to obtain images with high lateral resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a probe.
A scanning probe for examining the surface condition of a sample by moving the sample in a direction (Z direction) perpendicular to the sample surface according to the surface condition of the sample while scanning the sample in two dimensions (XY directions) parallel to the sample surface to be observed. For a microscope.

[0002]

2. Description of the Related Art A scanning probe microscope is a device capable of observing a fine shape of a sample surface at an atomic level, and includes a scanning tunnel microscope (STM) and an atomic force microscope (AFM). I have.

As described in Japanese Patent Application Laid-Open No. Sho 62-130302, AFM utilizes the interatomic force acting between the atom at the tip of the probe and the atom at the surface of the sample to form the surface of the sample. Is a device for measuring When the probe is brought close to the surface of the sample, as shown in FIG.
A small force called interatomic force (repulsive force, van der Waalska, covalent force, etc.) is generated, which is represented by the Lennard-Jones potential. In the AFM, the probe is supported at the free end of a flexible cantilever, and the atomic force acting between the probe and the sample is detected as the amount of deflection of the cantilever (lever) (the amount of displacement of the probe). By measuring the control voltage when scanning the probe while controlling the positional relationship between the probe and the sample so as to be constant, the surface shape and interaction of the sample (atomic force, contact force, magnetic force, etc.) Is measured with atomic resolution. For this reason, AFM
Can be measured independently of the conductivity of the sample, unlike STM.

In such a scanning probe microscope, Japanese Patent Application Laid-Open No. 63-189911 and Japanese Patent Application Laid-Open
No. 6237 has proposed a control method for improving the response in the two-dimensional (XY) scanning direction and the Z direction.

FIG. 7 shows an example of an atomic force microscope. At the tip of the cylindrical scanner 1 that can be driven three-dimensionally in the XY and Z directions, a flexible and elastic cantilever 3 and a sensor 7 located above the free end back surface 5 of the cantilever 3 are provided. I have. A sharp needle-shaped probe 6 is formed at the free end of the cantilever 3, and the probe 6 is arranged close to the surface of the sample 8. Sensor 7
Detects the amount of movement of the tip of the cantilever 3. A feedback voltage for moving the cylindrical scanner 1 in the Z direction is applied so that the amount of deflection of the cantilever is constant, that is, the force acting between the cantilever 3 and the sample 8 is kept constant.

FIG. 8 is a control block diagram for controlling the cylindrical scanner 1 in the Z direction. In FIG. 8, while the cantilever 3 is scanned in the XY directions by the scanner 1, the difference e1-e2 between the drive signal e1 in the Z direction and the sensor signal e2 corresponding to the deformation of the cantilever 3 is moved to the piezoelectric body by the integrating amplifier. Convert to command voltage E. By this movement command voltage E, the scanner 1 expands and contracts in the Z direction so as to keep the signal e1 of the deflection amount of the cantilever constant. In this state, the probe 6 and the cantilever 3 are simultaneously scanned in the XY directions by the control circuit 10 on the sample 8 and the feedback voltage at that time is recorded by the computer 11, so that an AFM image (an uneven image) of the surface of the sample 8 is obtained. ) Is measured and displayed on the AFM image display means 12.

[0007]

According to the control methods proposed so far, the XY directions are XY directions, and the Z direction is Z direction, and the responsiveness is increased independently of each other. Not considered. In general, the amount of two-dimensional (XY) scanning of the surface in the three-dimensional driving is larger than the amount of movement in the Z direction. Specifically, the scanning range is
The moving amount in the XY directions is about 10 to 100 times the moving amount in the Z direction. For this reason, the scanning means in the Z direction can be made small and high in rigidity, but the scanning means in the XY direction can be made small and high in rigidity, resulting in large and low rigidity. The response performance in the Z direction needs to be 100 times or more that of the XY direction. Such a three-dimensional piezoelectric scanner vibrates at its mechanical natural frequency in the XY direction due to the response in the Z direction, and the conventional method of independently controlling the XY direction and the Z direction causes mutual The problem that the interference of resonance and the interference of resonance in the XY directions affect the positional accuracy in the Z and XY directions cannot be solved.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a scanning probe microscope in which the XY vibration generated by the response of the scanner in the Z direction is reduced. It is to be.

