JPH08313433A - Infrared microspectroscopic analysis method and apparatus - Google Patents

Abstract

PURPOSE: To enable the measurement of an infrared spectral distribution by locating a slit-shaped opening with a microscopic width in a field of an evanescent wave to detect light via it. CONSTITUTION: In measurement of a transmission mode, light of an infrared ray source 91 is turned to spectroscopic light by an interferometer 92 to be reflected 63 and incident light is condensed to a sample 50 by a Cassegrain objective mirror 60. The sample 50 irradiated with the spectroscopic light generates diffraction light containing an evanescent wave. A microscopic slit- shaped opening 21 of a microscopic opening probe 20 is positioned at the field of the evanescent wave and the evanescent wave is converted to propagation light by the opening 21. A Cassegrain objective mirror 30 focuses all the propagation light to be condensed to an MCT detector 70. A computer 80 inputs a photoelectric conversion signal of the detector 70, interferogram in this case to perform a Fourier transform thereof to obtain an infrared absorption spectral distribution and the results are visualized to be outputted. In other words, the intensity of measuring light proportional to the area of the opening 21 is obtained thereby enabling the measurement of the spectral distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared microspectroscopy method and apparatus, and more particularly, to a red field detector capable of detecting an evanescent wave using a probe in the near field (near field) and realizing a spatial resolution exceeding the diffraction limit. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external spectroscopic analysis method and apparatus.

[0002]

BACKGROUND ART In recent years, microfabrication technology has advanced in many industrial fields. Integrated circuit technology is a typical example, and submicron-order processing is performed. Further, the drastic reduction in the size of existing products found in micromachines and the like and the increase in the density of information storage such as compact discs and video discs require further progress in miniaturization and high technology. With the progress of such microfabrication technology, from the viewpoint of quality control, it is becoming indispensable to measure these microfabricated products in a minute area. The measurement in a minute area is, for example, observation of a surface shape of an object after fine processing, local composition analysis on the surface, or inspection of impurities. As the microstructures produced by processing technology become smaller and higher in density, the resolution required for measurement technology will inevitably increase. Infrared microspectroscopy, which is one of the measurement methods in such a minute region, is widely used in the inspection process of products and the analysis of materials. For example, a wide range of fields such as analysis of deposits and impurities on the surface of magnetic disks and semiconductors, confirmation of products in the field of synthetic chemistry, composition analysis and structure analysis of polymer materials, and microstructure analysis of biological samples. Has been applied in. However, this infrared microspectroscopy method is about 2-1
Since the light in the wavelength range of about 5 μm is used, the spatial resolution is about 10 μm at most due to the diffraction limit. Therefore, it is not possible to meet the demand for measuring the distribution of a substance with a spatial resolution of micron order or even submicron order.

Recently, near-field scanning optical microscopes have been studied which can realize high spatial resolution without being limited by the wavelength of light. In this microscope, an evanescent wave that is localized on the sample surface and cannot propagate in space is detected using a probe. The probe includes an optical fiber with a sharp tip, a micropipette, a small opening,
Metal needles, microspheres, etc. are used. By making the size of these probes (the diameter of the tip of the fiber, the size of the aperture diameter, etc.) smaller than the wavelength, it is possible to observe a structure finer than the wavelength, which has not been observed by light.

[0004]

2. Description of the Related Art As prior art, Japanese Patent Laid-Open No. 4-30751
The technique "near-field scanning optical microscope" of Japanese Patent No. 0 is known. This technology is configured to supply probe light to a sample through a pinhole formed at the tip of an optical probe. The probe light is pulsed and the photodetector is operated in synchronization with this to generate background light. S / to reduce the effect
N is to improve the resolution by detecting the probe light well.

On the other hand, an apparatus capable of realizing a spatial resolution exceeding the diffraction limit by utilizing an evanescent wave in infrared microscopic measurement is known from Japanese Patent Application Laid-Open No. 6-94613. The technology disclosed herein is an infrared transparent and high refractive index hemispherical prism placed in close contact with the upper surface of the test sample,
The focused spot diameter is narrowed down by using the high refractive index of the prism, and at the same time, the low refractive index medium (test sample) is used by using total reflection.
An evanescent wave is generated inside, and light that has interacted with a substance is collected to obtain a spectral distribution.

[0006]

Problems with the Prior Art Near-field (near-field) scanning optical microscopes are said to be able to achieve high resolution without being limited by wavelength, but the aperture diameter and tip diameter of the probe must be smaller than the wavelength. However, in any case of illuminating the sample with the probe light or picking up the light from the sample with the probe, the detected light to be a signal is extremely weak, and there is a big problem that the SN ratio is very small. ing. On the other hand, in the above infrared microscopic measuring device (JP-A-6-94613), since the evanescent wave is generated by utilizing the total reflection of the high refractive index prism, the spatial resolution that can be realized is the high refractive index. There are problems of being restricted by the refractive index of the prism, and a problem that special contrivance is required for the illumination optical system in order to obtain an incident light beam having a critical angle or more. The present invention aims to solve the above problems.

[0007]

The gist of the present invention is to apply a slit-shaped opening having a minute width as a probe.

The infrared microspectroscopic analysis method according to the present invention forms a field of an evanescent wave in the vicinity of the surface of an object using spectroscopic light in the infrared region, and a slit having a minute width is formed in the field of the evanescent wave. The slit-shaped opening, or the propagated light from the slit-shaped opening or from the micro area of the subject facing the slit-shaped opening is collected, and the collected light is photoelectrically converted to obtain a signal. The basic feature is that the spectral distribution is obtained based on.

Further, the infrared microspectroscopic analyzer according to the present invention collects and projects the light from the infrared spectroscope toward the stage on which the subject is placed and the subject placed on the stage. Means, an infrared transmissive prism having a slit-shaped opening having a minute width on the side facing the surface of the subject, and means for condensing the light passing through the slit-shaped opening of the infrared transmissive prism,
It is basically characterized in that it comprises means for photoelectrically converting the condensed light into a signal, and means for calculating a spectral distribution based on the signal.

