JPH08248039A - Scanning probe microscope and measuring method thereof - Google Patents

Abstract

PURPOSE: To realize high speed scanning while shortening the measuring time by fixing the position of a cantilever in the direction of height at the time of scanning and imparting a predetermined continual vibration to the cantilever at each data acquisition point. CONSTITUTION: A sample 11 is shifted by means of an XYZ scanner 12 and scanned relatively by means of a probe 16. A shaker 14 imparts a vibration of predetermined duration continually to a cantilever 15 at a predetermined time interval. A laser light 19 is reflected on a lever 15 and enters into a photodetector 18. The surface of the sample 11 is then scanned in XY direction by means of the probe 16 being spaced apart therefrom by a predetermined distance while sustaining the voltage of a driving signal VZ at a predetermined level and a vibration is imparted continually to the lever 15. At the time of shaking, the scanning operation is interrupted and the position of the probe 16 is detected by means of the detector 18 and a detection signal Vin is delivered. The maximum peak value of the signal Vin is detected by a circuit 25 and delivered, as the height information of the sample 11, to a controller/processor 20. The controller/processor 20 operates the irregular shape on the surface of the sample 11 which is presented on a display 21.

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 and a measuring method therefor, and more particularly to a scanning probe microscope and a measuring method therefor which perform high-speed scanning to shorten the measuring time.

[0002]

2. Description of the Related Art A scanning probe (probe) microscope has a measurement resolution of an atomic order and is used in various fields such as surface shape measurement. The scanning probe microscope includes a scanning tunneling microscope (STM), an atomic force microscope (AFM), a magnetic force microscope (MFM), etc., depending on the physical quantity to be detected. Among them, the atomic force microscope is suitable for detecting the shape of the sample surface with high resolution, and is used for measuring the surface shape of semiconductors, optical disks, and the like.

As an example of the measuring method of the scanning probe microscope, there is a method disclosed in Japanese Patent Laid-Open No. 1-169304. The measuring method shown in this document is an STM measuring method, which avoids collision with the sample surface during scanning movement of the probe during measurement and enables high-speed movement. The specific content of the measurement method is that when moving along the sample surface, it moves at a distance sufficiently away from the sample surface, and the distance that a tunnel current flows on the sample surface when reaching the position to be measured. After moving to a predetermined tunnel current and measuring the flow of a predetermined tunnel current, the sample is moved away from the sample surface to the above distance, and thereafter, scanning movement between measurement points and measurement movement at the measurement points are repeated in the same manner. Except for the portion where the measurement is performed in this way, the sample surface can be moved at a high speed without being worried about collision, so that the scanning time can be shortened and the sample surface having a large area can be measured.

[0004]

When a large area on the surface of a sample is measured by a scanning probe microscope, it is desirable to shorten the time required for the measurement. In order to satisfy this demand, the measuring method of the scanning tunneling microscope disclosed in Japanese Patent Laid-Open No. 1-169304 can be used. However, according to this measurement method, since the movement toward and away from the sample surface has to be performed at each measurement point, the scanning speed cannot be increased so much, and there is a possibility of shortening the measurement time. There was the problem of being limited in degree.

In view of the above problems, an object of the present invention is to provide a scanning probe microscope capable of scanning at high speed and in a short time and a measuring method thereof when measuring a large range of several hundred microns on the surface of a sample. Especially.

[0006]

In order to achieve the above-mentioned object, a scanning probe microscope according to the present invention is arranged such that a probe provided on the tip of a cantilever is brought close to the surface of a sample at a desired distance. The probe is moved along the surface of the sample while keeping this distance to obtain information about the uneven shape of the sample surface. A vibrating means for intermittently giving vibration to the probe whose amplitude gradually increases, and a probe. Position detecting means for detecting a position change of the position detecting means, an amplitude peak detecting means for detecting a maximum peak value from an output signal of the position detecting means, a storing means for storing conversion data in advance, and the amplitude peak detecting means based on the conversion data. And a processing means for obtaining the surface shape of the sample from the detection value obtained by the means.

In order to achieve the above-mentioned object, the measuring method of the scanning probe microscope according to the present invention makes the probe provided at the tip of the cantilever approach the surface of the sample at a desired fixed distance. The probe is moved along the sample surface while keeping it, and the probe is intermittently given vibrations of gradually increasing amplitude during this scanning. Is a method of obtaining information about the uneven shape (profile) of the sample surface based on the conversion data regarding the distance, for example, table data showing the relationship between the two.

It is desirable that the amplitude of the above-mentioned vibration increases linearly.

Further, it is characterized in that the above-mentioned vibration is applied to each measurement scheduled portion.

