JPH08166392A - Scanning probe microscope - Google Patents

Abstract

PURPOSE: To provide the scanning probe microscope, which can accurately measure the irregularities of the surface of a sample, wherein large irregularities of about several μm and minute irregularities of about several nm are mixed, without distortion. CONSTITUTION: The scanning probe microscope has a tube scanner 12 for moving a sample 8, a probe 14, which is supported by a cantilever 16, a driver 20 for driving the scanner 12, a displacement sensor 30 for detecting the displacement of the scanner, an operating circuit 34, which forms the irregularity image of the surface of the sample, and a monitor 36 for displaying the irregularity image. Furthermore, the following parts are provided. A low-pass filter 40 removes the high-frequency component from a Z displacement signal dz outputted from the displacement sensor 30. A bypass filter 42 removes the low-frequency component from a Z driving signal Zdrv outputted from the driver 20. An adder 44 adds the low-frequency signal ZL and the high-frequency signal ZH. A switch 52 selects the signal of the height information, which is inputted into the operating circuit 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope for measuring irregularities on the surface of a sample.

[0002]

2. Description of the Related Art A scanning probe microscope is known as an apparatus capable of observing a fine shape of a sample surface at an atomic level, and is known as a scanning tunneling microscope (STM).
pe) and Atomic Force Microscop (AFM)
e) is particularly well known.

As described in US Pat. No. 4,343,993, the STM applies a bias voltage between a conductive probe and a conductive sample to bring the probe close to the sample at a distance of about several nm. At this time, a tunnel current flowing between the probe and the sample is detected, and the probe is scanned along the sample surface while controlling the distance between the probe and the sample so as to keep the tunnel current constant. The magnitude of the tunnel current exponentially depends on the distance between the probe samples,
The image of the sample surface formed from the height information of the probe and the position information of the probe with respect to the sample surface, which is controlled based on this, changes greatly even with a minute change in the distance between the sample and the probe, and the image of the sample surface is at the atomic level. It will have resolution.

AFM is also disclosed in US Pat. No. 4,724,31.
As described in No. 8 etc., when a probe supported by the tip of a flexible cantilever is brought close to a sample up to a distance of about several nm, a minute force called atomic force generated between atoms on the probe tip and the sample surface is called. The displacement of the tip of the cantilever caused by various forces is detected, and the probe is scanned parallel to the sample surface while controlling the distance between the probe and the sample so as to keep this displacement constant. Since the magnitude of the interatomic force greatly changes even with a minute change in the distance between the probe and the sample, it is formed from the height information of the probe controlled based on this and the position information of the probe with respect to the sample surface. The image of the sample surface has atomic resolution.

In such a scanning probe microscope, scanning is performed by moving the probe and moving the sample, and the probe is also moved by controlling the distance between the probes. Some are performed by moving the sample. Regardless of the type, a piezoelectric actuator that can be controlled with an accuracy of nm unit is generally used for scanning and controlling the distance between probe samples.

The displacement of the piezoelectric actuator, that is, the amount of movement of the probe or the sample is usually estimated from the drive voltage assuming that the characteristic of the drive voltage of the piezoelectric actuator versus the displacement is linear. However, in reality, the characteristics of drive voltage vs. displacement are not linear in a strict sense, and have hysteresis.
There is a gap between the displacement estimated from the drive voltage and the actual displacement. If the hysteresis loop is small, that is, if the displacement variation is limited to a small range, this deviation is
Since the approximate straight line passing through both ends of the hysteresis loop and the hysteresis loop almost overlap, they can be sufficiently ignored. However, when the hysteresis loop is large, that is, when the displacement variation covers a wide range, the deviation between the approximate straight line and the hysteresis curve becomes large, and the error due to hysteresis cannot be ignored.

For this reason, recently, there has been proposed a scanning probe microscope having a structure in which the displacement of the piezoelectric actuator is not directly estimated from the drive voltage but the movement amount of the probe or the sample is directly measured by an optical means or the like. An example of such a scanning probe microscope is disclosed in JP-A-6-174460. The apparatus is configured to move a sample using a cylindrical piezoelectric actuator, a so-called tube scanner, and detects the amount of movement of the sample in the xyz directions by using four two-division photodiodes arranged around the sample stage. An image of the sample surface is obtained based on the amount of movement. Moreover, the non-linearity of the cylindrical piezoelectric scanner is also corrected based on the amount of movement of the sample in the xy directions.

