JPH09171028A - Scanner system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To alter the movement detection resolution and movement detection region easily by detecting any one of a plurality of optical spot detection means selectively while switching thereby eliminating the effect of hysteresis or creep caused by variation of a piezoelectric. SOLUTION: Position detectors 14, 15 are connected, on the output side thereof, with the fixed contact of a switch 18 through preamplifiers 16, 17 and the movable contact of switch 18 is connected with the input side of an arithmetic circuit 19. Output signal to the arithmetic circuit 19 can be switched between the detectors 14, 15 by means of the switch 18. The arithmetic circuit 19 determines the displacement of a scanner 1 based on the amplified output signals from detectors 14, 15 and delivers a displacement signal to a scan controller 20. The controller 20 delivers control signals in X and Y directions to a scanner driver 22 which produces an output signal for applying a voltage selectively to four drive electrodes of the scanner 1 thus displacing the scanner 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a scanning probe microscope such as a scanning tunneling microscope (STM) or atomic force microscope (AFM), and a scanner system for scanning a sample with a scanning member such as a probe. Regarding

[0002]

2. Description of the Related Art For example, "Method and apparatus for forming image of sample surface" in Japanese Patent Laid-Open No. 62-130302.
As described above, scanning probe microscopes such as a scanning tunneling microscope (STM) and an atomic force microscope (AFM) have been proposed that have a simple configuration and high vertical and horizontal resolution at the atomic size level.

In order to realize high resolution with such a scanning probe microscope, a scanner system capable of controlling the relative position between the probe and the sample with high precision is required. In general, a tripod type or tube type piezoelectric body scanner using a piezoelectric body is used for the scanner system.

Such a tube type piezoelectric body scanner (tube scanner) is provided with a single common electrode on the inner peripheral surface of a tube-shaped piezoelectric body, for example.
Four drive electrodes are provided on the outer peripheral surface in the circumferential direction.
Thus, by appropriately controlling the voltage application to the four driving electrodes, the free end portion of the piezoelectric body is bent to 3 by bending or stretching.
It can be displaced dimensionally. In this scanner, a stage is fixed to a free end of a piezoelectric body, and a probe or a sample is supported on this stage, so that the sample is scanned by the probe by the displacement of the end of the piezoelectric body.

However, PZT (lead zirconate titanate)
It is well known that such piezoelectric materials exhibit phenomena such as hysteresis and creep in displacement when they are driven by voltage. Therefore, when the probe or sample is scanned using the piezoelectric scanner as described above, the movement characteristic of the stage (that is, the probe or sample) exhibits non-linearity (voltage-displacement non-linear characteristic). In a scanning probe microscope, such non-linearity appears as distortion of an observed image, which impedes quantitative measurement.

In order to solve such a problem, there is known a technique previously proposed by the present applicant, for example, as disclosed in Japanese Patent Laid-Open No. 6-229753. As shown in FIG. 3, this conventional scanner system includes a tube scanner 1 and a reflecting mirror 4 provided on the upper end thereof and on the lower surface thereof.
Is attached to the stage 3, a quarter wavelength plate 5, a collimator lens 6, a polarization beam splitter 7, and four areas A to D, which are sequentially arranged below the tube scanner 1. The position detector 9 and the position detector 9.

In such a scanner system, when a voltage is applied to the drive voltage of the tube scanner 1 and the tube scanner is displaced as shown in the figure, the
The reflecting mirror 4 is tilted at a predetermined angle with respect to the optical axis of the light beam that enters the tube scanner 1 via the polarization beam splitter 7, the collimator lens 6, and the quarter-wave plate 5. Therefore, the light beam is obliquely incident on the reflecting mirror 4. In this case, when the inclination of the upper end of the scanner 1 with respect to the reference state of the stage 3 is θ, the beam reflection angle is 2θ.
It is. The light beam reflected by the reflecting mirror 4 is linearly polarized by the quarter-wave plate 5, and then forms a light spot on the light receiving surface of the position detector 9 while being condensed through the lens 6 and the polarization beam splitter 7. At this time, since the light beam is reflected by the reflecting mirror 4 at an angle of 2θ with respect to the incident light beam, the formation position of the focused spot is
The reflecting mirror 4 is displaced from the center of the position detector 9 by a predetermined distance d depending on the tilt direction and the tilt angle. Therefore, the movement amount of the stage can be detected by the movement amount producing means based on the displaced spot position.