[0010]

[Function] Since the probe has a slit-shaped opening with a very small width, the measurement light intensity is obtained in proportion to the area of the slit-shaped opening, and the SN ratio is remarkably increased, which is impossible with a minute circular opening. It became possible to obtain the spectral distribution. A spatial resolution determined by the width of the slit-shaped opening can be obtained, and in principle, a spatial resolution on the order of submicrons can be realized.

[0011]

Principle Background of the Invention The present invention utilizes evanescent waves. Therefore, first, a method of generating an evanescent wave will be described. The method of generating the evanescent wave is
There are a method using a high refractive index crystal, a method using a diffraction grating, and a method using a minute aperture. In the above, when light is incident from the high-refractive index medium to the low-refractive index medium at an incident angle equal to or greater than the critical angle, total reflection occurs, and at this time, an evanescent wave is generated in the low-refractive index medium. The method of using the diffraction grating of 1 only needs to make light incident on the diffraction grating. An evanescent wave is generated regardless of the incident angle of light or the lattice spacing. The size of the wavelength of the diffracted light (including the evanescent wave) generated by the diffraction grating exists from the same size as the wavelength of the propagating light to infinitely small one. In addition, if the lattice spacing is reduced, of all orders of diffracted light,
The proportion of diffracted light that becomes an evanescent wave increases. When a diffraction grating is used, even when an evanescent wave is incident on the diffraction grating instead of entering the propagating light, the diffracted light contains the evanescent wave together with the propagating light.

The method using the minute aperture can be considered by reducing it to a diffraction grating. That is, the structure of the one-dimensional aperture is considered to be a transmittance distribution represented by a rect function, and when this rect function is Fourier transformed, it has a spatial frequency component from 0 to infinity. That is, the structure of the one-dimensional aperture can be considered as a superposition of diffraction gratings having various grating intervals. Therefore, the diffracted wave from the aperture can be considered like the diffracted wave from the diffraction grating. When the wavelength of the incident light is λ, the spatial frequency component smaller than 1 / λ represents the diffracted wave component of the diffraction grating having a grating interval longer than the wavelength, and the spatial frequency component larger than 1 / λ represents the grating interval shorter than the wavelength. Represents the diffracted wave component from the diffraction grating with. Therefore, if the size of the aperture is made sufficiently smaller than the wavelength, the proportion of the diffracted wave component from the grating shorter than the wavelength occupies the entire diffracted wave, so that a large amount of the evanescent wave component exists. That is, most of the diffracted waves are evanescent waves that give resolution exceeding the wavelength. Therefore, if a diffracted wave from an aperture sufficiently smaller than the wavelength is used, spatial resolution exceeding the diffraction limit can be realized. However, even if the size of the aperture is smaller than the wavelength, the diffracted wave from the aperture contains a propagating light component. Also, as is well known, the evanescent wave decays exponentially, so the evanescent wave exists only immediately after the opening (near field).

As described above, propagating light and non-propagating evanescent wave exist in the diffracted wave by the minute aperture. An object having some structure such as a shape such as unevenness and a transmittance distribution can be described as a superposition of several diffraction gratings when the structure is subjected to Fourier series expansion, not limited to a minute aperture. Since the diffracted wave from the diffraction grating always contains the evanescent wave component, the evanescent wave exists in the diffracted wave from any structure. Then, of the spatial frequency components of the structure, the higher the proportion of high frequency components (the greater the number of lattice components having an interval shorter than the wavelength in Fourier series expansion), the greater the proportion of the evanescent waves in the diffracted waves. The near-field optical microscope is an apparatus for observing a sample placed in the near-field region by light by applying a probe to the field of the evanescent wave generated in the near-field region by any of the above methods.

In a near-field microscope using a minute aperture as a probe, it is the size of the aperture that determines the spatial resolution, and in principle there is no limit to the spatial resolution that can be realized. The operation of the microscopic optical system using the microscopic aperture according to the present invention, particularly the microscopic aperture associated with the sample, will be described with reference to FIGS. 1 and 2.

FIG. 1A shows an incident light 2 incident on an optical minute aperture 1.
Is an optical system in which a sample 3 having an absorption distribution is placed immediately after the aperture 1 and the transmitted light 4 from the sample 2 is detected. At this time, the opening 1 plays the role of a minute light source of a wavelength or less. Of the diffracted light from the opening 1, the evanescent wave E exists immediately after the opening 1 in a region having the same size as the size of the opening (for example, opening diameter). Since the sample 3 having a structure such as absorption distribution is placed in this region, the evanescent wave E is diffracted by the structure of the sample 3 and the propagating light component of the diffracted light is emitted as the transmitted light 4, This is detected. By making the size of the aperture 1 sufficiently small, a spatial resolution exceeding the wavelength can be realized.

On the other hand, FIG. 1B shows an optical system in which the incident light 5 is incident on the sample 3 and the diffracted light due to the structure of the sample 3 is detected by the minute aperture 1. The light diffracted by the structure of the sample 3 also contains the propagating light component and the evanescent wave component, as in the case of the minute aperture. Of these, the evanescent wave component E is diffracted light that is diffracted by a spatial frequency component of a wavelength or less in the structure of the sample 3, and therefore, by detecting this light, a spatial resolution exceeding the diffraction limit can be obtained. it can. By placing the microscopic aperture 1 immediately after the sample 3, the evanescent wave E from the sample 3 is transmitted to the microscopic aperture 1
Is diffracted by and the propagating light component 6 of the diffracted light is detected. Although FIG. 1 shows a transmission type optical system for a transparent sample 3, it cannot be applied to measurement of an opaque sample.
For an opaque sample, a reflection type optical system as shown in FIG. 2 is used.

In FIG. 2A, incident light 7 is incident on the minute aperture 1 and the sample 8 is illuminated by the diffracted light (including the evanescent wave) from the aperture 1 so to speak, and the diffracted light (evanescent light) from the sample 8 is emitted. (Including waves) is an optical system for detecting reflected light 9 as propagating light through the same minute aperture 1. Since the illumination of the sample 8 and the detection of the reflected light 9 can be performed by the single opening 1, the optical system becomes simple. However, the light wave passes through the aperture 1 smaller than the wavelength twice, and the S / N
It is unavoidable that the ratio becomes very bad. In order to improve this, as shown in FIG.
The light does not pass through the sample 8 and is directly incident on the sample 8. In this case, the incident light 10 is diffracted by the structure of the sample 8, and the evanescent wave component of the diffracted light (reflected light) is reflected by the minute aperture 1.
Is diffracted by and reflected light 11 as propagating light is detected.

