JP2001165842A - Angle of incidence determining method, and scan near- field optical microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for determining the angle of incidence of the irradiating light to irradiate a portion in the vicinity of a tip of a probe to realize the high resolution and high contrast, and a scan near-field optical microscope. SOLUTION: The method for determining the angle of incidence of the irradiating light to irradiate the portion in the vicinity of the tip of the prove in the scan near-field optical microscope comprises a step of irradiating the irradiating light on a portion to be observed of a sample and receiving the reflected light while changing the angle of incidence of the irradiating light, and seeking the angle of incidence to minimize the angle dependency of the intensity of the reflected light. The scan near-field optical microscope comprises a light source for irradiating light on the location to be observed of the sample and adjusting the angle of incidence, and a detecting means to detect the irradiating light reflected by the sample, and can measure the angle dependency to the angle of incidence of the intensity of the reflected light detected by the detecting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for determining an incident angle and a scanning near-field optical microscope, and more particularly to a scanning near-field optical microscope for measuring surface information and optical information of a sample, and the scanning near-field optical microscope. The present invention relates to a method for determining an incident angle of irradiation light for irradiating the vicinity of a probe tip in an optical microscope.

[0002]

2. Description of the Related Art As is well known, a scanning probe microscope (SPM) scans a probe along a sample surface while detecting an interaction between the probe and the probe when the probe approaches the sample surface. A two-dimensional mapping of the interaction.

[0003] Such an SPM is, for example, a scanning tunneling microscope (STM) or an atomic force microscope (AF).
M), a magnetic force microscope (MFM), and a scanning near-field optical microscope (SNOM).

In particular, SNOM has been used since the late 1980's to detect evanescent waves, and as an optical microscope having a resolution exceeding the diffraction limit, to observe fluorescence of biological samples and evaluate materials and elements for photonics. Research and development are being actively pursued for applications to (evaluation of various characteristics of dielectric optical waveguides, measurement of emission spectra of semiconductor quantum dots, evaluation of various characteristics of semiconductor surface emitting devices, etc.).

[0005] This SNOM is basically a device for bringing a sharp probe close to a sample while irradiating the sample with light, and detecting the state of a light field (near field) near the sample.

[0006] Betzi dated December 21, 1993
U.S. Pat. No. 5,272,330 to G et al.
By introducing light into an open-ended probe whose tip is thinned, an evanescent field is generated near the small aperture at the tip of the probe, and this evanescent field is brought into contact with the sample to generate an evanescent field. SNOM that detects light generated by contact of a sample with a photodetector arranged below the sample and performs two-dimensional mapping of transmitted light intensity
Is disclosed.

[0007] Van Hulst et al.
l. Phys. Lett. 62 (1993), pp46
1-463). Using the AFM microcantilever as a SNOM probe, the tip of the probe scatters the evanescent field generated on the sample surface by the dark-field illumination optical system, and the AFM and SN
It reports the first successful simultaneous observation of OM.

An SNOM of a type in which an evanescent field localized in a sample structure is scattered by the tip of a probe having no minute aperture (scattering probe) and converted into propagating light, which is detected by an external optical system, has been known. In recent years, it has attracted attention because resolution and SN ratio can be improved.

Also, Bockara et al., Reference 2 (Op.
t. Lett. 20, 1924 (1995)) that, by irradiating light from the probe side that scans the sample, the reflection mode scattering SNOM that detects optical information on the sample surface near the tip of the probe succeeded in observing an opaque sample. Has been reported.

Further, Sasaki et al., Reference 3 (J.
Appl. Phys. 85, 2026 (1999)), a high-resolution observation using a reflection mode scattering SNOM was performed (J. Appl. Phys. 85, 2026).
(1999)).

[0011]

By the way, when observing an opaque sample by the reflection mode SNOM, light is emitted from the probe side for scanning the sample.

In this case, (the radius of curvature of the probe tip)
Is generally on the order of 10 to 100 nm, and the beam diameter of the illumination light has a larger value. Therefore, as shown in FIG. The light flux once reflected near the tip of the probe on the sample surface and reaches the tip of the probe can be considered separately.

That is, the tip of the probe is illuminated by the two light beams.

Among them, the light beam that directly illuminates the probe tip always illuminates the probe tip with a constant intensity, and this optically interacts with a local portion of the sample surface to generate scattered light. A field optical image is obtained.

On the other hand, a light beam which illuminates the probe tip once reflected on the sample surface is affected by a local difference in reflectance on the sample surface during scanning.

This light beam is important for obtaining a near-field optical image in the same manner as the light beam directly reaching the tip of the probe, because it contains a local difference in reflectance on the sample surface.

However, in the reflection mode SNOM, various attempts have been made for the probe itself in order to realize high resolution and high contrast. There are few reports examined.

The present invention has been made in view of the above circumstances. For example, in a reflection mode SNOM, a probe capable of realizing a high resolution and a high contrast by actively examining the incident condition of illumination light to the probe. An object of the present invention is to provide a method for determining an incident angle of irradiation light for irradiating the vicinity of the tip and a scanning near-field optical microscope.

