JPH10267945A - Scanning optical microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To very precisely detect only a scattered light near a front end of a probe which strongly reflects optical data of a sample by a method wherein signal processing means removes a signal component in response to the scattered light other than the light near a front end of a probe. SOLUTION: This scanning optical microscope has a piezoelectric scanner 6 to which a sample pedestal 4 is attached, and a cantilever 8 for detecting surface data (AFM measurement data) and optical data (SNO measurement data) of a sample 2. A SNOM illumination unit 68 irradiates a SNOM illuminating illumination light M1 to a surface of the sample 2 from obliquely, and a SNOM detection unit 70 detects the SNOM measurement data of the sample 2. From an output signal of the detection unit 70, a computer 22 (signal processing means) calculates for removing a signal component in response to a scattered light other than near a front end of a probe. As this reason, only the scattered light from near a front end of the probe (the scattered light strongly reflecting the optical data of the sample 2) is detected with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning light microscope capable of simultaneously measuring surface information and optical information of a sample.

[0002]

2. Description of the Related Art An optical microscope capable of measuring surface information of a sample with a resolution exceeding the diffraction limit of light has been developed. In particular, since the late 1980's, a resolution exceeding the diffraction limit of light has been realized by detecting an evanescent wave having a characteristic of being “localized in a region (thickness) smaller than the wavelength and not propagating in free space”. Scanning Near-Field Op Microscope
tical Microscope (SNOM) has been proposed.

In the SNOM, for example, an optical fiber having a sharpened detection tip, a glass rod or a quartz probe is used as a detection probe, and various SNOM measurement methods using such a probe are known. I have.

[0004] For example, Japanese Patent Laid-Open No. Hei 4-291310
(REBetzig, AT & T) discloses a SNOM device that measures optical information of a sample by two-dimensionally mapping the intensity of light transmitted through the sample when the sample is irradiated with light from a small opening formed at the probe tip. Have been.

[0005] For example, for example, Fanfurst (NFvan H
ulst) et al. have proposed an SNOM device that can simultaneously measure the optical information of a sample and simultaneously measure the surface information of the sample by AFM by applying SNOM technology (Appl. Phys. Lett. 62). (5) See P.461 (1993)).
That is, in the SNOM apparatus of the fan full-strobe, the evanescent wave localized near the sample surface is subjected to the silicon nitride A
When an FM probe is inserted and evanescent waves are scattered and converted into propagating light, optical information of the sample is SNOM-measured by detecting light transmitted through the cantilever through the probe, and the displacement of the cantilever is simultaneously measured. The surface information of the sample is AFM-measured based on the AFM.

Incidentally, in the above-mentioned Japanese Patent Application Laid-Open No. 4-291310 and the SNOM apparatus of Van Furst, at least the tip of the probe must be optically transparent in order to transmit light through the probe.

In order to improve the lateral resolution of the SNOM using such a probe, it is necessary to form a light-transmitting opening at the tip of the probe after applying a light-shielding coating of metal or the like. It is not easy to produce a large number of probes with openings formed at their tips and evenly.

In particular, since the SNOM apparatus requires a high resolution exceeding the diffraction limit achievable with a general optical microscope, the opening diameter at the tip of the probe is at least 0.1 μm.
m or less (preferably 0.05 μm or less).

Under such limited conditions, it is extremely difficult to form a probe opening with good reproducibility. Furthermore,
The amount of light passing through the aperture decreases in proportion to the square of the aperture radius, so that the resolution of the SNOM image is improved.
Conversely, when the aperture diameter is reduced, the amount of detected light decreases and S /
The N ratio becomes worse.

In order to solve such a problem of the SNOM device, the SNOM device disclosed in Japanese Patent Publication No. 2-300709 is provided with a needle-shaped probe having no opening, and irradiates the sample surface with light. The optical information of the sample is measured by detecting scattered light scattered from the tip of the probe and the surface of the sample when the probe is relatively moved in the direction perpendicular and parallel to the surface of the sample.