As described above, when the sample is illuminated by the aperture, when light is incident on the aperture, the evanescent wave component having a wavelength shorter than the propagating light is attenuated exponentially directly from the aperture, and also passes through the aperture. Since the intensity distribution of the propagating light component spreads spatially as the distance from the aperture increases, the spatial resolution that can be realized decreases as the distance from the aperture to the sample increases. The same applies to the optical system that detects the diffracted light from the sample through the aperture. Therefore, in any optical system, the closer the aperture is to the sample, the higher the spatial resolution can be measured.

Further, in the transmission type system, since the light passing through the sample is scattered and detected by the structure of the sample surface, it is not possible to obtain information only on the sample surface. On the other hand,
In the reflection type optical system, the light from the aperture on the surface of the sample is irradiated and only the light scattered on the surface is detected, so the information on the surface of the sample is not mixed into the signal light and the information on the surface is not mixed. Only can be detected. Therefore, for such a purpose, the measurement by the reflection type optical system is more suitable than the transmission type. Regarding the aperture shape of the probe, as the minute aperture 1, what has been conventionally applied (in a broad sense) is a circular aperture. In a near-field microscope using a micro-aperture probe, only the light that has passed through the aperture is detected out of the light from the light source, so the light utilization efficiency is very poor. Further, in order to obtain a spatial resolution exceeding the diffraction limit, it is necessary to make the size of the aperture smaller than the wavelength, so that the detected signal light is very weak and measurement is difficult.

In practice, using the method of the embodiment described later,
As shown in FIG. 3 (a), a circular aperture with a diameter r of 2 μm was made, and an attempt was made to measure the infrared spectrum distribution using this, but the intensity of the light from the aperture was extremely weak, and Was not clearly separated and could not be detected. Further, in the infrared spectroscopic analysis as intended by the present invention, the purpose is to obtain an infrared spectrum distribution rather than the signal light itself, and noise may be excessively superimposed on this infrared spectrum distribution. In the first place, it cannot be put to practical use. Therefore, it is necessary to obtain the signal light in a form separated from the noise component to some extent, and it is essential to realize an S / N ratio above a certain level.

Therefore, in order to solve the above problems, the inventors have focused on the opening shape of the probe and devised to make it into a slit shape. When the opening has a slit shape, the measurement light intensity proportional to the area of the slit is obtained, the S / N is significantly improved, and the spatial resolution determined by the size of the width is obtained in the slit width direction. However, a high spatial resolution cannot be obtained in the slit length direction. That is, the spatial resolution exceeding the wavelength can be realized only in the one-dimensional direction.

[0022]

EXAMPLE FIG. 4 shows a main part of the example, and FIG. 5 shows the whole example for explanation. In FIG. 4, reference numeral 20 denotes a prism provided with a slit-shaped opening 21 having a minute width, which transmits infrared light. Reference numeral 30 is a Cassegrain objective mirror including a primary mirror and a secondary mirror, and 31 is a luminous flux of infrared light. The prism 20 has a spherical surface 22 on the upper surface and a conical surface 2 on the lower surface.
3 is formed. A thin metal coating film 24 is formed on the conical surface 23, and the slit-shaped minute openings 21 are opened in the top of the conical surface 23 by cutting out the coating film 24. Slit-shaped minute opening 21
The infrared transmissive prism 20 having a structure constitutes a micro aperture probe, and is fixed to the Cassegrain objective mirror 30 with its optical axis aligned in the embodiment. The upper surface of the prism 20 is a spherical surface 2
Since it is set to 2, the focused light from the Cassegrain objective mirror 30 can be efficiently focused on the minute aperture 21, or the diffracted light from the minute aperture 21 can be efficiently focused on the Cassegrain objective mirror 30, respectively. In addition, the conical surface 23 on the lower surface of the prism 20
In order to easily confirm the position of the tooth and the opening of the sample located below the opening 21 in the sample surface, and the opening 2
In order to make it easy to check the distance between 1 and the sample, it has a conical shape.

In FIG. 5 showing the system configuration, the micro aperture probe 20 fixed to the Cassegrain objective mirror 30 is
It is located above the stage 40 having an opening in the center.
On the stage 40, a sample 50 of the subject's age is placed. The stage 40 can be finely moved up and down, and can be scan-driven in two directions, that is, in the X or Y direction of a plane XY orthogonal to the microscope optical axis. The Cassegrain objective 60 is
When the sample 50 is transparent (transmission mode), it is used for illuminating the sample 50, and the incident light flux is focused and projected on the sample 50. The mirror 61 is for mode selection, and is retracted from the optical path in the transmission mode, and when the sample 50 is an opaque reflective object (reflection mode), the mirror 61 is located in the optical path as shown in FIG. Reflect to. Both the mirror 62 and the mirror 63 are mirrors for optical path conversion, and the mirror 64
Is a semi-transparent mirror. The MCT detector 70 as the photoelectric detecting means is disposed above the semi-transparent mirror 64 so that the detecting portion is located at a position where the slit-shaped micro aperture 21 of the micro aperture probe 20 is imaged by the Cassegrain objective mirror 30. ing. The MCT detector 70 is a detector made of a quantum compound semiconductor containing mercury, cadmium, and tellurium, and can detect infrared light with high sensitivity in a wide wavelength range.

The computer 80 is composed of, for example, a personal computer, and is connected to the MCT detector 70 and the infrared spectroscope 90 via a suitable interface. In this embodiment, the infrared spectroscope 90 is a Fourier transform infrared spectroscope composed of an infrared light source 91 and a Fourier transform interferometer 92, and the computer 80 scans the moving mirror in the interferometer 92. Control.
In this case, the photoelectric signal obtained by the MCT detector 70 is an interferogram, and in synchronization with the computer 80 controlling the operation of the infrared spectroscope 90, the MCT detector 7
Input the interferogram signal from 0. The computer 80 also has means (mostly a program) for calculating an infrared spectrum distribution from the obtained interferogram, and the obtained infrared spectrum distribution can be visualized by an attached monitor or recording means. It can be output as information.