[0010]

In the present invention, the cantilever is moved at a predetermined time interval so as to give vibration to the probe whose amplitude gradually increases while the sample surface is scanned by the probe in order to measure the fine unevenness of the sample surface. Excitation is applied intermittently. When the amplitude of the probe gradually increases, the swing distance of the probe becomes almost equal to the predetermined distance maintained between the surface of the sample due to the scanning movement,
The probe comes very close to the sample surface. After that, the amplitude of the probe decreases and the vibration state disappears. Such vibrations are repeated at predetermined time intervals during scanning, and the vibration data resulting from the contact of the probe with the sample surface (which may be non-contact) obtained during the vibration of the probe is used. Obtain information about the uneven shape of the sample surface. In order to obtain information about the uneven shape of the sample surface based on the vibration data, the relationship between the vibration of the probe (cantilever) and the distance between the probe and the sample surface should be prepared beforehand in the storage means as conversion data such as a numerical table. Keep it. Normally, keep a constant distance from the sample surface during scanning of the probe, and give a predetermined vibration to the probe during measurement to measure the distance from the sample surface. There is no need to move specially.
Therefore, the time required for scanning movement can be shortened.

[0011]

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

FIG. 1 shows the structure of an atomic force microscope (AFM) as an example of a scanning probe microscope according to the present invention.
The sample 11 to be measured is placed on the XYZ scanner 12. The XYZ scanner 12 includes a piezoelectric element that causes a displacement in the X-axis direction, a piezoelectric element that causes a displacement in the Y-axis direction, and a piezoelectric element that causes a displacement in the Z-axis direction, and the control device drives each piezoelectric element. By being given a signal, the sample 11 is slightly moved in an arbitrary direction. X
The YZ scanner 12 is fixed to the lower part of the frame 13.
On the other hand, a cantilever 15 is arranged above the frame 13 via a vibrator 14. The vibrator 14 is configured using a piezoelectric element. At the tip of the cantilever 15, a probe 16 is attached.
Is provided. The tip of the probe 16 faces the surface of the sample 11. By moving the position of the sample 11 in the X-axis and Y-axis directions by the XYZ scanner 12, the sample 11 is relatively moved.
The probe 16 can be moved by scanning on the surface of the. Further, the cantilever 15 is vibrated by the vibration exciter 14, and as a result, the probe 16 vibrates. A laser light source 17 and a photodetector 18 are arranged above the cantilever 15. The laser light 19 emitted from the laser light source 17 is applied to a reflection surface provided on the back surface of the cantilever 15, and the optical path is set so that the light is reflected there and enters the photodetector 18.
When the tip of the cantilever 15 moves in the height direction in the figure, that is, the Z-axis direction, the incident position of the laser light 19 on the photodetector 18 changes. Laser light 1 at photodetector 18
By detecting the incident position of 9, the positional displacement of the probe 16 in the Z-axis direction can be detected. Laser light source 1
7 and the photodetector 18 constitute a position detecting device for detecting the position of the probe 16.

A control / arithmetic processing section is provided for the above mechanical section. Reference numeral 20 is a control / arithmetic processing device, and 21 is a display device. The control / arithmetic processing device 20 gives a drive control signal to the X-axis direction piezoelectric element and the Y-axis direction piezoelectric element included in the XYZ scanner 12, and the drive control signal is supplied via the XY drive circuit 22 to the drive signal Vx. , Vy. Further, the control / arithmetic processing device 20 gives a drive control signal to the Z-axis direction piezoelectric element included in the XYZ scanner 12, and this drive control signal is supplied as a drive signal Vz via the Z drive circuit 23. Drive signals Vx and Vy generated under the control of the control / arithmetic processing unit 20
The measurement range on the surface of the sample 11 is set by
The probe 16 can scan the measurement range. Further, the distance between the probe 16 and the surface of the sample 11 is adjusted by the drive signal Vz generated under the control of the control / arithmetic processing device 20.

Further, the control / arithmetic processing device 20 outputs a vibration control signal, and this vibration control signal is applied to a vibration drive signal (hereinafter referred to as a vibration signal) Vou by the cantilever vibration circuit 24.
The vibration signal Vout is converted to t and is applied to the vibration exciter 14. The vibration exciter 14 to which the vibration signal Vout is given gives vibration to the cantilever 15 having a characteristic as described later. The vibration signal Vout is intermittently generated for a fixed time (T1) at a predetermined time interval (T2) as shown in FIG.

On the other hand, the signal input to the control / arithmetic processing device 20 is the position detection signal Vin output from the above-mentioned photodetector 18, and this position detection signal Vin is input to the amplitude peak detection circuit 25. The output signal of the amplitude peak detection circuit 25 is input to the control / arithmetic processing device 20. In the amplitude peak detection circuit 25, the maximum peak value of the amplitude fluctuation of the position detection signal Vin is extracted, and this maximum peak value is input to the control / arithmetic processing device 20 as height information on the sample surface and the surface of the sample 11 is detected. It is used as data for measuring uneven shapes. The uneven shape of the measurement range on the surface of the sample 11 obtained by the control / arithmetic processing unit 20 is displayed on the display unit 2.
1 is displayed.