[0011]

[Problems to be Solved by the Invention]
In the SNOM device disclosed in Japanese Patent Application Publication No. 9 (hereinafter referred to as “prior art”), optical information of a sample can be measured by detecting scattered light from the vicinity of the probe tip.

However, according to the SNOM apparatus of the prior art, since light is emitted from the surface of the sample, not only the elastic beam holding the probe and the part separated from the tip of the probe but also the measurement area of the sample are measured. Scattered light is also generated from other sample surfaces. In this case, it is sufficient if only the scattered light near the probe tip that strongly reflects the optical information of the sample can be detected with high accuracy. However, as described above, the scattered light from a portion distant from the probe tip (tentatively referred to as external scattered light) is also required. If this external scattered light is detected because it is generated,
This becomes noise and is superimposed on the measurement data, which may make it difficult to obtain measurement information with a high S / N ratio.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a scanning method capable of detecting only scattered light near the tip of a probe, which strongly reflects optical information of a sample, with high accuracy. To provide a scanning light microscope.

[0014]

In order to achieve the above object, a scanning optical microscope according to the present invention includes a cantilever having a probe for scanning the surface of a sample, and irradiating illumination light to the surface of the sample. A possible illumination unit, and a detection unit capable of detecting optical information of the sample, wherein the detection unit includes a light detection unit capable of detecting scattered light generated during scanning of the probe, and Signal processing means for removing a signal component corresponding to scattered light other than near the tip of the probe from an output signal of the light detection means;

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning light microscope according to an embodiment of the present invention will be described below with reference to FIGS. The scanning light microscope according to the present embodiment is an AFM / SN
It is configured so that simultaneous measurement of OM can be performed and observation with an optical microscope can be performed.

As shown in FIGS. 1 and 2, the scanning light microscope comprises a piezoelectric scanner 6 on which a sample table 4 on which a sample 2 can be set is mounted, surface information (AFM measurement information) of the sample 2 and optical information. And a cantilever 8 for detecting information (SNOM measurement information).

The cantilever 8 is composed of a lever portion 12 having a probe 10 provided at the tip thereof, and a support portion 14 for supporting the proximal end of the lever portion 12 (see FIG. 2). It is held by holding means 18 so as to be positioned within the field of view of the objective lens 16.

The cantilever 8 is manufactured by a semiconductor processing process using a single crystal silicon material. Note that in the manufacturing process applied to this embodiment,
As an example, the lever portion 12 has a length of about 207 μm.
m, the width is set to about 30 μm, and the thickness is set to about 3 μm, and the tip of the lever portion 12 is formed in an isosceles triangle with a vertex angle of 48.5 °. The probe 10 has a tetrahedral shape with a height of about 10 μm and an apex angle of 35 °.
Is set to The vertex 10a of the probe 10 is positioned vertically above the tip 12a of the lever 12 (see FIG. 2), and the rear surface of the lever 12 (the side on which the probe 10 is not formed) has a thickness. An aluminum film 20 having a thickness of 80 nm is coated.

The piezoelectric scanner 6 has a computer 22
Piezoelectric scanner 6 based on the scanning signal output from
Is connected to a scanner driving circuit 24 for driving the scanner. According to this configuration, by applying a scanning signal to the piezoelectric scanner 6 via the scanner drive circuit 24, the sample 2 on the sample table 4 can be displaced in the XYZ directions together with the sample table 4. For example, as the amount of displacement of the sample 2, the amount of displacement in the XY directions is set to about 30 μm, and the amount of displacement in the Z direction is set to about 5 μm.

The piezoelectric scanner 6 is fixed to a coarse movement stage 26 movable in the Z direction. The coarse movement stage 26 has a coarse movement stage based on a drive signal output from the computer 22. A coarse movement stage drive circuit 28 for controlling the movement of the motor 26 is connected. According to this configuration, by inputting a drive signal from the computer 22 to the coarse movement stage drive circuit 28, the piezoelectric body scanner 6 can be moved in the Z direction. By moving the piezoelectric scanner 6 in this manner, it is possible to roughly perform the alignment of the sample 2 on the sample stage 4 (for example, the approximate alignment between the sample 2 and the cantilever 8).

