JP2009068930A - Atomic force microscope and probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a probe of an atomic force microscope having high characteristic frequency, even in air or in liquid, while reducing the fluid resistance. <P>SOLUTION: In a probe 10 of an atomic force microscope, surface shape information is acquired by fixing a probe 16 on a rotating body 17, having circular cross section, rotatable with respect to supporting beams 12, 13 of the both ends and scanning an object to be measured. The rotating body 17 is connected to the supporting beams 12, 13 through elastic bodies 14, 15 having circular cross section. With the torsional vibrating of an elastic mechanism 18 which is constituted with the rotational body 17 and the elastic bodies 14, 15 at a fixed frequency, driving of the probe 16 can be easily realized. Since the center axis of the probe 16 has a positional relation of the spacial torsion with the central axis of the rotational body 17, influence due to friction can be reduced with the driving the probe 16 in the vertical direction of the object to be measured. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention detects the attractive force or repulsive force (atomic force) between the probe and the object to be measured by bringing the probe installed at the tip of the probe close to the object to be measured and scanning. The present invention relates to an atomic force microscope and a probe for measuring a surface shape.

  The principle of the atomic force microscope is disclosed in Patent Document 1. According to this, a probe fixed to one end of a spring-like cantilever (cantilever) is brought close to the object to be measured, and the atomic force generated between the atoms at the apex of the probe and the atoms on the surface of the object is measured. , Bend the cantilever. The distance between the probe and the object to be measured is controlled so that the amount of deflection is constant (tracking control), and a control signal is taken out as a scanning position signal indicating the position of the probe, and the surface of the object to be measured is extracted. An image is formed.

  In Patent Document 1, the amount of deflection of the cantilever is detected by tunnel current detection, but the optical lever method is also common as a conventional technique. That is, a mirror surface that reflects laser light is formed on the back surface of the cantilever. In the displacement measurement optical system, a laser diode that emits a laser beam toward the mirror surface and a two-divided light receiver that receives the laser beam from the mirror surface on the cantilever are installed. The two-divided light receiver has two light receiving areas, and is arranged so that the center of the laser beam from the mirror surface is irradiated to the boundary between the two light receiving areas when the cantilever is in the reference state at the time of measurement. Since the two light receiving regions output voltage signals according to the intensity of the received light, the inclination of the mirror surface, that is, the displacement of the cantilever can be measured by examining the output difference.

  In an atomic force microscope, a DC mode that scans with the probe in contact with the object to be measured and an object to be measured are scanned while vibrating an elastic mechanism represented by a cantilever at a constant frequency and amplitude. There is an AC mode that measures changes in amplitude, phase, and frequency.

  A portion including an elastic mechanism represented by a cantilever that supports a probe and a base is called a probe. In order to accurately detect the atomic force in the AC mode, it is desirable that the amplitude, phase, and frequency changes sensitively correspond to the atomic force between the probe and the object to be measured. It is necessary that the Q value of is high. A cantilever with a probe formed at the tip of a thin film flat plate cannot follow the fluid velocity between the probe and the object to be measured, and exhibits a large resistance due to the squeeze effect. In addition, the viscosity of the surrounding fluid alone is a great resistance. This resistance becomes a damping effect, and the Q value of the probe natural frequency decreases.

  As an improvement measure against this, in the probe disclosed in Patent Document 2, a through hole is provided in the cantilever tip region so that the fluid between the probe and the object to be measured can be easily passed, thereby reducing the squeeze effect. The Q value of the natural frequency of the probe is increased.

  Moreover, in the probe disclosed by patent document 3, the protruding item | line part is formed in the single side | surface or both surfaces which oppose the to-be-measured object of a cantilever. By configuring in this way, when the cantilever vibrates, the surrounding fluid smoothly flows along the ridges, and the resistance is reduced, thereby increasing the Q value of the probe natural frequency.

JP-A-62-130302 JP 2004-198134 A JP 2006-145510 A JP-A-10-282130

  However, although the fluid resistance can be reduced in the above conventional example, since the cantilever moves so as to push away the surrounding fluid, a fundamental solution has not been reached. That is, in Patent Document 2, the squeeze effect at the tip is reduced by the through-hole, but the plate portion and many flexible beam portions ahead of the through-hole have a large fluid resistance due to fluid exclusion and separation flow due to movement during vibration. Will receive.

  Further, in Patent Document 3, since the cross section of the flexible beam portion of the cantilever is circular or curved, the fluid resistance due to fluid exclusion due to movement during vibration can be reduced, but the separation flow is also eliminated. Therefore, the fluid resistance at the flexible beam portion remains. In addition, in order to achieve more effects, when the cross section of the flexible beam part is circular or curved on both the opposite surface and the opposite surface, the direction facing the object to be measured and the horizontal direction The natural frequencies of these coincide or are close to each other. Therefore, there are unsolved problems that separation becomes difficult and measurement error increases.

