JPH06281445A - Scanner system - Google Patents

Abstract

PURPOSE:To provide a scanner system to be operated to exclude the effects of the variance of the characteristics of the parts of each driving electrode of a tube scanner. CONSTITUTION:A scanner system is provided with a tube scanner 12 mounted on a fixed table 52, four scanning signal generating circuits 32, 34, 36, 38, and high voltage amplifiers 42, 44, 46, 48 to amplify the signals from the respective scan signal generating circuits 32, 34, 36, 38. A tube scanner 12 is provided with a cylindrical piezoelectric body, a common electrode mounted on the inner circumferential surface, and four driving electrodes provided on the outer circumferential surface. The scan signal is supplied to four driving electrodes from the high voltage amplifiers 42, 44, 46, 48 respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanner system used as a scanning means in a scanning probe microscope.

[0002]

2. Description of the Related Art A scanning probe microscope (SPM) is used as a surface inspection apparatus having a high resolution in the vertical and horizontal directions at the atomic level.
Is proposed. Scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) are well known as SPMs, and since AFMs can also be used as pattern inspection devices for insulators and semiconductors, they have received special attention in recent years.

Generally, in SPM, a piezoelectric scanner capable of controlling the movement amount with high precision is used as the scanning means. The piezoelectric scanner is basically composed of a piezoelectric body and an electrode provided on the surface thereof, and the displacement can be controlled in nm order by controlling the voltage applied to the electrode. Among the piezoelectric body scanners, a tube scanner using a cylindrical piezoelectric body has high rigidity due to its cylindrical shape, and has recently become the mainstream of piezoelectric body scanners. Next, this tube scanner will be described with reference to the drawings.

As shown in FIG. 4, the tube scanner 12 has a cylindrical piezoelectric ceramic 14, a common electrode 16 provided on its inner peripheral surface, and four drive electrodes 22, 24, 26 provided on its outer peripheral surface. , 28 and. The tube scanner 12 is driven in the XY directions by applying voltages of opposite polarities having the same absolute value to the two electrodes 22 and 24 or 26 and 28 which face each other, and the movement amount (displacement) is based on the applied voltage. Calculated by estimation. For example, the common electrode 16 is kept at 0 potential, the drive electrode 22 has + φ (eg, + 100V), and the drive electrode has −φ (eg, −100V).
Is applied. Then, the piezoelectric body on the side of the drive electrode 22 expands and the piezoelectric body on the side of the drive electrode 24 contracts, so that its upper end (in SPM, the sample stage is attached here) is displaced in the direction of arrow a. In such a tube scanner 12, the common electrode 16 and the four drive electrodes 22, 24, 26,
By appropriately changing the ratio of the voltage applied to 28, the upper end can be moved three-dimensionally. This allows the SPM to perform the desired scan between the probe and the sample.

In a scanner system including a tube scanner and its peripheral circuit, there are a case where an open loop is formed by the tube scanner and its drive circuit, and a case where a displacement sensor of the tube scanner is added to this to form a closed loop. is there. In the case of the open loop, there is an advantage that the scanner system can be configured at a relatively low cost because the configuration is simple. In the case of the closed loop, it is possible to remove the influence of the hysteresis of the piezoelectric body and the like, so that there is an advantage that highly accurate scanning can be performed.

[0006]

Generally, the piezoelectric body 14 of the tube scanner 12 is not uniform in thickness as shown in FIG. Such variations are unavoidable in manufacturing, and the tube scanners currently available generally have variations of about 5%. Such nonuniformity of the thickness of the piezoelectric body 14 causes an error in the movement amount (displacement). For example, the common electrode 16 is set to 0 potential, and the four drive electrodes 22, 24, 26,
When the same voltage ψ (+100 V, for example) is applied to the piezoelectric element 28, the piezoelectric substance 1 is applied on the drive electrode 22 side and the drive electrode 24 side.
The magnitude of the electric field generated inside 4 differs, and the amount of extension also differs. In other words, if the thickness of the piezoelectric body 14 is ideally uniform, it should extend straight, but due to the variation in thickness, it does not extend straight but in the lateral direction (XY direction).
The displacement component is included, resulting in an undesired displacement. As for this phenomenon, in FIG. 5, the hysteresis of the piezoelectric body 14 is d + on the electrode 22 side.
It can be explained that this is because the electrode 24 has a d-like shape.

