JPH1138021A - Scanning probe microscope and approach mechanism thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an approach mechanism of a scanning probe microscope which utilizes a commercial cantilever chip, has a simple constitution, can be easily adjusted, has a high degree of freedom for designing the device, and enables a high speed and high accurate approach of a probe. SOLUTION: This microscope is provided with a cantilever for measurement 18b provided with a probe 17b and optical lever-type detection optical systems 24 and 25 detecting the movement of the cantilever, making a sample and the cantilever approach by a transfer mechanism. In addition, the microscope is provided with a longer cantilever 18a for approach monitoring installed in parallel with the cantilever 18b, a piezoelectric element 21 vibrating the cantilever for approach monitoring 18a at the resonance frequency, a piezoelectric element 22 generating a sound wave of which frequency is made by adding the resonance frequencies of the two cantilevers, and a judging apparatus 26 detecting contact of the cantilever for approach monitoring to the sample based on the output signals of the detection optical systems.

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 an approach mechanism thereof, and more particularly, to an approach mechanism for rapidly approaching a cantilever and a sample in a scanning probe microscope such as an atomic force microscope operating in the atmosphere. About.

[0002]

2. Description of the Related Art An example of a conventional approach mechanism is disclosed in JP-A-6-34.
No. 1808. This approach mechanism is an approach mechanism used in a scanning tunneling microscope, and allows the probe to approach the sample with a simple configuration. In this scanning tunneling microscope, the holding member to which the probe is attached
Similarly to the probe, a support screw rod is provided such that the tip is directed toward the sample, and the tip of the support screw rod is made to slightly project from the tip of the probe. The holding member is attached to the moving blanket via a leaf spring. The moving blanket moves along the rail, thereby forming a moving mechanism. When the probe approaches the sample by the operation of the moving mechanism, the supporting screw bar also approaches the sample at the same time.
The tip of the supporting screw bar contacts the surface of the sample before the probe. When the tip of the supporting screw bar comes into contact with the sample surface, the leaf spring bends. When the leaf spring bends, the curve deformation is detected by a sensor attached to the leaf spring, and it can be seen that the tip of the supporting screw bar has come into contact with the sample surface. As a result, the operation of the moving mechanism is stopped, and the probe is stopped in a state in which the probe is quite close to the surface of the sample. After that,
The supporting screw rod is retracted by a DC servomotor so that its tip is separated from the sample surface. Further, thereafter, an operation of bringing the tip of the probe close to the sample surface is performed by the moving mechanism.

In the above configuration, when the probe is brought close to the sample, the supporting screw rod is provided so as to slightly protrude toward the sample from the tip of the probe, so that the supporting screw rod is brought into contact with the sample first. Therefore, the probe can be brought as close as possible to the sample by high-speed movement. After that,
The supporting screw rod is retracted so that only the probe approaches the sample surface.

[0004]

The approach mechanism of the above-described conventional scanning tunneling microscope has a sensor (supporting screw rod) that comes into contact with the sample prior to the probe, so that the probe approaches the sample. In operation, high-precision approach and high-speed approach can be performed. However, as shown in FIG. 1, the structure of the holding member provided with the probe, the supporting screw rod and its related parts is complicated, and there is a problem that the weight increases. Further, when considered as a scanning probe microscope, since the probe microscope is usually used in combination with an optical microscope or the like, there has been a problem that the complexity of the above configuration limits the degree of freedom in the configuration of the apparatus.

In the case of a scanning probe microscope constructed using a cantilever such as an atomic force microscope, another problem is raised. Since commercially available cantilevers are manufactured by batch processing, which is a semiconductor element manufacturing technology, a single chip generally incorporates a plurality of cantilevers having different lengths. Here, long and short 1
When assuming a chip that incorporates a set of cantilevers, considering the configuration of the conventional approach mechanism described above, it is not possible to use a long cantilever as a preliminary sensor for approach and a short cantilever as a sensor for original observation. You can easily guess. However, if such a configuration is adopted in an atomic force microscope using an optical lever type detection optical system, two sets of optical systems for each of the long and short cantilevers are required. Therefore, the configuration becomes complicated and large, and adjustment for setting the apparatus in the operation state is troublesome and difficult to use.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to use a commercially available cantilever tip, to have a simple configuration, to be easily adjusted, and to have a high degree of freedom in the configuration of the apparatus. Another object of the present invention is to provide a scanning probe microscope that enables a high-speed approach movement of a probe and a high-precision approach, and an approach mechanism thereof.