  An object of the present invention is to provide an atomic force microscope and a probe having a probe with a high Q value of natural frequency and a high response resolution with respect to the unevenness of the surface of the object to be measured, with reduced surrounding fluid resistance. To do.

  In order to solve the above problems, the atomic force microscope of the present invention detects an atomic force when a probe placed at the tip of a probe and an object to be measured are brought close to each other, and the atomic force is constant. In the atomic force microscope that acquires the surface shape information of the object to be measured by scanning while maintaining the above, the probe includes a rotating body having a circular cross section, and a support member that rotatably supports the rotating body, And the probe is fixed to a circumferential surface of the rotating body.

  The probe of the present invention detects the atomic force when the probe and the object to be measured are approached, and acquires the surface shape information of the object to be measured by scanning while keeping the atomic force constant. An atomic force microscope probe, comprising: a rotating body having a circular cross section; and a support member that rotatably supports the rotating body, wherein the probe is fixed to a circumferential surface of the rotating body. Features.

  According to the above configuration, the fluid resistance during driving is reduced in the AC mode in which the object to be measured is scanned while vibrating the probe with a constant frequency and amplitude, and changes in the amplitude, phase, and frequency are measured. A probe having a very high natural frequency Q value can be realized. Thereby, it is possible to provide an atomic force microscope having a high response resolution with respect to the unevenness of the surface of the object to be measured.

  By resonating and vibrating a vibrating portion including a circular rotating body serving as a base on which the probe is installed at a constant frequency, the probe can be reciprocated with a simple mechanism based on the rotational movement of the rotating body.

  When the center axis of the probe is made to coincide with the center axis of the rotating body, the movement of the probe becomes substantially horizontal with the object to be measured as the rotating body rotates, and between the probe and the object to be measured. With frictional force. However, when the center axis of the probe is arranged in a spatial torsional positional relationship with respect to the center axis of the rotating body, the movement of the probe due to the rotation of the rotating body is in the substantially vertical direction of the object to be measured. The frictional force is not generated.

  In addition, by providing a diffraction grating on the surface of the rotating body having a circular cross section, the position of the first-order diffracted light obtained by irradiating light can be obtained as the angular displacement of the rotating body. Make it possible.

  By scanning the object to be measured with such a probe and performing tracking control so that, for example, changes in amplitude, phase, and frequency are constant, highly accurate surface shape information can be acquired.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a perspective view showing a probe 10 according to an embodiment. A pair of support beams 12 and 13 which are support members protrude from the probe base 11, and between them, elastic bodies 14 and 15 having a circular cross section, a rotary body 17 having a circular cross section, and a probe fixed thereto. An elastic mechanism (vibrating portion) 18 constituted by 16 is coupled. The probe 16 is fixed to the circumferential surface of the rotating body 17 and vibrates with the reciprocating rotation of the rotating body 17. The natural frequency of the probe 10 is configured so that the mass of the lowest mode is the rotating body 17 and the elastic constant is determined by the torsional rigidity of the elastic bodies 14 and 15. Therefore, the probe 16 can be vibrated by applying vibration from the outside of the probe at a predetermined constant frequency.

  FIG. 2 is a schematic diagram for explaining the operation and action of the atomic force microscope according to the present embodiment. The probe (including the probe base 11, the support beams 12 and 13, the probe 16, the rotating body 17, and the like) having the above-described configuration is connected to the excitation piezo 21 and has a predetermined frequency with respect to the object 20 to be measured. Can be vibrated. Thereby, the probe 16 can be vibrated by torsionally vibrating the elastic mechanism 18. The vibration piezo 21 is connected to a Z scanner 23 via a probe mounting base 22. The Z scanner 23 is made of a cylindrical piezoelectric element, and electrodes (not shown) are formed on the inner and outer surfaces of the cylinder. By applying a voltage to this, it is possible to expand and contract in the cylindrical axis direction.

  The Z scanner 23 is connected to the XY scanner 25 via the scanner connecting member 24. The XY scanner 25 is an orthogonal minute displacement mechanism composed of an elastic hinge and a driving piezoelectric element, and can be displaced in two axial directions within a plane perpendicular to the displacement direction of the Z scanner 23. In order to measure the rotation angle of the probe 16, laser light is irradiated onto the rotating body 17 from the laser light source 26, and the reflected light is guided to the photodiode 28 via the folding mirror 27. The angular displacement of the rotator 17 can be measured on the photodiode 28 by partially cutting away the circumferential surface of the rotator 17 to form a reflecting surface or forming a diffraction grating.

  This probe detects an attractive force or repulsive force when the probe 16 installed at the tip and the object to be measured 20 are brought close to each other, and scans while keeping the force (interatomic force) constant, thereby measuring the object to be measured. 20 surface shapes are obtained.

