JPH09281119A - Probe-sample approach mechanism of scanning type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the responsiveness, to attain a high-speed automatic approach in an operation for approach between a probe and a sample, to have a fail-safe function and to prevent breakdown of the probe and the sample. SOLUTION: This scanning type probe microscope executes an operation for approach in the atmospheric environment and it is equipped with a cantilever 11 having a probe 12 in the tip part. An adsorption layer is formed on the surface of a sample. A probe-sample approach mechanism includes a Z stage 31 conducting a rough motion. The Z stage includes a stepping motor and is driven by a pulse signal. Besides, a piezoelectric element 13 for vibrating the cantilever is provided. The pulse signal for driving the Z stage is generated on the basis of the vibrating operation of the cantilever.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe / sample approach mechanism for a scanning probe microscope, and more particularly to a probe for a scanning probe microscope driven by a pulse signal and having a high-speed automatic approach function and a fail-safe function. Regarding the sample approach mechanism.

[0002]

2. Description of the Related Art For example, when observing the surface of a sample with an atomic force microscope, it is necessary to bring a probe close to the sample surface to a predetermined minute distance before the observation. Therefore, the atomic force microscope has a probe / sample approach mechanism. In controlling the operation of the probe / sample approach mechanism, it is important to avoid damage to the probe and the sample due to collision of the probe with the sample. As an example of a conventional probe / sample approach mechanism having such a function, Japanese Patent Laid-Open No. 5-4
The technique disclosed in Japanese Patent No. 5111 will be given. The technical document is a probe (probe) in a scanning probe microscope.
A probe self-propelled approach mechanism for automatically approaching the sample without colliding with the sample is disclosed. This probe automatic approach mechanism is composed of a fine movement mechanism for finely moving the probe, a coarse movement mechanism for moving the sample stage, and a control means for controlling each operation of these fine movement mechanism and coarse movement mechanism.
When the distance between the sample and the probe is detected and it is determined that the distance has reached the predetermined distance, the operation of the coarse movement mechanism is stopped,
Moreover, the operation of the fine movement mechanism is retracted in the direction in which the probe is separated from the sample. In this way, the coarse movement mechanism that causes a large movement is stopped, and the fine movement mechanism retracts the probe to avoid collision between the probe and the sample. When the fine movement mechanism is caused to perform the retracting operation, the feedback circuit used in the normal control is not used to improve the responsiveness.

[0003]

In the above-mentioned conventional apparatus,
By combining the operation of the coarse movement mechanism and the operation of the fine movement mechanism, the approach of the probe to the sample is suddenly stopped to prevent contact between the probe and the sample. In such a configuration, the responsiveness is determined by the operating characteristics of the fine movement mechanism, and the frequency related to the responsiveness is generally several kHz. However, at present, the atomic force microscope is required to have a higher speed, and the responsiveness of the fine movement mechanism is an obstacle to the increase in the approach speed. This is a common problem for scanning probe microscopes.

A first object of the present invention is to solve the above-mentioned problems, and to improve the responsivity, a probe for a scanning probe microscope capable of achieving high-speed automatic approach in the approach operation between the probe and the sample. It is to provide a needle / sample approach mechanism.

Another object of the present invention is to provide a probe / sample approaching mechanism of a scanning probe microscope which can realize a fail-safe function by itself without adding a special structure and prevent destruction of a probe or a sample. To do.

[0006]