[0008]

In this prior art, although the above-mentioned problem due to non-linearity is solved, the focal length of the collimator lens 6 determines the resolution of movement amount detection and the movement detection region. However, these are contradictory to each other, and there is a problem that if the detection resolution of the movement amount is increased, the movement detection region is narrowed, and conversely, if the movement detection region is widened, the resolution is lowered.

Therefore, the present invention has been made in consideration of such circumstances, and an object thereof is to eliminate the influence of hysteresis, creep and the like caused by the change of the piezoelectric body, thereby enabling good scanning. However, it is an object of the present invention to provide a scanner system capable of easily changing the resolution of movement amount detection and the movement detection area.

[0010]

A scanner system according to the present invention uses a piezoelectric scanner for selectively moving a stage, and a light reflecting means provided on the stage and a beam parallel to the light reflecting means. Light source means for making incident light, a plurality of light spot detecting means for respectively detecting the positions of incident light spots, and a plurality of light spot detecting means provided corresponding to the plurality of light spot detecting means for condensing reflected light from the light reflecting means. A plurality of condensing lenses each having a different focal length, which form a light spot on each of the light spot detection means,
Based on the switching means for selectively operating any one of the plurality of light spot detecting means and the light spot position detected by the operable light spot detecting means, the movement amount of the stage is determined. And a moving amount calculating means for obtaining.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a partially cutaway view showing a schematic configuration of a scanner system according to this embodiment. In the figure, reference numeral 1 indicates a tube-type piezoelectric scanner (hereinafter referred to as a scanner). Although the detailed configuration of the scanner 1 is omitted, a single common electrode is provided on the inner peripheral surface of a piezoelectric body formed in a tube shape, that is, a cylindrical shape with both ends open, and the outer periphery is Four drive electrodes are provided on the surface in the circumferential direction. This scanner 1
Its lower end is fixed on the fixed base 2. The stage 3 is fixed to the upper end of the scanner 1, that is, the free end so as to close the opening. The stage 3 is formed so that the upper surface and the lower surface are exactly parallel to each other. A sample or a probe is mounted on the upper surface of the stage 3, and a flat mirror 4 is fixed on the lower surface with the reflection surface thereof facing downward. A through hole 2a is formed in the fixed base 2 coaxially with the scanner 1 so as to penetrate from the upper surface to the lower surface. Inside the through hole 2a, the quarter-wave plate 5, the first polarization beam splitter 10 and the plane mirror 4 are arranged in a straight line. The quarter-wave plate 5 is provided on the small diameter portion above the through hole 2a.
Further, the polarization beam splitters 10 are fixed to the fixed base 2 so as to be positioned in the lower large diameter portion. And
A light source 8 is arranged below the polarization beam splitter 10 and supported by a supporting means (not shown). This light source 8 includes a semiconductor laser 8a and a semiconductor laser 8a.
It is composed of a collimator lens 8b provided on the exit side of a and an LD driver 8c for driving the semiconductor laser 8a. The light beam emitted from the semiconductor laser 8a becomes a parallel beam by the lens 8b and enters the first polarization beam splitter 10.

A second beam splitter 11 is provided on the side of the first polarization beam splitter 10 so as to receive the beam emitted from the first polarization beam splitter 10. A first condenser lens 12 is provided on the first exit side of the second beam splitter 11, and a second condenser lens 13 is provided on the second exit side. These condenser lenses 12 and 13 have different focal lengths f
_1, has a f _2, in this embodiment, the focal length f ₁ of the first condenser lens 12 is set shorter than the focal length f ₂ of the second focusing lens 13. . First and second position detectors 14 and 15 are arranged at the focal positions of the first and second condenser lenses 12 and 13, respectively. These position detectors 14 and 15 form a light spot on the light receiving surface by the light condensed by the condenser lens, and those equivalent to those disclosed in JP-A-6-229753 can be used. Therefore, the description is omitted.