On the other hand, a probe
A means 100 for observing between samples is additionally provided, and the observation means 100 is composed of a long-acting objective lens 101, a CCD camera 102, and a monitor 103. The long working objective lens 101 has a magnification of 20 times, an NA of 0.28, and a working distance of 30.5 mm. With this observation means, the distance between the slit-shaped minute opening 21 and the surface of the sample 50 can be enlarged and visually observed, and the distance between the two can be finely controlled and set. The above Cassegrain objective 3
0 and 60 have 25x magnification and NA of 0.62
I use the one. In addition, the apparatus system shown in FIG. 5 is an existing infrared microspectroscopy system except for the microaperture probe 20 and the observation means 100, for example, an infrared microspectroscopy system manufactured by Horiba, Ltd., part number FT-520. Can be used.

In the operation of the system of FIG. 5, in this system, as described above, there are two modes: a transmission mode in which light is transmitted through the sample 50 for measurement and a reflection mode in which the reflected light from the sample 50 is measured. Can be switched according to the sample 50 and measured. The light from the infrared light source 91 is
First, it is guided to the interferometer 92. The spectroscopic light emitted from the interferometer 92 is reflected by the mirror 6 when the mirror 61 is retracted from the optical path.
Proceed to 3 and reflect here, the lower Cassegrain objective 60
The Cassegrain objective lens 60 makes the incident light incident on the sample 5.
Focus on 0. Diffracted light including an evanescent wave is generated in the sample 50 irradiated with the spectral light. The slit-shaped micro aperture 21 of the micro aperture probe 20 is located in the field of the evanescent wave formed on the surface of the sample 50, the evanescent wave is converted into propagating light by the slit micro aperture 21, and the propagating light is the micro aperture probe. Go up through 20 prisms. The upper Cassegrain objective mirror 30 focuses all of the propagating light coming from the slit-shaped minute aperture 21 and MC
The light is focused on the T detector 70.

On the other hand, when the mirror 61 is placed in the optical path,
It is a reflection type measurement. In this case, the spectroscopic light from the interferometer 92 is reflected by the mirrors 61, 62, 64 and enters the upper Cassegrain objective mirror 30. Cassegrain objective 30
Collects the incident light and collects it on the slit-shaped micro aperture 21 of the micro aperture probe 20. At this time, since the slit-shaped minute aperture 21 of the minute aperture probe 20 is located at the center of the probe spherical surface, light goes straight without being diffracted by the spherical surface, and the minute aperture prism 20 is made of a material having a relatively high refractive index. Therefore, even if the aberration is taken into consideration, the degree of focusing of the focused light is high. The spectral light focused on the slit-shaped minute opening 21 generates diffracted light including an evanescent wave by the slit-shaped minute opening 21, and the sample 50
Illuminate the surface of. The light reflected by the sample 50 forms a field of an evanescent wave, produces diffracted light, and becomes propagation light due to interaction with the slit-shaped minute aperture 21,
The microaperture probe 21 moves upward in the prism. The upper Cassegrain objective mirror 30 focuses all of the propagating light traveling upward through the slit-shaped minute aperture 21 and condenses it on the MCT detector 70 via the semitransparent mirror 64.

The computer 80 controls the operation of the interferometer 92 and synchronously fetches the photoelectric conversion signal from the MCT detector 70. Since the spectroscope 90 is an infrared Fourier transform spectroscope, the photoelectric conversion signal is an interferogram in this case, and the computer 80 captures this interferogram and stores it as data in the storage means.
When the Fourier transform means (for example, configured by a program) built in the computer 80 is activated and the interferogram converted into data is Fourier transformed, an infrared absorption spectrum distribution or an infrared reflection spectrum distribution can be obtained and visualized. And output.

The sample 50 is placed on the XY biaxial stage 40. The stage 40 is scanned in the slit width direction of the slit-shaped minute opening 21. By this scanning, one-dimensional distribution of infrared absorption or reflection spectrum can be measured with a spatial resolution according to the slit width. If the direction of the wavelength λ is added to the dimension, it can be said to be a two-dimensional spectrum distribution of (λ, X) or (λ, Y). Further, the above-described device and method are applied to a sample having a structure only in one-dimensional direction such as an organic multilayer film (in actual measurement, a cross section in the film thickness direction or a direction crossing the film thickness direction is measured). Infrared microspectroscopy can be performed with a spatial resolution exceeding the diffraction limit. Therefore, when a small region of the sample 0 corresponding to the slit-shaped opening of the slit-shaped minute opening 21 has, for example, a part of a two-dimensional structure having an absorption distribution, a correct spectral distribution cannot be obtained. However, it is extremely remarkable that the material distribution and the fine structure of the sample in the organic multi-layer film can be analyzed in the micron order or in the submicron order by narrowing the slit width. Have

When there is an absorbing object having a two-dimensional distribution in the observation region of the sample, it is possible to reconstruct the absorption image of the two-dimensional distribution by the projection method described later. This reconstructed absorption image has a spatial resolution on the order of microns. In order to perform the projection method, the stage 40 shown in FIG. 5 is also configured to be rotatable about the optical axis, and can be scanned in the slit width direction by indexing control by a predetermined angle φ. Is being done. Of course, the XY biaxial scanning control and the angle φ indexing control can be performed under the control of the computer 80.

Next, the micro aperture probe 20, which is an important element in the embodiment of the present invention, will be described in more detail. FIG. 6 shows the outer structure. It is obtained by processing a hemisphere of an infrared transmitting crystal having a radius R of 7.5 mm. The lower conical surface 23 is 15.0 against the bottom surface of the hemisphere.
It is processed to form a bus line of °. The metal thin film 24 as an optical shield applied to the conical surface 23 is a gold coating film and is formed by sputtering. The slit-shaped minute opening 21 is formed by cutting out the gold coating film. Slit width is about 2μ
m, and the slit length is about 70 μm. The annular zone 25 between the spherical surface 22 and the conical surface 23 is a gripping portion during processing, and also serves as a fixing portion when the probe 20 is assembled to an optical system. The diameter of this zone 25 is 1
It is 3 mm.

The infrared transmitting crystal that serves as a substrate for forming the slit openings is ZnSe. Other applicable crystals are shown in Table 1 together with their characteristics.

