JPH04348204A - Scanning probe apparatus - Google Patents

Abstract

PURPOSE:To obtain a scanning probe apparatus which can maintain the distance between a probe and a sample constant in the atomic level even at the high- speed scanning time. CONSTITUTION:A probe 33 provided opposite to a sample 32 is coupled to a driving part 35 which is constituted of a piezoelectric element 38 for ensuring a large expansion/contraction amount and a piezoelectric element 39 for a small amount of expansion/contraction coupled to the piezoelectric element 38 in the Z-axis direction. In order to maintain the gap between the sample 32 and the probe 33 constant at all times, when the gap distance is changed, the piezoelectric element, 38 is driven by a first gap control system 41, and the piezoelectric element 39 is driven by a second gap control system 42 having a smaller driving time constant than the first gap control system 41.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe device used in surface measurement devices, surface treatment devices, surface processing devices, and the like.

0002

[Prior Art] In recent years, scanning tunneling microscopes (hereinafter referred to as
It is abbreviated as STM. ) has appeared. This STM is
The structure of the sample surface can be measured at the atomic level by scanning the surface of a conductive sample with a pointed conductive probe and measuring the tunneling current that flows between the sample and the probe. I have to. This STM uses a tunnel current flowing between the sample and the probe for measurement, so it is limited to conductive samples only. On the other hand, recently, ST
Microscopes that apply M to the surface of electrical insulator samples have appeared. This method measures the structure of the sample surface by supporting the probe with a cantilever and measuring the displacement of the cantilever caused by the force acting between the sample surface and the probe using the STM principle. Atomic Force Microsc
It is called AFM). In this AFM, as in STM, if the displacement of the cantilever is measured while scanning the sample surface with the probe, the shape of the sample surface (
structure) can be measured in three dimensions.

[0003]STM and AFM can be applied not only to the surface measurement of a sample but also to various other applications. For example, after measuring the surface structure, by moving the probe to a desired position on the surface and applying a pulse voltage between the probe and the sample, it is also possible to perform atomic-scale microfabrication directly below the probe. Furthermore, it is also possible to form fine irregularities on the sample surface by colliding the probe with the sample surface. In other words, it can also be applied to processing equipment. Furthermore, if there are gas or liquid molecules between the probe and the sample, the electric field caused by the applied voltage can cause the molecules to be adsorbed to or detached from the sample, and can also be applied to surface treatment devices.

By the way, in such STM and AFM, it is necessary to scan the surface of the sample with the probe as described above. The so-called scanning probe device that realizes this scanning usually has a gap length control system that always maintains a constant gap length between the probe and the sample, and a gap length control system that moves the probe and sample in a direction along the sample surface. The scanning system is configured as shown in FIG. This figure shows one for STM, and in particular shows in detail the gap length control system 1 that always maintains the gap length between the probe and the sample constant during scanning.

[0005] In the figure, 2 indicates a sample, and 3 indicates a probe disposed opposite to the surface of the sample 2. The probe 3 is fixed to a shaft 4, and this shaft 4 is connected to a piezoelectric element 5, which is an actuator for driving in the Z-axis direction. The shaft 4 is also connected via a connecting shaft 6 to a piezoelectric element 7 which is an actuator for driving in the X and Y axis directions.

A bias power supply 8 is connected to the sample 2 for causing a tunnel current to flow between the sample 2 and the probe 3 . The tunnel current flowing between the sample 2 and the probe 3 is I/
After being converted into a voltage signal by V amplifier 9, log amplifier 10
will be introduced in This log amplifier 10 has a tunnel current,
In other words, the exponential change in the output of the I/V amplifier 9 depending on the gap length between the sample 2 and the probe 3 is linearized. The output of log amplifier 10 is introduced into one input of subtractor 11. This subtracter 11 introduces the output of the reference power supply 12 into the other input terminal and outputs a difference signal. This difference signal is amplified by an error amplifier 13, and then introduced into an amplifier 17 for driving the piezoelectric element via a time constant circuit 16 consisting of a resistor 14 and a capacitor 15. Then, the piezoelectric element 5 is driven by the output of the amplifier 17. Note that the piezoelectric element 7 for driving in the X and Y axis directions is driven by a scanning control system (not shown).