[0009]

According to the present invention, while scanning a probe in XY directions parallel to the surface of a sample, the probe is moved in a Z direction perpendicular to the surface of the sample in accordance with the surface state of the sample to check the surface state of the sample. In a scanning probe microscope, XY vibration of a scanner generated by a response applied voltage in the Z direction is detected by an XY displacement sensor that monitors displacement in the XY directions, and the signal is fed back to a servo signal in the Z direction. It is characterized in that abnormal vibration of the scanner in the XY directions is suppressed.

Alternatively, the XY vibration of the scanner, which is generated by the response application voltage in the Z direction, is detected from the signal of the electric charge of the piezoelectric body that generates the displacement in the XY directions, and the signal is converted into a servo signal in the Z direction. It is characterized in that abnormal vibration of the scanner in the XY directions is suppressed by feedback.

Alternatively, the XY vibration of the scanner generated by the response application voltage in the Z direction is calculated in the controller, and the XY vibration of the scanner reference model modeled in the XY direction is calculated in the controller. It is characterized in that abnormal vibration of the scanner in the X and Y directions is suppressed by feeding back to a signal.

Thus, the servo response in the Z direction is XY
The XY direction stops responding violently until the directional vibration stops, and the XY direction generally caused by responding in the Z direction in the piezoelectric scanner of the scanning probe microscope having lower mechanical rigidity in the XY direction than the Z direction can be reduced. . As a result, the lateral resolution of the scanning probe microscope is improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a scanning atomic force microscope according to the first embodiment. In FIG.
A flexible and elastic cantilever 3 is provided at the tip of the cylindrical scanner 1 that can be driven three-dimensionally in the XY and Z directions. A sharp needle-like probe 6 is formed on the back surface of the free end 5 of the cantilever 3, and the probe 6 is arranged close to the surface of the sample 8. The sensor 7 detects the amount of movement of the tip of the cantilever 3. As the sensor 7 used at this time, an optical sensor is mainly used,
For example, an optical lever type displacement sensor described in JP-A-3-296612 is effective. The AFM unit 14 is positioned by the Z stage 15 so that a predetermined force acts between the probe 6 and the sample 8.

The probe 6 is scanned by the cylindrical scanner 1 on the surface of the sample 8 in the XY directions. The displacement in the XY directions is measured by the lateral sensor 4. The lateral direction sensor 4 includes a laser length measuring device, an interferometer, and the like.

During the XY scan, the force acting between the probe 6 and the sample 8 changes in response to minute irregularities on the surface of the sample 8. The amount of deformation of the cantilever 3 changes in accordance with the change in the force, so that the distance between the back surface 5 of the cantilever 3 and the sensor 7 changes, and as a result, the output of the sensor 7 changes.

The cylindrical scanner 1 has a
Feedback control is performed so that the elastic deformation of the cantilever 3 is kept constant from the output of the sensor 7, that is, the force acting between the probe 6 and the sample 8 is kept constant.

FIG. 2 is a control block diagram of a scanner in the apparatus of the present embodiment. In this control, the shift amount E2 from the scan target position in the XY direction due to the vibration in the XY directions is subtracted from the movement command voltage E1 in the Z direction.

In FIG. 2, a movement command voltage E1 in the Z direction is shown.
Is obtained by amplifying the difference e1-e2 between the drive signal e1 in the Z direction and the sensor signal e2 corresponding to the deformation of the cantilever 3 by an integrating amplifier (K1 / S). In the reference state of the cantilever, e2 = 0 is set. The vibration in the X and Y directions is determined according to the mechanical natural frequency of the cylindrical scanner 1 and is substantially constant.
Is obtained by extracting only the vicinity of the frequency of the mechanical natural vibration from the detection signal of Therefore, the deviation E2 from the XY scanning target position due to the XY vibration is obtained by amplifying the difference between the XY vibration and the horizontal scanning target position by an integrating amplifier (K3 / S). Therefore, the final Z-direction movement command voltage E3 = E
1-E2 is obtained.

