JPH05157554A - Probe microscope incorporated with optical micsroscope - Google Patents

Abstract

PURPOSE:To obtain a probe microscope, which can obtain the accurate image of the surface shape of a sample. CONSTITUTION:On a supporting stage 1, an optical-system supporting stage 12, which can be moved up and down (direction (z)) with a coarse micrometer 3 for the optical-system supporting stage, is provided. An object lens 7, a displacement measuring optical system 6 and an observing optical system 4 are attached to the optical-system supporting stage 2. A (z)-scanner supporting stage 15, which can be moved up and down with a coarse micrometer 14 for the (z) scanner supporting stage, is provided on the optical-system supporting stage 2. A cylindrical piezoelectric element 8 for finely moving a (z)-direction probe is fixed to the (z)-scanner supporting stage 15. A probe supporting ring 9 is provided at the lower end of the element 8. The ring 9 is arranged so that a probe 10 at the free end of a cantilever 31 is located at the center of the opening of the ring. Meanwhile, the lower end of a cylindrical piezoelectric element 13 for scanning the sample in the directions of (x) and (y) is fixed to the lower part of the supporting stage 1. A sample stage 12 for mounting the sample 11 is provided at the upper end.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe microscope incorporating an optical microscope.

[0002]

2. Description of the Related Art Since a scanning tunneling microscope (STM) capable of observing the surface of a sample in atomic units was developed in 1982, various techniques such as an atomic force microscope (AFM) can be utilized by utilizing the technology. Type probe microscope (Scanning
Probe Microscope) has been developed. The scanning probe microscope uses, for example, a z-direction servo operation by utilizing a tunnel current flowing between the probe and the sample, an atomic force generated between a constituent atom at the tip of the probe and a constituent atom on the surface of the sample. By scanning the probe along the sample surface (xy directions) while keeping the interval between the probe and the sample constant, the fine shape of the sample surface is read as the motion of the probe.

Generally, the probe is attached to a piezoelectric element made of a piezoelectric material and capable of being displaced in three dimensions, and the piezoelectric element performs the above-described servo operation and scanning. As a method of driving the piezoelectric element for performing such a servo operation, a voltage applied to the piezoelectric body that controls the displacement of the probe in the z direction can be obtained from a change in tunnel current or atomic force.
A general voltage control method in which the direction servo signal is used to directly change the voltage is known.

A cylindrical piezoelectric element is known as such a piezoelectric element that can be displaced in three-dimensional directions. As shown in FIG. 8, the cylindrical piezoelectric element includes a hollow cylindrical piezoelectric driving body 111 and four electrodes 11 provided on the outer surface thereof.
2a to 112d and a common electrode 113 provided on the inner side surface thereof
It consists of and. The cylindrical piezoelectric element has its upper end fixed, and the probe 115 is attached to the center of a fixed disk 114 provided at the lower end of the piezoelectric driver 111. For this cylindrical piezoelectric element, a common electrode 113 is formed by using a high voltage amplifier or the like.
When a voltage is selectively applied between the electrode and the electrodes 112a to 112d on the outer peripheral surface, the free end (lower end) of the piezoelectric driver 111 moves in accordance with the deformation of the piezoelectric driver 111 in the electrode portion to which the voltage is applied. Therefore, the probe 115 is scanned by controlling the voltage applied to the electrodes.

[0005]

In STM and AFM, the probe and the sample are moved relative to each other while controlling the z position of the probe so as to keep a constant distance between the sample surface and the tip of the probe. The probe is scanned along the surface of the sample. Meanwhile, the voltage applied to the piezoelectric element is used as a signal indicating the z position of the probe,
That is, it is taken out as an uneven signal of the sample surface, and this signal is processed in synchronization with the position signal on the sample surface to obtain an image of the sample surface. By the way, the displacement of the piezoelectric element is not linear with respect to the applied voltage. Therefore, the obtained image does not accurately represent the surface shape of the sample in a strict sense.

It is an object of the present invention to provide a probe microscope capable of obtaining an image that accurately reflects the surface shape of a sample.

[0007]

DISCLOSURE OF THE INVENTION The present invention is an optical microscope built-in probe microscope having an observation optical system for optically observing the surface of a sample, the cantilever having a probe at its free end. And supporting the cantilever in the opening,
A piezoelectric device that moves the sample in a direction parallel to the surface of the sample.It has a cylindrical piezoelectric element that moves the cantilever in a direction perpendicular to the sample surface, a displacement measurement optical system that measures the displacement of the cantilever, and a sample table on which the sample is placed. And an element.