Next, an optical microscope incorporated in the scanning optical microscope of the present embodiment will be described. The optical microscope includes a microscope illumination system for irradiating the sample 2 on the sample stage 4 with illumination light, a light condensing means for condensing illumination light from the microscope illumination system on the sample 2, and an observation surface of the sample 2. And an eyepiece optical system for adjusting the distance.

The microscope illumination system includes a light source 3 for emitting illumination light.
0, an illumination barrel 34 optically connected to the light source 30 via an optical fiber 32, and an illumination beam splitter 36 provided in the illumination barrel 34. According to this configuration, the illumination light guided into the illumination lens barrel 34 via the optical fiber 32 is reflected from the illumination beam splitter 36 and then guided from the lens 38 to the main beam splitter 40.

As the light condensing means, the above-mentioned objective lens 16 is used together. Therefore, the illumination light guided from the lens 38 to the main beam splitter 40 is reflected from the main beam splitter 40 and then radiated to the sample 2 on the sample stage 4 by the focusing means, that is, the objective lens 16. . At this time, the reflected light reflected from the observation surface of the sample 2 is transmitted by the objective lens 16 to the main beam splitter 4.
After being radiated to 0, the light passes through the lens 38 and the illumination beam splitter 36 and is guided to the eyepiece optical system.

The eyepiece optical system includes an eyepiece beam splitter 44 and an eyepiece barrel 46 for guiding the reflected light reflected from the observation surface of the sample 2 to the CCD camera 42, and the reflected light received by the CCD camera 42. And an image processor 50 that performs image processing on the image and displays the image on a monitor television 48. According to this configuration, the reflected light guided through the lens 38 and the illumination beam splitter 36 is reflected from the eyepiece beam splitter 44, and then guided to the CCD camera 42 through the eyepiece barrel 46. You. As a result, the image of the observation surface of the sample 2 is displayed on the monitor television 48 by the image processor 50. The eyepiece barrel 46
Is fixed to the moving stage 52, and by driving the moving stage 52, the observation surface of the sample 2 can be adjusted.

Next, an AFM measurement system incorporated in the scanning light microscope of the present embodiment will be described. AFM
The measurement system includes a piezoelectric body 54 attached to the holding means 18 so as to measure surface information of the sample 2 while exciting the cantilever 8. An excitation circuit 56 that applies a sine wave signal having a predetermined amplitude and frequency to the piezoelectric body 54 based on an excitation signal output from the computer 22 is connected to the piezoelectric body 54. According to this configuration, when a sine wave signal is applied to the piezoelectric body 54 from the excitation circuit 56 to excite the piezoelectric body 54, the exciting motion generated at this time is transmitted from the holding unit 18 to the lever 14 via the support 14 of the cantilever 8. By being transmitted to the section 12, the lever section 12 is excited with a predetermined vibration amplitude.

The AFM measurement system is provided with an optical lever type cantilever displacement sensor. ) And the reflected light L reflected from the back of the lever 12
2 (see FIG. 4 (a)), and a two-part photodetector 60 capable of receiving light, and a signal processing circuit 62 for performing signal processing on the displacement signal output from the two-part photodetector 60. The laser output of the semiconductor laser 58 is controlled by the control circuit 64. According to this configuration, when the semiconductor laser 58 irradiates the lever unit 12 with the AFM measurement light L1, the reflected light L2 reflected from the lever unit 12 is converted into a predetermined displacement signal by the two-segment photodetector 60. The signal is input to the signal processing circuit 62. At this time, the signal processing circuit 62 performs feedback control of the piezoelectric scanner 6 via the scanner drive circuit 24 based on the input displacement signal so that the vibration amplitude of the cantilever 8 is kept constant. During the feedback control, the feedback signal (that is, the AFM signal) output from the signal processing circuit 62 is taken into the computer 22 and then subjected to image processing. As a result, the AFM measurement information (surface information of the sample 2) is displayed on the monitor 66. The signal processing circuit 62 is controlled based on the sine wave signal from the excitation circuit 56 so as to extract a signal synchronized with the frequency of the sine wave signal.