A scanning probe microscope having such a structure, which is represented by JP-A-6-174460, will be described with reference to FIG. As shown in FIG. 1, this scanning probe microscope has a cylindrical piezoelectric actuator for moving the sample 8 in the xyz directions, a so-called tube scanner 12, a probe 14 supported by a cantilever 16, and a space between the probe 14 and the sample 8. Z driving means for driving the tube scanner 12 so as to keep it constant, and the tube scanner 1 for performing xy scanning of the probe 14.
It has an xy drive means for driving 2, a scanner displacement detection means for detecting the displacement of the tube scanner 12, an arithmetic circuit 34 for forming an image of the sample surface, and a monitor 36 for displaying the image of the sample surface. The z drive means is composed of a probe displacement sensor 18 and a driver 20. The xy driving means includes a waveform generator 22, a waveform generator 24, a correction circuit 26, and a driver 20. Further, the scanner displacement detecting means includes a scanner displacement sensor 30 and a preamplifier 32.
Composed of.

The scanner displacement sensor 30 detects displacements of the free end of the tube scanner 12 in the x-direction, the y-direction, and the z-direction. A signal indicating the displacement is amplified by the preamplifier 32 to generate the x-displacement signal dx and the y-displacement signal. It is output as dy and z displacement signal dz.

At the time of measurement, the distance between the probe 14 and the sample 8 is
It is adjusted so that an atomic force of a predetermined magnitude is generated between them. That is, the probe displacement sensor 14
Is adjusted so that the probe displacement signal z _prv output by the above-mentioned signal has a predetermined value.

The waveform generator 22 is a single waveform x scan signal x.
_{The ref} is generated and output to the correction circuit 26. The waveform generator 24 generates a single-waveform y scanning signal y _ref and outputs it to the correction circuit 26. The correction circuit 26 adjusts the moving speed of the tube scanner 12 in the x direction to be constant.
correcting the x scan signal x _ref based on the x displacement signal dx,
The corrected x scan signal x _cmp is output to the driver 20. Further, the correction circuit 26 uses the y of the tube scanner 12.
The y scanning signal y _ref is corrected based on the y displacement signal dy so that the moving speed in the direction becomes constant, and the corrected y scanning signal y _cmp is output to the driver 20. The driver 20 generates the x drive signal x _drv and the y drive signal y _drv based on the corrected x scan signal x _cmp and the corrected y scan signal y _cmp , and supplies them to the tube scanner 12. Tube scanner 1
2, the upper end moves in the x direction and the y direction according to the x drive signal x _drv and the y drive signal y _drv . As a result, the probe 14
Are scanned along the surface of the sample 8.

During scanning, the probe 14 is displaced in the z direction according to the unevenness of the surface of the sample 8, and the displacement is monitored by the probe displacement sensor 18. The driver 20 drives the tube scanner 12 so as to keep the probe displacement signal z _prv constant. As a result, the probe 14 moves along the surface of the sample while keeping a constant distance from the surface. The position of the probe 14 in the z direction and the position of the probe 14 in the x direction and the y direction with respect to the sample surface are obtained from the displacement of the free end of the tube scanner 12. The displacement of the free end of the tube scanner 12 is detected by the scanner displacement sensor 30. Arithmetic circuit 34
Forms an image of the sample surface based on the x displacement signal dx, y displacement signal dy, and z displacement signal dz output from the scanner displacement sensor 30, and the monitor 36 displays the image.

In the scanning probe microscope having this structure, the displacement signals dx, dy, and dz are all unrelated to the hysteresis of the tube scanner, and an image of the sample surface without distortion can be obtained.

Now, the resolution in the z direction will be considered.
The scanner displacement sensor 30 is generally configured to simultaneously detect displacements in three axial directions in order to meet the demand for downsizing of the apparatus, and its detection accuracy is not so high. On the other hand, the probe displacement sensor 18 has higher accuracy than the scanner displacement sensor 30 because the displacement of the target is limited to one dimension. When the unevenness of the sample surface is limited to about several nm, the influence of the hysteresis of the tube scanner 12 can be ignored, so the height information obtained based on the z drive voltage z _drv is the scanner displacement sensor 30. The accuracy is higher than the height information obtained based on the displacement signal dz. Therefore, when the unevenness of the sample surface is limited to about several nm as described above, not the z displacement signal dz from the scanner displacement sensor 30 but the z drive signal z supplied to the tube scanner 12 as before.
It is preferable to obtain the height information based on _drv .