[0008]

According to the present invention, when scanning the probe, the probe is moved in the direction perpendicular to the sample surface by the cylindrical piezoelectric element while keeping the interval between the probe and the sample constant, and the sample is moved by the piezoelectric element. It is moved in a direction parallel to the sample surface. Preferably, the observation optical system and the displacement measuring optical system share one objective lens, and this objective lens is arranged inside the cylindrical piezoelectric element. The displacement measuring optical system includes means for measuring the free end of the cantilever, that is, the position of the probe in the direction perpendicular to the sample surface. The observed image of the sample is obtained based on the position of the probe in the direction perpendicular to the sample surface and the position of the probe in the direction parallel to the sample surface.

[0009]

EXAMPLE A first example of the present invention will be described with reference to FIG.

An optical system support base 2 is provided on the support base 1 so as to be movable in the vertical direction (z direction) via a linear guide. An objective lens 7, a displacement measuring optical system 6 and an observing optical system 4 are attached to the optical system support 2, and these are integrally moved up and down by adjusting an optical system support coarse movement micrometer 3. To be done. In addition, the optical system support 2
A z-scanner support base 15 is provided in the above so as to be vertically movable via a linear guide. A z-direction probe fine movement cylindrical piezoelectric element 8 is fixed to the z-scanner support base 15, and a probe support ring 9 is provided at the lower end thereof.
The probe 10 at the free end of the cantilever 31 is arranged in the center of the opening. The z scanner support base 15 is moved up and down with respect to the optical system support base 2 by adjusting the z scanner support base coarse movement micrometer 14. On the other hand, the lower end of the xy-direction sample scanning cylindrical piezoelectric element 13 is fixed to the lower portion of the support 1. A sample table 12 is provided at the upper end of the sample table 11 and
Is placed.

Next, the observation optical system 4 and the displacement measuring optical system 6
Will be described with reference to FIG.

The laser light emitted from the laser diode 87 is shaped into parallel light by the collimator lens 90 and is incident on the polarization beam splitter 86. The laser light reflected by the polarization beam splitter 86 is
Further, it is reflected by the half mirror 85, and the quarter wavelength plate 84
Incident on.

On the other hand, the illumination light emitted from the light source 96 of the observation illumination device 16 is collimated by the lens 97 and reflected by the half mirror 92. The illumination light reflected by the half mirror 92 passes through the filter 91 and the half mirror 85, and enters the quarter wavelength plate 84.

The laser light and the illumination light passing through the quarter-wave plate 84 have different chief rays and enter the objective lens 83. When passing through the quarter-wave plate 84, the laser light is converted from linearly polarized light into circularly polarized light and is condensed on the upper surface of the probe 10 by the objective lens 83. On the other hand, the illumination light is condensed near the tip of the probe 10 and illuminates the entire field of view.

The illumination light reflected from the sample 11 passes through the objective lens 83, the quarter-wave plate, the half mirror 85, the filter 94, and the half mirror 92, and the imaging lens 9
An image is formed by 3 and enters the prism 94. Part of the light incident on the prism 94 is reflected by the interface of the prism 94 and reaches the eyepiece lens 95. The light passing through the prism 94 is the video camera 1 including a CCD image element and the like.
It is incident on 7, converted into an image signal, and video monitor 1
It is sent to 8 and displayed. The quarter-wave plate 84 prevents the reflected light of the illumination light from directly entering the observation optical system.
It is arranged at a slight angle with respect to, and provides a clear visual field observation image without flare.

The laser light reflected on the upper surface of the probe 10 passes through the objective lens 7 and the quarter-wave plate, is reflected by the half mirror 85, and is guided to the polarization beam splitter 86. When passing through the quarter-wave plate 84, the laser light is converted into linearly polarized light whose vibrating surface is rotated by 90 ° with respect to the time of incidence. The laser light incident on the beam splitter 86 is divided into two, one of which is radiated to the first two-divided light receiving element 89a through the first critical angle prism 88a, and the other of which is second light through the second critical angle prism 88b. The two-divided light receiving element 89b is irradiated.

The critical angle method is used to detect the position of the probe 10. The principle of the critical angle method will be briefly described with reference to FIGS.

In the critical angle method, the critical angle prism c is
When the parallel light flux is incident from the lens b, the angle formed by the parallel light flux and the reflecting surface of the prism is arranged to be a critical angle.