Means and Actions for Solving the Problems The probe / sample approaching mechanism of the scanning probe microscope according to the first aspect of the present invention (corresponding to claim 1) is as follows in order to achieve each of the above objects. Is composed of. The scanning probe microscope according to the present invention is used for measuring operation and approaching operation in an atmospheric environment.
A cantilever having a probe (also referred to as a probe) arranged at the tip so as to face the measurement surface of the sample at the time of measurement is provided, and further, a mechanism portion for making the cantilever and the sample approach or separate from each other. As a matter of course, an adsorption layer is formed on the surface of the sample in the atmospheric environment. The probe moves closer to the surface of the sample at a required interval by the approaching motion of either the cantilever or the sample, and as a result, based on the interaction between the probe and the surface of the sample, the fine characteristics of the surface (uneven shape, etc.) To measure. The probe / sample approaching mechanism according to the present invention is applied to such a scanning probe microscope, and relates to the configuration of the above-mentioned mechanism portion that causes the cantilever and the sample to approach or separate from each other. The probe / sample approach mechanism includes an approach device (Z stage) that performs a moving operation (coarse motion) so that the probe and the sample approach each other at a relatively large distance. This approaching device is constituted by, for example, a stepping motor, and is driven by a pulse signal. Further, the cantilever is configured to oscillate (vibrate), and an oscillation device therefor is provided. A characteristic configuration of the present invention is that a pulse signal generated based on an oscillation signal obtained from an oscillation operation of a cantilever is used as a pulse signal for driving the approaching device.

According to the structure of the first aspect of the present invention, when the probe and the sample are brought close to each other, the cantilever is oscillated, and the alternating electric signal obtained by the oscillating operation of the cantilever is used,
A pulse signal for driving the approaching device is generated. Therefore, the adsorption layer on the surface of the sample draws in the probe just before the sample comes into contact with the probe, which stops the oscillation of the cantilever, eliminates the generation of the pulse signal, and stops the approach operation automatically. Becomes While performing a high-speed approaching operation, it is possible to stop the probe and the sample at an appropriate distance while preventing the probe from colliding with the sample and preventing damage to the probe and the sample.

A probe / sample approaching mechanism of a scanning probe microscope according to a second aspect of the present invention (corresponding to claim 2) is a conversion mechanism for converting an oscillation operation of a cantilever into an AC electric signal in the structure of the first aspect of the invention. A wave shaper for converting an AC electric signal into a square wave signal, and a frequency divider for dividing the square wave signal, and the frequency division signal obtained by this frequency divider is used as the pulse signal. Composed.

[0009]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the present invention. For example, an atomic force microscope (hereinafter AFM) in a normal contact mode equipped with a probe / sample approach mechanism according to the present invention.
That is, the embodiment will be described. The AFM operates in contact mode when observing the sample surface. Also the AF
M is premised on that the measurement is performed in the atmospheric environment. Therefore, before the start of the measurement, an adsorption layer is formed on the surface of the sample placed in the atmosphere. This adsorption layer is formed in layers when water molecules in the atmosphere reach the surface of the sample, and is a layer of about several nanometers. The probe / sample approach mechanism according to the present invention is
This is a device for bringing the probe and sample closer to the required distance in the stage before measuring and observing the sample surface in the atmospheric environment and contact mode by FM, and with a relatively large movement distance (coarse movement). Perform an approaching motion. According to FIG. 1, a contact mode AFM including a probe / sample approach mechanism according to the present embodiment.
The configuration and operation of will be described.

Reference numeral 11 is a cantilever, and the probe 1 is attached to its tip.
2 are provided. The base of the cantilever 11 is fixed to the upper part of the frame 14 via the piezoelectric element 13 for vibration. An XYZ scanner 15 and a Z stage 31 are provided below the frame 14. The XYZ scanner 15 is provided on a Z stage 31, and the Z stage 31
4 is fixed to the lower part. A sample 16 is arranged on the upper surface of the XYZ scanner 15. The XYZ scanner 15 includes a fine movement drive unit (X-axis direction drive unit, Y-axis direction drive unit) including a piezoelectric element for generating minute displacement in each of three orthogonal axes (X-axis, Y-axis, Z-axis). Drive section, Z-axis direction drive section). As a result, the sample 16 can be moved by a minute distance in any direction. XYZ scanner 15
Has a function as a fine movement mechanism for adjusting the distance between the probe and the sample during measurement and observation, and for XY scanning movement. Z
The stage 31 moves the XYZ scanner 15 and the sample 16 in a relatively large distance in the Z-axis direction, and performs the operation when the probe 12 and the sample 16 are brought close to each other.
The Z stage 31 has a function as a coarse movement mechanism for approaching movement. The specific structure of the Z stage 31 has, for example, a stepping motor built therein, and the stepping motor performs an operation for the above movement. Therefore, the Z stage 31
A pulse signal 32 as a drive signal for operating the stepping motor is input to the external.