[0015]

With such a scanning probe microscope, it is difficult to obtain a concavo-convex image of a sample in which large concavities and convexities of about several μm and minute concavities and convexes of about several nm coexist in the z direction without distortion. This is because when the z displacement signal is monitored as a signal of height information, large irregularities can be measured without distortion, but minute irregularities cannot be measured because they are buried in sensor noise, and the z of the tube scanner 12 cannot be measured.
When the drive signal z _drv is monitored as a height information signal, all the irregularities can be measured, but the obtained image is distorted in the z direction due to the nonlinearity of the piezoelectric body. .

An object of the present invention is to provide a scanning probe microscope capable of accurately measuring the surface of a sample in which large irregularities of about several μm and minute irregularities of about several nm coexist with almost no distortion.

[0017]

A scanning probe microscope according to the present invention comprises a probe that is displaced in a direction (z direction) perpendicular to the sample surface in accordance with the uneven shape of the sample surface, and the probe is parallel to the sample surface. Xy scanning means for scanning in various directions (xy directions), probe displacement detection means for detecting the displacement of the probe in the z direction and outputting a signal corresponding thereto, and a piezoelectric element for adjusting the distance between the probe and the sample. And a z drive signal for driving the z actuator so that the distance between the probe and the sample surface is kept constant based on the output signals of the z actuator and the probe displacement detection means.
A driver, a z-displacement detecting means for detecting a z-direction position of an object moved by a z-actuator, and outputting a z-displacement signal corresponding thereto, and a low-frequency component removing means for removing a low-frequency component from the z-driving signal. , Z displacement signal for removing high frequency components from the z displacement signal, and addition means for adding the output of the low frequency component removing means and the output of the high frequency component removing means.

[0018]

The z driver controls the z actuator so that the output signal of the probe displacement detecting means is kept constant.
The z drive signal output by the z driver is a few nm on the sample surface.
It includes a high frequency component corresponding to a minute unevenness of a certain degree and a low frequency component corresponding to a large unevenness of a few μm, and this low frequency component includes a distortion due to hysteresis of the piezoelectric body. This low frequency component is removed by low frequency component removing means such as a high pass filter. Therefore, the output signal of the low-frequency removing means represents minute irregularities of about several nm on the sample surface with almost no distortion. On the other hand, the z displacement signal output by the z displacement detecting means includes a low frequency component corresponding to a large unevenness of about several μm on the sample surface and a high frequency noise component. This noise component is removed by high frequency component removing means such as a low pass filter. Therefore, the output signal of the high frequency removing means accurately represents a large unevenness of about several μm on the sample surface. The output signal of the low frequency removing means and the output signal of the high frequency removing means are added by the adding means. Therefore, the output signal of the adding means accurately represents both minute irregularities of about several nm and large irregularities of several μm on the sample surface.

[0019]

EXAMPLE A scanning probe microscope according to an example of the present invention will be described with reference to FIGS. As can be seen from FIG. 2, the configuration of this embodiment is similar to the above-described conventional example described with reference to FIG. 1, and the same members as those already described are denoted by the same reference numerals in FIG. 2 and will be described in detail in the following description. The description is omitted.

As shown in FIG. 2, the scanning probe microscope of this embodiment is different from the conventional example of FIG. 1 in the structure for obtaining the z displacement of the scanner 12, and in addition to the structure of the conventional example,
A low-pass filter 40 that removes high-frequency components from the z displacement signal dz output from the preamplifier 32, a high-pass filter 42 that removes low-frequency components from the z drive signal z _drv output from the driver 20, and a low-pass filter from the low-pass filter 40. Frequency signal z _L and high pass filter 4
It has an adder 44 for adding the high frequency signal z _H from 2 and a changeover switch 52 for selecting the height information signal input to the arithmetic circuit 34.

The control concerning the x direction and the y direction and the detection of the x displacement signal and the y displacement signal are exactly the same as the conventional example. The control in the z direction is also the same as the conventional example, and the detection of the z displacement signal is different from the conventional example. The detection of the z displacement signal will be described below with reference to FIG.

During the measurement, the driver 20 controls the tube scanner 12 in the z direction so as to keep the probe displacement signal z _prv constant. Z output by the driver 20
The drive signal z _drv has a high frequency component 58 corresponding to minute irregularities of about several nm on the surface of the sample and several μm that changes gently.
And a low frequency component 60 corresponding to a large unevenness. The low frequency component 60 contains distortion due to the effect of hysteresis of the piezoelectric body. The z drive signal z _drv is input to the high pass filter 42 having an appropriate cutoff frequency (for example, 100 Hz), the low frequency component 60 corresponding to the large unevenness is removed, and the high frequency component 58 including the high frequency component 58 corresponding to the minute unevenness is removed. It becomes the signal z _H. The high frequency signal z _H is supplied to the terminal 50 and the adder 44.

