JP2004333441A - Scanner system, and scanning type probe microscope using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact scanner system capable of acquiring XY-positional information without distortion and accurate Z-positional information, and a probe microscope unit using the scanner system. <P>SOLUTION: This scanner system is provided with a scanner 1 provided with a stage 2 movable three-dimensional-directionally, a light source 20, a measuring mirror 24 provided in the stage 2 to reflect illumination light from the light source, a fringe counting system 29 for detecting the light reflected by the measuring mirror 24 and for acquiring displacement amount information along a vertical direction of the stage 2, based on a relative phase change of the detected reflected light, and an angle detecting system 28 for detecting the light reflected by the measuring mirror 24 and for acquiring change information in relative inclination of the measuring mirror 24, based on the detected reflected light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a scanner system used for obtaining a minute displacement, for example, a scanner system used for a scanning probe microscope for obtaining sample surface information with a resolution on the order of nanometers.
[0002]
[Prior art]
A scanning probe microscope is a device that can observe fine information of a sample surface with a vertical and horizontal resolution of nanometer order. A scanning tunneling microscope (STM) There are various types of atomic force microscopes (AFM), which are widely used for high-resolution observation of a sample surface.
[0003]
In order to realize high resolution with these scanning probe microscopes, a scanner system that can control the relative position between the probe and the sample with high resolution is required. As this type of scanner system, a cylindrical piezoelectric element is used for three axes. There is a piezoelectric scanner (tube scanner) used as a drive actuator. The tube scanner has four divided electrodes in the circumferential direction of a cylindrical piezoelectric element. By appropriately controlling the application of voltage to each electrode, the free end of the piezoelectric body can be three-dimensionally bent or expanded and contracted. Is to be displaced.
[0004]
FIG. 3 shows a conventional scanning probe microscope using this piezoelectric scanner. A stage 2 is fixed to an upper end of the scanner 1, and a sample 3 is placed on the stage 2. When the cantilever 4 is brought close to the sample 3, the free end of the cantilever 4 is displaced by an interaction between the sample 3 and the cantilever 4, for example, an atomic force.
[0005]
The cantilever displacement sensor 5 detects this displacement amount and outputs a displacement signal S1 to the Z scan driver 6. The Z scan driver 6 outputs a Z drive signal Sz for driving the scanner 1 so as to keep the cantilever displacement signal S1 at a predetermined constant value. The scanner 1 receives the signal and moves the sample 3 in the Z direction.
[0006]
That is, the Z scan driver 6 controls the distance between the sample 3 and the cantilever 4, and performs feedback control so that the interaction between the two can be kept constant. On the other hand, the scan controller 7 outputs an X scan signal Tx and a Y scan signal Ty for XY scan to the XY scan driver 8.
[0007]
The XY scan driver 8 performs XY scanning of the sample 3 by changing the applied voltages Sx and Sy to the scanner 1 in accordance with the X and Y scanning signals Tx and Ty and bending the scanner.
The scan controller 7 outputs timing pulses Px and Py for data capture to the sampling unit 9 based on the X and Y scan signals Tx and Ty. The sampling section 9 samples the Z drive signal Sz, that is, the Z displacement signal, according to the timing pulse. The Z displacement signal sampled by the sampling section 9 is stored in the image memory 10 as an image signal, and an image is displayed on a CRT (not shown).
[0008]
As described above, if the deflection of the cantilever 4 due to the atomic force is to be controlled, the obtained information is the three-dimensional shape information of the sample 3.
However, the scanner 1 typified by the tube-type piezoelectric scanner can be driven at a high resolution, but the displacement characteristics of the scanner 1 with respect to the applied voltage are not linear. For example, as shown in FIG. Has a hysteresis shape. It also shows a creep phenomenon in which the amount of displacement changes with the passage of the voltage application time.
[0009]
In the conventional measurement method, the Z drive signal Sz is sampled and imaged while changing the applied voltage at a constant width. Therefore, the obtained image is distorted due to the influence of hysteresis and creep phenomenon, and reproducibility is not good.
