JP2007086083A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning probe microscope capable of increasing the rigidity of an XY fine movement mechanism without narrowing a scanning region, improving the scanning speed and reducing the size of the apparatus.
An XY fine movement mechanism 6 provided on the cantilever side for moving a cantilever 1 having a probe 1a at a tip two-dimensionally in a direction parallel to the surface of a sample 2, and a sample holder 13 on which a sample is placed. An XY fine movement mechanism 12 provided on the sample holder side for two-dimensional movement in the direction parallel to the surface is provided.
[Selection] Figure 1

Description

  The present invention relates to a scanning probe microscope for measuring unevenness information and physical properties of a surface of a sample.

  Here, the scanning probe microscope is a general term for a device that scans the surface of a sample with a probe and detects physical information acting between the probe and the sample. As a typical scanning probe microscope, an atomic force is used. There are microscopes, scanning tunneling microscopes, scanning magnetic force microscopes, scanning near-field microscopes, and the like.

  Based on FIG. 6, the conventional structure and operation principle of a contact-type atomic force microscope, which is a kind of scanning probe microscope, will be described. In the following description, the X axis and the Y axis are taken in the directions orthogonal to each other in the two-dimensional plane of the sample surface, and the Z axis is taken in the direction perpendicular to the XY plane.

  A cantilever 101 having a minute probe 101a at the tip is placed on the cantilever holder 102, and the cantilever holder 102 is attached to the tip of a three-axis fine movement mechanism 103 composed of a cylindrical piezoelectric element. The XY coarse movement stage 105 for positioning the measurement location is provided on the side facing the cantilever 101, and the sample 107 is placed on the sample holder portion 106 provided on the stage. While the cantilever 101 is brought close to the sample 107 and scanned in the XY plane by the XY fine movement mechanism 103a, the amount of bending of the cantilever 101 due to the atomic force acting between the probe 101a and the surface of the sample 107 is reduced by an optical lever. The sample is detected by the used displacement detection means 108 so that the amount of deflection is always constant. The distance between the surface and the probe performs control by the Z fine movement mechanism 103b, to obtain unevenness information of the sample from the application of voltage to the Z fine movement mechanism 103b, and subjected to measurement of topographic image of the sample surface.

  However, the conventional scanning probe microscope has a problem that the scanning speed of the cantilever is slow and it takes time to measure.

  Factors governing the scanning speed can be related to mechanical factors and electrical control systems.

  Considering mechanical factors, since the relative movement is performed between the XY fine movement mechanism, the Z fine movement mechanism, and the cantilever during scanning of the cantilever, the rigidity of these elements greatly affects the scanning speed.

  In a general scanning probe microscope, the resonance frequency of a cantilever is about several hundred kHz, and the most commonly used Z fine movement mechanism composed of a cylindrical piezoelectric element having a moving distance on the order of several μm. Although the resonance frequency is relatively high at several tens of kHz, the XY fine movement mechanism is an order of several hundred Hz to several kHz at most, even with an actuator having a displacement of several tens of μm using a cylindrical piezoelectric element. Rigidity is lower than that of one element, causing a reduction in scanning speed.

  The scanning area of current scanning probe microscopes is generally about several tens of μm, but there are many demands for increasing the scanning area for the purpose of measuring large samples. However, since the resonance frequency of the XY fine movement mechanism is further reduced by increasing the scanning region, the scanning speed is further decreased.

  In addition, when the scanning area is increased, the XY fine movement mechanism generally increases in size and often cannot fit in the required space, and the apparatus tends to increase in size.

  Therefore, an object of the present invention is to increase the rigidity of the XY fine movement mechanism without narrowing the scanning area, thereby improving the scanning speed and reducing the size of the apparatus.

  In order to solve the above problems, in the scanning probe microscope of the present invention, a cantilever having a microprobe at the tip, a cantilever holder for holding the cantilever, a displacement detection means for detecting the amount of displacement of the cantilever, A sample holder unit for placing a sample, a Z fine movement mechanism that changes a relative distance between the probe and the sample, and an XY fine movement mechanism that relatively scans the sample and the cantilever in a two-dimensional plane. The XY fine movement mechanism was provided on both the sample side and the cantilever side. In these two XY fine movement mechanisms, both the XY fine movement mechanisms were operated independently, and the probe and the sample were relatively scanned.