The output side of the first and second position detectors 14 and 15 is provided with a changeover switch 18 via preamplifiers 16 and 17 for amplifying output signals indicating the light spot positions of the position detectors 14 and 15, respectively.
Are connected to the first and second fixed contacts respectively. The movable contact of the changeover switch 18 is connected to the input side of an arithmetic circuit 19 described later. Thus, in the changeover switch 18, when the movable contact thereof is connected to the first fixed contact, the output signal from the first position detector 14 is sent to the arithmetic circuit 19, and the movable contact is changed to the second fixed contact. When connected to the contact, the output signal from the second position detector 15 can be switched so as to be sent to the arithmetic circuit 19. The switching of the movable contact may be performed manually or electrically.

Reference numeral 20 is a non-linearity correction means 2 described later.
2 shows a scan controller with 0a. The output side of the arithmetic circuit 19 is on the first input side of the scan controller 20, and the waveform generator 21 is on the second input side.
Are connected respectively. The arithmetic circuit 16 obtains the displacement state of the scanner 1 from the amplified output signal of the position detector, and supplies the displacement signal indicating the displacement state to the scan controller 20. The scan controller 20 performs a predetermined process (process for feedback control, which will be described later, or to rotate or shift the movement of the scanner 1 in the XY directions) on the reference voltage generated by the waveform generator 21. And the like) and outputs control signals in the X and Y directions. The control signals in the X direction and the Y direction are supplied to the scanner driver 22 connected to the output side thereof. The output side of the scanner driver 22 is connected to the scanner 1 so as to displace the scanner 1 to a state instructed by the control signal supplied thereto.
The selective voltage application to the four drive electrodes of is performed.

The non-linearity correction means 20a of the scan controller 20 applies a predetermined correction to the generated control signal based on the displacement signal supplied from the arithmetic circuit 19. Next, the operation of the scanner system configured as above will be described. First, when the scanner driver 22 does not apply a voltage to any of the four drive electrodes of the scanner 1, the scanner 1 is not displaced and is in the reference state. Further, when the scanner driver 22 selectively applies the voltage to the four drive electrodes of the scanner 1 based on the control signal output from the scan controller 20, the scanner 1 is displaced according to the state of the voltage application. .

The parallel beam emitted from the light source 8 and having a linearly polarized component in one direction passes through the first polarization beam splitter 10 and is incident on the quarter-wave plate 5. This 1/4
The wavelength plate 5 converts the linearly polarized light component of the incident light beam into a circularly polarized light component. Then, the light beam having the circularly polarized light component that has passed through the quarter-wave plate 5 exits the through hole 2 a of the fixed base 2 and enters the inside of the scanner 1 and enters the plane mirror 4. This incident light beam is reflected by the plane mirror 4 and again the quarter wave plate 5
Incident on. Here, the light beam is emitted as a light beam having a linear polarization component whose azimuth angle is rotated by 90 ° with respect to the linear polarization component of the light beam incident on the quarter-wave plate 5 through the beam splitter 10. It The emitted parallel light beam is reflected by 90 ° by the first polarization beam splitter 10 and enters the second beam splitter 11, where it is reflected by the first light beam that passes through the beam splitter 11. It is divided into a second light beam. The first light beam enters the first condenser lens 12 having a short focal length and is condensed on the light receiving surface of the first position detector 14 to form a light spot. Similarly, the second light beam enters the second condenser lens 13 having a long focal length and is condensed on the light receiving surface of the second position detector 15 to form a light spot. The light spots formed on these light receiving surfaces are formed at a position displaced from the center corresponding to the inclination of the stage 3, that is, the displacement of the scanner 1.

Here, when the scanner 1 is not displaced, the light spot is formed at the center of the light receiving surfaces of the position detectors 14 and 15. On the other hand, when the scanner 1 is displaced as shown in the figure, the plane mirror 4 is tilted with respect to the optical axis of the light beam incident on the inside of the scanner 1 (for example,
When the scanner 1 is displaced in the X direction, the plane mirror 4 tilts about the Y axis). Therefore, the light beam obliquely enters the plane mirror 4 and is reflected in the opposite direction.
Specifically, when the tip of the scanner 1 has an inclination of θ with respect to the reference state, the light beam incident on the plane mirror 4 is reflected at an angle of 2θ with respect to the incident light.