Next, a description will be given of a SNOM measurement system incorporated in the scanning light microscope of the present embodiment. SN
The OM measurement system includes a SNOM illumination unit 68 capable of irradiating the illumination light M1 for SNOM measurement (see FIGS. 1 and 4A) obliquely onto the surface of the sample 2, and SNOM measurement information (optical information ) Can detect SNOM detection unit 7
0 is provided. These SNOM lighting units 6
8 and the SNOM detection unit 70 are both arranged in an external region in the same direction with respect to the surface of the sample 2, and constitute a reflection-type measurement system as a whole.

The SNOM illumination unit 68 includes a laser light source 72 capable of emitting illumination light M1 for SNOM measurement. The illumination light M1 from the laser light source 72 is supplied to a sample via a filter 74, a lens 76, and a mirror 78. 2 is configured to irradiate the surface obliquely. In addition,
As the laser light source 72, for example, an argon laser having an output of 25 mW is preferably used.

The SNOM detection unit 70 drives the coarse movement stage 26 while the illumination light M1 for SNOM measurement is
When light is scanned relatively close to 0, light condensing means for condensing scattered light S1 scattered by the probe 10 (see FIGS. 3 and 4A), and scattered light condensed by this light condensing means S1
Light detecting means for detecting the

The above-mentioned objective lens 16 is also used as a light collecting means. Therefore, among the scattered light S1 scattered by the probe 10 (scattered light from the vicinity of the tip of the probe 10), the scattered light S1 in the field of view of the objective lens 16 is
As a result, the light is converged toward the light detecting means.

The light detecting means includes a photomultiplier tube 80 for converting incident light into an electric signal and amplifying the same, and a lens 82 for guiding the scattered light S1 collected by the objective lens 16 to the photomultiplier tube 80. It has. The photomultiplier tube 80
Is controlled by the controller 84.

According to such a configuration, in a state where the illumination light M1 for SNOM measurement is irradiating the sample 2 obliquely, the probe 10 is moved to the surface of the sample 2 while exciting the cantilever 8 with a constant vibration amplitude. While scanning along (A
During FM measurement), the scattered light S1 scattered by the probe 10
Are collected through the objective lens 16. Then, the scattered light S1 is guided to the photomultiplier tube 80 via the main beam splitter 40 and the lens 82. At this time, the electric signal output from the photomultiplier tube 80 is amplified by an amplifier 86 and then input to a lock-in amplifier 88.

The lock-in amplifier 88 is connected to the excitation circuit 5
On the basis of the sine-wave signal from No. 6, an electric signal synchronized with the frequency of the sine-wave signal, that is, an optical information signal is controlled so as to be extracted.

After that, the optical information signal (ie, SNOM signal) output from the lock-in amplifier 88 is subjected to signal processing by the computer 22 so that the optical information of the sample 2 (SNOM measurement information) is displayed on the monitor 66. Will be displayed.

The scanning optical microscope is provided with a filter 90 which can be inserted and removed in the optical path between the main beam splitter 40 and the light detecting means. Filter 9
By inserting 0 into the optical path, the fluorescence spectrometry of the sample 2 can be performed.

The direction of irradiation of the sample 2 with the illumination light M1 for SNOM measurement is, for example, as shown in FIG. 3, the illumination light M1 is irradiated from a direction perpendicular to the longitudinal axis of the lever portion 12 of the cantilever 8. Is preferred.

By the way, as shown in FIG.
As scattered light generated during simultaneous measurement of M / SNOM,
In addition to the scattered light S1 (scattered light from the vicinity of the tip of the probe 10), there is scattered light S2 scattered from a portion separated from the tip of the probe 10 in the direction of the lever portion 12. This scattered light S2
Is superimposed as noise on SNOM measurement information during SNOM measurement.