  Furthermore, in order to detect the relative position between the cantilever and the sample with higher accuracy, at least one of the XY fine movement mechanisms provided on both the sample side and the cantilever side is provided with a displacement detector having two or more axes, A control device is provided for monitoring the amount and controlling the displacement so as to maintain linearity with respect to the drive signal of the fine movement mechanism.

  By configuring the scanning probe microscope in this way, the amount of movement required for each XY fine movement mechanism is halved compared to the prior art, and the XY fine movement mechanism can be miniaturized and increased in rigidity. As a result, the scanning speed can be increased and the scanning time is shortened.

  Further, the movement amount of each XY fine movement mechanism is ½ of the required movement amount when the scanning speeds of the two XY fine movement mechanisms are equal, and even when the speeds are different, the two XY fine movement mechanisms are simultaneously moved. Since scanning is performed, the amount of movement is smaller than in the case of one XY fine movement mechanism, and as a result, the scanning time is shortened.

  In addition, since the required amount of movement is smaller than in the case of one fine movement mechanism, the XY fine movement mechanism is miniaturized, and a scanning probe microscope can be installed in a limited space.

  In the scanning probe microscope configured as described above, the scanning operation will be described with reference to FIG. In FIG. 7, the X axis and the Y axis are taken in directions orthogonal to each other in a plane including the surface of the sample 71, and the Z axis is taken in a direction perpendicular to the XY plane. Consider a case where the origin 0 is set at the center of the scanning area, and an area having a side of a is scanned from point A on the sample surface as indicated by an arrow. The XYZ coordinates are absolute coordinates set in the space, and the coordinate origin is not changed even when the sample or the cantilever is scanned.

  First, at the start of scanning, the probe 72a is moved to X = −a / 2 and Y = a / 2 by the XY fine movement mechanism 73 on the cantilever 72 side, and the sample 71 is moved to X = a / by the XY fine movement mechanism 74 on the sample 71 side. 2. Move to Y = −a / 2.

  In the scanning of the first line, the X coordinate on the cantilever side is continuously moved from −a / 2 to 0, and the X coordinate on the sample side is continuously moved from a / 2 to 0 in the direction opposite to the cantilever side. By this scanning, a line of length a on the sample surface is scanned. When the scanning of one line in the X direction is completed, the XY fine moving mechanism 73 on the cantilever 72 side is moved in the −Y direction, and the XY fine moving mechanism 74 on the sample 71 side is moved in the + Y direction, thereby scanning the next line. . By repeating such an operation until the Y coordinate on the cantilever side is 0 and the Y coordinate on the sample side is 0, the a × a region on the sample surface is scanned.

  The operation in the Y-axis direction will be described in more detail with reference to FIG. The numbers in FIG. 8 indicate the order of the scanning lines, the black circle on the solid line indicates the scanned line in the Y-axis section of the sample, and the white circle indicates the line being scanned. In the case where only one conventional XY fine movement mechanism is provided, the predetermined scanning region a cannot be scanned unless the probe indicated by the broken line is scanned, but the sample side and the cantilever side are indicated by arrows in the figure. By moving in the opposite direction as shown, the area a on the sample surface is scanned by displacing each fine movement mechanism by a / 2. However, as regards scanning in the Y-axis direction, when scanning is performed at the same pitch interval as when scanning is performed with the XY fine movement mechanism attached to only one of the cantilever side and the sample side as conventionally performed, the resolution, that is, the scanning line Since the number is ½, the pitch needs to be halved in order to obtain the same resolution as the conventional one. Therefore, the amount of movement required for the fine movement mechanism in the Y-axis direction may be half that of the conventional method, but in order to obtain the same resolution as the conventional method, double line scanning is required. Is the same.

  Using such a scanning method, the displacement of the cantilever is monitored, and each XY fine movement mechanism is raster scanned while the Z fine movement mechanism is servo-operated so that the displacement is constant. An image is obtained.

  In the present invention, the following effects can be obtained by the above method.