As described above, the gap length control system 1 of the conventional scanning probe device is designed to maintain a constant tunneling current flowing between the sample 2 and the probe 3, that is, to keep the tunnel current flowing between the sample 2 and the probe 3 constant. The piezoelectric element 5 for driving in the Z-axis direction is driven so that the gap length between the two is always constant. Then, the input signal of the amplifier 17 is taken out as an observation signal. Therefore, if the surface of the sample 2 has unevenness at the atomic level, the observation signal will change corresponding to the unevenness, and the surface shape of the sample 2 can be determined from this change.

However, the conventional scanning probe device configured as described above has the following problems. That is, the surface of the sample 2 is not necessarily parallel to the XY plane, but often has a certain inclination. For this reason,
In order to be able to measure surface irregularities over a wide range of the surface of the sample 2, it is necessary to use a piezoelectric element 5 with a large amount of expansion and contraction. For this reason, the piezoelectric element 5 is usually formed by laminating a plurality of piezoelectric element pieces, and a high voltage amplifier is used as the amplifier 17 to meet the requirements. However, high voltage amplifiers generally have slow response speed (large time constant) and large noise. For this purpose, for example, with a sample 2 having a surface shape as shown in FIG. As shown in Figure 7(a), the piezoelectric element for axial drive has a time of 15 minutes until the peak value.
When the probe 3 is reciprocated in the X-axis direction by applying a triangular wave as short as milliseconds, the observation signal corresponds only to the tilt of the sample 2 in the X-axis direction, as shown in Figure 7(b). Therefore, it does not correspond to the surface irregularities, that is, the atomic positions. FIG. 8 shows observation signal images obtained when the surface of a graphite sample was scanned 64 times in the Y-axis direction under similar driving conditions. The time required was 2 seconds, but it was not possible to observe atoms on the surface. Note that when the scanning speed was slowed and the region shown in FIG. 8 was scanned for 3 minutes, it was possible to observe even atoms.

As described above, in the conventional scanning probe device, the upper limit of the scanning speed at which the surface of the sample 2 can be scanned is the piezoelectric element 5.
The drive time constant of the gap length control system 1 that drives the piezoelectric element 5 is determined by the response speed of the high voltage amplifier that applies voltage to the piezoelectric element 5, and there is a problem that it cannot be made faster in principle. Such a slow scanning speed causes various problems. That is, the surface shape of a sample often changes over time. Therefore, when a conventional scanning probe device is used, the current surface condition cannot be measured in near real time. The performance of this type of device is determined by how fast it can measure surfaces. Furthermore, in surface processing, the performance of the equipment is determined by how fast surface micromachining can be performed.

[0010] Therefore, in order to eliminate such problems, it may be possible to manufacture a high-speed high-voltage amplifier with low noise and high response speed, but realizing this is accompanied by technical difficulties and costs. This means that it is inevitable that the increase in

[0011]

[Problems to be Solved by the Invention] As mentioned above, conventional scanning probe devices have the problem that they cannot contribute to high-speed measurements, processing, processing, etc. because the scanning speed cannot be increased. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a scanning probe device that can eliminate the above-mentioned problems.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a probe disposed opposite to the surface of a sample;
a gap length control means for always keeping the gap length between the probe and the sample constant; In the scanning probe device, the gap length control means includes a plurality of actuators that relatively move the probe and the sample by a displacement amount that is the sum of the displacement amounts of each actuator. and a plurality of control systems having different drive time constants that drive the corresponding actuators in response to changes in the gap length between the probe and the sample.

[0014] The sample referred to herein refers to the sample itself when applied to STM, and refers to a sample simulated by the displacement of a cantilever when applied to AFM.