Further, when the back surface of the lever unit 12 is irradiated with the AFM measurement light L1 by the optical lever type cantilever displacement sensor, the AFM measurement light L1 is normally reflected from the lever unit 12 and reflected by the objective lens 16. Go outside. At this time, if a rough portion exists on the back surface of the lever portion 12, scattered light S3 is generated from this portion. And
This scattered light S3 is also superimposed as noise on the SNOM measurement information during SNOM measurement.

Thus, the total S of the scattered light components taken in at the time of SNOM measurement is S = S1 + S2 + S3 (1), and "S2 + S3" is the noise component Nb.

Therefore, in the present embodiment, the noise component N
In order to remove b, in the probe pressure setting process (force curve measurement) generally performed before the simultaneous measurement of AFM / SNOM, the noise component “Nb = S2 +
S3 ″ is taken into the computer 22. AFM
Simultaneously or after measuring SNOM measurement information during the / SNOM measurement, an arithmetic process is performed to remove the noise component Nb taken into the computer 22 from equation (1) (see equation (2)). (S1 + S2 + S3) -Nb = S1 (2) Hereinafter, when the illumination light M1 for SNOM measurement is applied to the sample 2, the noise component N
The process of loading b into the computer 22 will be described with reference to FIGS.

FIG. 5A shows that when the force curve is measured,
A is input to the computer 22 when the probe 10 is relatively approached to the sample 2 while exciting the cantilever 8.
FIG. 5B shows the characteristics of the FM signal, and FIG. 5B shows the SN input to the computer 22 when the force curve is measured.
The characteristics of the OM signal are shown.

As shown in FIGS. 5A and 5B, the probe 1
When the sample 0 and the sample 2 approach each other, an interaction between the tip of the probe 10 and the surface of the sample 2 acts to gradually lower the AFM signal characteristic, and at the same time, the scattered light scattered by the probe 10 becomes approximately λ. The increase / decrease is repeated at a cycle of about / 2. When the lock-in amplifier 88 of the apparatus of FIG. 1 is set to the amplitude measurement mode, the SNOM signal characteristic changes at twice the cycle as shown in FIG. Region signal characteristics). Then, for example, a point P (see FIG. 5A) in the area D2 is set as a probe pressure set point, and AFM measurement is performed based on the probe pressure.

On the other hand, as is apparent from FIG. 5B, the probe 10 moves the sample 2 in a positional relationship where no interaction works.
It can be seen that some scattered light is generated even when the distance is away from (see the signal characteristics in the area indicated by the symbol D1 in the figure). Such scattered light is detected with a large intensity when the sample 2 itself is a sample having many irregularities or is large.

The scattered light generated in the area D1 is not scattered light depending on optical information (SNOM measurement information) of a minute area on the sample 2 that comes close to the tip of the probe 10, but is scattered light of the sample 2. This is light based on scattered light in a wider area.
Therefore, such light can be obtained by scanning the probe 10 for SN.
On the OM image, it acts as noise that lowers the horizontal resolution of the SNOM image.

In this embodiment, an arbitrary SNOM signal value in this area D1 is taken into the computer 22 as a noise component Nb, and is reflected in the arithmetic processing based on the above equation (2).

Specifically, in the present embodiment, the SNOM
SNO when scattered light depending on measurement information starts to be generated
The value of the M signal, for example, the SNOM signal based on the scattered light generated when the tip of the probe 10 comes into contact with the outermost part of the electromagnetic field is taken in as the noise component Nb (see FIG. 5B).

After the measurement of the force curve, the AF
When performing the simultaneous measurement of M / SNOM, for example, the arithmetic processing of the above equation (2) is performed for each data acquisition point or for one line after scanning one line. As a result, the probe 10
Since only the scattered light S1 from the vicinity of the tip (that is, the scattered light strongly reflecting the optical information of the sample 2) can be detected with high accuracy, it is possible to obtain SNOM measurement information with a high S / N ratio. Become.

As described above, according to this embodiment, noise is generated in real time at each data capturing point or at each scanning line by arithmetic processing after data capturing, as compared with the conventional image processing generally performed. Components can be removed. For this reason, compared to the case where filtering is collectively performed after fetching data for one screen, S
It is possible to improve the analysis speed for NOM measurement information.