[0033]

[Table 1]

Since the crystal is used as a probe as in the embodiment, some conditions must be satisfied. The condition is that the transmittance is high in the wavelength range (about 2 to 15 μm) required for spectrum measurement in the mid-infrared region, and that visible light is transmitted so that the shape and size of the aperture made on the crystal can be easily confirmed. , Deliquescent in consideration of the measurement of samples containing water, long-term use, and ease of handling.
Since it is necessary to process the crystal in forming an opening on the crystal, it is easy to process and polish, and the toxicity is as low as possible in consideration of handling during processing.
Is mentioned.

Then, considering the properties of each crystal, Zn
Se has high transmittance in a wide wavelength range from visible to infrared and has no deliquescent property. However, it must be handled with care because it is designated as a medical toxic substance. ZnS has the same properties as ZnSe, but the transmission wavelength range is slightly narrower than that of ZnSe. In addition, it must be handled with care because it is designated as a medical toxic substance. Halides such as KBr, KCl, and NaCl have high transmittance over a wide range from the visible region to the infrared region. Deliquescent. Further, it is difficult to process. Fluorides such as CaF ₂ and BaF ₂ as well as MgF ₂ have almost no deliquescent property and have good transmittance from visible to infrared. However, the transmittance becomes low in the wavelength region of 10 μm or more, and it becomes difficult to measure the spectrum in this region. Ge and Si semiconductors have no deliquescent property and have high transmittance up to the long-wavelength side of the infrared region, but they do not transmit visible light, so check the slits etc. made on the crystal under visible light. I can't. Oxides such as Al ₂ O ₃ and MgO have no deliquescent property and have high transmittance for visible light. However, the transmittance in the long wavelength region is low, and the crystal is hard, which makes processing difficult.

Therefore, each of the infrared transmitting crystals listed in Table 1 has advantages and disadvantages, and no crystal satisfies all the above conditions. However, regarding the toxicity of, there is no problem if sufficient care is taken during handling. So, ZnSe or Z
Considering that nS satisfies the condition best,
ZnSe has a wider transmission wavelength range and lower toxicity than ZnS. Therefore, ZnSe was selected as the optimum probe material in the examples. Z in Figure 7
The transmittance spectrum of a nSe crystal is shown. Gold is used as the coating metal for the film on the conical surface of the ZnSe crystal. Table 2 shows the complex refractive index of gold in the visible / infrared region and the skin depth. The skin depth is defined as the distance at which the intensity of light travels through a metal to be 1 / e (e is the base of natural logarithm).

[0037]

[Table 2]

The metal film for forming the opening needs to sufficiently block light at a place other than the opening. If the film thickness of the metal is sufficiently thick, light is blocked. On the other hand, if the film thickness is large, the light passing through the opening is scattered inside the opening, and the amount of light passing through the opening is reduced. Conceivable. Therefore, it is suitable that the film thickness of gold is a thickness that can sufficiently block light and is as thin as possible.

As can be seen from Table 2, the skin depth of gold in the visible and infrared regions is slightly deeper in the visible region.
Therefore, whether or not the coated gold film can block light in the infrared region can be determined by confirming that light does not leak in the visible region. When the gold thin film was irradiated with visible light and the transmitted light was confirmed, gold was about 300
It has been found that visible light can be blocked with a film thickness of about nm. Therefore, the crystal surface was coated with gold to a thickness of about 300 nm using a sputtering apparatus. Before the gold is coated on the crystal, the crystal surface needs to be sufficiently smooth. Since the coating film thickness is about 300 nm, if there is unevenness larger than this locally,
This is because light may leak from there. Therefore, before coating with gold, the crystal surface was polished with a polishing sheet until it was sufficiently smooth. A lapping film sheet having a particle size of 0.3 μm was used as the polishing sheet.

Next, the production of slit openings is performed. For example, a method may be considered in which a shield having the same shape as the slit is placed on the crystal and metal coating is performed. However, since the target slit has a slit width of about 1 to 2 μm, a shield having such a shape is produced. It is virtually impossible to do this or place it at the tip of the crystal. A method of coating a metal on the substrate and peeling the metal in the slit-shaped portion by etching can be considered, but since ZnSe dissolves in an acid, etching cannot be performed on ZnSe.

Therefore, the method as shown in FIG. 8 was used for producing the slits. That is, this is a method of colliding the metal needle 26 and the metal-coated crystal 20 '. As shown in the enlarged view, the tip of the metal needle 26 has a wedge shape having the same width as the slit to be opened. Then, the position of the crystal 20 'is controlled by the triaxial stage 27 and the piezo elements 28 and 29 to collide with the fixed metal needle 26. Piezo elements that control the position of the crystal are attached in two directions X and Z. That is, the direction in which the crystal approaches the tip of the needle (Z-axis direction in FIG. 8) and the direction in which the crystal and the needle are laterally displaced (X-axis direction in FIG. 8). When actually trying to open the opening by colliding the metal needle with the crystal, if the crystal is moved only in the Z-axis direction and collided with the needle, the metal on the crystal is damaged, but the light is transmitted. It was difficult to make such an opening. Therefore, when the crystal was moved in the Z-axis direction at the time of contact between the crystal and the metal needle 26 and simultaneously moved in the X-axis direction by the piezo element 28, a slit-shaped opening could be formed. In order to adjust the state of contact between the metal needle and the crystal, and the position of the minute slit on the crystal surface, the contact point between the tip of the metal needle and the tip of the crystal surface is set in the X-axis direction and the Y-axis direction in FIG. The slits were produced while observing with a microscope from two directions. Further, in order to adjust the movement amount of the crystal in the Z-axis direction after the contact between the metal needle and the crystal, it is necessary to accurately grasp the contact position between the metal needle and the crystal. However, it is difficult to accurately determine the moment of contact only by microscopic observation from two directions. Therefore, by passing an electric current between the metal needle and the metal on the surface of the crystal and confirming the position where the electric current starts to flow with an ammeter, the exact position where the metal needle and the crystal contact each other was confirmed.

The material of the needle 26 is a crystal 20 '.
Stainless steel, which has high hardness, was used so that the shape of the needle tip would not be destroyed by collision with. Titanium was also used as a material having high hardness, but it was difficult to process because it was brittle. The tip of a stainless steel rod with a diameter of about 1 mm is polished with a polishing sheet, and has the same width as the target slit,
It was processed into a wedge shape as shown in FIG. The polishing sheet used was a wrapping film sheet with a particle size of 0.3 μm. The polishing of the needle was performed while observing the tip of the needle with a microscope.