In the above structure, when the surface of the sample 16 is measured, the probe 12 approaches the sample 16 and its tip is substantially in contact with the surface of the sample 16 to be measured.
To face. The approach state between the probe 12 and the sample 16 is set by operating the Z stage 31 which is a coarse movement mechanism before the measurement in the normal contact mode is started.

On the other hand, a laser light source 17 is arranged above the cantilever 11, and a laser beam 18 emitted from the laser light source 17 irradiates a reflecting surface near the front tip of the cantilever 11. The laser beam 18 reflected by the reflecting surface is incident on a light receiving surface of a position sensor (photodetector) 19. The laser light source 17, the cantilever 11, and the position sensor 19 constitute an optical lever type displacement detector (detection optical system). The tip of the cantilever 11 has a probe 12 and a sample 16
When it is displaced in the Z-axis direction in FIG. 1 on the basis of an interatomic force (physical action) generated between the position sensor 19 and the surface, the spot position of the reflected light is displaced within the light receiving surface of the position sensor 19. Position sensor 1
Reference numeral 9 converts the displacement of the spot position of the reflected light into a change in voltage value and outputs it. Thus, a change in the Z-axis direction of the tip of the cantilever 11, that is, a change in the Z-axis direction of the probe 12 is extracted as a change in the output voltage of the position sensor 19.

Next, the control system (signal processing system) will be described. The voltage signal output from the position sensor 19 is supplied to one of the following two systems depending on the connection state of the changeover switch 33. The switching operation of the changeover switch 33 is performed automatically or manually.

The first system is composed of a signal amplifier 34 and a servo device 35 when the changeover switch 33 is connected to the lower terminal 33a in FIG. The first system is a control system related to the normal measurement of the surface of the sample 16. The voltage signal output from the position sensor 19 at the time of measurement is a signal indicating the position of the probe 12 in the Z-axis direction, that is, the amount of deflection of the cantilever 11, and the voltage signal is transmitted to the signal amplifier 34 and the servo device 35. Then, the signal is converted into a drive signal Vz for operating the Z-axis direction drive unit of the XYZ scanner 15 and supplied to the XYZ scanner 15. The signal amplifier 34 amplifies the output signal of the position sensor 19 to a required level. The output signal of the signal amplifier 34 is
5 is input. The servo device 35 includes an arithmetic control unit 3
The input signal is converted into the drive signal Vz according to the servo control conditions instructed via the bus 37 from the arithmetic processing unit 36 including the display unit 36a and the display unit 36b. The drive signal Vz operates the Z-axis direction drive unit in the XYZ scanner 15 to adjust the position of the sample 16 in the Z-axis direction, and the distance between the probe 12 and the sample 16 is a predetermined distance (substantial contact state). And the uneven shape of the surface of the sample 16 is measured.

More specifically, the arithmetic processing unit 36 is composed of a computer and has a CPU and a storage unit built therein. The storage unit stores a program (measurement program) for controlling the operation of the AFM for measuring a desired portion of the sample surface, and measurement data, and from this measurement data, an image relating to the fine shape of the observation surface of the sample 16 is stored. A program (image creation program) for performing processing for creating image data to be displayed on the display unit 36b is stored. The servo device 35 controls the distance between the probe and the sample so that the distance between the probe and the sample is a predetermined distance.
A drive signal Vz of the Z-axis direction drive unit is given to the YZ scanner 15. With the servo device 35 performing the servo operation with respect to the operation in the Z-axis direction by the Z-axis direction drive unit of the XYZ scanner 15, the XYZ scanning circuit unit is used.
Operate the drive units in the X and Y axis directions of the scanner 15,
The probe 12 is caused to scan the XY plane of the sample 16. At this time, the coordinates of the measurement points on the XY plane and Vz (output voltage value of the servo device 35) at each measurement point are stored as measurement data in the storage unit of the arithmetic processing device 36. The measurement data stored in the storage unit is sequentially or collectively processed by the above-described image creation program, creates image data relating to the surface shape of the measurement location on the sample 16, and uses this image data to display the display unit 36b. Display the measurement image on the screen. In this way, the surface shape of the measurement point of the sample 16 is obtained.