[0007]

A scanning probe microscope according to a first aspect of the present invention (corresponding to claim 1) has a tip provided with a probe in order to achieve the above object. A cantilever (short cantilever) and a detection mechanism (optical lever type detection optical system) for detecting the operation of the measurement cantilever are provided, and one of the sample on the sample stage and the measurement cantilever is moved by a moving mechanism (for example, a sample stage). )
And a proximity cantilever longer than the measurement cantilever (long cantilever) and a proximity cantilever, which are arranged side by side with the measurement cantilever. Exciting means for vibrating at the resonance frequency, a sound source for generating a sound wave having a frequency obtained by adding the resonance frequency of the measurement cantilever and the resonance frequency of the proximity monitoring cantilever, and a proximity monitoring cantilever based on an output signal of the detection mechanism. Is configured to include a determination unit that detects that the device contacts the sample.

According to a second aspect of the present invention (corresponding to claim 2), in the scanning probe microscope according to the first aspect, the measuring cantilever includes a sound wave generated from a vibrating approach monitoring cantilever and a sound wave generated from a sound source. Vibrates at its resonance frequency due to sound waves generated by interference with

A third aspect of the present invention (corresponding to claim 3) is the scanning probe microscope according to the first or second aspect, wherein the judging means detects that the approach monitoring cantilever has come into contact with the sample. Then, the operation of the moving mechanism is stopped.

According to a fourth aspect of the present invention (corresponding to claim 4), in the scanning probe microscope according to the first aspect, the measuring cantilever and the approach monitoring cantilever are integrally formed as a cantilever tip. I do.

Further, the approaching mechanism of the scanning probe microscope according to the present invention (corresponding to claim 5) comprises a short cantilever having a probe at the tip and a cantilever tip having a long cantilever, and a short cantilever having a short cantilever. A detecting mechanism for detecting the operation, a moving mechanism for bringing the cantilever tip closer to the sample, a vibration means for applying vibration of the resonance frequency of the long cantilever to the cantilever chip, and vibrating the long cantilever, and a vibration mechanism for the short cantilever. The sound source includes a sound source that generates a sound wave having a frequency obtained by adding the resonance frequency and the resonance frequency of the long cantilever, and a determination unit that detects that the long cantilever has come into contact with the sample based on an output signal of the detection mechanism. In this configuration, the short cantilever vibrates at its resonance frequency due to the sound wave generated by the interference between the sound wave generated from the vibrating long cantilever and the sound wave generated from the sound source. When the contact is detected based on the output signal of the detection mechanism, the operation of the moving mechanism is stopped.

The approaching mechanism according to the present invention or the scanning probe microscope equipped with the approaching mechanism has a short cantilever for measurement and a long cantilever for monitoring approach, and the two cantilevers are located at predetermined positions. It is preferably provided integrally so as to maintain the relationship. The optical lever type detection mechanism is attached only to the short cantilever for measurement, and the detection mechanism detects the operation of the short cantilever and provides a detection signal to the determination means. When the short and long cantilevers approach the sample, vibration is applied to the short and long cantilevers.
The long cantilever for monitoring approach is vibrated at its resonance frequency by vibrating means, and itself generates a sound wave at the resonance frequency. On the other hand, by separately providing the above sound source, a sound wave generated by the sound source and a sound wave generated by the long cantilever generate a sound wave having a frequency matching the resonance frequency of the short cantilever. Vibrated. Since the operation of the short cantilever for measurement is detected by the detection mechanism,
The detection mechanism also monitors whether the short cantilever is vibrating at its resonant frequency. As the two cantilevers approach the sample, the elongated cantilever first contacts the sample. When the long cantilever comes into contact with the sample, its vibration stops. When the vibration of the long cantilever stops, the vibration of the short cantilever naturally stops. Therefore, when the operation of the short cantilever for measurement is monitored by the detection mechanism, the approach state between the short cantilever for measurement and the sample can be accurately known, thereby achieving high-speed approach and accurate and safe. An approach can be made.

[0013]

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

FIG. 1 shows a typical configuration example of a scanning probe microscope provided with an approach mechanism according to the present invention. This scanning probe microscope is preferably an atomic force microscope, and may be a scanning tunnel microscope. 2 is a partial plan view of a main part of the access mechanism according to the present invention, and FIG. 3 is a front view of a main part of the access mechanism.