  (1) The amount of movement required for each fine movement mechanism is half that of the prior art, and the XY fine movement mechanism is miniaturized and the rigidity is increased.

  (2) Since the rigidity is increased, the scanning speed in the X direction can be increased, and the scanning time is shortened.

  (3) Since the scanning distance in the X direction of each fine movement mechanism is halved, the scanning time is halved.

Embodiments of the present invention will be described below with reference to the drawings.
(1) First Embodiment FIG. 1 is a schematic diagram of a first embodiment of the scanning probe microscope of the present invention, and FIG. 2 is a block diagram showing an operation method of the scanning probe microscope of FIG. . This embodiment relates to a contact-type atomic force microscope which is a kind of scanning probe microscope.

  In FIG. 1, a Z axis is taken in the direction in which the probe 1a and the sample 2 are brought close to each other, and an X axis and a Y axis are taken in directions perpendicular to each other in the plane of the sample surface. An XYZ fine movement mechanism 8 in which an XY fine movement mechanism 6 and a Z fine movement mechanism 7 are integrally formed by a cylindrical piezoelectric element is fixed on a Z coarse movement stage 5 constituted by a ball screw 3 and a stepping motor 4. A cantilever holder 9 is attached to the tip of the XYZ fine movement mechanism 8, and the cantilever 1 is fixed to the cantilever holder 9. The displacement of the cantilever 1 is detected by a small optical lever optical system 10 built in the cantilever holder 9. The optical lever optical system is a system in which laser light from a semiconductor laser 10a is bent by a beam splitter 10b and applied to the back surface of the cantilever 1, and reflected light is detected by a detector 10d via a mirror 10c.

  On the other hand, an XY stage 11 for coarse movement at the sample position is disposed on the side facing the cantilever 1, an XY fine movement mechanism 12 is fixed on the XY stage 11, and a sample 2 is placed on a sample holder 13 provided on the XY fine movement mechanism 12. Was placed. The XY fine movement mechanism 12 is a system in which a stainless steel plate is processed to constitute a displacement expansion mechanism using an elastic hinge, and the displacement expansion mechanism is driven by a laminated piezoelectric element.

  In the scanning probe microscope configured as described above, the cantilever 1 is brought close to the sample 2 to the region where the atomic force acts by the Z coarse movement stage 5. Next, in the X-axis direction, the two X-fine movement mechanisms 6a and 12a are scanned in opposite directions, and after one line measurement is completed, the Y-fine movement mechanisms 6b and 12b are moved in opposite directions in the Y-axis direction. Then, after moving to the adjacent line, the probe 1a is raster-scanned on the sample surface while repeating the operation of scanning the two X fine movement mechanisms 6a and 12a in opposite directions with respect to the X-axis direction again. At this time, the optical lever optical system 10 detects the displacement of the cantilever 1, and controls the Z fine movement mechanism 7 by applying a voltage so that the displacement amount becomes constant. Since the displacement amount of the cantilever 1 depends on the interatomic force acting between the probe 1a and the sample 2, and this interatomic force depends on the distance between the probe and the sample surface, from the voltage applied to the Z fine movement mechanism 7, Uneven information on the sample surface can be obtained.

On the other hand, the XY fine movement mechanisms 6 and 12 obtain the displacement amount with respect to the absolute coordinate from the voltage signal applied to each fine movement mechanism. This displacement amount is input to the computer, and the relative coordinates between the sample 2 and the probe 1a are obtained.

  The relative coordinates and the voltage signal applied to the Z fine movement mechanism 7 are stored in a computer, and the unevenness information on the sample surface is obtained by mapping on the three-dimensional coordinates.

Here, the displacement amounts of the XY fine movement mechanisms 6 and 12 and the displacement amount of the Z fine movement mechanism 7 were calibrated by obtaining the relationship between the voltage signal applied to each actuator and the displacement prior to measurement. Therefore, the amount of displacement of each fine movement mechanism can be obtained from the voltage signal applied to the actuator.

