JP2001116677A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance rigidity of XY slow motion mechanisms, to improve a scanning speed, and to miniaturize a device without narrowing a scanning area in a scanning probe microscope. SOLUTION: XY slow motion mechanisms 6, 12 of a scanning probe microscope are arranged on both the sample side and the cantilever side, both XY slow motion mechanisms 6, 12 are independently operated, and a probe 1a and a sample 2 are releatively scanned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope for measuring unevenness information and physical characteristics of a sample surface. Here, the scanning probe microscope is a general term for an apparatus that scans a sample surface with a probe and detects physical information that acts between the probe and the sample.
Typical scanning probe microscopes include an atomic force microscope, a scanning tunneling microscope, a scanning magnetic force microscope, a scanning near-field microscope, and the like.

[0002]

2. Description of the Related Art A conventional structure and operation principle of a contact type atomic force microscope which is a kind of a scanning probe microscope will be described with reference to FIG. In the following description, an X axis and a Y axis are set in directions orthogonal to each other in a two-dimensional plane of the sample surface, and a Z axis is set in a direction orthogonal to the XY plane.

A cantilever 101 having a small probe 101a at its tip is installed on a cantilever holder 102, and the cantilever holder 102 is a three-axis fine movement mechanism composed of a cylindrical piezoelectric element.
Attached to the tip of 103, attached to a Z coarse movement mechanism 104 that drives the three-axis fine movement mechanism in the center axis direction, and an XY coarse movement stage 105 for positioning a measurement point on the side facing the cantilever 101
And a sample holder section 106 provided on the stage.
Sample 107 is placed on cantilever 101 and sample 10
7, while scanning 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 detected by a displacement detecting means using an optical lever or the like. 108, the distance between the sample surface and the probe is controlled by the Z fine movement mechanism 103b so that the amount of deflection is always constant, and the unevenness information of the sample is obtained from the amount of voltage applied to the Z fine movement mechanism 103b. The measurement of the uneven image of the sample surface is performed.

[0004]

However, the conventional scanning probe microscope has a problem that the scanning speed of the cantilever is slow and the measurement takes a long time. Factors governing the scanning speed may be related to mechanical factors and electrical control systems.

Considering the mechanical factors, relative movement is performed between the XY fine movement mechanism, the Z fine movement mechanism and the cantilever during the scanning of the cantilever. Therefore, the rigidity of these elements greatly affects the scanning speed. . In a general scanning probe microscope, the resonance frequency of the cantilever is about several hundred kHz, and the most commonly used Z fine movement mechanism consisting of a cylindrical piezoelectric element with a moving distance on the order of several μm is used. Although the resonance frequency is relatively high at several tens of kHz, the XY fine movement mechanism can operate at a few hundred Hz at most even for an actuator with a displacement of several tens μm using a cylindrical piezoelectric element.
It is on the order of kHz and has lower rigidity than the other two factors, causing a reduction in scanning speed.

The scanning area of the current scanning probe microscope is generally about several tens of μm, but there are many demands to enlarge the scanning area for the purpose of measuring a large sample or the like. However, by increasing the scanning area,
Since the resonance frequency of the fine movement mechanism is lowered, the scanning speed is further reduced. Further, when the scanning area is enlarged, the XY fine movement mechanism generally becomes large, and in many cases, the XY fine movement mechanism cannot fit in the required space, and the apparatus tends to be large.

Accordingly, an object of the present invention is to increase the rigidity of the XY fine movement mechanism without narrowing the scanning area, improve the scanning speed, and reduce the size of the apparatus.

[0008]

In order to solve the above problems, a scanning probe microscope according to the present invention uses a cantilever having a fine probe at the tip, a cantilever holder for holding the cantilever, and a displacement amount of the cantilever. A displacement detecting means for detecting, a sample holder part for mounting the sample, a Z fine movement mechanism for changing a relative distance between the probe and the sample, and the sample and the cantilever in a two-dimensional plane relatively. The apparatus was composed of an XY fine movement mechanism that performs scanning by using the XY fine movement mechanism, and was provided on both the sample side and the cantilever side. In these two XY fine movement mechanisms,
The probe and sample were scanned relatively by independently operating the XY fine movement mechanism.