[0015]

[Operation] Now, two actuators are provided, one actuator is formed by a first piezoelectric element, and the other actuator is formed by a second piezoelectric element that can obtain a larger displacement than the first piezoelectric element. If the drive time constant of the control system that drives the first piezoelectric element is smaller than the drive time constant of the control system that drives the second piezoelectric element, then the second piezoelectric element and the control system that drives it are Since the response speed is slow, the probe and the sample are moved relative to each other by following the gentle slope of the sample. Furthermore, since the first piezoelectric element and the control system that drives it have a fast response speed, the probe and the sample are moved relative to each other by following the minute irregularities on the sample surface. Therefore, even if the scanning speed is increased, the gap length between the probe and the sample can always be kept constant, and the surface microstructure can be measured with high resolution while scanning over a wide range of the sample surface at high speed. You can contribute to processing.

[0016]

Embodiments Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 shows a scanning probe device according to an embodiment of the present invention, which is a scanning probe device for STM, and only the gap length control system 31 is shown in detail.

In the figure, 32 indicates a sample, and 33 indicates a probe disposed opposite to the surface of the sample 32. The probe 33 is fixed to a shaft 34, and this shaft 34 is connected to a drive section 35 for driving in the Z-axis direction. In addition, the shaft 34
is connected via a connecting shaft 36 to a piezoelectric element 37 which is an actuator for driving in the X and Y axis directions.

The drive unit 35 includes an actuator formed of a piezoelectric element 38 that can expand and contract to accommodate large displacements of about 3000 to 5000 angstroms such as inclination and deformation of the surface of the sample 32, and The actuator is connected in the Z-axis direction with an actuator formed of a piezoelectric element 39 that can expand and contract an amount that can correspond to minute displacements. Specifically, the piezoelectric element 38 has an expansion/contraction rate of 5 angstroms per volt, and the piezoelectric element 39 has an expansion/contraction rate of 1 angstrom/volt.

A bias power supply 40 is connected to the sample 32 for causing a tunnel current to flow between the sample 32 and the probe 33. A battery is used as the power source 40 to avoid noise.

The piezoelectric element 38 is driven by a first gap length control system 41, and the piezoelectric element 39 is driven by a second gap length control system 4.
2.

The first gap length control system 41 converts the tunnel current flowing between the sample 32 and the probe 33 into I/V amplifiers (with amplification factors of 107 V/A, 108 V/A, and 109 V/A).
You can switch to ) 43 into a voltage signal, and this converted signal is introduced into one input terminal of a subtracter 45 via a log amplifier 44. This subtracter 45 inputs the output of the reference power supply 46 to the other input terminal and outputs a difference signal. After this difference signal is amplified by an error amplifier 13, it is introduced into a high voltage amplifier 51 via a time constant circuit 50 consisting of a resistor 48 and a capacitor 49. The high voltage amplifier 51 has an input amplitude of ±5V, an amplification factor of 100 times, and an output amplitude of ±500V.
V, the noise level is 7 mV at the maximum amplitude, and the response time constant varies between about 0.1 and 10 seconds. The piezoelectric element 38 is driven by the output of the high voltage amplifier 51.

On the other hand, the second gap length control system 42 introduces the output of the above-mentioned log amplifier 44 into one input terminal of the subtracter 52. Then, the output of the reference power supply 46 is introduced into the other input terminal of the subtracter 51 to output a difference signal, and this difference signal is amplified by an error amplifier 53 and then passed through a time constant circuit 56 consisting of a resistor 54 and a capacitor 55. It is introduced into the amplifier 57. The amplifier 57 used has an amplification factor of 1, an input amplitude and an output amplitude of ±5 V, a noise level of 0.5 mV or less at the maximum amplitude, and a response time constant of about 1 to 100 milliseconds. The piezoelectric element 39 is driven by the output of the amplifier 57. Further, the input signal of the amplifier 57 is used as an observation signal, and the input signal of the high voltage amplifier 51 is also used as an observation signal if necessary.

The piezoelectric element 37 for driving the probe 33 in the X-axis direction and the Y-axis direction is driven by the output of a scanning control system (not shown).

Next, the operation of the scanning probe device constructed as described above will be explained.