In the normal measurement of the sample surface, as described above, in addition to the control in the Z-axis direction for adjusting the distance between the probe and the sample, the position for scanning the sample surface with the probe is used. Control is needed. The drive signal for controlling the scanning position is given to the XYZ scanner 15 as signals Vx and Vy from the XY scanning circuit section incorporated in the arithmetic processing unit 36.

In the contact mode AFM, the cantilever 11 is in a non-vibrating state during the measurement operation, and the probe 12 and the sample 16 are kept in a substantially contact state. Further, during the approaching operation, the cantilever 11 is vibrated (oscillated) by the piezoelectric element 13 as will be described later, and high-speed automatic approaching is performed using an AC signal obtained based on the vibrating state. And the function of fail-safe at the time of contact are formed.

Next, the second system is a case where the changeover switch 33 is connected to the upper terminal 33b in FIG.
It comprises a waveform shaper 41 and a frequency divider 42. This second
The system is the control system associated with the high speed automatic approach mode. The waveform shaper 41 inputs an AC voltage signal, which will be described later, output from the position sensor 19, and based on this, forms a periodic signal having a rectangular waveform of the same frequency. The frequency divider 42
The output signal of the waveform shaper 41 is frequency-divided to generate a pulse signal having a predetermined frequency, and the pulse signal 32 for driving the Z stage 31 is output. The pulse signal 32 is given to the Z stage 31 as a drive signal. Waveform shaper 4
The operation of each of the 1 and divider 42, as well as the method of controlling the high speed automatic approach mode are detailed below.

Reference numeral 43 is an oscillator for giving a signal for driving the vibration piezoelectric element 13 for vibrating the cantilever 11. The oscillator 43 is supplied with a periodic signal for generating a drive signal from the arithmetic processing unit 36.

Next, the operation and control procedure of the control system related to the above-described high-speed automatic approach mode will be described with reference to FIG. 1, FIG. 2 and FIG.

The sample 16 is placed on the XYZ scanner 15 and set. At this time, sample 16 and cantilever 11
Are separated by a few millimeters. In this state, the vibration piezoelectric element 13 is driven by the output signal of the oscillator 43 to cause the cantilever 11 to oscillate at the resonance frequency f ₀ .
Laser light is emitted from the laser light source 18 to the cantilever 11 in the vibrating state, and the reflected light enters the position sensor 19. The vibration operation of the cantilever 11 is monitored by the position sensor 19. FIG. 2A shows the state of the AC electric signal output from the position sensor 19,
The vibration state of the cantilever 11 is substantially shown. The frequency of the AC electric signal 44 is about several tens of kHz.

In the automatic approach mode, the changeover switch 33 is connected to the upper terminal 33b in FIG. In this state, the output signal of the position sensor 19, that is, the electric signal 4
4 is shaped into a square wave signal 45 as shown in FIG. 2B by the waveform shaper 41. This square wave signal 45 is input to the frequency divider 42, and the frequency divider 42 performs frequency division processing. In this embodiment, as shown in FIG. 2 (c), a frequency-divided signal divided into, for example, 1/4 is generated. This frequency-divided signal corresponds to the pulse signal 32 described above. The frequency division ratio is instructed from the arithmetic processing unit 36.

The frequency-divided signal output from the frequency divider 42, that is, the pulse signal 32 is supplied to the Z stage 31.
As described above, the Z stage 31 has a built-in stepping motor, and the stepping motor moves the sample 16 closer to the probe 12 by 0.5 μm per pulse, for example, by using the input frequency dividing signal.