The integral amplification factor K3 is adjusted in accordance with the XY (horizontal) scanning speed of the cylindrical scanner 1 to be controlled and the size of the step in the height direction to be measured. X
The command value voltage in the height direction is | E1 |> | E2 | so that the feedback of the vibration in the Y direction is not excessively set.

In such control, when the sensor 7 and the cantilever 3 are simultaneously scanned in the XY directions of the sample 7,
By recording the feedback voltage applied to the cylindrical scanner 1 for movement in the Z direction in the computer 11, an AFM image (concavo-convex image) of the surface of the sample 8 is obtained,
It can be displayed on the AFM image display means 12.

In the above-described control, when the vibration in the XY directions caused by the movement in the Z direction becomes severe, the response of the servo in the Z direction is reduced, and the vibration in the XY directions is reduced. Therefore, the AFM image obtained by such control has a high horizontal resolution.

FIG. 3 shows a scanning atomic force microscope according to the second embodiment. Referring to FIG. 3, this atomic force microscope uses a three-dimensional scanner to provide three laminated piezoelectric bodies 16x, 1
A tripod type piezoelectric scanner 15 made by joining 6y and 16z is used. A flexible and elastic cantilever 3 is provided at the tip of the tripod type piezoelectric scanner 2 which can be driven three-dimensionally in the XY and Z directions. A sharp needle-shaped probe 6 is formed on the back surface of the free end 5 of the cantilever 3, and the probe 6 is arranged close to the surface of the sample 8. The sensor 7 detects the amount of movement of the tip of the cantilever 3. An optical sensor is mainly used as the sensor 7 used at this time.
The displacement sensor of the optical lever type described in JP-A-3-296612 is effective. AFM unit 14 is Z
The stage 15 is positioned so that a predetermined force acts between the probe 6 and the sample 8.

The probe 6 is scanned by the tripod type piezoelectric scanner 15 on the surface of the sample 8 in the XY directions. The displacement in the XY directions is measured by the lateral sensor 4. In the present embodiment, the lateral direction sensor 4 is a laminated piezoelectric body 16 in the X and Y directions of the tripod type piezoelectric scanner 15.
The displacement in each direction is obtained from the electric charge stored in each of x and 16y.

During the XY scan, the force acting between the probe 6 and the sample 8 changes in response to minute irregularities on the surface of the sample 8. The amount of deformation of the cantilever 3 changes in accordance with the change in the force, so that the distance between the back surface 5 of the cantilever 3 and the sensor 7 changes, and as a result, the output of the sensor 7 changes.

Z of the tripod type piezoelectric scanner 15
The laminated piezoelectric body 16z for the direction keeps the elastic deformation of the cantilever 3 constant from the output of the sensor 7, that is,
Feedback control is performed so that the force acting between the probe 6 and the sample 8 is kept constant.

The control of the tripod type piezoelectric scanner 15 is performed using the same control system as in the first embodiment shown in FIG. However, in the present embodiment, the lateral sensor detects the displacement in the XY directions based on the electric charges accumulated in each of the laminated piezoelectric bodies 16x and 16y. The rest is the same as the first embodiment, so that the description will be made below with reference to FIG. 2 as in the first embodiment.

As can be seen from FIG. 2, the movement command voltage E1 in the Z direction is obtained by integrating the difference e1-e2 between the drive signal e1 in the Z direction and the sensor signal e2 corresponding to the deformation of the cantilever 3 by an integrating amplifier (K1 / S). Obtained by amplification. The vibration in the X and Y directions is determined according to the mechanical natural frequency of the tripod type piezoelectric scanner 15 and is substantially constant.
By extracting only the vicinity of the frequency of the mechanical natural vibration. Therefore, the deviation E2 from the XY-direction scanning target position due to the XY-direction vibration is obtained by integrating the difference between the XY-direction vibration and the horizontal-direction scanning target position with the integrating amplifier (K3 / S).
Amplified by Therefore, a final movement command voltage E3 = E1 -E2 in the Z direction is obtained.