In FIG. 1, reference numeral 11 denotes a sample to be measured. It is assumed that the sample 11 is, for example, a silicon substrate having a semiconductor device formed on its surface, and has a disk shape having a relatively large surface area. The sample 11 is arranged on a sample stage 12. The sample stage 12 has a built-in drive unit made of a pulse motor or a piezoelectric body, performs an ascending operation, and functions as a moving mechanism for bringing the sample 11 closer to a probe located above. Also, the sample stage 12 can perform a lowering operation to lower the sample 11 and increase the distance between the sample 11 and the probe. The sample stage 12 is provided at a lower portion 14 of a support frame 14 of the microscope.
a. The support frame 14 is
b, and an upper portion 14 c extending from the lateral direction above the sample stage 12.

In FIG. 1, reference numeral 15 denotes a cantilever tip. The cantilever tip 15 is arranged above the sample 11 and at a position relatively close to the sample. The cantilever tip 15 is composed of a holder 16 and two cantilevers 18a and 18b provided on the same side of the holder 16 and having tips 17a and 17b at their ends, respectively. As is clear from FIG. 2, one cantilever 18a is long and the other cantilever 18b is short. The long cantilever 18a is called a long cantilever, and the short cantilever 18b is called a short cantilever. Each of the long cantilever 18a and the short cantilever 18b preferably has a triangular planar shape, and a probe is provided below the distal end thereof.

The upper portion 14c of the support frame 14 is
Cantilever chip mounting section 19 and sound source mounting section 20
It has. The sound source mounting portion 20 extends further forward than the cantilever chip mounting portion 19. The holder 16 of the cantilever chip 15 is fixed to the lower surface of the cantilever chip mounting portion 19 via the piezoelectric element 21 for vibration. In this mounting state, the cantilevers 18a and 18b are arranged so as to extend forward.
On the other hand, as apparent from FIGS. 1 and 2, the sound source mounting portion 20 is positioned so as to be substantially parallel to the extending direction of the long cantilever 18a and the short cantilever 18b. A piezoelectric element 22 is fixed to the lower surface of the front end of the sound source mounting section 20. The piezoelectric element 22 vibrates to generate a sound wave of a predetermined frequency, and acts as a sound source (speaker). The sound source piezoelectric element 22 is positioned substantially obliquely above the cantilevers 18a and 18b.

In the cantilever chip 15, the short cantilever 18b is a cantilever for measurement,
The long cantilever 18a is a cantilever for monitoring approach. Short cantilever 18b and long cantilever 18
a is located on the same plane and slightly downward on the sample side. Since the long cantilever 18a is approximately twice as long as the short cantilever 18b, the position of the probe 17a is necessarily lower than the probe 17b of the short cantilever 18b, and is closer to the sample 11. It is in. An optical lever type detection optical system is attached to the short cantilever 18b for measurement. That is, a laser light source 24 that irradiates the laser light 23 to the back surface of the short cantilever 18b and a photodetector (position sensor) 25 that receives the reflected laser light 23 are arranged. Photodetector 25
The cantilever 18b at the incident position of the laser beam at
Can be detected as the amount of flexure deformation (behavior of the cantilever), and thus the position of the probe 17b can be detected. The optical lever detection optical system is usually provided as a detection mechanism for detecting a measurement signal in a conventional scanning probe microscope. On the other hand, no optical lever type detection optical system is provided for the long cantilever 18a for monitoring the sample.

A commercially available cantilever chip 15 having a long cantilever 18a and a short cantilever 18b is used. 4 and 5 show commercially available cantilever tips. FIG. 4 is a plan view and FIG. 5 is a side view. The cantilever chip 40 has a long cantilever 18a and a short cantilever 18b at both edges. In the cantilever chip 15, a commercially available cantilever 40 is used.
Is drawn with one side omitted. In the commercially available cantilever chip 40, the length of the long cantilever 18a is, for example, 200 μm, and the length of the short cantilever 18b is, for example, 100 μm. In FIGS. 1 to 3, the long cantilever and the short cantilever are exaggerated in size for the sake of illustration.

The signal output from the photodetector 25 is input to a decision unit 26. A signal output based on the content of the determination by the determiner 26 is provided to the approach signal generator 27. The signal output from the approach signal generator 27 is the sample stage 1
2 to control the elevating operation of the sample stage 12.