The cantilever 1 in this embodiment
1 is made of, for example, silicon nitride, has a total length of 100 μm,
Spring constant is about 0.1N / m, resonance frequency is about 20kHz
It is.

Now, it is assumed that the Z stage 31 is operated by applying a pulse signal 32 to bring the sample 16 toward the cantilever 11 which is oscillating with an amplitude of several μm. When the frequency division ratio in the frequency divider 42 is set to, for example, 1/16, 1250 pulses are given per second, so Z
The approach speed of the sample 16 by the stage 31 is 625 μm /
Seconds. The sample 16 gradually approaches the cantilever 11 in a vibrating state, that is, the tip probe 12, and a contact state is generated. A state that occurs at the moment of contact between the probe 12 and the surface of the sample 16 will be described with reference to FIGS.

FIG. 3A shows a vibrating cantilever 11.
And the tip 12 of the tip and the sample 16 approaching this
Shows a partial surface of the. The adsorption layer 16 a described above is formed on the surface of the sample 16. Eventually, the tip of the probe 12 tries to contact the surface of the adsorption layer 16a, and the state shown in FIG. Then, the adsorption layer 16a is attached to the probe 12.
The surface tension of the probe acts to draw the probe 12 into the adsorption layer 16a. This state is shown in FIG. Figure 3 (c)
Then, the displacement of the cantilever 11 becomes larger than that in the state of FIG. 3B, and the oscillation of the cantilever 11 is stopped in this state.

On the other hand, referring again to FIG. 2, when the cantilever 11 is displaced in the direction in which the probe 12 moves away from the sample 16, a pulse is output from the waveform shaper 41, and the pulse is continuously generated to generate a square wave signal 45. Is generated. In this way, the square wave signal 45 output from the waveform shaper 41 is frequency-divided to generate a frequency-divided signal, that is, a pulse signal 32 for operating the Z stage 31. Therefore, when the oscillation of the cantilever 11 stops, the square wave signal 45 is not generated, and hence the pulse signal 32 is not generated.

In FIGS. 3A and 3B, the cantilever 1 is
The pulse signal 32 is generated by the oscillation operation of No. 1 to drive the Z stage 31 to bring the sample 16 close to the probe 12, and in the state of FIG. 3C, the probe 12 is drawn into the adsorption layer 16a on the sample surface, Unless the probe 12 is released from the adsorption layer 16a,
The oscillation of the cantilever 11 is held in a stopped state. When the oscillation of the cantilever 11 is stopped, the pulse signal 32 is not output from the frequency divider 42, so that the pulse signal 32 for driving is not input to the Z stage 31 thereafter. Therefore, the sample 16 is held in a stopped state, and high-speed automatic approach is achieved. In this way, the sample 16 approaches the probe 12 (cantilever 11) by the Z stage 31 which is the coarse movement mechanism, and the probe 12 causes the adsorption layer 1 on the sample surface to move.
Upon contact with 6a, the oscillation of the cantilever 11 is stopped by the pulling force of the adsorption layer 16a, the sample 16 does not approach the probe 12 any further, and the automatic approach operation is completed.

According to the above configuration, the desired approach speed can be set by setting the frequency division ratio in the frequency divider 42, and a high speed approach speed can be set. Further, by the action between the adsorption layer 16a on the sample surface and the probe 12, the oscillation of the cantilever 11 can be stopped and the approaching operation between the sample 16 and the probe 12 can be stopped. Fail-safe function to avoid the collision of

Further, when the operation of the Z stage 31 is suddenly stopped, there is a concern that the mechanical system may overshoot as shown by the sample lift 46 in FIG. 3D, but FIG.
As shown in (1), since there is a margin 47 between the probe and the sample, which is the sum of the maximum oscillation amplitude of the cantilever 11 and the displacement due to the suction force of the adsorption layer 16a, the overshoot is absorbed by this margin. It is possible to avoid applying a repulsive force to the cantilever 11 from the sample side. In other words, when the probe 12 first tries to contact the surface of the sample, the adsorption layer 16a causes the cantilever 11 to stand still with a displacement of several μm from the rest position to the sample side.
Moreover, since the operation amount for one pulse in the Z stage 31 is preferably set to be smaller than the displacement amount, there is no concern that a large repulsive force acts between the probe and the sample, and the probe, the sample, etc. Can be prevented from being destroyed. Also in the above meaning, the probe / sample approaching mechanism according to the present embodiment exerts a fail-safe function.