Further, in order to detect the relative position of 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.
The XY fine movement mechanism is equipped with a displacement detector with two or more axes, monitors the amount of displacement, and has a control device that controls the amount of displacement to maintain linearity with respect to the drive signal of the fine movement mechanism.

[0010]

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

First, at the start of scanning, the cantilever 72 side
The probe 72a is moved to X = −a / 2 and Y = a / 2 by the XY fine movement mechanism 73, and the sample 71 is moved to X = −a / 2 by the XY fine movement mechanism 74 on the sample 71 side.
Move to a / 2, 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 opposite direction to the cantilever side. This scanning scans a line of length a on the sample surface. When scanning of one line in the X direction is completed, the XY fine movement mechanism 73 on the cantilever 72 side is next.
Are moved in the −Y direction, and the XY fine movement mechanism 74 on the sample 71 side is moved in the + Y direction, and scanning of the next line is performed. By repeating such an operation and repeating scanning until the Y coordinate on the cantilever side is 0 and the Y coordinate on the sample side is 0, an 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 cross section of the sample, and the white circle indicates the line being scanned. When only one conventional XY fine movement mechanism was provided, the scanning area a could not be scanned unless the probe indicated by the broken line was scanned, but the sample side and the cantilever side were indicated by arrows in the figure. By moving in the opposite direction as shown, each fine movement mechanism
By displacing by two, the area a on the sample surface is scanned. However, with regard to scanning in the Y-axis direction, when scanning is performed at the same pitch interval as when scanning by attaching the XY fine movement mechanism only to either the cantilever side or the sample side as conventionally performed,
Since the resolution, that is, the number of scanning lines is halved, the pitch needs to be halved to obtain the same resolution as in the past. Therefore, the amount of movement required for the fine movement mechanism in the Y-axis direction may be half that of the conventional, but double line scanning is required to obtain the same resolution as in the past. Is the same as

Using such a scanning method, the displacement of the cantilever is monitored, and the XY fine movement mechanism is raster-scanned while the Z fine movement mechanism is servo-operated in the Z direction so that the displacement becomes constant. An uneven image of the surface is obtained. In the present invention, the following effects can be obtained by the above-described method. The amount of movement required for each fine movement mechanism is reduced to half of the conventional one, and the XY fine movement mechanism is reduced in size and rigidity is increased.

Since the rigidity is increased, the scanning speed in the X direction can be increased, and the scanning time can be shortened. Since the scanning distance in the X direction of each fine movement mechanism is halved,
The scanning time is halved.

[0015]

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 a scanning probe microscope.

In FIG. 1, the Z axis is taken in a direction in which the probe 1a and the sample 2 are brought close to each other, and the X axis and the Y axis are taken in directions orthogonal 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 composed of a ball screw 3 and a stepping motor 4. The 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 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 of a sample position is arranged on the side opposite to the cantilever 1, a XY fine movement mechanism 12 is fixed on the XY stage 11, and a sample holder 13 provided on the XY fine movement mechanism 12 is provided. The sample 2 was placed on the sample. The XY fine movement mechanism 12 is configured such that a stainless steel plate is processed to constitute a displacement magnifying mechanism using an elastic hinge, and the displacement magnifying 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 by the Z coarse movement stage 5 to the region where the atomic force acts.
Next, in the X-axis direction, the two X fine movement mechanisms 6a and 12a are scanned in opposite directions, and after the measurement of one line is completed, the Y fine movement mechanisms 6b and 12b are moved in the opposite direction in the Y-axis direction. After moving to the next 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 directions opposite to each other again in the X-axis direction. At this time, the optical lever optical system 10
, The displacement of the cantilever 1 is detected, and control is performed by applying a voltage to the Z fine movement mechanism 7 so that the displacement amount becomes constant. The amount of displacement of the cantilever 1 depends on the interatomic force acting between the probe 1a and the sample 2, and since 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,
Asperity information of the sample surface can be obtained.

On the other hand, in the XY fine movement mechanisms 6, 12, the displacement amount with respect to the absolute coordinates is obtained from the voltage signal applied to each fine movement mechanism. This displacement amount is input to a computer and sampled.
The relative coordinates between 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.

