JP3034383B2 - Microscopic total reflection attenuation measurement optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system for measuring attenuated total reflection, and more particularly to an optical system for measuring attenuated total reflection, which can observe and position the measurement position of a minute sample clearly without parallax.

[0002]

2. Description of the Related Art Conventionally, a total reflection surface such as a hemispherical prism, a triangular prism, a multi-reflection parallel flat plate having a large refractive index is closely attached to a sample, and the total reflection light is attenuated more sensitively due to non-uniformity near an interface of the sample. An attenuated total reflection measurement method (hereinafter, referred to as ATR measurement) for performing spectroscopic measurement or the like of a surface of a polymer film, a coating film, paper, or the like, which is difficult to measure by the transmission method, using the light receiving method is known. .

[0003] When the ATR measurement of a minute sample is performed, the measurement is usually performed by infrared light. At this time, the position of the sample to be actually measured must be accurately determined by observing the sample with visible light. To do so, conventionally, as described in, for example, US Pat. No. 5,093,580, the lens-shaped ATR crystal is separated from the sample, the sample is observed through the auxiliary lens and the objective lens, and the sample position with respect to the ATR crystal is determined. Next, the ATR crystal is brought into close contact with the sample, and thereafter, visible illumination light is made incident at the incident angle and the reflection angle position of the ATR measurement, and the measurement sample surface is observed.

[0004] Further, A
As a TR crystal, a prism P having a special shape as shown in FIG. 4 is used, a scale B is arranged on a surface A that is in close contact with the sample S, and the scale B passes through a surface D different from the measurement illumination light incident surface C of the prism P. There is known a method in which a measurement position is confirmed by a scale of a scale B while observing a sample S on which is superimposed.

[0005]

Conventionally, silicon, germanium, zinc selenide, etc., which are transparent in the infrared region and have a high refractive index, have been used as ATR crystals such as hemispherical prisms. However, since silicon and germanium are opaque in the visible region, it is impossible to observe the sample with visible light, and thus the measurement position cannot be confirmed by observation with visible light. On the other hand, since zinc selenide is transparent in the visible region, the measurement position can be specified by observing the sample with visible light, but the refractive index fluctuation in the visible region is too large, and large chromatic aberration occurs when observing the sample with visible light. Is generated, and it is difficult to clearly observe the measurement position of the sample.

The present invention has been made in view of such a situation, and an object of the present invention is to specify a configuration of a hemispherical prism by specifying a configuration of the hemispherical prism in a micro ATR measurement of a small sample using a hemispherical prism as an ATR crystal. The purpose is to make it possible to observe and position the measurement position clearly without parallax.

[0007]

According to the present invention, there is provided an optical system for measuring attenuated total internal reflection, which has a hemispherical prism in close contact with a surface of a sample, and attenuates the total reflected light on the surface of the hemispherical prism. In the optical system for measuring the total reflection attenuation, the objective lens for enlarging and projecting the sample surface in close contact with the plane through the spherical surface of the hemispherical prism is arranged, and the radius of the hemispherical prism is 2 to 10 mm. Within the range, the wavelength of the material constituting the hemispherical prism 400 n
The refractive index from m to 800 nm is n ', and the central value is n
_{When 0} ′, 0.95 ≦ n ′ / n ₀ ′ ≦ 1.05 (1) is satisfied, the refractive index at a wavelength of 2.5 μm to 10 μm is n, and the central value is n ₀ . In this case, 0.98 ≦ n / n ₀ ≦ 1.02 (2) is satisfied, and | (n ₀ ′ −n ₀ ) / (n ₀ ′ + n ₀ ) | ≦ 0.05 is satisfied. (3) is satisfied.

In this case, as a material satisfying the conditions (1) to (3), for example, zinc sulfide can be mentioned.

[0009]