The slit-shaped minute opening 21 produced by the above method illuminates the back side of the conical surface from the spherical side of the probe 20, and observes the surface of the conical surface with a microscope to confirm the shape and length. You can In one example, the slit width is 2μ
It was confirmed that m and the slit length were about 70 μm. In addition, several examples were prepared and applied in specific examples described later.

[0044]

[More specific example] With the apparatus system shown in FIG. 5, a metal film 52 coated on a substrate 51 as shown in FIG.
Dimensional scanning was performed to measure the change in the infrared transmission spectrum at the edge portion of the metal film 52. The metal film 52 as a subject of the sample 50 is gold (Au) having a film thickness of about 15 nm, and the base 51 is made of BaF ₂ having a high transmittance for infrared light and has a thickness of about 1 mm. The slit-shaped opening 21 has a slit width of about 2 μm and a slit length of about 50 μm. In the case of this embodiment, the micro aperture probe 20 is provided at each measurement position.
The slit-shaped opening 21 and the sample 50 are brought into contact with each other for measurement.

FIG. 10 shows the change in the transmittance spectrum near the edge of the metal film 52, which was obtained when the sample 50 was scanned in the direction of the arrow. (A) of FIG.
(b), (c) and (d) are spectra measured at four points 2.5 μm apart. The number of integrations of each spectrum measurement was 100 times. From FIG. 10, (a)-(b),
It can be seen that, in the cases of (c)-(d), the decrease in the transmittance is about 10% over the entire measurement wave number, but it is about 50% in the area between (b)-(c). That is, the metal film 52 is formed between (b) and (c).
It is considered that the edge of is detected. The large change in the transmittance in the vicinity of 2350 cm ^{−1 of} each spectrum is due to the absorption of CO ₂ .

Next, (1) 4000 cm ^-1 (2.5 μm),
(2) 2500 cm ^-1 (4 μm), (3) 1666 cm ^-1 (6 μm
m), (4) 1250 cm ^-1 (8 μm), (5) 1000 cm
Changes in transmittance at each wave number (wavelength) of ⁻¹ (10 μm) are shown in FIGS. 11 and 12. (N) -a in both figures is the probe 20.
(N) -b is the result when it was not used. The field stop at the time of measurement of b is about 8 μm ×
It was 8 μm. In order to examine the resolution for each wave number in each of a and b measurements, the difference D between the maximum value and the minimum value of the measured transmittance changes from 0.75D to 0.25D. The distance required for is defined as the spatial resolution R in this example. The straight lines representing 0.75D and 0.25D in FIG. 11 and FIG. 12 are also shown. The values of R read from each graph are summarized in Table 3.

[0047]

[Table 3]

From Table 3, the resolution R measured with the probe is about 2-3 μm for each wavelength, while the R measured without the probe is about 7 μm for each wavelength. There is a large difference up to about 15 μm. Since the spatial resolution without a probe is determined by the size of the field stop and the spread of the image determined by the wavelength and the numerical aperture NA of the Cassegrain objective mirror, the longer the wavelength, the larger R becomes. . On the other hand, in near-field measurement using a slit probe, R takes a substantially constant value at each wavelength from (1) to (5),
It can be seen that the spatial resolution does not depend on the wavelength but depends on the slit width.

The numerical aperture NA of the Cassegrain objective mirror used in this example is 0.62. Therefore, Rayleigh's formula
The diffraction limit obtained from (Δr = 0.61λ / NA) is almost the same as the wavelength used. Looking at the results in Table 3,
It can be seen that when the slit is used, the spatial resolution exceeding the diffraction limit is realized at any wavelength.

Another example is the measurement of infrared absorption spectra of polymer films. As shown in FIG.
An infrared absorption spectrum was obtained by one-dimensionally scanning the polyimide-based heat-resistant polymer film 54, which was closely adhered and fixed on a BaF ₂ substrate 53 having a thickness of about 1 mm, in the slit width direction of the slit 21 of the slit-shaped microaperture probe 20. It is a thing.
The scanning direction is the direction of the arrow in the figure, and the number of times of measurement of each spectrum is 100 times. The slit width of the slit-shaped opening 21 of the applied micro-aperture probe 20 is about 2
In μm, the slit length is about 30 μm. The thickness of the polyimide heat resistant polymer film 54 is about 50 μm. FIG. 14 shows the transmittance spectrum and the absorbance spectrum of this sample 54, which are obtained by ordinary infrared spectroscopy.
Shown in (a) and (b). In this embodiment, scanning is performed without the slit-shaped opening 21 contacting the sample 54. The distance between the sample 54 and the slit-shaped minute opening 21 is the observation means 1 including the CCD camera 102 shown in FIG.
It was about 1.5 μm when observed with No. 00.

FIGS. 15A, 15B, and 15C show transmittance spectra measured at intervals of 2 μm near the edge of the sample 54. Sample 4 was measured within 4 μm from (a) to (c).
It can be confirmed that the absorption peak of disappears.

Among the absorption peaks of the sample 54 shown in FIG. 14 (b), (1) 2964 cm ⁻¹ (3.37 μm) indicated by the arrow
m), (2) 1778 cm ^-1 (5.62 μm), (3) 1722c
m ^-1 (5.81 μm), (4) 1600 cm ^-1 (6.25 μm),
(5) 1502 cm ^-1 (6.66 μm), (6) 1382 cm ^-1
Changes in transmittance at six wave numbers (wavelengths) of (7.24 μm) are shown in FIGS. 16 and 17. In the figure, (n)-(a) shows the case of measurement using the probe 20, and (n)-(b) shows the case of measurement without using the probe. In addition, in (b), it is measured using a field stop of about 5 μm × 5 μm.