The scanning control system is operated to drive the piezoelectric element 37 to scan the surface of the sample 32 in the X and Y axis directions with the probe 33 placed close to the surface of the sample 32. At this time, the first gap length control system 41 and the second gap length control system are used so that the value of the tunnel current flowing between the sample 32 and the probe 33 is always the value specified by the output level of the reference power source 46. The system 42 causes the piezoelectric element 3 to follow the irregularities on the surface of the sample 32.
Controls the amount of expansion and contraction of 8 and 39. Therefore, the gap length between the sample 32 and the probe 33 is always kept constant.

In this case, since the first gap length control system 41 uses the high voltage amplifier 51 because it is necessary to ensure a large amount of expansion and contraction, a fast response speed cannot be expected; It is able to sufficiently follow small and gradual displacements. On the other hand, since the second gap length control system 42 does not require a large amount of expansion and contraction, the amplifier 57 with a fast response speed can be used, so that it can sufficiently follow minute irregularities on the surface of the sample 32. Therefore, the operation of these two gap length control systems 41 and 42 makes it possible to always keep the gap length between the sample 32 and the probe 33 constant even when the scanning speed is high, and the STM When incorporated into AFM, AFM, or processing equipment or surface treatment equipment that utilizes these, it can contribute to realizing good measurement and processing at a high scanning speed.

In FIGS. 2(b) and 2(c), the sample having the surface shape shown in FIG. Using a scanning probe device in which the drive time constant of the long control system 42 is about 1 millisecond, the piezoelectric element for driving in the X-axis direction has a time to peak value of 15 milliseconds, as shown in Figure 2(a). A change in the input signal of the high voltage amplifier 51 and a change in the input signal (observation signal) of the amplifier 57 are shown when the probe 33 is reciprocated in the X-axis direction by applying a short triangular wave. As can be seen from these figures, the input signal to the high voltage amplifier 51 corresponds only to the gentle inclination of the sample, and the input signal to the amplifier 57 corresponds to minute irregularities on the sample surface, that is, the atomic positions. Become.

FIG. 3 shows observation signal images obtained when the surface of a graphite sample was scanned 64 times in the Y-axis direction under similar driving conditions. The time required to scan this area was 2 seconds, which is a two-digit improvement in scanning speed compared to conventional devices.

FIG. 4 shows the ratio between the drive time constant τ41 of the first gap length control system 41 and the drive time constant τ42 of the gap length control system 42, and the high voltage amplifier 51 that changes in accordance with the unevenness of the surface atoms. A plot of the ratio of S42 to the sum of the input signal S41 of the amplifier 57 and the input signal S42 of the amplifier 57 is shown. As can be seen from this figure, the effect appears when the ratio of drive time constants is 10 or more.

In this way, the gap length control system 31 that keeps the gap length between the sample 32 and the probe 33 constant is controlled by the first gap length control system that has a slow response speed but can obtain a large amount of expansion and contraction. system 41 and a second gap length control system 42 which does not provide a large amount of expansion and contraction but has a fast response speed. Therefore, the first gap length control system 41 can follow the slope and gentle displacement of the surface of the sample 32, and the second gap length control system
The gap length control system 42 makes it possible to faithfully follow the minute irregularities on the atomic level of the surface of the sample 32, and as a result, even when the scanning speed is high, the sample 3
The gap length between the probe 2 and the probe 33 can always be kept constant. Therefore, when applied to STM, AFM, or surface treatment equipment or processing equipment that applies this, measurement can be performed before the surface state of the sample changes due to thermal drift, etc.
Processing or machining can be completed.

Furthermore, since the first gap length control system 41 does not require a fast response speed, it is possible to use a high voltage amplifier 51 with a low frequency response, that is, an inexpensive high voltage amplifier 51 with less noise. Furthermore, since the voltage applied to the piezoelectric element 39 may be low in the second gap length control system 42, it is also possible to directly apply the output of a general-purpose operational amplifier (IC) with high frequency response and low output noise. can.