In order to solve this drawback, feedback control has been proposed in which the inclination of the stage is detected by using a four-division photodiode and converted into displacement in the XY directions, and an XY drive signal corrected based on this is supplied to the scanner. (For example, Patent Document 1).
[0010]
According to this method, the non-linearity in the XY directions is eliminated, and an image without distortion can be obtained with good reproducibility.
In addition, a means has been proposed in which a laser interferometer is arranged on three XYZ axes, the displacement of the scanner 1 is directly detected, and the XY position is controlled. Reference 1).
[0011]
[Patent Document 1]
Japanese Patent No. 3349779 (page 1-11, FIG. 1-16)
[Non-patent document 1]
"Three-dimension displacement measurement of a tube scanner for a scanning tunneling microscopic by optical interferometer, No. 6, 1995, Nanotechnology, UK. 121-126
[0012]
[Problems to be solved by the invention]
In recent years, due to the high spatial resolution of a scanning probe microscope, height information is particularly important in thin film step measurement, fine roughness measurement, etc., and the linearity in the XY directions and the reliability of the measurement data in the Z direction are important. It can be important. In such a case, in the conventional apparatus, hysteresis of the piezoelectric body remains in the Z direction, and accurate height information cannot be obtained.
[0013]
Further, Non-Patent Document 1 has a disadvantage that the system becomes large and complicated because the laser interferometers are arranged on three axes.
In view of the above problems, the present invention provides a compact scanner system capable of obtaining accurate Z position information together with XY position information without distortion, and a probe microscope apparatus using the same.
[0014]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a scanner that includes a displaceable stage on which a measurement target is placed, and that scans the scanning member and the measurement target relatively, and irradiates light. Irradiating means, a reflecting means provided on the stage, for reflecting the irradiating light irradiated by the irradiating means, and a relative phase change of first reflected light which is light reflected by the reflecting means. A displacement information acquiring unit for acquiring displacement information indicating information on a displacement amount of the stage in a vertical direction, and a relative position of the reflecting unit based on a second reflected light that is light reflected by the reflecting unit. And an angle change information obtaining unit that obtains angle change information indicating information on a change in inclination.
[0015]
With this configuration, accurate Z position information can be obtained together with XY position information without distortion.
According to the second aspect of the present invention, the above object can be achieved by providing the scanner system according to the first aspect, wherein the scanner has the reflection means inside the scanner.
[0016]
With this configuration, the internal space of the piezoelectric body of the scanner system can be effectively used.
According to a third aspect of the present invention, the displacement information acquiring unit acquires a relative change amount of interference fringes due to interference between predetermined light and the second reflected light. This can be achieved by providing a scanner system according to claim 1.
[0017]
With this configuration, displacement information in the Z direction can be obtained.
The above object can be achieved by providing the scanner system according to the first aspect, wherein the stage is displaced only in the vertical direction.
[0018]
With this configuration, the scanner system can move with extremely high straightness only in one axis in the Z direction.
According to a fifth aspect of the present invention, the above object can be achieved by providing a scanning probe microscope using the scanner system according to any one of the first, second, third, and fourth aspects. .
[0019]
With this configuration, the scanner system according to claims 1 to 4 can be used for a scanning probe microscope.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
As an embodiment of the present invention, a scanner for moving a measurement target, and a displacement detection system provided to detect the displacement of the measurement target, comprising a displacement detection system near the measurement target object The arranged reflection means, a light source for irradiating light to the reflection means, a displacement detection system for detecting a displacement of the measuring object from a phase change of the reflected light from the reflection means, and a part of the reflected light is taken out and reflected. A scanner system comprising an angle detection system for detecting a change in the angle of light, and a scanning probe microscope apparatus using this scanner system.
[0021]
Now, an example in which the scanner system according to the embodiment of the present invention is incorporated in a scanning probe microscope will be described below. In the description, the same parts as those of the configuration shown in the conventional example are denoted by the same reference numerals, and description thereof will be omitted.