The vibrating piezoelectric element 21 for fixing the holder 16 of the cantilever chip 15 is driven by an oscillation signal having a frequency f1 output from an oscillator 28. The frequency f1 matches the primary resonance frequency ( _fr1 ) of the long cantilever 18a. The sound source piezoelectric element 22 is driven by an oscillation signal having a frequency f2 output from the oscillator 29. The frequency f2 is determined by the primary resonance frequency (f) of the long cantilever 18a.
coincides with the frequency (f _r1 + f _r2) obtained by adding _r1) and short form cantilever 18b of the primary resonant frequency (f _r2).

FIG. 1 shows only components related to the approaching mechanism according to the present invention, such as a measuring portion of a scanning probe microscope, for example. The illustration of a control system for keeping the distance between the probe of the short cantilever for measurement and the sample constant and a portion for processing and displaying measurement data is omitted.

Next, the operation of the approach mechanism when the sample stage 12 is raised and the sample 11 approaches the probes 17a and 17b will be described. At this time, it is premised that the drive unit in the sample stage 12 is given a drive signal from the approach signal generator 27 and performs a rising operation.

The vibrating piezoelectric element 21 is driven by an oscillator 28 and generates vibration at a frequency f1. As a result, the elongated cantilever 18a is vibrated by its resonant frequency, wave 31 of frequency f1 (1-order resonance frequency f _r1 of the elongated cantilever 18a) around the elongated cantilever 18a as shown in FIG. 3 is diffused. On the other hand, the oscillator 29 oscillates at the frequency f2. The piezoelectric element 22 for sound is driven at a frequency f2 or frequency f _r1 + f _r2, to diffuse the sound waves 32 of frequency f _r1 + f _r2 therearound.

As shown in FIG. 3, the long cantilever 18
A sound wave 31 of frequency f1 ( _fr1 ) is generated around a, and a sound wave 32 of frequency f2 ( _fr1 + _fr2 ) is generated around the piezoelectric element 22 for the sound source. Two sound waves 31 having different frequencies,
32 interference occurs between, thereby resulting in the sound waves and the frequency f _r1 + 2f _r2 frequency f _r2 is generated.
When waves of the frequency f _r2 occurs, since the frequency is the primary resonance frequency of the short form cantilever 18b, rectangle cantilever 18b is excited in the wave begins to oscillate at a result the frequency f _r2. The vibration operation of the short cantilever 18b is detected by an optical lever type detection optical system provided. That is, the photodetector 25 detects and outputs the vibration of the short cantilever 18b. Determiner 26, the frequency of the signal output from the photodetector 25 is determined whether the f _r2.
The determiner 26 determines that the frequency of the output signal of the photodetector 25 is _fr2.
, An output instruction signal is given to the approach signal generator 27. Upon receiving the output instruction signal, approach signal generator 27 supplies a drive signal to a drive unit in sample stage 12 to continue the ascending operation. On the other hand, the determiner 26 is a light detector 2
When the frequency of the output signal of _{No. 5} is not _fr2 , an output stop signal is given to the approach signal generator 27. Approach signal generator 2
When receiving the output stop signal, the control unit 7 stops supplying the drive signal to the drive unit in the sample stage 12 and stops the raising operation.

Next, the operation of the approaching mechanism in the scanning probe microscope in a state where the sample 11 approaches the long cantilever 18a and the short cantilever 18b will be described. It is assumed that the scanning probe microscope is installed in the atmosphere. The sample stage 12 is raised and the sample 1
1 is a long cantilever 18a of the cantilever tip 15
And approach the short cantilever 18b. When the sample 11 comes into contact with or attracts the probe 17a at the tip of the long cantilever 18a, the vibration of the long cantilever 18a stops. When the vibration state of the long cantilever 18a stops, the sound wave 31 of the frequency f1 disappears. When the sound wave 31 of the frequency f1 disappears, the frequency f generated by the interference of the sound wave
_Since the sound wave of _r2 also disappears, the vibration of the short cantilever 18b stops. When the vibration of the short cantilever 18b stops, the determiner 26 determines that the output of the photodetector 25 is not a signal of the frequency _fr2 , and outputs an output stop signal to the approach signal generator 27. As a result, the approach signal generator 27 stops outputting the drive signal, and the sample stage 12
To stop the ascent operation (approaching operation). Since the long cantilever 18a is longer than the short cantilever 18b, when the probe 17a of the long cantilever 18a is in contact with the surface of the sample 11, the probe 17b of the short cantilever 18b for measurement is moved away from the surface of the sample 11. It is far away.