The measurement operation of the AFM having the above structure is
Description will be made with reference to FIG. 1 and FIGS.

According to the measurement of this AFM, when the XYZ scanner 12 is operated to scan the measurement range set on the surface of the sample 11 by the probe 16,
The vibration signal Vout is applied to the vibration exciter 1 at a predetermined time interval T2.
4, and the cantilever 15 is vibrated. The waveform of the vibration signal Vout output from the cantilever vibration circuit 24 is shown in FIG. The vibration signal is generated only during a fixed time T1, is an AC signal having a resonance frequency of the cantilever 15 or a frequency in the vicinity thereof, and has a period T
The AC signal has an amplitude characteristic that the amplitude gradually increases from 0 during 1 and finally takes the peak value of Vo1 at the maximum amplitude and then returns to 0 again. The envelope connecting the amplitude peaks of the excitation signal is preferably a straight line having linearity.
When the vibration signal shown in FIG. 2A is applied to the cantilever 15 from the vibration generator 14, the probe 16 vibrates with the same amplitude characteristic as the vibration signal.

Assuming that the probe 16 vibrates with the excitation signal Vout shown in FIG. 2A, the probe 16 is affected by the physical action of atomic force from the surface of the sample 11 from the surface. When they are separated by a sufficient distance, the detection signal Vin shown in FIG. 2B is obtained from the photodetector 18. The amplitude of this detection signal Vin gradually increases from 0,
It is an AC signal that has a peak value of Vi1 at the final maximum amplitude and then returns to zero. Further, when the probe 16 vibrates by the vibration signal Vout and the probe 16 approaches a certain distance and is affected by the atomic force from the sample surface, (C) in FIG.
As shown in, the detection signal Vin is attenuated at a certain peak value Vi2 due to the interaction between the tip of the probe and the sample surface due to the atomic force before reaching the peak value Vi1. This peak value Vi2 becomes the maximum peak value in this vibration, and is determined based on the distance between the probe 16 and the surface of the sample 11. When the maximum peak value Vi2 is generated, there are cases where the tip of the probe 16 is in contact with the sample surface and cases where it is not in contact. These can be judged by the attenuation characteristic of Vin after the maximum peak value Vi2. Amplitude peak detection circuit 25
Detects the maximum peak value Vi2 from the detection signal Vin output from the photodetector 18, and controls this peak value Vi2.
Output to the arithmetic processing unit 20. In this way, the cantilever 15 is vibrated at the planned measurement location (data acquisition point), and the maximum peak value Vi2 is obtained from the signal Vin detected each time, so that information about the surface unevenness shape of the sample 11 can be obtained. . When obtaining the uneven shape of the sample surface, it is necessary to investigate the relationship between the maximum peak value and the distance between the probe and the sample, express the relationship in a table, etc., and have it as converted data in the storage unit etc. is there.

FIG. 3 shows a part of the probe scanning section in the X-axis direction, the generation state of the vibration signal Vout, and the generation states of the drive signals Vx and Vz in this section. In FIG. 3, the horizontal axis represents the time axis t, and the vertical axis represents the voltage axis. Note that the voltage on the vertical axis does not show the magnitude relationship between the excitation signal Vout and the drive signals Vx and Vz, and FIG. 3 merely shows the correspondence of the change state of each signal with the passage of time.

The drive signal (voltage signal) Vz applied to the Z-axis piezoelectric element in the XYZ scanner 12 is held at a constant voltage value. This means that by fixing the drive signal Vz to a constant value, the cantilever 15, that is, the distance between the probe 16 and the sample 11 is not servo-controlled during the scanning movement at the non-measurement point, and the desired constant distance from the sample surface is maintained. Means to be fixed at a distance. In addition, the XYZ scanner 12
The voltage value of the drive signal (voltage signal) Vx applied to the piezoelectric element in the X-axis direction built in the disk gradually increases. Therefore, the probe 16 is displaced in the X-axis direction on the surface of the sample due to the relative position change, and performs scanning movement. When the cantilever 15 is intermittently vibrated at time intervals T2 during such scanning movement, at each vibration, the scanning is stopped for the time T1 and the above-mentioned vibration occurs in the probe 16, resulting in , The maximum peak value Vi2 is obtained. The measurement point, that is, the data acquisition point is set at the time interval T2, and the maximum peak value can be obtained at each data acquisition point. The maximum peak value Vi2 at each data acquisition point reflects the uneven shape of the surface of the sample 11. The maximum peak value Vi2 is used to generate display data by the control / arithmetic processing device 20, and the display device 21 The uneven shape of the sample surface is displayed on.