Prior to the measurement, the displacement amounts of the XY fine movement mechanisms 6 and 12 and the Z fine movement mechanism 7 were calibrated by obtaining the relationship between the voltage signal applied to each actuator and the displacement. 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, the scanning area required for each of the XY fine movement mechanisms 6 and 12 can be half the required scanning area, so the XY fine movement mechanisms 6 and 12 are downsized and the rigidity is improved. did. As a result, the scanning speed can be increased. Also, when scanning one line in the X direction,
Since the displacement of the XY fine movement mechanism is halved, the time required for scanning has also been reduced. (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, two axes of the XY fine movement mechanism 6 on the cantilever 1 side and two axes of the XY fine movement mechanism 12 on the sample 2 side are provided with displacement sensors 14 and 1 of the capacitance type.
5 (Displacement sensors in the Y-axis direction are not shown for both the sample side and cantilever side) are incorporated to detect the displacement of each XY fine movement mechanism and control the displacement amount specified by the computer in a closed loop. Was. The relative positional relationship between the probe 1 and the sample 2 was calculated by a computer from the respective displacement amounts at that time, and a method of measuring the uneven shape of the sample was adopted. In addition, the capacitance-based displacement sensor 16 was also incorporated into the Z-axis on the cantilever side, and the measured displacement was input to the computer. An uneven image of the sample surface can be obtained from these positional information.

In general, a fine movement mechanism using a piezoelectric element causes an error due to hysteresis or creep. However, the scanning probe microscope configured as described above has improved the XYZ linearity compared to the first embodiment. did. (3) Third Embodiment FIG. 5 is a schematic diagram of a third embodiment 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. A scanning probe microscope was configured. The XY fine movement mechanism 54 for the sample is constituted by an elastic hinge mechanism and a laminated piezoelectric element as in the first embodiment.

In the stand-alone scanning probe microscope, a three-axis fine movement mechanism 57 composed of a cylindrical piezoelectric element is installed on a base plate 56, and a cantilever holder 58 is attached to the tip of the three-axis fine movement mechanism 57.
Is supported by three columns 59, and one column 59a is extended and contracted by a stepping motor 60, and the cantilever 61 is brought closer to the sample 53 by leverage. The displacement of the cantilever 61 is the same as in the first embodiment. A small optical head 62 using an optical lever system is attached to the tip of a three-axis fine movement mechanism 57. Three
The shaft fine movement mechanism has a hollow interior, can irradiate the sample with the light of the illumination 63, and has a configuration capable of observing an optical microscope image.

The scanning probe microscope of this embodiment is mainly used for observing a biological sample such as a cell, and a general fluorescence microscope image and an atomic force microscope image having a higher resolution than the fluorescence microscope image are identical. It is a device that can be observed with the device. Scanning probe microscopes for biological samples are required to scan a wider area than other uses, so that the XY fine movement mechanism becomes large, rigidity is low, and the scanning speed tends to be low. 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 reduce the size as much as possible.

By constructing the scanning probe microscope on the inverted microscope as described above, these problems have been improved. (4) Other Examples In addition to the examples described above, the probe is brought close to the sample surface while the cantilever is vibrated near the resonance frequency, and the amplitude due to the interaction between the probe and the sample surface is obtained. Vibration mode atomic force microscope that monitors the amount of attenuation of the sample, controls the distance between the sample and the probe so as to always maintain a constant amplitude, and measures the uneven image and other physical characteristics of the sample surface, A bias voltage is applied between the sample and the probe using a conductive probe, the tunnel current when the probe is brought close to the sample is monitored, and the distance between the sample and the probe is controlled. A scanning tunneling microscope for measuring uneven images and other physical characteristics, or a scanning proximity using a probe whose optical fiber tip is processed into a probe shape and an opening with a diameter smaller than the wavelength is formed at the tip. The present invention is applicable to all microscopes generally called scanning probe microscopes, such as field microscopes.

The structure of the fine movement mechanism is not limited to the cylindrical type piezoelectric element described in the above embodiment, the system combining the elastic hinge mechanism and the laminated piezoelectric element, or the fine movement mechanism using a voice coil. All fine movement mechanisms used for the purpose of fine movement in the XY plane, such as a mechanical stage driven by an electric motor, are included, and a combination of these is also optional.