(Example 1)
FIG. 1 shows the outline of the structure of the scanner system in the present embodiment. As shown in the figure, a measuring mirror 24 is attached to the back side of the stage 2 fixed to the free end side of the scanner 1. On the fixed end side of the scanner 1, a laser light source 20, a polarizing beam splitter 21, quarter-wave plates 22a and 22b, a reference mirror 23, a corner cube 25, and a beam splitter 26 are fixedly arranged.
[0022]
Light emitted from the laser light source 20 enters the polarization beam splitter 21. The light transmitted through the polarizing beam splitter 21 is reflected by the reference mirror 23 via the quarter-wave plate 22b as reference light, and is incident on the polarizing beam splitter 21 again via the quarter-wave plate 22b.
[0023]
At this time, since the polarization state of the re-entered polarization beam splitter is a linear polarization rotated by 90 degrees from that at the time of transmission through the polarization beam splitter 21, the polarization state is reflected by the polarization beam splitter 21, The light is reflected at 21 and again enters the reference mirror 23 via the quarter-wave plate 22b. The light reflected by the reference mirror 23 again passes through the polarizing beam splitter 21 via the quarter-wave plate 22b.
[0024]
Similarly, the light emitted from the laser light source 20 and reflected by the polarization beam splitter 21 passes through the quarter-wave plate 22a and the corner cube 25 due to the same polarization state change as the light reflected by the above-mentioned reference mirror. Are reflected twice, overlap with the reflected light passing through the reference mirror 23, exit, and enter the fringe counting system 29. In the fringe counting system 29, a phase difference is detected by homodyne detection from interference fringes caused by reflected light from the measuring mirror 24 and the reference mirror 23.
[0025]
Here, the positions 24a and 24b of the light incident on the measuring mirror 24 on the measuring mirror 24 are adjusted to positions symmetrical with respect to a perpendicular mirror surface P passing through the measuring point by the cantilever 4. A beam splitter 26 is provided on the optical path side to be guided to the measuring mirror 24, and is arranged so as to branch the first reflected light from the measuring mirror 24 and to lead it to the four-divided photodetector 27. The reflected light incident on the four-segment photodetector 27 forms a condensed spot on the light receiving surface of the four-segment photodetector 27.
[0026]
Here, the light receiving surface of the four-divided photodetector 27 is composed of four equally divided regions D1, D2, D3, and D4, and these four regions are configured to be in contact at the center of the light receiving surface. When the stage 2 is not displaced, the condensed spot is formed at the center of the light receiving surface of the 4-split photodetector 27. That is, the same amount of light is incident on each of the four regions D1, D2, D3, and D4. The four-divided photodetector 27 is connected to an angle detection system 28.
[0027]
Here, detection of the amount of displacement of the stage 2 in the Z direction (vertical direction) will be described. When a predetermined voltage is applied to the scanner 1, the free end side of the scanner 1 expands and contracts in the Z direction. For example, if the free end of the scanner 1, that is, the stage 2 is displaced dz upward, the length of the optical path reflected twice by the measuring mirror 24 increases by 4 · dz.
[0028]
Therefore, a phase difference of α = (4 · dz) · 2π / λ (λ: wavelength) is included between the two reflected lights from the measuring mirror 24 and the reference mirror 23 that enter the fringe counting system 29. The interference light intensity I of the two reflected lights is represented by the following equation.
I = A ² + {1 + cos (4.dz · 2π / λ)} (1)
Here, A is the amplitude.
[0029]
From equation (1), the Z-direction displacement dz of the stage 2 can be measured by counting the intensity change that is repeated each time the stage 2 changes dz = λ / 4 in the Z direction.
The measurement result obtained above is output to the sampling unit 9 as a Z displacement signal. The Z displacement signal is stored in the image memory 10 as an image signal by the sampling section 9, and an image is displayed on a CRT (not shown).