In this scanning probe microscope, since the scanning area required for each XY fine movement mechanism 6, 12 may be half of the required scanning area, the XY fine movement mechanisms 6, 12 are downsized and the rigidity is improved. did. As a result, the scanning speed can be increased. Further, since the amount of displacement of each XY fine movement mechanism when scanning one line in the X direction is halved, the time required for scanning is shortened.
(2) Second Embodiment FIG. 3 is a schematic diagram of a second embodiment of the scanning probe microscope of the present invention, and FIG. 4 is a block diagram showing an operation method of the scanning probe microscope of FIG. .

  In this embodiment, in the first embodiment, displacement sensors 14 and 15 (sample side) of the electrostatic capacity method are provided on the two axes of the XY fine movement mechanism 6 on the cantilever 1 side and the two axes of the XY fine movement mechanism 12 on the sample 2 side. In addition, a displacement sensor in the Y-axis direction is not shown on the cantilever side, and the displacement of each XY fine movement mechanism is detected, and the displacement instructed by the computer is controlled in a closed loop. A relative positional relationship between the probe 1 and the sample 2 was calculated from the respective displacements at that time by a computer, and the uneven shape of the sample was measured. Further, the displacement amount measured with the electrostatic capacity type displacement sensor 16 was also inputted to the computer for the Z axis on the cantilever side. An uneven image on the sample surface can be obtained from the position information.

In general, a fine movement mechanism using a piezoelectric element causes errors due to hysteresis, creep, and the like, but the linearity of XYZ is improved by the scanning probe microscope configured as described above than in the first embodiment.
(3) Third Example FIG. 5 is a schematic view of a third example of the scanning probe microscope of the present invention.

  In this embodiment, an XY fine movement mechanism 54 for a sample 53 is arranged on a stage 52 of a commercially available inverted microscope 51, and a stand-alone scanning probe microscope 55 is mounted thereon, and an inverted microscope integrated scanning probe. A microscope was constructed.

  Similar to the first embodiment, the sample XY fine movement mechanism 54 includes an elastic hinge mechanism and a laminated piezoelectric element.

  In a stand-alone scanning probe microscope, a triaxial fine movement mechanism 57 composed of a cylindrical piezoelectric element is installed on a base plate 56, a cantilever holder 58 is attached to the tip of the triaxial fine movement mechanism 57, and the base plate 56 is attached to the base plate 56. One column 59a is extended and contracted by the stepping motor 60, and the cantilever 61 is brought close to the sample 53 by lever movement. As in the first embodiment, the cantilever 61 is displaced by attaching a small optical head 62 using an optical lever system to the tip of the triaxial fine movement mechanism 57. The three-axis fine movement mechanism has a hollow interior, can irradiate the sample with light from the illumination 63, and can observe an optical microscope image.

  The scanning probe microscope of this example is mainly used for observing biological samples such as cells, and a general fluorescence microscope image and an atomic force microscope image with higher resolution than the fluorescence microscope image are observed with the same device. It is a possible device. A scanning probe microscope for a biological sample is required to scan a wide area as compared with other applications, so that the XY fine movement mechanism is large, has low rigidity, and tends to be slow in scanning speed. Further, since the scanning probe microscope is configured in a limited area on the stage of the inverted microscope, the size of the XY fine movement mechanism is limited, and it is necessary to make it as small as possible.

By configuring the scanning probe microscope on the inverted microscope as described above, these problems were improved.
(4) Other Embodiments In addition to the embodiments described above, while the cantilever is vibrated near the resonance frequency, the probe is brought closer to the sample surface, and the amplitude due to the interaction between the probe and the sample surface The vibration mode atomic force microscope with a method of measuring the unevenness image of the sample surface and other physical properties, controlling the distance between the sample and the probe so as to always maintain a constant amplitude, Using a conductive probe, a bias voltage is applied between the sample and the probe, and the tunnel current when the probe is brought close to the sample is monitored to control the distance between the sample and the probe. Scanning tunnel microscope that measures uneven images and other physical characteristics, or scanning proximity using a probe with a tip of an optical fiber processed into a probe shape and an opening with a diameter less than the wavelength at the tip The present invention can be applied to all microscopes generally called a scanning probe microscope, such as a field microscope.