As described above, the variation in thickness of the cylindrical piezoelectric body causes nonuniformity of the expansion and contraction amount of the piezoelectric body depending on the location, which causes variation in the characteristics of the tube scanner. Such variations in the characteristics of the tube scanner are extremely unfavorable for the SPM that requires highly accurate position control.

By the way, when a tube scanner is driven by a closed loop circuit using the sensor for measuring the displacement in the XY directions of the scanner described in Japanese Patent Application No. 4-222902,
Feedback control is performed in the xy direction, so even if there are variations in the characteristics of the tube scanner, x
The displacement in the y direction is defined with good accuracy. In a tube scanner, a cylindrical piezoelectric body warps to cause displacement, so when scanning a square in the xy direction, the locus of a certain point on the tube scanner is actually a spherical surface even if it is an ideal tube scanner. , Z-direction movement. Furthermore, in an actual tube scanner, the spherical surface is distorted due to variations in characteristics. Therefore, in the driving by the closed loop circuit, the xy coordinate value at the moment is correct, but the z coordinate value is different from the ideal value.

It is said that such a phenomenon can be measured with high accuracy in any of the xyz directions.
PM is extremely unfavorable for ensuring quantitativeness in the z direction. It is an object of the present invention to provide a scanner system that does not have an operation error due to variations in the thickness of a cylindrical piezoelectric body.

[0010]

A scanner system according to the present invention comprises a tube scanner composed of a cylindrical piezoelectric body, a common electrode provided on the inner peripheral surface thereof, and a plurality of drive electrodes provided on the outer peripheral surface thereof. , And means for supplying independent scanning signals to the plurality of drive electrodes of the tube scanner according to their characteristics.

[0011]

In the present invention, the characteristics of each drive electrode portion of the tube scanner are investigated in advance, and according to the characteristics,
Scanning signals that are independent of each other so that the characteristics of the respective parts are uniform are supplied to the respective drive electrodes. That is, each drive electrode is supplied with a scanning signal in which the influence of variations in the thickness of the piezoelectric body in that portion is considered in advance. Therefore, the tube actuator operates without including the influence of variations in characteristics.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. The scanner system of this embodiment is
As shown in FIG. 1, the tube scanner 12 fixed to a fixed base 52 and four scanning signal generating circuits 32, 34, 3
6, 38 and the scanning signal generating circuits 32, 34, 36, 3
High-voltage amplifiers 42, 44, 46 for amplifying the signal from 8
And 48. The tube scanner 12 is shown in FIG.
As shown in FIG. 3, the piezoelectric body 14 has a cylindrical shape, a common electrode 16 provided on the inner peripheral surface thereof, and four drive electrodes 22, 24, 26, 28 provided on the outer peripheral surface thereof. Drive electrode 2
2, 24, 26 and 28 respectively include a high voltage amplifier 42,
Scan signals are supplied from 44, 46, and 48.

The characteristic of the tube scanner 12 is inspected in advance, and the relationship between the applied voltage and the displacement is examined for each part of the drive electrodes 42, 44, 46 and 48. The scanning signal generating circuits 32, 34, 36 and 38 output scanning signals based on the inspection result so that the operating characteristics of the respective electrodes 22, 24, 26 and 28 are uniform. This scanning signal is amplified through the high voltage amplifiers 42, 44, 46 and 48, and then the drive electrodes 22 and 24 of the tube scanner 12,
26, 28.

As a result, the tube scanner 12 performs an ideal operation in which its displacement does not include an error due to variations in the characteristics of the respective portions of the drive electrodes 22, 24, 26 and 28.