The light beam reflected by the plane mirror 4 is ¼
After being linearly polarized by the wave plate 5, it is incident on the first and second condenser lenses 12 and 13 through the first and second beam splitters 10 and 11, and is received by the respective position detectors 14 and 15. Form a light spot on the surface. At this time, since the light beam is reflected by the plane mirror 4 at an angle of 2θ with respect to the incident light beam, the formation position of the light spot is from the center of the position detectors 14 and 15 depending on the tilt direction of the plane mirror 4. Displace.

Here, between the deviation amount d of the formation position of each light spot on the first and second position detectors 14 and 15 and the tilt angle θ of the plane mirror 4, d = f · sin ( 2θ) (1) In this equation, f is the focal length of the first and second condenser lenses 12 and 13 (note that, as described above, the first condenser lens 12 and the second condenser lens 13 are Although they have different focal lengths f ₁ and f ₂ , they are collectively indicated by f in this formula).

As can be seen from this equation, by increasing the focal length f of the condenser lens, the displacement amount d of the light spot formation position increases. That is, the detection resolution of the movement amount becomes high. The position detector has a finite size, and when the amount of movement becomes long, the position detector begins to be worn and the dynamic range of movement detection becomes small.

Therefore, in the above embodiment, the _first condenser lens 12 having a short focal length is used by using the condenser lenses 12 and 13 having different focal lengths f ₁ and f ₂ . The output signal from the position detector 14 has a high resolution by detecting the movement amount in a small area, and the second position detector 15 using the second condenser lens 13 having a long focal length has a low resolution by detecting the movement in a large area. . Therefore, by switching the changeover switch 18, one of the signals can be selected and supplied to the arithmetic circuit 19.

The calculation circuit 19 calculates the tilt angle θ of the plane mirror 4 by performing the above calculation based on the output signals of the position detectors 14 and 15. Further, each position detector has, for example, a light receiving surface divided into four regions, and the displacement direction of the light spot can be detected based on which region the light spot is formed. Since the displacement direction of the light spot corresponds to the tilt direction of the plane mirror 4, the plane mirror 4 is calculated by the arithmetic circuit 19 based on the output signals of the position detectors 14 and 15.
Find the tilt direction of. Thus, in the arithmetic circuit 19, the tilt angle θ and the tilt direction of the plane mirror 4, that is, the stage 3
The tilt angle and the tilt direction are specified, and the state of the stage 3 is detected.

Output information from the arithmetic circuit 19 calculated based on the output signals of the position detectors 14 and 15 is shown in FIG. 2 by curves 14g and 15g, respectively. The arithmetic circuit 19 converts the information thus obtained into monitor signals representing the displacements of the stage 3 in the X direction and the Y direction, and supplies the monitor signals to the scan controller 20. In particular,
Letting A, B, C, and D be light receiving information in each of the four light receiving regions of each position detector, dx = (A + D)-(B + C) (2) dy = (A + B)-(C + D) (3) ) The monitor signals dx and dy are obtained based on the following equation, and this is given to the scan controller 20.

The scan controller 20 generates control signals in the X and Y directions based on the reference waveform output from the waveform generator 21 in order to displace the stage 3 into a predetermined state. In this state, the nonlinearity is generated. Control means 2
0a monitors the monitor signal, and the currently desired stage 3
And the actual state of the stage 3 indicated by the monitor signal. A deviation occurs between the desired state of the stage 3 and the actual state of the stage 3 due to hysteresis, creep, or the like that occurs in the displacement of the piezoelectric body that constitutes the scanner 1. Therefore, the nonlinear control means 20a uses this deviation. Ask for. Then, the non-linearity control means 20a changes the control signal so as to compensate for this deviation. That is, feedback control is performed so that the actual state of the stage 3 obtained by the arithmetic circuit 19 becomes a desired state.