FIG. 4 shows a movement section 32 for moving the scanning movement 31 in a non-measurement state, and a measurement point, that is, a data acquisition point 33. As shown in FIG. 4, the center position (center of vibration, for example, the position of the base end) of the cantilever 15 which is exaggerated is held at a constant height position in the Z-axis direction. The data acquisition points 33 are set discretely, and interlaced scanning is performed.

In the above embodiment, in order to obtain the information on the uneven shape of the measurement range of the sample 11 by using the maximum peak value obtained by the measurement, the maximum peak value V is previously set as described above.
It is necessary to investigate the relationship between i2 and height. The relationship is examined by the following procedure. First, the scanning is stopped, and the sample 16 is separated from the surface of the sample 11 to a distance that is not affected by the interatomic force. Next, in FIG.
The cantilever 15 is vibrated by the signal shown in FIG. 2 and the detection signal Vin for the maximum peak value V01 of the vibration signal Vout at this time is detected.
Record the maximum peak value Vi1 of. Amplitude peak detection circuit 2
While monitoring the output signal of No. 5, the piezoelectric element of the XYZ scanner 12 in the Z-axis direction is driven to bring the sample 11 closer to the probe 16, and the position where the output signal starts to decrease is set as the origin of the Z-axis. Further, the sample 11 is moved closer to the probe 16 side,
The relationship between the movement distance in the Z-axis direction and Vi2 is recorded. A table relating the correspondence between Vi2 and height can be created based on the information obtained in this way, and height data can be obtained based on the maximum peak value Vi2 obtained at each data acquisition point during measurement. After conversion, the height data is used to display the uneven shape of the sample surface.

Although the AFM has been described in the above embodiment, the above measuring method can be generally applied to the scanning probe microscope.

[0024]

As is apparent from the above description, according to the present invention, when the relative position of the cantilever and the sample is changed and the probe is scanned and moved, the position of the cantilever in the height direction is fixed and the scan is moved. Since the cantilever is given a predetermined vibration at each data acquisition point to perform the measurement and the movement in the height direction is not required, the scanning movement for the measurement can be speeded up and the measurement time can be shortened. Can be realized,
Even in a wide measurement range, the measurement can be performed in a short time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a scanning probe microscope according to the present invention.

FIG. 2 is a waveform diagram showing a waveform of vibration (excitation signal) applied to a cantilever, a waveform of a detection signal obtained by a position detection device, and a waveform of a detection signal generated during actual measurement.

FIG. 3 is a diagram showing changes in a vibration signal, an X-axis direction drive signal, and a Z-axis direction drive signal.

FIG. 4 is a diagram showing a relationship between a vibration state of a cantilever during scanning, a moving section, and a data acquisition point.

[Explanation of symbols]

 11 sample 12 XYZ scanner 13 frame 14 exciter 15 cantilever 16 probe 17 laser light source 18 photodetector 19 laser light 20 control / arithmetic processing device 21 display device 22 XY drive circuit 23 Z drive circuit 24 cantilever excitation circuit 25 amplitude Peak detection circuit

Claims (5)

[Claims] 1. A probe provided on the tip of a cantilever is brought close to the surface of a sample at a certain distance, and the probe is scanned and moved along the surface of the sample while maintaining the distance, and In a scanning probe microscope that obtains information about the shape, a vibrating unit that intermittently gives the probe a vibration whose amplitude gradually increases, a position detecting unit that detects a position change of the probe, and a position detecting unit. Amplitude peak detection means for detecting the maximum peak value from the output signal, storage means for storing conversion data in advance, and the surface shape of the sample is obtained from the detection value obtained by the amplitude peak detection means based on the conversion data. A scanning probe microscope, comprising: a processing means. 2. The scanning probe microscope according to claim 1, wherein the amplitude of the vibration increases linearly. 3. A probe provided on the tip of the cantilever is brought closer to the surface of the sample at a certain distance, and while maintaining the distance, the probe is moved along the surface of the sample by scanning to move the probe to the surface of the sample. It is a measuring method of a scanning probe microscope to obtain information about the shape, the vibration is intermittently given to the probe the amplitude of which gradually increases,
Measuring method of a scanning probe microscope, characterized in that information on the shape of the sample surface is obtained based on the maximum peak value obtained by the vibration of the probe and conversion data on the distance between the probe and the sample surface. . 4. The measuring method of a scanning probe microscope according to claim 3, wherein the amplitude of the vibration linearly increases. 5. The method for measuring a scanning probe microscope according to claim 3, wherein the vibration is applied at each of the predetermined measurement points.