In this embodiment, four scanning signal generating circuits are prepared. However, four scanning signal generating circuits are combined into two systems of x-direction and y-direction, and signals outputted from the respective systems are inverted and non-inverted to obtain four scanning lines. You may get a signal. However, in this case, the drive electrodes 22, 2 of the tube scanner 12 are
It is necessary to adjust the gains of the high-voltage amplifiers 42, 44, 46, and 48 in order to match the characteristics of the parts 4, 26, and 28. Further, in order to realize ideal driving, it is also effective to increase the number of driving electrodes from four to eight in order to increase the degree of freedom of adjustment.

Next, the second embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. The scanner system of the present embodiment is provided with a computer 58 for controlling the scanning signal generating circuits 32, 34, 36, 38 in addition to the configuration of the first embodiment described above. In addition, the tube scanner 12
Is integrated with the fixed base 52 and the ROM 54 provided therein to form one unit. ROM
Characteristic information of each drive electrode 22, 24, 26, 28 portion of the tube scanner 12 of the unit is written in 54, and a connector 56 for extracting the characteristic information to a computer is provided.

In the SPM device, the tube scanner 12 is exchanged for each unit. After placing the new unit in place, the ROM 54 in the unit is connected to the computer 58 via the connector 56. The computer 58 reads the information written in the ROM 56 and performs an operation to generate a scanning signal suitable for the characteristic of each drive electrode 22, 24, 26, 28 portion of the tube scanner 12 in each scanning signal generation circuit 32, 34 ,. 36, 3
8 is controlled to output.

As described above, by unitizing the tube scanner and previously writing the characteristic information in the memory element such as the ROM, the tube scanner can be easily incorporated into the device when the tube scanner is replaced due to a failure or the like. The scanning characteristics after incorporation can be immediately put in an ideal state.

In this embodiment, the computer 58 controls the scanning signal generating circuits 32, 34, 36, 38, but the high voltage amplifiers 42, 44, 46,
The gain adjustment of 48 may be performed. For example,
The high-voltage amplifiers 42, 44, 46, 48 in the figure can be adjusted in gain by adjusting the feedback resistance.
If the resistance is a multi-rotation high-precision variable resistor and its rotation is controlled by a motor according to an instruction from a computer, the same effect can be realized automatically. Of course, a high-voltage amplifier with programmable gain may be used.

As a third embodiment of the present invention, an AFM incorporating the scanner system of the first embodiment is shown in FIG.
In the AFM of the present embodiment, the displacement of the cantilever 64 is measured using a critical angle type optical displacement sensor. This optical sensor basically comprises a semiconductor laser 68, a collimator lens 70, a polarization beam splitter 72,
It is composed of a quarter-wave plate 74, a dichroic mirror 76, an objective lens 78, a critical angle prism 80, two-divided photodiodes 82a and 82b, and a differential amplifier 84.

The laser light emitted from the semiconductor laser 68 is collimated by the collimator lens 70,
The light is reflected by the polarization beam splitter 72, passes through the quarter-wave plate 74, and becomes circularly polarized light.
It is reflected by 6, and is focused on the upper surface of the free end portion of the cantilever 64 on the opposite side of the probe 62 by the objective lens 78. The reflected light passes through the objective lens 78, is reflected by the dichroic mirror 76, passes through the quarter-wave plate 74, and becomes linearly polarized light whose polarization direction is different by 90 ° from the light emitted from the semiconductor laser 68. The light passes through the polarization beam splitter 72, is reflected by the critical angle prism 80, and enters the two-divided photodiodes 82a and 82b. The two-divided photodiodes 82a and 82b output a voltage signal corresponding to the amount of received light, and the difference signal is output from the differential amplifier 84.