As described above, according to the approach mechanism of the scanning probe microscope according to the present embodiment, before the short cantilever 18b for observation / measurement sufficiently approaches the surface of the sample 11, the long cantilever 18a is first moved. Touching the sample 11,
As a result, the vibration of the short cantilever 18b stops, so that it is possible to know that the short cantilever 18b for measurement has approached the vicinity of the sample 11, and the sample stage 12
Can quickly stop the approaching operation. At the time when the long cantilever 18a for approach monitoring comes into contact with the sample 11, the short cantilever 18b for measurement and the sample 11
Since there is a margin in the distance between the cantilever and the sample, the short cantilever for measurement and the sample can be approached at a higher speed as compared with the related art, and more accurately and safely.

Although the moving mechanism is provided on the sample stage 12 in the approach mechanism according to the above-described embodiment, it is needless to say that a moving mechanism can be provided on the cantilever chip side so that the cantilever approaches the sample.

[0029]

As is apparent from the above description, according to the present invention, a short cantilever is used for measurement and a long cantilever is used for monitoring proximity by using a cantilever chip having two long and short cantilevers. By using it, an approaching mechanism of the scanning probe microscope can be realized with a simple configuration.

Also, the long cantilever is vibrated at its resonance frequency, a sound source of a predetermined frequency is provided, and the short cantilever is vibrated by the interference between the sound wave and the sound wave from the long cantilever. Since the approaching state between the sample and the short cantilever is controlled by monitoring the vibration operation of the cantilever, the configuration is simple and easy to adjust. High-speed approach movement and high-precision approach of the needle can be performed. As a result, the total measurement time can be shortened.

[Brief description of the drawings]

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

FIG. 2 is a plan view of a cantilever chip and a sound source portion.

FIG. 3 is a diagram illustrating a state of generation of a sound wave from a long cantilever and a sound wave from a sound source.

FIG. 4 is a plan view of a commercially available cantilever chip.

FIG. 5 is a side view of a commercially available cantilever tip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Sample 12 Sample stage 14 Support frame 15 Cantilever chip 16 Holder 17a, 17b Probe 18a Long cantilever for proximity monitoring 18b Short cantilever for measurement 21 Piezoelectric element for vibration 22 Piezoelectric element for sound source 23 Laser light 24 Laser light source 25 Photodetector 31, 32 Sound wave

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takashi Morimoto 650, Kandamachi, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Inside Tsuchiura Factory

Claims (5)

[Claims] 1. A measuring cantilever having a probe at a tip thereof, and a detecting mechanism for detecting an operation of the measuring cantilever. One of the sample on the sample stage and the measuring cantilever is moved by a moving mechanism. In a scanning probe microscope configured to move and approach both, a proximity monitoring cantilever, which is longer than the measurement cantilever and is juxtaposed to the measurement cantilever, the proximity monitoring cantilever Vibrating means for vibrating at the resonance frequency, a sound source for generating a sound wave having a frequency obtained by adding the resonance frequency of the measurement cantilever and the resonance frequency of the approach monitoring cantilever, and an output signal of the detection mechanism. Scanning characterized by comprising judgment means for detecting that the approach monitoring cantilever has contacted the sample. Probe microscope. 2. The measurement cantilever vibrates at its resonance frequency by a sound wave generated by interference between a sound wave generated from the vibrating approach monitoring cantilever and the sound wave generated from the sound source. Item 2. A scanning probe microscope according to Item 1. 3. The apparatus according to claim 1, wherein the judging means stops the operation of the moving mechanism when detecting that the approach monitoring cantilever comes into contact with the sample.
Or the scanning probe microscope according to 2. 4. The scanning probe microscope according to claim 1, wherein the measurement cantilever and the approach monitoring cantilever are integrally formed as a cantilever tip. 5. A cantilever tip having a short cantilever and a long cantilever each having a probe at a tip thereof, a detection mechanism for detecting an operation of the short cantilever, and a moving mechanism for bringing the cantilever tip close to a sample. Vibration means for applying vibration of the resonance frequency of the long cantilever to the cantilever chip to vibrate the long cantilever; and a frequency obtained by adding the resonance frequency of the short cantilever and the resonance frequency of the long cantilever. A sound source that generates an acoustic wave, and determination means for detecting that the long cantilever has come into contact with the sample based on an output signal of the detection mechanism.The short cantilever is configured to oscillate from the long cantilever. The sound wave generated by the interference between the generated sound wave and the sound wave generated from the sound source causes resonance thereof. Vibrates at the frequency,
The approach mechanism of a scanning probe microscope, wherein the determining means stops the operation of the moving mechanism when detecting that the elongated cantilever has contacted the sample based on an output signal of the detecting mechanism. .