[0030]
In addition, since the position of the measuring light with respect to the measuring mirror 24 is symmetrically aligned with the cantilever 4 measuring point P interposed therebetween, the Z displacement measuring point P is on the perpendicular to the cantilever 4 measuring point, and is geometrical. The error has a minimum arrangement. For this reason, even when the stage 2 has an angle, the measurement in the Z direction can be performed with high accuracy.
[0031]
Next, the angle detection system 28 outputs a change in the XY direction position of the reflected light on the four-divided photodetector 27. The light incident on the four-segment photodetector 27 is light once reflected by the measuring mirror 24 and includes the influence of the free end face angle of the scanner 1, that is, the inclination angle of the stage 2. When the scanner 1 is displaced by Δdx in the X direction due to the bending operation, and the effect of the stage 2 tilting by θ in the X direction is the optical path length L from the measuring mirror 24 to the four-divided photodetector 27,
Δdx = L × tan (2θ) = 2Lθ (2)
Will occur.
[0032]
Similarly, when the scanner 1 is displaced in the Y direction, the measuring mirror 24 is inclined about the X axis. Therefore, if the inclination angle of the stage 2 in the Y direction is φ, the displacement amount in the Y direction at this time is It is expressed by the following equation.
Δdy = L × tan (2φ) = 2Lφ (3)
Therefore, by detecting the shift amount Δdxy of the spot forming position by the four-segment photodetector 27 from the comparison of the amounts of light incident on the regions D1, D2, D3, and D4 of the four-segment photodetector 27, the equations (2) and ( The inclination angles θ and φ of the measuring mirror 24 can be obtained based on 3).
[0033]
Here, since the spot shift amount Δdxy corresponds to the tilt direction of the measuring mirror 24, the angle detection system 28 performs the calculations of the equations (2) and (3) based on the output signal of the four-divided photodetector 27. Thus, the inclination angles θ and φ of the measuring mirror 24 are calculated. In this manner, the angle detection system 28 can calculate the inclination angle (θ, φ) and the inclination direction of the measuring mirror 24, that is, the displacement amount in the X direction and the displacement amount in the Y direction.
[0034]
In this way, the angle detection system 28 detects the XY displacement from the displacement of the reflected light and outputs it. Thus, the XY displacement is obtained from the angle detection system 28, and the Z displacement value is obtained from the fringe counting system 29.
The angle detection system 28 converts the signals output from the four-divided photodetector 27 into monitor signals Rx and Ry representing the respective displacements of the stage 2 in the X and Y directions, and provides the monitor signals Rx and Ry to the scan controller 30. Specifically, assuming that the light receiving information in the four light receiving regions D1, D2, D3, and D4 of the divided photodetector 27 is Rd1, Rd2, Rd3, and Rd4, respectively, the monitor signals Rx and Ry are:
Rx = (Rd1 + Rd4)-(Rd2 + Rd3) (4)
Ry = (Rd1 + Rd2)-(Rd3 + Rd4) (5)
Is represented by The monitor signals Rx and Ry are information corresponding to the above-mentioned Δdx and Δdy, and θ and φ are calculated from equations (2) and (3), respectively. Information on the calculated inclination angles θ and φ is output to the scan controller 30.
[0035]
The scan controller 30 sends the deviation between the current position and the target position as the X and Y scanning signals Tx and Ty to the XY scan driver 8 based on the inclination angles θ and φ of the stage 2 obtained as the XY displacement information. Controls the XY position. Here, as one of the methods of detecting the deviation amount, for example, there is a method of obtaining a deviation between a desired state of the stage 2 and an actual state of the stage 2 indicated by the monitor signal.
[0036]
Since a displacement occurs between the desired state of the stage 2 and the actual state of the stage 2 due to hysteresis, creep, or the like generated in the displacement of the piezoelectric body constituting the scanner 1, the XY scan driver 8 calculates this deviation. The scanning signals Tx and Ty are changed so as to compensate for this deviation. In this way, feedback control is performed so that the actual state of the stage 2 becomes a desired state.