The vertical axis in each of the graphs of FIGS. 16 and 17 indicates the transmittance at each wave number, which is 2 without absorption of the sample 54.
It is the value divided by the transmittance of 160 cm ⁻¹ . The reason for the division is as follows. That is, during the measurement, a phenomenon was observed in which the intensity of the entire signal decreased near the edge of the sample. This means that when the sample was present immediately before the slit, the transmitted light from the sample and the scattered light from the sample surface were incident on the slit, whereas the edge part of the sample passed directly under the slit and the sample was It is considered that when it does not exist immediately before the slit, only the light transmitted through the substrate about 50 μm (thickness of the sample) away from the slit enters the slit, and the scattered light from the substrate surface does not reach the slit. Therefore, it is considered that, by referring (dividing) the transmittance at the wave number where there is no absorption by the sample, it is possible to see only the absorption of the sample among the spectral changes.

As is apparent from FIGS. 16 and 17, it can be seen that when measured using the probe 20, the value of R according to the above-mentioned definition of each wave number is constant at about 3 to 4 μm. Further, in the case of (b), R tends to increase. In addition, in (b), it is understood that the S / N ratio is low and the error of R is large. Also in this embodiment, as described above, in the measurement without the probe, the longer the wavelength is, the lower the spatial resolution becomes, whereas in the measurement using the slit probe, the spatial resolution does not depend on the wavelength. , It is clearly confirmed that it depends on the slit width.

In the example of (a) using the probe, the slit width is 2 μm and R is about 3 to 4 μm, whereas in the previous embodiment, the slit having the same width is used. Despite this, R is about 2.5 μm and the value is different,
It is considered that the latter case had a larger distance between the probe and the sample than the former case. In addition, since the thickness of the sample used in the latter example is about 50 μm,
It is considered that the shape of the edge portion is dull as compared with the former embodiment.

The above example shows that the infrared spectroscopic spectrum can be measured with a spatial resolution exceeding the diffraction limit by using a probe having a slit-shaped aperture having a width shorter than the wavelength of light used for measurement. Moreover, in ordinary infrared microspectroscopy, the spatial resolution is limited by the diffraction limit, and since the limit depends on the wavelength, the phenomenon that the spatial resolution decreases as the measurement wave number becomes smaller appears. In the near-field microspectroscopic measurement used, the spatial resolution is not limited by the wavelength, and basically it is determined only by the size of the slit width of the slit-shaped opening. According to the embodiment, over a wavelength range of 2.5-10 μm, about 2.5
A spatial resolution of μm has been realized.

Therefore, if the infrared near-field microspectroscopic system as in the embodiment is used, it is possible to analyze the one-dimensional material distribution and the fine structure of the sample such as the organic multilayer film sample with the spatial resolution exceeding the diffraction limit.

The slit width of the probe of the embodiment is about 2 μm.
However, by making this slit width smaller,
Higher spatial resolution can be achieved and sub-micron orders can be practically achieved. However, if the slit width is made narrower to improve the spatial resolution, the signal light becomes weaker, but the slit length is lengthened, the light source intensity and detector sensitivity are improved, and the number of measurements and integrations during spectrum measurement is increased. , Using a Cassegrain objective with a higher numerical aperture NA, making special measures to suppress noise light, and stricting the linearity of the slit-shaped opening and eliminating the unevenness of the opening edge, etc., individually or in combination. It is possible to solve it by devising it.

When a slit-shaped minute aperture is used as a probe, spatial resolution exceeding the diffraction limit is obtained in the slit width direction, and high resolution cannot be obtained in the slit length direction. Therefore, when measuring a sample such as a cross section of a multilayer film, the slit-shaped minute aperture is one-dimensionally scanned in the width direction to distribute the sample (beyond the boundaries based on the composition, A, B, C, D ... Can be identified)
However, if different types of substances are scattered two-dimensionally in the sample, the distribution can be observed simply by scanning the slit-shaped minute openings in the one-dimensional direction. I can't.

As a method of measuring the two-dimensional distribution of the sample while using the slit-shaped minute aperture, it is conceivable to scan the slit-shaped minute aperture not only in one direction but also in various directions within the sample surface. As illustrated in FIG. 18, considering the case of measuring a sample in which an object 55 having a two-dimensional distribution such as absorption exists in the sample, the slit 21 is set to 1
Information on the sample in the length direction of the slit cannot be obtained only by scanning only in the dimension direction. Therefore, slit 2
1 is rotated and scanning is similarly performed in the slit width direction.
By this operation, information on the sample in the direction of the slit width after rotation can be obtained. If the rotation angle φ of the slit is fixed and finely divided and the slit is scanned in multiple directions of φ ₁ , φ ₂ , φ ₃ , φ ₄ , ..., Amount of two-dimensional information of the sample can be obtained. The two-dimensional transmittance distribution at a certain wavelength λ ₀ can be obtained by reconstructing the one-dimensional transmittance distribution at each rotation angle φ _n . In other words, it uses the principle of two-dimensional CT, and is a method of measuring one-dimensional projection data and reconstructing a two-dimensional cross-sectional image of the original object from it (method called Radon transform and Radon inverse transform). As such a measurement method for reconstructing the structure of the sample from the observation results of the sample from multiple directions, X
The technique of line CT is known. The back projection technique used in X-ray CT can be directly applied to the infrared transmittance distribution measurement using the slit-shaped minute aperture.

First, as shown in FIG. 18, the slit is rotated by an angle φ to obtain an absorption intensity distribution in the X _φ direction. This is called projection or projection, and is mathematically a Radon transform operation. Next, by changing φ, a large number of directions (φ _n : n = 1, 2, 3, 4, ...
Get the projection in ...). In each projection, the absorption distribution in the X _phi direction, arranged along the Y _phi direction. This is an operation called back projection. Then, this is performed for each φ, and the sum is taken over the entire measurement region. The reconstructed image obtained from the back projection (for example, absorption distribution image)
Is a structure in which the spatial frequency is low among the structures of the sample, so generally, after the above operation,
After performing a filtering process for suppressing low frequencies on each projection, the operation of is performed. This is called filtered back projection,
The same is done in X-ray CT.

In the above embodiment, the infrared spectroscope 90 is a Fourier transform type spectroscope, but of course, a dispersion type infrared spectroscope can be applied. Further, the stage 50 on which the sample or the subject 50 is placed has a configuration in which a driving mechanism is attached to the stage 50 to scan the stage 50.
It is also possible to have a structure in which the stage is fixed and the slit-shaped minute aperture 21 scans above the stage, that is, a configuration in which the minute aperture probe 20 is driven and scanned. Similarly, although the stage 50 is also rotatable and index-controlled at a predetermined angle, the stage is fixed and the micro-aperture probe 20 can be rotated so that the micro-aperture probe 20 can be indexed at a predetermined angle. It may be configured to be supported by.