In the above embodiment, the case where the cantilever 8 is excited (dynamic mode AFM) has been described. However, when the cantilever 8 is not excited (static mode AFM), the surface of the sample 2 is similarly measured when the force curve is measured. The noise component Nb of the scattered light may be fetched when the tip of the probe 10 is separated from, and reflected in the arithmetic processing of the above equation (2). In the above embodiment, the sample scanning microscope has been described.
The configuration of the above embodiment can be applied to a probe scanning microscope.

In the above embodiment, the reflection type SN
Although the OM measurement system has been described, it goes without saying that the invention can also be applied to a transmission type. FIG. 4B shows a transmission type SN.
The configuration of the main part of the OM measurement system is shown.
It is mounted on the sample mounting surface 3a of the total reflection prism 3.
In this case, an evanescent light field is formed on the surface of the sample 2 by causing the substantially parallel illumination light (parallel light) M2 to enter the total reflection prism 3 at an angle at which the light is totally reflected by the sample mounting surface 3a.

In this state, when the probe 10 formed at the tip of the cantilever 8 is brought close to the sample 2, the evanescent light field is scattered. The above-mentioned reflection type SNOM
Similarly to the measurement method, when the lock-in detection is performed while exciting the cantilever 8 and the probe 10 and the sample 2 are gradually approached, the AFM signal changes in the same manner as in FIG. , SNOM signals change as shown in FIG. As shown in FIG. 5C, since the noise component Nb is present, after the noise component Nb is fetched, an arithmetic processing is performed so that the noise component Nb is subtracted at each data fetch point or at each scanning line. Is performed, as in the reflection type SNOM measurement method, the SNO with a high S / N ratio is obtained.
M measurement information can be obtained.

Furthermore, if the scanning light microscopy of the present embodiment is used for the inspection process, after the measurement, high S / N can be achieved without performing data processing depending on the judgment of the apparatus operator.
Since the data of the ratio can be obtained, it is possible to shorten the inspection time and improve the inspection efficiency.

[0053]

According to the present invention, it is possible to provide a scanning light microscope capable of detecting only the scattered light near the tip of the probe, which strongly reflects the optical information of the sample, with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a scanning light microscope according to an embodiment of the present invention.

FIG. 2 is a perspective view of a cantilever provided in the scanning light microscope.

FIG. 3 is a perspective view showing a state in which scattered light is generated from a probe tip of a cantilever.

FIG. 4A shows a reflection type SNOM measurement system.
The figure which shows the generation state of the scattered light which arises during simultaneous measurement of AFM / SNOM, (b) is the figure which shows the generation state of the scattered light which arises during simultaneous measurement of AFM / SNOM in the transmission type SNOM measurement system. .

5A is a diagram showing characteristics of an AFM signal at the time of force curve measurement, and FIG. 5B is a diagram showing characteristics of an AFM signal at the time of force curve measurement in a reflection type SNOM measurement system; () Is a diagram showing characteristics of SNOM signals at the time of force curve measurement in a transmission SNOM measurement system.

[Explanation of symbols]

 2 Sample 8 Cantilever 68 SNOM illumination unit 70 SNOM detection unit M1 Illumination light for SNOM measurement

Claims (2)

[Claims] 1. A cantilever having a probe for scanning a surface of a sample, an illumination unit capable of irradiating illumination light onto the surface of the sample, and a detection unit capable of detecting optical information of the sample. The detection unit has a light detection unit capable of detecting scattered light generated during scanning of the probe, and a signal component corresponding to scattered light other than near the tip of the probe from an output signal of the light detection unit. A scanning optical microscope, comprising: signal processing means for removing. 2. A program for detecting a first signal corresponding to scattered light scattered by the probe before the start of scanning, and a second signal corresponding to scattered light scattered during scanning. 2. The scanning light microscope according to claim 1, wherein image display is sequentially performed based on a program for detecting the first signal and a result of a program for calculating the difference between the second signal and the first signal. 3. .