  The portion where the probe 16 is installed is composed of a rotary member 17 having a circular cross section, and the probe 16 is driven by the rotational movement of the rotary member 17. Since there is no movement to push away the fluid that moves the flat plate in the fluid, the fluid resistance can be greatly reduced.

  Both ends of the rotator 17 are rotatably connected to the support beams 12 and 13 by elastic bodies 14 and 15 having circular cross sections. Surface shape information is acquired by scanning the object to be measured 20 in a state where the elastic mechanism 18 constituted by the rotating body 17 and the elastic bodies 14 and 15 is torsionally vibrated at a constant frequency.

  In this way, both ends of the rotating body 17 are supported by the elastic bodies 14 and 15 having a circular cross section, and if a vibration is applied to the elastic mechanism 18 composed of the elastic bodies 14 and 15 and the rotating body 17 from the outside, a constant frequency is obtained. Torsional vibration. If the torsional vibration is near the natural frequency of the elastic mechanism 18, the amplitude can be increased, and a large movement of the probe 16 can be obtained by a simple method.

  The central axis of the probe 16 that scans the surface of the object to be measured is arranged at a position that does not intersect the central axis of the rotating body 17 that becomes a base on which the probe 16 is installed, that is, a so-called spatial twist position. By adopting such a positional relationship, the movement of the probe 16 due to the torsional vibration of the elastic mechanism 18 can be set in the substantially vertical direction of the object 20 to be measured.

  The angular displacement of the rotating body 17 may be obtained from the first-order diffracted light by irradiating the diffraction grating provided on the surface of the rotating body 17 with light.

  In FIG. 2, when the probe 16 approaches the object to be measured 20, an attractive force such as van der Waals force acts at a long distance, and a repulsive force acts at a short distance of about the atomic bond distance.

  The atomic force microscope has several modes, and typical modes are described below. The contact mode operates in the above repulsive force region and is used in a state where the probe is in contact with the object to be measured. In the non-contact mode, on the contrary, scanning is performed at a distance where the probe does not always contact the object to be measured. In this case, there are a DC mode in which the probe is not vibrated and an AC mode in which the probe is forcibly vibrated by a vibrating piezoelectric element and relatively close to and away from the object to be measured. In addition, as a compromise between the contact mode, which has high resolution but may damage the probe and the object to be measured, and the non-contact mode, which generally has poor resolution, the probe that is forced to vibrate is partially brought into contact. There is a tapping mode that reduces the possibility of damage.

  The above three modes are the movements of the probe in the direction perpendicular to the object to be measured, but there is a torsion mode in which the probe is vibrated in parallel with the object to be measured and the frictional force and the like are measured.

  The probe and the atomic force microscope of the present invention can exhibit the effect in any of the above modes in the AC mode in which the probe is vibrated, but here, the tapping mode will be mainly described.

  In FIG. 2, first, the natural frequency of the probe is obtained by frequency sweeping the vibration piezo 21. The amplitude measuring means is an optical lever method composed of a laser light source 26, a folding mirror 27, and a photodiode 28.

  As shown in FIG. 3, the rotating body 17 is formed with a diffraction grating 17a on the cylindrical surface (circumferential surface) where the inclination of the grating changes with the rotation angle. This is irradiated with laser from the laser light source 26. Further, the first-order diffracted light of the incident light is guided to the photodiode 28. By doing so, the first-order diffracted light moves on the photodiode 28 by the rotation of the rotating body 17. Therefore, the rotation angle of the rotator 17 is enlarged by the length of the optical path and can be measured on the photodiode 28.

  Further, as shown in FIG. 4, a reflecting surface 17 b may be formed on a part of the circumferential surface of the rotating body 17.

  The probe displacement measuring means may be a method of measuring the angular displacement by disposing a piezoresistor on a part of an elastic body serving as a rotational axis of torsional vibration, as described in Patent Document 4. With this configuration, the probe itself is complicated, but the optical lever measurement system is unnecessary, so the overall configuration is simplified and optical axis alignment is also unnecessary.

  When measuring the shape of the object 20 to be measured, the excitation piezo 21 is driven at a frequency in the vicinity of the obtained primary natural frequency of the probe. It is possible to obtain a large torsion angle by designing the primary natural frequency of the probe to be a frequency determined by the mass of the rotating body 17 and the torsion spring constant of the elastic bodies 14 and 15.

  Here, as shown in FIG. 5B, if the rotation center axis of the rotator 37 and the center axis of the probe 36 are arranged to intersect, measurement in the torsion mode is possible. However, in the present embodiment, as shown in FIG. 5A, the rotation axis of the rotating body 17 and the center axis of the probe 16 do not intersect with each other, that is, are arranged in a spatial relationship of spatial twist. For this reason, since the probe 16 vibrates in the vertical direction of the DUT 20 by the rotation of the rotating body 17, measurement in the tapping mode is possible.