When the reflecting surface a is at the focal position of the objective lens b (the position shown by the solid line B), that is, when the beam is in focus, the reflected light from the reflecting surface a is collimated by the lens b. It is incident on the critical angle prism c. At this time, all the light flux is totally reflected by the reflecting surface of the prism, and 2
An equal amount of light is supplied to each photodiode of the divided light receiving element.

On the other hand, when the reflecting surface a is located closer to the focal point of the lens b (the position shown by the dotted line C), the light passing through the lens b becomes a divergent light beam and enters the critical angle prism c. On the contrary, when the reflecting surface a is at a position far from the focal point of the lens b (position shown by the dotted line A), the light passing through the lens b becomes a focused light flux and enters the critical angle prism c. In either case, the non-parallel light flux is incident on the critical angle prism c. In these cases, only the central ray is incident at the critical angle,
Since the incident angle of the light beam on one side from the center is smaller than the critical angle, part of the light is emitted outside the refraction prism and only the remaining light is reflected. On the contrary, the light beam on the opposite side of the center is totally reflected because the incident angle becomes larger than the critical angle. As a result, the amount of light incident on the two-divided light receiving element differs between the left and right photodiodes, and a signal corresponding to the difference in light amount is output from the output terminal f via the differential amplifier e. That is, the position of the reflection surface a is detected as the light amount difference on the detection surface of the two-divided light receiving element d.

As described above, since the light incident at an angle smaller than the critical angle is partially emitted to the outside of the critical angle prism every time it hits the reflecting surface, the light amount of the refraction component is significantly reduced. Therefore, the difference in the amount of light between the light incident at an angle smaller than the critical angle and the light incident at the angle larger than the critical angle is greatly expanded. Therefore, in order to improve the measurement accuracy, it is desirable that the reflection be repeated several times in the critical angle prism. In this embodiment, the detection light is reflected twice in the critical angle prism. The output of the photodiode PD1 of the first two-divided light receiving element is input to the inverting input terminal of the comparator 102, and the output of the photodiode PD2 is input to the non-inverting input terminal of the comparator 102, and is connected to the photodiode PD1. The difference between the outputs of the photodiode PD2 is output from the comparator 102. On the other hand, the output of the photodiode PD3 of the second two-divided light receiving element is input to the inverting input terminal of the comparator 104, and the photodiode P3
The output of D4 is input to the non-inverting input terminal of the comparator 104, and the photodiode PD1 and the photodiode PD2 are input.
The difference in the outputs of the above is output from the comparator 104. Comparator 10
2 and the output of the comparator 104 are added and input to one terminal of the comparator 106, and the result of comparison with the reference value is output. Therefore, a signal indicating the difference in the amount of light in a region divided into two with the center line of the beam spot applied to the two-divided light receiving element as a boundary, that is, the position of the probe 10, is output from the terminal 108.

Next, the procedure for observing the sample will be described.
First, the coarse movement micrometer 14 of the z scanner support base is adjusted to move the z scanner support base 15 up and down so that the measurement beam of the displacement measurement optical system 6 is focused on the free end of the cantilever 31, that is, the upper surface of the probe 10. Next, until the distance from the tip of the probe 10 to the surface of the sample 11 placed on the sample table 12 becomes the distance at which the tunnel current flows in the STM, and the distance at which the atomic force acts in the AFM.
The optical system support base 2 is lowered by operating the coarse movement micrometer 3 of the optical system support base to bring the probe 10 close to the sample 11. At this time, the observation light of the observation optical system 4 is focused on the surface of the sample 11 as shown in FIG.
It is possible to detect the position of the probe 10 while optically observing the surface of the probe 1. Then, the cylindrical piezoelectric element 1 for xy-direction sample scanning
8 is supplied with an xy scanning voltage, and as shown in FIG.
Move 1 horizontally. During that period, the cylindrical piezoelectric element 8 for fine movement of the z-direction probe is feedback-controlled so that the tunnel current or the atomic force is kept constant, that is, the gap between the tip of the probe 10 and the surface of the sample 11 is kept constant.
Therefore, the cylindrical piezoelectric element 8 for fine movement of the z-direction probe expands and contracts according to the unevenness of the surface of the sample 11, and the probe 10 moves up and down with a certain distance from the surface of the sample. At this time, probe 1
The z position of 0 is detected by the displacement measuring optical system 6, and the z position signal and the xy scanning signal are processed in synchronization to obtain an image of the surface shape of the sample 11.

A second embodiment of the present invention will be described with reference to FIG. The present embodiment is a probe microscope having both STM and AFM functions, and its device configuration is the same as that of the microscope device of FIG.