According to the above-described embodiment, by utilizing the pulse drive type Z stage 31 such as the stepping motor, the apparatus for automatically bringing the cantilever 11 and the sample 16 close to each other to the extent that the measurement as the AFM becomes possible is simple. It can be realized by the configuration, and sufficient protection is achieved by the fail-safe function. For example, due to a defect in the laser light source 17 or the position sensor 19, the cantilever 11
Even when the operation of is no longer monitored, the approaching operation of the probe / sample is stopped.

In the above-described embodiment, the Z stage 31, which is the coarse movement mechanism, is provided on the sample side, but it goes without saying that it can be provided on the cantilever side.

Although the AFM has been described in the above embodiments, it is needless to say that the probe / sample approaching device according to the present invention can be applied to a scanning probe microscope having a similar structure and action.

Furthermore, in the above embodiment, the operation at the time of measurement is the contact mode, but the operation is not necessarily limited to this, and the contact mode or the periodic contact mode A is used.
Even in the case of FM, the probe / sample approach mechanism according to the present invention can be applied to set the desired distance between the probe and the sample at the stage before starting the measurement / observation. is there. Further, it is needless to say that the probe / sample approaching mechanism according to the present invention can be applied to scanning probe microscopes in general.

[0036]

As is apparent from the above description, according to the present invention, in the approach between the probe and the sample by the scanning probe microscope, the approach operation in the atmospheric environment in which the adsorption layer is formed on the sample surface. And oscillate the cantilever,
Since the sample-to-sample approach was performed using the pulse drive coarse movement mechanism, and the pulse signal for driving the coarse movement mechanism was made based on the oscillation operation of the cantilever, it is possible to speed up by making the pulse signal appropriately. In addition to being able to automatically approach, the oscillation operation of the cantilever can be safely stopped without damaging the probe or the sample based on the characteristics of the probe pulling action of the adsorption layer and the stopped state of the cantilever.
In this way, the responsiveness can be increased, high-speed automatic approach can be achieved, and further, the fail-safe function can be provided by itself without adding a special configuration.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a typical embodiment of the present invention.

FIG. 2 is a waveform chart showing waveforms of signals of respective parts of the device.

FIG. 3 is a diagram illustrating a contact state between a probe and a sample.

[Explanation of Codes] 11 Cantilever 12 Probe 13 Vibrating Piezoelectric Element 15 XYZ Scanner 16 Sample 16a Adsorption Layer 17 Laser Light Source 19 Position Sensor 31 Z Stage 32 Pulse Signal 34 Signal Amplifier 35 Servo Device 36 Arithmetic Processing Device 41 Waveform Shaper 42 frequency divider 43 oscillator

Claims (2)

[Claims] 1. A cantilever having a probe at its tip is provided, the probe and the sample are brought close to each other, and the microscopic characteristics of the surface are measured in an atmospheric environment based on the interaction between the probe and the surface of the sample. In a scanning probe microscope for measurement, it is configured to operate with a pulse signal, and includes an approaching device for approaching the probe and the sample, and an oscillating device for oscillating the cantilever, and the approaching device with the pulse signal. A probe / sample approach mechanism of a scanning probe microscope, wherein the pulse signal is generated based on an oscillation signal obtained from an oscillation operation of the cantilever when the probe and the sample are brought close to each other by driving. 2. A converter for converting the oscillation operation of the cantilever into an AC electric signal, a waveform shaper for converting the AC electric signal into a square wave signal, and a frequency divider for dividing the square wave signal. The probe / sample approaching mechanism of the scanning probe microscope according to claim 1, wherein the frequency-divided signal obtained by this frequency divider is used as the pulse signal.