  When the probe 16 vibrates in the vertical direction of the object 20 to be measured, an attractive force such as van der Waals force acts at a long distance as described above, and a repulsive force acts at a short distance of about the atomic bond distance as described above. . For this reason, when the vibration piezo 21 is driven while keeping the position of the probe and the DUT 20 constant, the frequency and amplitude change depending on the position of the probe 16 even if the frequency and amplitude are constant. To do. Therefore, the XY scanner 24 scans in a plane parallel to the measured object 20 so that the amount of change in frequency or amplitude is constant, and performs tracking control of the Z scanner 22 according to the unevenness of the measured object 20. Thus, the surface shape of the DUT 20 can be obtained.

  On the other hand, a probe used in a conventional atomic force microscope has a probe formed at the tip of a flat cantilever called a cantilever. For this reason, when the probe is vibrated, it moves at high speed so that the flat plate cantilever crosses the surrounding stationary fluid (air in the atmosphere, environmental liquid in the liquid). As a result, a separation flow is generated behind the flat plate cantilever in the vibration traveling direction, resulting in a large fluid resistance. Since this fluid resistance is proportional to the velocity of the flat plate cantilever, it becomes a viscous term in the equation of motion, and the amplitude of vibration near the natural frequency is reduced. Further, the fluid between the probe and the object to be measured cannot follow the movement of the flat plate cantilever, and is compressed when approaching and expanded when leaving. Even with this squeeze effect, the viscous resistance becomes large. These causes are mainly due to the fact that the flat plate cantilever vibrates at high speed in the fluid because the probe itself is small. Therefore, the conventional probe essentially has the effect of reducing the Q value of the natural frequency in the fluid, and can increase the Q value of the natural frequency only in a limited environment such as in a vacuum.

  On the other hand, the probe of the present invention is a rotational movement of a rotating body having a circular cross section, and unlike a conventional flat plate cantilever, it does not essentially move to cause a separation flow or a squeeze effect. Therefore, the viscous resistance is negligible, and the Q value of the natural frequency can be increased even in a fluid such as air or liquid. As a result, the amplitude, phase, and frequency change sensitively in response to changes in the atomic force between the probe and the object to be measured, and measurement with high detection resolution can be performed.

  In addition to the method of manufacturing the probe integrally by ion beam processing, for example, the elastic mechanism 18 in FIG. 1 and the portion including the probe base 11 and the support beams 12 and 13 are separately provided for manufacturing the probe of this embodiment. And may be joined together.

  Further, although the embodiment by the torsional vibration having a simple configuration has been described, the portion corresponding to the elastic mechanism 18 in FIG. 1 is rotatable with respect to the support beams 12 and 13, and reciprocating rotation (vibration) motion is performed by external driving. It may be allowed.

It is a perspective view which shows the probe by one Embodiment. It is a schematic diagram which shows the atomic force microscope using the probe of FIG. It is a figure which shows the measuring method which displaces a probe. It is a figure which shows another method of measuring the displacement of a probe. It is a figure explaining arrangement | positioning of a probe.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Probe base 12, 13 Support beam 14,15 Elastic body 16 Probe 17 Rotating body 18 Elastic mechanism 20 Measured object 21 Piezo for vibration 22 Probe mounting base 23 Z scanner 24 Scanner connection member 25 XY scanner 26 Laser light source 27 Folding mirror 28 Photodiode

Claims (5)

By detecting the interatomic force when the probe placed at the tip of the probe and the object to be measured are approached, and scanning while keeping the atomic force constant, the surface shape information of the object to be measured is acquired. In the atomic force microscope that
The probe is
A rotating body having a circular cross section;
A support member that rotatably supports the rotating body,
An atomic force microscope, wherein the probe is fixed to a circumferential surface of the rotating body.   Both ends of the rotating body are respectively connected to the support member by elastic bodies having a circular cross section, and by scanning the probe while torsionally vibrating a vibrating portion constituted by the rotating body and the elastic body at a constant frequency 2. The atomic force microscope according to claim 1, wherein surface shape information of the object to be measured is acquired.   The atomic force microscope according to claim 1, wherein the central axis of the probe is in a positional relationship of spatial twist with the central axis of the rotating body.   2. The atomic force microscope according to claim 1, wherein the angular displacement of the rotating body is obtained by irradiating light to a diffraction grating provided on the rotating body and using the first-order diffracted light. An atomic force microscope probe that detects the interatomic force when the probe and the object to be measured are brought close to each other, and obtains surface shape information of the object to be measured by scanning while keeping the atomic force constant. In
A rotating body having a circular cross section;
A support member that rotatably supports the rotating body,
A probe characterized in that the probe is fixed to a circumferential surface of the rotating body.

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