On the other hand, the z displacement signal dz output from the scanner displacement sensor 30 includes a low frequency component 56 corresponding to a large unevenness that changes gently and a noise component 54 generated by the scanner displacement sensor 30 and the preamplifier 32. It has become. This noise is noise with a random frequency like white noise. The minute irregularities of about several nanometers are buried in the noise component 54 and cannot be seen. Since the z displacement signal dz is a measurement of the actual displacement of the tube scanner 12 in the z direction, the relationship between the signal and the displacement is linear. This z displacement signal dz is input to the low pass filter 40, and the high frequency noise component 5
4 is removed, and a low-frequency signal z _L composed of a low-frequency component 56 corresponding to large unevenness is formed. Low frequency signal z _L is terminal 4
6 and the adder 44.

The adder 44 adds the low frequency signal z _L and the high frequency signal z _H. The added signal z _HL includes a low frequency component 56 corresponding to large unevenness and a high frequency component 58 corresponding to minute unevenness. The high frequency component 58 is
With the drive voltage of the tube scanner 12 corresponding to minute irregularities, the influence of non-linearity inherent in the piezoelectric body can be ignored. Therefore, the added signal z _HL very accurately represents the actual unevenness on the sample surface.

The height information signal input to the arithmetic circuit 34 is selected by the changeover switch 52. That is, when the terminal 46 is selected by the changeover switch 52, the low frequency signal z _L is input to the arithmetic circuit 34 as the height information signal, and when the terminal 48 is selected, the addition signal z _HL is the height information signal. The signal is input to the arithmetic circuit 34 as a signal, and when the terminal 50 is selected, the low frequency signal z _H is input to the arithmetic circuit 34 as a signal of height information. The arithmetic circuit 34 processes the input height information signal in synchronization with the x displacement signal dx and the y displacement signal dy of the tube scanner 12 to form an uneven image of the sample surface. This uneven image is displayed on the monitor 36.

When the changeover switch 52 is switched to the terminal 48 and the addition signal z _HL is selected as the height information signal, when minute irregularities of several nm and large irregularities of several μm are mixed on the sample surface. Also, as described above, as can be seen from the property of the added signal z _HL , a concavo-convex image of the sample surface with less distortion can be obtained.

When it is desired to accurately measure only large irregularities of several μm on the sample surface, the changeover switch 52 may be switched to the terminal 46 to select the low frequency signal z _L as the height information signal. Further, when it is desired to accurately measure only minute irregularities of about several nm on the sample surface, the changeover switch 52 may be switched to the terminal 50 to select the low frequency signal z _L as the height information signal. When the measurement target is limited in this way, the adder 4 is added to the height information signal.
This is preferable in terms of accuracy because noise due to 4 is not included.

In this embodiment, with respect to the x and y directions,
The tube scanner 12 is feedback-controlled based on the displacement signals dx and dy output from the scanner displacement sensor 30, but the feedback control is not necessarily required. That is, the x-direction and the y-direction may be open-controlled, and in this case, the only difference is that the intervals between the measurement points become uneven when sampling is performed at a constant timing, and the image of the sample surface is as described above. Similar to the embodiment, it can be obtained with almost no distortion.

Further, in the embodiment, the scanning probe microscope of the type in which the sample is moved has been described as an example, but the technical idea of the present invention can of course be applied to the scanning probe microscope in the type of moving the probe. is there.