It should be noted that the present invention is not limited to the above-mentioned embodiments. That is, in the embodiments described above, the sample is fixed and the probe is moved relative to the sample, but conversely, the probe may be fixed and the sample is moved. In addition, the piezoelectric element 38 is placed on the probe side, and the piezoelectric element 38 is placed on the probe side.
9 may be placed on the sample side, or each piezoelectric element may be placed in the opposite relationship. Further, in the above-described embodiment, the gap length control system has a two-stage structure, but it may have a three-stage structure or more. Furthermore, the scanning probe device according to the present invention includes:
All devices that scan the sample surface with a probe while maintaining a constant gap length between the sample and the probe during measurement, processing, and processing, such as STM, AFM, capacitance microscopes, surface treatment equipment,
It can be applied to devices that perform micromachining on surfaces. Note that when applied to a capacitance microscope, gap length information is obtained from the capacitance between the probe and the sample. In addition, various modifications can be made without departing from the gist of the present invention.

[0034]

[Effects of the Invention] As described above, according to the present invention, the gap length control system that always keeps the gap length between the sample and the probe constant is configured in multiple stages, and a specific stage of these is configured to It is constructed with a drive time constant that is smaller than other types. Therefore, it is possible to follow the inclination or gradual displacement of the sample surface with a drive time constant that is large, and it is possible to faithfully follow the minute irregularities on the atomic level of the sample surface using a specific stage with a small drive time constant. As a result, even when the scanning speed is high, the gap length between the sample and the probe can be kept constant without requiring an expensive amplifier or the like.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of main parts of a scanning probe device according to an embodiment of the present invention.

[Figure 2] Waveform diagrams of various parts when the same scanning probe device is applied to STM and the surface of a sample with a gentle slope is scanned back and forth at high speed.

[Figure 3] Observation signal image diagram obtained when the same scanning probe device was applied to STM to scan a certain area on the surface of a graphite sample at high speed.

FIG. 4 is a diagram showing the drive time constant and signal intensity ratio of the first and second gap length control systems that constitute the gap length control system in the scanning probe device.

[Fig. 5] Schematic diagram of the main parts of a conventional scanning probe device

[Figure 6] Diagram showing an enlarged view of the relationship between the sample and the probe

[Figure 7]
Waveform diagrams of various parts when applying a conventional scanning probe device to STM and scanning back and forth at high speed on the surface of a sample with a gentle slope as shown in Figure 6.

[Fig. 8] Observation signal image diagram obtained when a conventional scanning probe device was applied to STM to scan a fixed area on the surface of a graphite sample at high speed.

[Explanation of symbols]

31...Gap length control system,
32...sample, 33...probe,
35... Drive unit, 37... Piezoelectric element for driving in the X and Y axis directions, 38,
39... Piezoelectric element, 40... Bias power supply,
41...First gap length control system, 42...Second gap length control system,
43...I/V amplifier, 44...log amplifier,
45, 52...Subtractor, 46...Reference power supply,
51...High voltage amplifier, 57...Amplifier.

Claims (3)

[Claims] 1. A probe disposed opposite to the surface of a sample; gap length control means for always maintaining a constant gap length between the probe and the sample; and scanning means for scanning the surface of the sample with the probe by relative movement in a direction along the surface of the sample, wherein the gap length control means is configured to adjust the distance between the sum of the respective displacement amounts. A plurality of actuators that relatively move the probe and the sample by a displacement amount, and a plurality of actuators having different drive time constants that drive the corresponding actuators in response to a change in the gap length between the probe and the sample. A scanning probe device comprising a control system. 2. Two actuators are provided, one of which is formed of a first piezoelectric element,
The other actuator is formed of a second piezoelectric element that can obtain a larger displacement amount than the first piezoelectric element, and
2. The scanning probe device according to claim 1, wherein a drive time constant of the control system for driving the second piezoelectric element is smaller than a drive time constant for the control system for driving the second piezoelectric element. 3. A drive time constant of a control system that drives the first piezoelectric element is one-tenth or less of a drive time constant of a control system that drives the second piezoelectric element. The scanning probe device according to claim 2.