  The structure of the fine movement mechanism is not limited to the cylindrical piezoelectric element described in the above embodiment, the combination of the elastic hinge mechanism and the laminated piezoelectric element, the fine movement mechanism using a voice coil, and the electric motor drive. All of the fine movement mechanisms used for the purpose of fine movement in the XY plane, such as the mechanical stage, are included, and combinations thereof are also arbitrary.

  Further, any displacement sensor such as a strain gauge or a laser displacement meter can be used as the displacement sensor incorporated in the fine movement mechanism.

  Further, the displacement detection method of the cantilever or probe is not limited to the optical lever method described in the above embodiment, and the displacement is detected from the interference waveform between the incident light and its return light by irradiating the cantilever or probe with laser light. There are also optical interference methods that are used, piezoelectric methods such as attaching a piezoelectric body to a cantilever or probe, causing the cantilever or probe to bend due to physical characteristics, and converting the amount of charge from the piezoelectric body to electrically detect displacement It is included in the present invention.

  The scanning method of the present invention is not limited to the raster scan, and the cantilever-side XY fine movement mechanism and the sample-side XY fine movement mechanism can be operated independently at arbitrary speeds at arbitrary speeds. When such an arbitrary operation is performed, each XY fine movement mechanism is controlled by causing a computer to calculate an optimal operation method from a relative trajectory of a sample and a probe given in advance.

It is the schematic of the 1st Example of the scanning probe microscope of this invention. It is a block diagram which shows the operating method of the scanning probe microscope of FIG. It is the schematic of the 2nd Example of the scanning probe microscope of this invention. FIG. 4 is a block diagram illustrating an operation method of the scanning probe microscope of FIG. 3. It is the schematic of the 3rd Example of the scanning probe microscope of this invention. It is the schematic of a conventional scanning probe microscope. It is explanatory drawing explaining the scanning method of the scanning probe microscope of this invention. It is explanatory drawing explaining the scanning method of a Y-axis direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cantilever 2 Sample 5 Z coarse movement stage 6 XY fine movement mechanism 7 Z fine movement mechanism 9 Cantilever holder 10 Optical lever optical system 12 XY fine movement mechanism 13 Sample holder 14 X-axis displacement sensor 15 X-axis displacement sensor 16 Z-axis displacement sensor 53 Sample 54 XY fine movement mechanism 57 XYZ fine movement mechanism 58 Cantilever holder 61 Cantilever 62 Optical lever optical system 64 Sample holder 71 Sample 72 Cantilever 73 XY fine movement mechanism 74 XY fine movement mechanism 75 Sample holder 101 Cantilever 102 Cantilever holder 103a XY fine movement mechanism 103b Z fine movement mechanism 104Z Coarse stage 106 Sample holder 107 Sample 108 Optical lever optical system

Claims (5)

A cantilever with a tip at the tip;
A sample holder on which the sample is placed;
A first XY fine movement mechanism provided on the cantilever side for two-dimensionally moving the cantilever in a plane direction substantially parallel to a plane in which the sample surface substantially exists;
A scanning probe microscope comprising: a second XY fine movement mechanism provided on the sample holder side for moving the sample holder two-dimensionally in a plane direction substantially parallel to a plane on which the sample surface substantially exists.   In the two XY fine movement mechanisms, both the XY fine movement mechanisms are moved in an arbitrary locus in a two-dimensional plane with independent trajectories and independent speeds, and the probe and the sample are relatively scanned. The scanning probe microscope according to claim 1.   At least one of the two XY fine movement mechanisms is provided with a displacement detector having two or more axes, the displacement amount of the XY fine movement mechanism is monitored, and the displacement amount is linear with respect to the drive signal of the XY fine movement mechanism. The scanning probe microscope according to claim 1, further comprising a control device that performs control so as to maintain the above.   The scanning probe microscope according to any one of claims 1 to 3, wherein the scanning probe microscope is operated as a scanning tunneling microscope using a metal probe instead of the cantilever.   4. The method according to claim 1, wherein the cantilever is operated as a scanning near-field microscope using any one of a waveguide probe using a metallic probe or an optical fiber and a waveguide cantilever instead of the cantilever. The scanning probe microscope according to one item.

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