[0063]

As described above, according to the present invention, a field of an evanescent wave is formed in the vicinity of the surface of a subject, and a slit-shaped opening having a minute width is exposed in the field of the evanescent wave. Since the light passing through the slit-shaped aperture is detected, the intensity of the signal light is increased and the SN ratio is remarkably improved, and a significant signal that could not be obtained with a minute circular aperture is obtained and the infrared spectrum is obtained. It is possible to obtain the distribution, and it is possible to realize the spatial resolution exceeding the diffraction limit determined by the width of the slit-shaped opening in the width direction.

[Brief description of drawings]

1A and 1B are explanatory views of the principle of the present invention.

2A and 2B are explanatory views of the principle of the present invention in yet another embodiment.

FIG. 3A is a detailed explanatory view according to the present invention showing a minute circular opening and FIG. 3B showing a slit-shaped opening.

FIG. 4 is a cross-sectional explanatory diagram of a main part of one embodiment of the present invention.

FIG. 5 is a configuration diagram showing an entire embodiment of the present invention.

FIG. 6 is a front view showing a specific shape and structure of a micro aperture probe.

FIG. 7 is a graph showing a transmittance spectrum of ZnSe.

FIG. 8 is an explanatory diagram showing an apparatus for producing slit-shaped minute openings.

FIG. 9 is a diagram illustrating scanning of a sample in a specific example.

10 (a), (b), (c) and (d) are graphs showing changes in the transmittance spectrum.

FIG. 11: (1) -a, (1) -b, (2) -a, (2) -b,
(3) -a and (3) -b are graphs showing changes in transmittance at each wave number.

FIG. 12 (4) -a, (4) -b, (5) -a, (5) -b are graphs showing the change in transmittance at each wave number.

FIG. 13 is a diagram illustrating scanning of a sample in another specific example.

FIG. 14A is a graph showing a transmittance spectrum of a polyimide-based heat-resistant polymer film, and FIG. 14B is a graph showing the same absorption spectrum.

15 (a), (b), and (c) are graphs showing changes in transmittance.

16] (1)-(a), (1)-(b), (2)-(a), (2)
-(B), (3)-(a), (3)-(b) are graphs showing the change in transmittance at each wave number.

FIG. 17: (4)-(a), (4)-(b), (5)-(a), (5)
-(B), (6)-(a), (6)-(b) are graphs showing the change in transmittance at each wave number.

FIG. 18 is an explanatory diagram of a method of measuring a two-dimensional distribution using a slit-shaped minute opening.

[Explanation of symbols]

 1, 21 Slit-shaped micro aperture 3 Transmission type sample 8 Reflection type sample E Evanescent wave or evanescent wave field 20 Infrared transmission prism, micro aperture probe 24 Metal coating film 30, 60 Cassegrain objective mirror 40 Stage 50 Sample or subject 70 MCT detector 80 Computer 90 Infrared Fourier transform spectrometer

Claims (15)

[Claims] 1. A field of an evanescent wave is formed in the vicinity of the surface of a subject using spectral light in the infrared region, and a slit-shaped opening having a minute width is exposed in the field of the evanescent wave. From the microscopic area of the subject facing the slit-shaped opening or the light propagating from the, the photoelectric conversion of the collected light to obtain a signal, based on this signal to determine the spectral distribution. Infrared microspectroscopy analysis method. 2. The infrared microspectroscopic analysis method according to claim 1, wherein the width of the slit-shaped opening is not more than the shortest wavelength of the infrared spectroscopic light used. 3. The infrared microspectroscopic analysis method according to claim 1, wherein the object and the slit-shaped opening are relatively scanned in the width direction of the slit-shaped opening. 4. The red according to claim 3, wherein the object and the slit-shaped opening are relatively rotated by a predetermined angle, the scanning is performed a plurality of times, and the two-dimensional distribution of the object is obtained from the obtained plurality of information. External microspectroscopy analysis method. 5. The infrared microspectroscopic analysis method according to claim 1, wherein the signal is an interferogram. 6. A stage on which a subject is placed, a means for collecting and projecting light from an infrared spectroscope toward the subject placed on the stage, and a side facing the surface of the subject. An infrared transmissive prism having a slit-shaped opening with a very small width, means for condensing light that has passed through the slit-shaped opening of the infrared transmissive prism, and means for photoelectrically converting the condensed light into a signal,
Means for calculating a spectral distribution based on the signal,
An infrared microspectroscopic analyzer comprising: 7. The infrared microspectroscopic analyzer according to claim 6, wherein the width of the slit-shaped opening of the infrared transmission prism is not more than the shortest wavelength of the infrared spectroscopic light used. 8. The infrared microspectroscopic analyzer according to claim 6, further comprising means for relatively scanning the stage and the infrared transmission prism in the width direction of the slit-shaped opening. 9. A means for relatively rotating the stage and the infrared transmission prism by a predetermined angle, and means for forming a two-dimensional distribution of an object on the basis of a signal by the scanning at each rotation position. The infrared microspectroscopic analyzer according to claim 8, further comprising: 10. The infrared microspectroscopic analyzer according to claim 6, wherein the infrared transmission prism has a hemispherical upper portion and a conical lower portion. 11. The infrared transmission prism is made of ZnSe crystal or ZnS crystal.
Infrared microspectroscopic analyzer according to any one of 1. 12. The slit-shaped opening is formed by notching a gold coating film.
Infrared microspectroscopic analyzer according to any one of 1. 13. The infrared spectrometer is a Fourier transform spectrometer and the signal is an interferogram.
13. The infrared microspectroscopic analyzer according to any one of 1 to 12. 14. The infrared microspectroscopic analyzer according to claim 6, wherein the infrared spectroscope is a dispersive spectroscope. 15. The Cassegrain objective mirror according to claim 6, wherein at least one of the projecting means and the condensing means is a Cassegrain objective mirror.
15. The infrared microspectroscopic analyzer according to any one of 1 to 14.