[0019]

According to the present invention, there is provided a method for determining the incident angle of irradiation light for irradiating near the tip of a probe in a scanning near-field optical microscope. Irradiating the illuminating light on the sample observation site while changing the incident angle of the illuminating light, receiving the reflected light, and searching for an incident angle at which the angle dependence of the reflected light intensity is minimized. Is provided.

Further, according to the present invention, in order to solve the above-mentioned problems, (2) a light source capable of adjusting an incident angle for irradiating irradiation light to an observation portion of a sample, and the irradiation light reflected by the sample is provided. There is provided a scanning near-field optical microscope which comprises a detecting means for detecting, and is configured to be able to measure the angle dependency of the reflected light intensity detected by the detecting means with respect to the incident angle.

According to the present invention, in order to solve the above-mentioned problems, the present invention further comprises (3) a motor driving means capable of changing an incident angle of the light source.
A scanning near-field optical microscope as described is provided.

[0022]

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

FIG. 2 is a diagram showing a conceptual configuration of a main part of the SNOM device applied as an embodiment of the present invention.

That is, as shown in FIG.
The light scattered between the tip portion 3 of the sample and the local surface of the sample 1 is collected by an objective lens 9 provided above the probe 2, and detected by a photomultiplier 11 via an analyzer 10.

This is imaged and displayed as a SNOM signal by signal processing means (not shown).

Here, the target sample 1 is an optical recording medium 6 having a reflectance difference between the recording mark 4 and the non-recording portion 5 as shown in FIG.

It is assumed that the distribution of the recording marks 4 is sufficiently smaller than the spot diameter of the illumination light from the light source 7 and is uniformly distributed in the spot diameter.

First, in FIG. 2, the probe 2 is separated from the observation site, and in this state, the light beam from the light source 7 is allowed to pass through the polarizer 8 so as to enter the observation site of the sample 1 as p-polarized light. ing.

Then, the intensity of the light beam reflected from the sample 1 is detected by the detector 12 set at an angle equal to the incident angle.

The detector 12 is on the incident surface 40 of the light beam from the light source 7 and detects the angle dependence of the reflection intensity of the light beam reflected from the sample 1 while changing the incident angle φ (similarly, the reflection angle φ). I do.

In this case, the rotation of the light source 7 and the polarizer 8 and the rotation of the analyzer 24 and the detector 12 around the observation site are performed manually or by driving with a motor (not shown).

Assuming that the reflectance of the recording mark 4 is smaller than that of the non-recording portion 5 as the optical recording medium 6, the reflectance of each of the non-recording portion 5 and the recording mark 4 is represented by a curve in FIG. It has angle dependence as shown by A and B.

Here, the difference between the reflectance of the recording mark 4 and the reflectance of the non-recording portion 5 becomes large because of the Brewster angle (a transparent body having an extinction coefficient of 0) or the main incident angle (an extinction coefficient of 0). (Not an absorber).

In FIG. 4, at the incident angle where the angle dependence of the reflected light intensity is minimum, that is, at the position where the tangent to the reflectance curve is horizontal, the difference in reflectance between the recording mark 4 and the non-recording portion 5 is maximum. It has become.

Based on this phenomenon, a high-contrast image can be obtained by irradiating irradiation light at an incident angle at which the angle dependence of the reflected light intensity is minimized.

Here, the value of the incident angle is measured by an encoder (not shown) provided in association with the light source 7 (not shown), and the reflected light intensity at the incident angle can be obtained from the output of the detector 12.

The signal indicating the value of the incident angle and the intensity of the reflected light is processed by an A / D converter, a memory, and a computer which constitute signal processing means (not shown).

First, a signal indicating the value of the incident angle and the reflected light intensity is converted into a digital signal by an A / D converter (not shown), and is sequentially stored in a memory (not shown).

That is, as the incident angle is changed, data of the incident angle and the reflected light intensity at the incident angle are stored in this memory.

This is formed into a graph via a computer (not shown) so that it can be observed on a screen.

This graph becomes curves A and B as shown in FIG.

In FIG. 4, curves A and B indicate the reflectance of each of the non-recording portion 5 and the recording mark 4, and each has an angle dependency as shown.

The horizontal lines C and D in contact with the reflectance curves A and B of the non-recording portion 5 and the recording mark 4 shown in FIG. 4 are obtained by a computer, and the incident angle at the contact is obtained.

Obviously, it is not necessary to display such a graph, and by monitoring the output of the detector 12, the operator can read the value of the incident angle and the value of the reflected light intensity. Is enough.

In this way, if the angle dependence of the reflection intensity is detected and the incident angle at which the value is minimized is found and set, the reflection intensity is average, but the recording mark 4
And the non-recording portion 5 can be realized with the largest difference in reflectance.

At this time, the angle of incidence is set manually as described above by monitoring the output of the detector 12 or by taking the output of the detector 12 into a computer or the like and setting the minimum value. The calculation may be performed by driving the motor.

Then, with the angle of incidence set in this manner, SNOM observation is performed by aligning the probe 2 with the observation site, and once reflected on the surface of the sample 1, the tip portion of the probe 2 is reflected. The luminous flux illuminating 3 contributes to imaging while including a difference in the local reflectance of the sample 1, so that high contrast in SNOM observation can be realized.