In the critical angle method, the displacement of the cantilever 64 is detected as a difference in the amount of light incident on the two-divided photodiodes 82a and 82b, and the difference signal is output from the differential amplifier 84 as a displacement signal. This displacement signal is input to the servo control circuit 86, and the servo control circuit 8
6 is a cantilever 6 generated according to the unevenness of the measurement sample S.
Tube scanner 12 to keep the displacement of 4 constant
The scanner driver 10 that drives the scanner is controlled. The scanner driver 10 also supplies a scanning signal in the xy directions to the tube scanner 12 based on a signal from the computer 88. The displacement signal from the differential amplifier 84 is input to the computer 88 via the servo control circuit 86, and the computer 88 processes the displacement signal in synchronization with the scanning signal input from the scanner driver 10 to form an AFM image. , Is displayed on the monitor 90.

The AFM also has an observation optical system for optically observing the measurement sample S. The observation optical system is basically
Objective lens 78, illumination light source 92, illumination dimming circuit 92, lens 96, half mirror 98, eyepiece lens 100, CC
D solid-state image sensor 102, CCD control unit 1
04, the television monitor 106.

The illumination light emitted from the illumination light source 94 passes through the lens 96, is then reflected by the half mirror 98, passes through the dichroic mirror 76, is focused by the objective lens 78, and illuminates the entire visual field of the sample S. . The light reflected from the sample S is the objective lens 78 and the dichroic mirror 7.
6. After passing through the half mirror 98, an image is formed by the image forming lens 100, converted into a video signal by the CCD solid-state image sensor 102, and displayed on the television monitor 106.

The scanner driver 10 includes the scanning signal generating circuits 32, 34, 36 and 38 and the high voltage amplifier 4 of FIG.
It is composed of 2, 44, 46 and 48. The scanner driver 10 supplies the scanning signals in consideration of the variation in the characteristics of the tube scanner 12 to the drive electrodes 22, 24, 26,
28. Furthermore, the scanner driver 10
A z-direction drive signal for controlling the z-direction position is supplied so as to be superimposed on the scanning signal so as to keep the displacement of the cantilever 64 constant.

In this way, the common electrode 16 is kept at a constant potential, and the z-direction drive signal is applied to the drive electrodes 22, 24, 26 and 2.
In the z direction, when the z direction drive signal is supplied to the common electrode, an operation that does not include an undesired displacement in the xy directions caused by the characteristic variation can be obtained.

Even if the z-direction driving signal is applied to the common electrode and the xy scanning signal reflecting the z-direction driving signal is applied to the driving electrode, the ideal scanning as described above can be realized. In this case, control is complicated, but there is an advantage that an inexpensive low-voltage amplifier can be used as the high-voltage amplifier for driving the scanner.

Further, if a displacement sensor for measuring the displacement of the tube scanner 12 in the xyz direction is incorporated in the AFM of this embodiment and feedback control is performed using this displacement sensor, even better scanning can be realized.

[0029]

As described above, according to the present invention, there is provided a scanner system that performs an ideal operation that does not include the influence of variations in the characteristics of the drive electrodes of the tube scanner.
This is very useful for SPM and the like that requires highly accurate position control, and is effective in improving measurement accuracy.

[Brief description of drawings]

FIG. 1 shows a configuration of a first embodiment of a scanner system of the present invention.

FIG. 2 shows the configuration of a second embodiment of the scanner system of the present invention.

FIG. 3 is an AFM incorporating the scanner system of FIG.
Shows the configuration of.

FIG. 4 is a perspective view showing the configuration of a tube scanner (A).
It is a top view (B).

FIG. 5 is a hysteresis curve showing the characteristics of the tube scanner.

[Explanation of symbols]

12 ... Tube scanner, 14 ... Piezoelectric body, 16 ... Common electrode, 22, 24, 26, 28 ... Drive electrode, 32, 3
4, 36, 38 ... Scan signal generating circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuichi Ito 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd. (72) Akira Yagi 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd.

Claims (1)

[Claims] 1. A tube scanner comprising a cylindrical piezoelectric body, one common electrode provided on the inner peripheral surface thereof, and a plurality of drive electrodes provided on the outer peripheral surface, and characteristics of the plurality of drive electrodes of the tube scanner. Scanner system having means for supplying scan signals independent of each other.