[0037]
As described above, the XY displacement obtained by the angle detection system 28 does not cause positional distortion in the XY directions, and the surface following by the cantilever 4 is a measurement result based on the accurate Z displacement detected by the fringe counting system 29. be able to.
(Example 2)
This embodiment is a modification of the first embodiment. In the present embodiment, a scanner system specialized for displacement in the Z direction will be described.
[0038]
FIG. 2 shows an outline of the structure of the scanner system in the present embodiment. In the present embodiment, unlike the first embodiment, the output side of the angle detection system 28 is connected to the XY scan driver 8, and the XY displacement value indicating the XY displacement is output from the angle detection system 28 to the XY scan driver 8. .
[0039]
The XY scan driver 8 applies a voltage to the scanner 1 so that the XY displacement value output from the angle detection system 28 becomes a preset constant value, similarly to the Z scan driver in the conventional example. The set value in this case is equal to the XY displacement value when no voltage is applied. Thus, the free end of the scanner 1, that is, the movement of the stage 2 in the XY directions is fixed, and no XY displacement occurs.
[0040]
As described above, the stage 2 can be moved with extremely high straightness only in one axis in the Z direction, and a small geometric error (Abbe error) can be generated from the Z displacement value output from the fringe counting system 29. It is possible to eliminate and to obtain Z displacement with extremely high certainty.
[0041]
In order to actually operate as a probe microscope, the relative position relationship between the cantilever 4 and the sample 3 is changed by a moving stage (not shown) in the XY direction, thereby moving the cantilever 4 and the sample 3 one-dimensionally or two-dimensionally. It is possible to obtain an exact change of.
[0042]
Further, the present invention is not limited to the interferometers used in the first and second embodiments. For example, a Fizeau interferometer, a Michelson interferometer, or another interferometer may be used. In the first and second embodiments, the homodyne method is used to acquire the position information. However, the heterodyne method using a light source as a heterodyne light source may be used.
[0043]
【The invention's effect】
According to the present invention, it is possible to obtain accurate Z position information based on XY position information without distortion in a compact scanner system configuration, and to provide a probe microscope apparatus using the same. it can.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an outline of a structure of a scanner system according to a first embodiment.
FIG. 2 is a diagram illustrating an outline of a structure of a scanner system according to a second embodiment.
FIG. 3 is a diagram showing a conventional example of a scanning probe microscope using a piezoelectric scanner.
FIG. 4 is a graph showing a conventional displacement characteristic of a scanner with respect to an applied voltage.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Scanner 2 Stage 3 Sample 4 Cantilever 5 Cantilever displacement sensor 6 Z scan driver 8 XY scan driver 9 Sampling unit 10 Image memory 20 Laser light source 21 Polarization beam splitters 22a, 22b Quarter wave plate 23 Reference mirror 25 Corner cube 26 Beam splitter 27 4-part photodetector 28 Angle detection system 29 Stripe counting system 30 Scan controller

Claims (5)

With a displaceable stage on which the measurement target is placed, a scanner that relatively scans the scanning member and the measurement target,
Irradiating means for irradiating light;
Reflecting means provided on the stage, for reflecting irradiation light irradiated by the irradiation means,
Displacement information acquisition means for acquiring displacement information indicating information on the amount of displacement of the stage in the vertical direction based on a relative phase change of first reflected light that is light reflected by the reflection means;
Angle change information acquisition means for acquiring angle change information indicating information on a change in relative inclination of the reflection means, based on second reflected light that is light reflected by the reflection means,
A scanner system comprising: The scanner system according to claim 1, wherein the scanner includes the reflection unit inside the scanner. 2. The scanner system according to claim 1, wherein the displacement information acquisition unit acquires a relative change amount of an interference fringe due to interference between a predetermined light and the second reflected light. The scanner system according to claim 1, wherein the stage is displaced only in a vertical direction. A scanning probe microscope using the scanner system according to any one of claims 1, 2, 3, and 4.

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