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 the probe is not limited to the optical lever method described in the above embodiment, and the displacement can be detected from the interference waveform between the incident light and the return light by irradiating the cantilever or the probe with laser light. An optical interference method, or a piezoelectric method in which a piezoelectric body is attached to a cantilever or probe, causing the cantilever or probe to bend due to physical characteristics, converting the amount of electric charge from the piezoelectric body to electrically detect displacement, etc. Included in the present invention.

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

[0030]

As described above, according to the present invention, a cantilever having a small probe at the tip, a cantilever holder for holding the cantilever, displacement detecting means for detecting the amount of displacement of the cantilever, and a sample are provided. Consists of a sample holder part for mounting, a Z fine movement mechanism that changes the 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. In the scanning probe microscope, 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.

By configuring the scanning probe microscope in this manner, the amount of movement required for each XY fine movement mechanism is reduced by half, and the XY fine movement mechanism can be reduced in size and increased in rigidity. Was. 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 1/2 of the required movement amount when the scanning speed of the two XY fine movement mechanisms is equal, and even when the speeds are different, the two XY fine movement mechanisms are scanned simultaneously. Therefore, the moving amount is smaller than in the case of one XY fine movement mechanism, and as a result, the scanning time is shortened.

Further, since the required movement amount is smaller than in the case of one fine movement mechanism, the XY fine movement mechanism is downsized,
Scanning probe microscopes can be installed even in limited spaces.

[Brief description of the drawings]

FIG. 1 is a schematic view of a scanning probe microscope according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an operation method of the scanning probe microscope of FIG.

FIG. 3 is a schematic view of a second embodiment of the scanning probe microscope of the present invention.

FIG. 4 is a block diagram showing an operation method of the scanning probe microscope of FIG.

FIG. 5 is a schematic view of a scanning probe microscope according to a third embodiment of the present invention.

FIG. 6 is a schematic diagram of a conventional scanning probe microscope.

FIG. 7 is an explanatory diagram illustrating a scanning method of the scanning probe microscope of the present invention.

FIG. 8 is an explanatory diagram illustrating a scanning method in the Y-axis direction.

[Explanation of symbols]

 Reference Signs List 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 104 Z Coarse movement stage 106 Sample holder 107 Sample 108 Optical lever optical system

Claims (6)

[Claims] 1. A cantilever having a minute probe at a tip thereof, a cantilever holder for holding the cantilever, a displacement detecting means for detecting a displacement amount of the cantilever,
A sample holder section for mounting the sample, a Z fine movement mechanism for changing a relative distance between the probe and the sample,
A scanning probe microscope comprising an XY fine movement mechanism that relatively scans a sample and a cantilever in a two-dimensional plane, wherein the XY fine movement mechanism is provided on both the sample side and the cantilever side. microscope. 2. In the two XY fine movement mechanisms,
2. The scanning probe microscope according to claim 1, wherein the probe and the sample are relatively scanned by operating the XY fine movement mechanism at independent trajectories and at independent speeds. 3. An X-axis and a Y-axis are set in directions orthogonal to each other in a two-dimensional plane, and two X fine movement mechanisms are scanned in directions opposite to each other in the X-axis direction, thereby completing the measurement of one line. Then, in the Y-axis direction, the Y fine movement mechanism is moved in the opposite direction to the next line, and the operation of scanning the two X fine movement mechanisms in the X-axis direction in the opposite direction is repeated. The scanning probe microscope according to claim 1 or 2, wherein the probe is raster-scanned on the probe. 4. A displacement detector having two or more axes is provided for at least one of the XY fine movement mechanisms provided on both the sample side and the cantilever side to monitor the amount of displacement, and to respond to a drive signal of the fine movement mechanism. The scanning probe microscope according to any one of claims 1 to 3, further comprising a control device that controls the displacement amount so as to maintain linearity. 5. Operating as a scanning tunneling microscope using a metallic probe instead of the cantilever,
The scanning probe microscope according to claim 1. 6. The scanning according to claim 1, wherein the scanning probe is operated as a scanning near-field microscope using a probe with a waveguide using a metallic probe or an optical fiber, or a cantilever with a waveguide. Probe microscope.