Thus, the actual state of the stage 3 (inclination angle θ and inclination direction) is optically detected, and feedback control is performed so that the detected actual state of the stage 3 becomes a desired state. Even if hysteresis or creep occurs in the displacement of the piezoelectric body constituting the scanner 1, this is prevented from affecting the displacement of the stage 3, and the state of the stage 3 can be well controlled.

According to the above-described embodiment, the two condenser lenses 12 and 13 having different focal lengths are used to form the light spots on the position detectors 14 and 15, and the outputs from these position detectors are used. By selecting the input of the signal to the arithmetic circuit 19 by the changeover switch 18, the movement detection region and the movement amount resolution can be easily switched appropriately and can be well controlled. That is, stage 3
When observing a symmetric object placed on the first position detector 14, the scanner 1 is first scanned by a large amount and detected on the side of a large movement detection region based on the output signal from the second position detector 15, and then the first position detector 14 is detected. It is possible to switch the switch 18 so as to obtain an output signal from and to switch the region to be observed to the high resolution side for scanning.

Although feedback control is performed in the above embodiment, for example, in the case of STM and AFM, XY coordinates are newly generated on the computer in accordance with the monitor signal from the arithmetic circuit 19. The object of the present invention can also be achieved by performing image processing such as rearranging the STM signal and the AFM signal on the XY coordinates.

Further, in the above embodiment, the semiconductor laser 8a is arranged in the light source 8, but other light emitting means such as an LED can be applied, and when an LED is applied, an adverse effect due to interference occurs. Therefore, the quarter wavelength plate 5 can be omitted, and a half mirror can be used instead of the polarization beam splitter 10, and the configuration can be simplified.

Although the plane mirror is used as the means for reflecting the incident light heme to the stage, it is not limited to this, and for example, a concave mirror or a convex mirror may be used. The light spot detection means is not limited to the position detector having the above-mentioned configuration, and may be, for example, a two-division type or a multi-division type. Further, the switching means is not limited to the mechanical switch as in the embodiment, but enables the position detector to operate so that the output means from the selected position detector can be processed. Then, for example, an electric switch may be used.

Further, although two condenser lenses having different focal lengths are used, two or more condenser lenses may be used. In this case, a changeover switch may be designed corresponding to the number of condenser lenses, It will be easy for those skilled in the art to arrange the position detector.

[0031]

According to the scanner system of the present invention, it is possible to eliminate the influence of hysteresis and creep caused by the change of the piezoelectric body to enable good scanning, but at the same time, the resolution of the movement amount detection and the movement detection area can be improved. And can be easily replaced.

[Brief description of the drawings]

FIG. 1 is a partially cutaway view showing a schematic configuration of a scanner system according to an embodiment of the present invention.

2 is a diagram showing a state of an output signal from an arithmetic circuit in the scanner system shown in FIG.

FIG. 3 is a diagram schematically showing a part of a conventional scanner system.

[Explanation of symbols]

1 ... Piezoelectric scanner, 3 ... Stage, 4 ... Plane mirror, 8
... light source, 10 ... polarization beam splitter, 12 ... first condenser lens, 13 ... second condenser lens, 14 ... first position detector, 15 ... second position detector, 18 ... changeover switch, 19 ... Arithmetic circuit, 20 ... Scan controller, 21 ... Waveform generator, 22 ... Scanner driver.

Claims (1)

[Claims] 1. A scanner system using a piezoelectric scanner for selectively moving a stage, a light reflecting means provided on the stage, a light source means for making a parallel beam incident on the light reflecting means, and an incident means. A plurality of light spot detecting means for detecting the positions of the respective light spots, and the plurality of light spot detecting means, which are provided corresponding to the plurality of light spot detecting means, collect the reflected light from the light reflecting means, and respectively detect the light spots. A plurality of condensing lenses each having a different focal length for forming a light spot, a switching means for selectively operating any one of the plurality of light spot detecting means, and the operable light spot. A scanner system, comprising: a movement amount calculating means for obtaining a movement amount of the stage based on the light spot position detected by the detecting means. .