The sample 1 to be observed has an optically characteristic structure on the surface which is sufficiently smaller than the spot diameter of the illumination light from the light source 7 and has a uniform distribution. good.

For example, such a sample 1 is shown in FIG.
GaAs layer 51 and AlG
The present invention is also applicable to observation of an interface where the bands of the aAs layer 52 are arranged.

The SN having the components as described above
The OM device has an effect that high contrast can be realized in SNOM observation by analyzing using a reflected light from the sample surface of a light beam incident on the sample surface.

This indicates that, according to the present invention, the conditions under which the illumination light is incident on the probe are positively studied, and high resolution and high contrast can be realized.

In the present specification described in the above-described embodiment, in addition to claims 1 to 3 described in the claims, the inventions shown as supplementary notes 1 and 2 below are provided. include.

(Supplementary Note 1) In order to obtain a near-field optical image, the apparatus has an incident portion in which the angle of incidence of illumination light incident on the probe and the sample surface from the outside is variable, and further detects reflected light of the illumination light from the sample surface. In the scanning near-field optical microscope, characterized in that it has a light-receiving portion capable of adjusting the angle, the incident portion around the observation site, and the rotation of the light-receiving portion is performed manually or automatically by motor driving.
By detecting the average reflectance of the sample surface by the incident part and the light receiving part, it is possible to set an optimum incident angle of illumination light for obtaining a near-field optical image having a strong contrast. Field optical microscope.

(Supplementary Note 2) The scanning near-field optical microscope according to supplementary note 1, wherein the setting of the optimum incident angle of the illumination light is performed manually or automatically by driving a motor.

(Effects) That is, the present invention relates to a SNOM apparatus in which light is incident on a sample arranged so as to approach the tip of a probe and the sample is observed based on scattered light information from the probe derived from the light. A light-receiving unit capable of changing the angle of incidence of incident light from the illumination light source on the sample surface and the like, and an angle-adjustable light-receiving unit for detecting reflected light from the sample surface.

Then, before the SNOM observation, the average reflectance of the sample is detected by changing the incident angle of the incident light from the illumination light source on the sample surface in a state where the probe is not present at the observation site. It is possible to set the optimal incident angle of the illumination light to obtain a high contrast.

[0057]

Therefore, as described above, according to the first aspect of the present invention, for example, in the reflection mode SNOM, the condition of the illumination light incident on the probe is positively studied, and high resolution and high contrast are obtained. It is possible to provide an incident angle determining method for determining an incident angle of irradiation light that irradiates the vicinity of the probe tip, which can be realized.

According to the second and third aspects of the present invention, for example, in the reflection mode SNOM, the condition of the incident light of the illumination light to the probe is positively examined, and the probe tip capable of realizing high resolution and high contrast is realized. A scanning near-field optical microscope employing a method for determining the incident angle of irradiation light for irradiating the vicinity can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing two types of light beams, that is, a light beam from a light source directly reaching a probe tip and a light beam once reflected near a probe tip on a sample surface and reaching a probe tip in a reflection mode SNOM. It is a figure showing that it is divided.

FIG. 2 is a diagram showing a conceptual configuration of a main part of an SNOM device applied as an embodiment of the present invention;

FIG. 3 is a view showing an optical recording medium 6 having a reflectance difference between a recording mark 4 and a non-recording portion 5 as a sample 1 to be observed in the present invention.

FIG. 4 is a graph showing a case where the reflectance of a recording mark of an optical recording medium used as a sample 1 to be observed in the present invention is smaller than that of a non-recorded portion, and each reflectance is angle-dependent. FIG.

FIG. 5 is a diagram illustrating, as a sample 1 to be observed in the present invention, a semiconductor material 50 having an interface in which bands of a GaAs layer 51 and an AlGaAs layer 52 are sequentially arranged.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sample, 2 ... Probe, 3 ... Probe tip part, 9 ... Objective lens, 10 ... Analyzer, 11 ... Photomultiplier, 4 ... Recording mark, 5 ... Non-recording part, 6 ... Optical recording medium, 7 ... 8 light source, 8 polarizers, 12 detectors, 24 analyzers, 40 incident surfaces, A and B curves, C and D horizontal lines in contact with curves A and B, 51 GaAs layers, 52 AlGaAs layers, 50 ... Semiconductor material.

Claims (3)

[Claims] 1. A method for determining the incident angle of irradiation light for irradiating near the tip of a probe in a scanning near-field optical microscope, and irradiating irradiation light to an observation site of a sample while changing the incident angle of irradiation light. Receiving the reflected light and searching for an incident angle at which the angle dependence of the reflected light intensity is minimized. 2. A light source for irradiating an irradiation part on an observation part of a sample, the light source having an adjustable incident angle, and a detecting means for detecting the irradiation light reflected by the sample, wherein the detecting means detects the irradiation light. A scanning near-field optical microscope characterized in that the angle dependence of the reflected light intensity with respect to the incident angle can be measured. 3. The scanning near-field optical microscope according to claim 2, further comprising a motor driving means capable of changing an incident angle of said light source.