The present invention includes the technical ideas described below, and naturally, the present invention includes modifications, improvements, and modifications without departing from the technical ideas. 1. A scanning probe microscope for measuring unevenness of a surface of a sample, the probe being displaced in a direction (z direction) perpendicular to the surface of the sample corresponding to the unevenness of the surface of the sample, and the probe being parallel to the surface of the sample. Xy scanning means for scanning in the directions (xy directions), probe displacement detection means for detecting the displacement of the probe in the z direction and outputting a signal corresponding thereto, and a piezoelectric element for adjusting the distance between the probe and the sample. Based on the output signals of the z actuator and the probe displacement detection means, az driver that outputs az drive signal that drives the z actuator so as to keep the distance between the probe and the sample surface constant, and az of an object that is moved by the z actuator. Z-displacement detecting means for detecting a position in the direction and outputting a z-displacement signal corresponding thereto, and a low frequency for removing low-frequency components from the z-driving signal. And component removing means, z and the high frequency component removing means for removing high frequency components from the displacement signal, the low frequency component removing means and the output of the high frequency component removing means has a scanning probe microscope and an adding means for adding the output of. 2. In the first term, the xy scanning means outputs an xy actuator composed of a piezoelectric element for changing the relative position of the probe and the sample in the xy direction, and an xy scanning signal for driving the xy actuator to perform xy scanning. The scanning probe microscope has an xy driving means, and an xy of an object moved by an xy actuator.
The xy drive means further includes xy displacement detection means for detecting a position in the direction and outputting an xy displacement signal corresponding thereto.
Scanning signal generating means for generating an xy scanning signal, correction means for correcting the xy scanning signal based on the xy displacement detection signal and outputting a corrected xy scanning signal, and xy for driving an xy actuator based on the corrected xy scanning signal. A scanning probe microscope including a driver, wherein the xy actuator and the z actuator constitute a single xyz actuator, and the xy displacement detecting means and the z displacement detecting means constitute a single xyz displacement detecting means. 3. The scanning probe microscope according to the second item, wherein the xyz actuator is a cylindrical piezoelectric actuator. 4. In the second item, the scanning probe microscope further includes a calculation unit that forms an image of the sample surface based on the addition signal output from the addition unit and the xy displacement signal output from the xy displacement detection unit. Scanning probe microscope. 5. In the second item, the scanning probe microscope forms an image of the sample surface based on any one of the output of the addition unit, the output of the high frequency component removal unit, and the output of the low frequency component removal unit, and the xy displacement signal. And a switch means for selecting any one of the output of the adding means, the output of the high frequency component removing means and the output of the low frequency component removing means and inputting it to the computing means. microscope. 6. The scanning probe microscope according to the second item, wherein the xyz actuator moves the sample. 7. A scanning probe microscope according to the second item, wherein the xyz actuator moves the probe.

[0031]

According to the present invention, even for a sample in which large irregularities of about several μm and minute irregularities of about several nm are mixed, the irregularities on the surface can be accurately measured with almost no distortion. A probe microscope is obtained.

[Brief description of drawings]

FIG. 1 schematically shows the configuration of a conventional scanning probe microscope.

FIG. 2 schematically shows a configuration of an embodiment of a scanning probe microscope of the present invention.

FIG. 3 shows waveforms of various signals related to height information.

[Explanation of symbols]

12 ... Piezoelectric tube scanner, 14 ... Probe, 18
... probe displacement sensor, 20 ... driver, 30 ... scanner displacement sensor, 40 ... low pass filter, 4
2 ... High-pass filter, 44 ... Adder.

Claims (2)

[Claims] 1. A probe which is displaced in a direction perpendicular to the sample surface (z direction) corresponding to the uneven shape of the sample surface, and an xy scanning means for scanning the probe in a direction parallel to the sample surface (xy directions). , A probe displacement detecting means for detecting the displacement of the probe in the z direction and outputting a signal corresponding thereto, a z actuator composed of a piezoelectric element for adjusting the distance between the probe and the sample, and an output signal of the probe displacement detecting means Based on this, the z driver that outputs the z drive signal that drives the z actuator so as to keep the distance between the probe and the sample surface constant, and the position in the z direction of the object that is moved by the z actuator are detected, and the corresponding z displacement A z displacement detecting means for outputting a signal, a low frequency component removing means for removing a low frequency component from the z drive signal, and a high frequency component for removing a high frequency component from the z displacement signal A scanning probe microscope comprising: high-frequency component removing means for removing; and adding means for adding the output of the low-frequency component removing means and the output of the high-frequency component removing means. 2. The xy scanning means according to claim 1, wherein the xy scanning means comprises an xy actuator made of a piezoelectric element for changing the relative position of the probe and the sample in the xy direction, and an xy actuator for driving the xy actuator to perform xy scanning. The scanning probe microscope further includes xy driving means for outputting a scanning signal, and the scanning probe microscope further includes xy displacement detecting means for detecting an xy position of an object moved by an xy actuator and outputting an xy displacement signal corresponding to the position. The xy driving means includes a scanning signal generating means for generating an xy scanning signal, a correcting means for correcting the xy scanning signal based on the xy displacement detection signal, and outputting a corrected xy scanning signal, and a correction x
an xy driver that drives an xy actuator based on the y scan signal, wherein the xy actuator and the z actuator are a single x
A scanning probe microscope that constitutes an yz actuator, and that the xy displacement detecting means and the z displacement detecting means constitute a single xyz displacement detecting means.