In the present invention, since the material constituting the hemispherical prism satisfies the conditions (1) to (3), chromatic aberration does not occur much in the observation image in the visible region on the sample surface, and the sample can be clearly observed. In addition, the chromatic aberration in the infrared measurement range is small, accurate total reflection attenuation characteristics can be measured, and the measurement position of the sample specified in the visible range matches the actual measurement position in the infrared range. As a result, the position can be specified and measured accurately.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the ATR measuring optical system according to the present invention will be described below. FIG. 1 is an optical path diagram of an embodiment of an ATR measuring optical system according to the present invention. A hemispherical prism 1 made of a material having a high refractive index transparent in both the visible region and the infrared region is used as an ATR crystal. Is fixed in a state in which it is in close contact with the lens, enlarged by the same objective lens 2, observed in the visible region, and measured in the infrared region. That is, the sample S is disposed obliquely to the optical axis a of the microscope optical system, and the hemispherical prism 1 is pressed against the surface of the sample S. In this case, the light coming from the sample S passing through the hemispherical prism 1 forms an image at the position of the mask 3 through the Cassegrain objective lens 2, the measurement position is limited by the mask 3, and the light is reflected by the half mirror or the switching mirror 4. The light is divided into two light paths, the observation light in the visible region is enlarged by the eyepiece 6, and the measurement position of the sample S is observed.
In addition, the measurement light in the infrared region is photoelectrically converted by the photodetector 5 and, in the case of Fourier spectroscopy, is subjected to Fourier transform and spectral analysis is performed.

In the present invention, the critical angle θ _{c of the} hemispherical prism 1 (the refractive index of the hemispherical prism 1 is n ₁ ,
Assuming that the refractive index of the sample S is n ₂ , sin θ _c = n ₂ /
the n _1. ) Greater than β (see FIG. 2; N in FIG. 2).
Represents the normal line of the sample S surface. ) In to use a light emitted from the surface of the sample S, and as the observation light incident on the objective lens 2, the sample S at the critical angle theta _c smaller than the angle alpha (Fig. 2)
Use light emitted from the surface. For this purpose, as shown in FIG. 1, the measurement light (double arrow) follows only one side (left side in the figure) of the optical axis a of the microscope optical system, enters the objective lens 2, and observes it. The light (single arrow) is incident on the objective lens 2 by following only the optical path on the opposite side (right side in the figure) of the optical axis a. Then, the incident directions of the illumination light for measurement 8 and the illumination light for observation 7 with respect to the sample S are set so as to satisfy such an angular relationship and satisfy the specular reflection condition, and the inclination of the sample S with respect to the optical axis a is set. Set.

Since the ATR measurement optical system is arranged as described above, the position of the sample S observed from the eyepiece 6 through the objective lens 2 and the mask 3 and the position of the sample S measured by the photodetector 5 are determined. Identity is guaranteed (no parallax).
Moreover, the optical path followed by the measurement light satisfies the condition for total reflection of the ATR measurement, while the optical path followed by the observation light is observed at an angle smaller than the critical angle and that satisfies the specular reflection condition. You should be able to observe it.

However, when zinc selenide is used as the hemispherical prism 1 as in the prior art, the chromatic aberration in the visible region is too large, and even when the sample S surface is to be observed, the measurement surface of the sample S becomes clear due to this chromatic aberration. I can't observe. As a result of various studies, the material constituting the hemispherical prism 1 has a wavelength of 4
Assuming that the refractive index from 00 nm to 800 nm is n ′ and the center value is n ₀ ′, a material satisfying 0.95 ≦ n ′ / n ₀ ′ ≦ 1.05 (1) can be used. It has been found desirable to avoid image blur due to this chromatic aberration. When the value exceeds the range of the condition (1), the sample surface cannot be clearly observed due to chromatic aberration, and it is not possible to specify a point to be measured.

By the way, even if the problem of the chromatic aberration in the visible region is solved, if there is the chromatic aberration in the actual infrared measurement region, it is not possible to measure the accurate total reflection attenuation characteristic. The measurement wavelength range is usually about 2.5 μm to 10 μm, and if there is a measurement sample position error of ± 2% or more in this range, correct measurement cannot be performed. Therefore, a wavelength of 2.5 μm to 10 μm
When the refractive index of n is n and its center value is n ₀ , it is necessary to satisfy 0.98 ≦ n / n ₀ ≦ 1.02 (2).

Further, for example, the position of the sample S is specified in the visible region using an optical system as shown in FIG. 1 and the position coincides with the measurement position in the infrared region. It is necessary that the difference in the refractive index in the outer region be within 10%. Therefore, | (n ₀ ′ −n ₀ ) / (n ₀ ′ + n ₀ ) | ≦ 0.05 (3) is necessary. Beyond this range, even if the measurement position of the micro sample S is determined by observation in the visible region, the ATR measurement position using infrared light does not always coincide with the position, and the measurement becomes inaccurate.

The radius of the hemispherical prism 1 is as follows.
It is desirable to be in the range of 2 to 10 mm. If the diameter is smaller than 2 mm, it becomes difficult to handle the hemispherical prism 1 and it is difficult to perform an operation of pressing against the sample S. On the other hand, if the radius of the hemispherical prism 1 exceeds 10 mm, the absorption becomes too large and the working distance of the objective lens 2 becomes longer.
Micro ATR measurement cannot be performed.