The integral amplification factor K3 is adjusted according to the XY (horizontal) scanning speed of the tripod type piezoelectric scanner 15 to be controlled and the size of the step in the height direction to be measured. The command voltage in the height direction is | E1 so that the feedback of the vibration in the XY directions is not set excessively.
|> | E2 |.

In such control, when the sensor 7 and the cantilever 3 are simultaneously scanned in the XY directions of the sample 8,
Multilayer piezoelectric body 16 of tripod type piezoelectric scanner 15
The feedback voltage applied to the z
The AFM image (concavo-convex image) of the surface of the sample 8 can be obtained by recording the information on the AFM image display unit 12 and can be displayed on the AFM image display unit 12.

In the above-described control, when the vibration in the XY directions caused by the movement in the Z direction becomes intense, the response of the servo in the Z direction is reduced, and the vibration in the XY directions is reduced. Therefore, the AFM image obtained by such control has a high horizontal resolution.

FIG. 4 shows a scanning atomic force microscope according to the third embodiment. In FIG. 4, this atomic force microscope uses a parallel spring type three-dimensional scanner 24 as a three-dimensional scanner. A flexible and elastic cantilever 3 is provided at the tip of the scanner 24 for expanding the amount of movement of the piezoelectric body that can be driven three-dimensionally in the XY and Z directions. A sharp needle-shaped probe 6 is formed on the back surface of the free end 5 of the cantilever 3, and the probe 6 is arranged close to the surface of the sample 8. The sensor 7 detects the amount of movement of the tip of the cantilever 3. As the sensor 7 used at this time, an optical sensor is mainly used, and for example, an optical lever type displacement sensor described in JP-A-3-296612 is effective. The AFM unit 14 is positioned by the Z stage 15 so that a predetermined force acts between the probe 6 and the sample 8.

The probe 6 is a parallel spring type three-dimensional scanner 24.
Scans the surface of the sample 8 in the X and Y directions.
During the XY scanning, the force acting between the probe 6 and the sample 8
Changes sensitively to minute irregularities on the surface. The amount of deformation of the cantilever 3 changes in accordance with the change in the force, so that the distance between the back surface 5 of the cantilever 3 and the sensor 7 changes, and as a result, the output of the sensor 7 changes.

The parallel spring type three-dimensional scanner 24 keeps the elastic deformation of the cantilever 3 constant from the output of the sensor 7, that is, keeps the force acting between the probe 6 and the sample 8 constant. A feedback voltage is applied to and controlled by the laminated piezoelectric body for moving in the direction.

FIG. 5 is a control block diagram of a scanner in the apparatus of the present embodiment. In this control, the shift amount E2 from the scan target position in the XY direction due to the vibration in the XY directions is subtracted from the movement command voltage E1 in the Z direction.

In FIG. 5, the movement command voltage E1 in the Z direction is shown.
Is obtained by amplifying the difference e1-e2 between the drive signal e1 in the Z direction and the sensor signal e2 corresponding to the deformation of the cantilever 3 by an integrating amplifier (K1 / S). The vibration in the XY directions is
It is obtained by calculating inside the control circuit 10 a reference model of the movement in the X and Y directions due to the movement in the Z direction. Accordingly, the deviation E2 from the XY-direction scanning target position due to the XY-direction vibration is obtained by amplifying the difference between the XY-direction vibration and the horizontal-direction scanning target position by an integrating amplifier (K3 / S). Therefore, the final Z-direction movement command voltage E3 = E1
-E2 is obtained.