As shown in FIG. 7, the displacement measuring optical system 6 includes
A free end displacement measuring optical system 6a for measuring the z position of the free end of the cantilever 31 and a fixed end displacement measuring optical system 6b for measuring the z position of the fixed end of the cantilever 31 are provided. The signal processing circuits 41 and 42 convert the outputs of the displacement measuring optical systems 6a and 6b into a free end position signal S1 and a fixed end position signal S2, respectively. These signals S1 and S2 are differentially amplified by the differential amplifier circuit 43, and the differential amplifier 43 outputs a cantilever displacement signal S corresponding to the displacement of the cantilever 31.
3 is output. The cantilever displacement signal S3 is input to the z control circuit 46 via the switch 48.

On the other hand, the probe 10 is electrically connected to the tunnel current detection circuit 44 via the cantilever 31 and the probe support ring 9. The tunnel current detection circuit 44 detects a tunnel current flowing between the probe 10 and the sample 11 and outputs a tunnel current signal S4. Tunnel current signal S4
Is input to the z control circuit 46 via the switch 48.

The switch 48 selects a signal input to the z control circuit 46. That is, the cantilever displacement signal S3 is input to the z control circuit 46 when the AFM measurement is performed, and the tunnel current signal S4 is input to the z control circuit 46 when the STM measurement is performed.
The z control circuit 46 operates the cylindrical piezoelectric element 8 for fine movement of the z-direction probe so that the cantilever displacement signal S3 or the tunnel current signal S4 is kept constant, that is, the space between the probe 10 and the sample 11 is kept constant. Feedback control.
In this state, when the xy scanning voltage S6 is supplied from the scanning circuit 50 to the xy-direction sample scanning cylindrical piezoelectric element 18 to move the sample 11 in the horizontal direction, the z-direction fine movement of the probe along the unevenness of the surface of the sample 11 is performed. The cylindrical piezoelectric element 8 expands and contracts. At this time, the z position of the probe 10 is detected by the displacement measuring optical system 6, and the z position signal and the xy scanning signal are processed in synchronization to obtain an image of the surface shape of the sample 11.
Cantilever fixed end position signal S2 output from fixed end displacement measurement optical system 6b and xy output from scanning circuit 50
The scanning signal S6 is taken into the image display system 47, and the image display system 47 receives the sample 11 based on these signals S2 and S6.
An image of the surface shape of is constructed and displayed.

[0027]

According to the present invention, since the position of the probe is measured by using the displacement measuring optical system, an image accurately showing the shape of the sample surface without any error due to the nonlinearity of the piezoelectric element can be obtained. Be done. Moreover, since the probe and the sample are moved by using different piezoelectric elements, a wide scanning range can be obtained. Furthermore, since the cylindrical piezoelectric element is used only to move the probe in the direction perpendicular to the sample surface, it becomes possible to use a small one with a high natural frequency, and thus a probe microscope that is not easily affected by vibration. Will be provided.

[Brief description of drawings]

FIG. 1 shows a probe microscope according to a first embodiment of the present invention.

FIG. 2 shows a positional relationship between observation light of an observation optical system and measurement light of a displacement measuring optical system.

FIG. 3 shows how the probe and sample move during scanning.

4 shows an observation optical system and a displacement measuring optical system of the probe microscope of FIG.

FIG. 5 is a diagram for explaining the principle of the critical angle method.

FIG. 6 shows a signal output circuit when the critical angle method is applied to the optical system of FIG.

FIG. 7 shows a probe microscope according to a second embodiment of the present invention.

FIG. 8 shows a structure of a cylindrical piezoelectric element.

[Explanation of symbols]

6 ... Displacement measuring optical system, 8 ... Cylindrical piezoelectric element for fine movement of z-direction probe, 10 ... Probe, 12 ... Sample stage, 13 ... Cylindrical piezoelectric element for xy-direction sample scanning, 16 ... Observation optical system, 31 ... Cantilever.

Claims (1)

[Claims] 1. A probe microscope incorporating an optical microscope, comprising an observation optical system for optically observing the surface of a sample, comprising: a cantilever having a probe at a free end, and a cantilever supported in an opening. Then, it has a cylindrical piezoelectric element that moves the cantilever in a direction perpendicular to the sample surface, a displacement measurement optical system that measures the displacement of the cantilever, and a sample table on which the sample is placed, and moves the sample in the direction parallel to the surface. An optical microscope built-in type probe microscope having a piezoelectric element for making it.