A specific material satisfying the above conditions (1) to (3) is zinc sulfide. N 'of zinc sulfide
Is 2.560 to 2.324 and n is 2.259 to
2.198, so both conditions are satisfied.

In the optical system shown in FIG. 1, when the other optical path is open during observation and measurement, light entering through the optical path becomes a background, making observation difficult or reducing measurement accuracy. I do. Therefore, as shown in FIG. 3A, at the time of observation, the light shielding plate 1 having the opening 10 is used.
1 is inserted in front of the objective lens 2 so that only observation light is incident on the objective lens 2 through the opening 10, and at the time of measurement, as shown in FIG. Opening 1
It is preferable that the measurement light be moved so that 0 is located in the optical path of the measurement light so that only the measurement light enters the objective lens 2.

In the embodiment shown in FIG. 1, a Cassegrain objective lens is used as the objective lens 2. However, the present invention is not limited to this, and various known reflection objective lenses and refraction objective lenses can be used. It should be noted that the hemispherical prism made of zinc sulfide satisfying the conditions (1) to (3) corresponds to the micro A
The present invention can be applied not only to the TR measurement optical system but also to an ATR measurement device using a known hemispherical prism.

Although the ATR measuring optical system of the present invention has been described based on the embodiments, the present invention is not limited to these embodiments, and various modifications are possible.

[0021]

As is clear from the above description, according to the ATR measuring optical system of the present invention, since the material constituting the hemispherical prism satisfies the conditions (1) to (3), the material in the visible region of the sample surface can be obtained. Chromatic aberration does not occur much in the observation image of, the sample can be clearly observed, the chromatic aberration in the infrared measurement range is small, accurate total reflection attenuation characteristics can be measured,
Since the measurement position of the sample specified in the visible region coincides with the actual measurement position in the infrared region, the position can be specified and measured accurately.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of one embodiment of an ATR measuring optical system according to the present invention.

FIG. 2 is an enlarged view of the vicinity of a sample in FIG.

FIG. 3 is an optical path diagram showing a main part of another embodiment.

FIG. 4 is a diagram for explaining a conventional example.

[Explanation of symbols]

 S ... Sample 1 ... Hemispherical prism 2 ... Objective lens 3 ... Mask 4 ... Half mirror or switching mirror 5 ... Photodetector 6 ... Eyepiece 7 ... Observation illumination light 8 ... Measurement illumination light 10 ... Aperture 11 ... Shield plate a …optical axis

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiromichi Hattori 3-1-2 Musashino, Akishima-shi, Tokyo Japan Inside Electronic Co., Ltd. (72) Hiroshi Terashima 3-1-2 Musashino, Akishima-shi, Tokyo Japan Electronics Co., Ltd. (56) References JP-A-5-10872 (JP, A) JP-A-4-116452 (JP, A) U.S. Pat. No. 5,093,580 (US, A) Moser WR, "A new FT-IR technology" for the situ study of the mechanism of solid state material preparations ", Mater Sci Res, 1985, VOL. 19, PAGE. 315-327 Debenham M, "Refractive indices of z inc sulfide in the 0.405-13 micro m wave level range", Appl Opt, 1984, VOL. 23, NO. 14, PAGE. 2238-2239 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 JICST file (JOIS)

Claims (2)

(57) [Claims] An optical system for measuring attenuated total reflection by a hemispherical prism in which a plane of a hemispherical prism is closely attached to a sample surface and attenuated by a total reflection light on the plane to measure a total reflection attenuation characteristic of a minute sample. An objective lens for enlarging and projecting the sample surface in close contact with the plane through the spherical surface is arranged, the radius of the hemispherical prism is in the range of 2 to 10 mm, and the refractive index of the material constituting the hemispherical prism at a wavelength of 400 nm to 800 nm is n ′. When the center value is n ₀ ′, 0.95 ≦ n ′ / n ₀ ′ ≦ 1.05 (1) is satisfied, and the refractive index at a wavelength of 2.5 μm to 10 μm is n. When the center value is n ₀ , 0.98 ≦ n / n ₀ ≦ 1.02 (2) is satisfied, and | (n ₀ ′ −n ₀ ) / (n ₀ ′ + n ₀ ) | ≦ 0.05 (3) Optical system for measuring total attenuated total reflection. 2. The optical system according to claim 1, wherein the hemispherical prism is made of zinc sulfide.