The integral amplification factor K3 is adjusted in accordance with the XY (lateral) scanning speed of the cylindrical scanner 1 to be controlled and the size of the step in the height direction to be measured. X
The command value voltage in the height direction is | E1 |> | E2 | so that the feedback of the vibration in the Y direction is not excessively set.

In such control, when the sensor 7 and the cantilever 3 are simultaneously scanned in the XY directions of the sample 8,
By recording the feedback voltage applied to the cylindrical scanner 1 for movement in the Z direction in the computer 11, an AFM image (concavo-convex image) of the surface of the sample 8 is obtained,
It can be displayed on the AFM image display means 12.

In the above-described control, when the vibration in the XY directions caused by the movement in the Z direction becomes severe, the response of the servo in the Z direction is reduced, and the vibration in the XY directions is reduced. Therefore, the AFM image obtained by such control has a high horizontal resolution.

The present invention is not limited to the above-described embodiment, and various modifications are possible. The type of the scanning microscope, the structure of the scanner, the type of the lateral sensor, and the like may be other than the above-described embodiment.

Further, in the embodiment, as the means for detecting the displacement of the probe in the Z direction, the configuration of the optical lever type displacement sensor is used. However, other displacement detecting means such as a laser interferometer and an electrostatic A capacitance sensor or the like may be used. That is, any means can be used for the displacement detection means of the probe as long as the displacement can be detected. Further, the reference model may be configured not only in the Z direction but also in the XY directions, and the XY behavior may be used as feedback information for the servo in the Z direction.

[0041]

According to the present invention, there is provided a scanning probe microscope in which vibrations in the X and Y directions generated by the response of the scanner in the Z direction are reduced and thereby the resolution in the horizontal direction is improved.

[Brief description of the drawings]

FIG. 1 shows a scanning atomic force microscope according to a first embodiment of the present invention.

FIG. 2 is a control block diagram of a scanner in the apparatus of FIG.

FIG. 3 shows a scanning atomic force microscope according to a second embodiment of the present invention.

FIG. 4 shows a scanning atomic force microscope according to a third embodiment of the present invention.

FIG. 5 is a control block diagram of a scanner in the apparatus of FIG.

FIG. 6 shows the interatomic force as a function of distance.

FIG. 7 shows a conventional scanning probe microscope.

8 is a control block diagram of a scanner in the apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical piezoelectric scanner 3 Cantilever 4 Lateral sensor 6 Probe 7 Sensor 8 Sample 9 Voltage application means 10 Control circuit 13 Band pass filter

Claims (3)

[Claims] 1. A scanning probe microscope for examining the surface state of a sample by moving a probe in the Z direction perpendicular to the surface of the sample according to the surface state of the sample while scanning the probe in the XY directions parallel to the surface of the sample. Of the scanner generated by the applied voltage
Scanning characterized by detecting vibration in the Y direction by an XY displacement sensor that monitors displacement in the XY direction, and feeding back the signal to a servo signal in the Z direction to suppress abnormal vibration of the scanner in the XY direction. Probe microscope. 2. A scanning probe microscope for examining the surface condition of a sample by moving a probe in the Z direction perpendicular to the sample surface according to the surface condition of the sample while scanning the probe in the XY directions parallel to the sample surface. Of the scanner generated by the applied voltage
Vibration in the Y direction is detected from a signal of the amount of electric charge of the piezoelectric body that generates displacement in the XY directions, and the signal is fed back to a servo signal in the Z direction to suppress abnormal vibration of the scanner in the XY directions. Features scanning probe microscope. 3. A scanning probe microscope for examining the surface condition of a sample by moving a probe in the Z direction perpendicular to the sample surface according to the surface condition of the sample while scanning the probe in the XY directions parallel to the sample surface. Of the scanner generated by the applied voltage
The vibration in the Y direction is calculated inside the controller by calculating the XY vibration of the scanner reference model modeled in the XY directions, and the signal is fed back to the servo signal in the Z direction to generate the X signal.
A scanning probe microscope characterized by suppressing abnormal vibration of a scanner in a Y direction.