JPH11241991A - High sensitivity atr analysis and prism used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high sensitivity ATR analysis (absorbed total reflection measurement) capable of analyzing a material with a higher sensitivity. SOLUTION: In this ATR analysis, an incident light 2 having an incident angle of a critical angle or more to a prism 100 is incident on the prism 100, and a total reflection is caused on the interface of the prism 100-a sample 101 to analyze the sample 101. The incident light 2 is reciprocated within the prism 100 at least three times while it is multiply reflected in the prism 100 inner part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method for measuring total reflection absorption (hereinafter, referred to as an ATR analysis method), and more particularly, to an improved method for realizing a highly sensitive analysis. High sensitivity ATR analysis method.
The present invention also relates to an optical prism used for such a highly sensitive ATR analysis method.

[0002]

2. Description of the Related Art In infrared spectroscopy using infrared light, for example, it is used for structural analysis and qualitative quantitative analysis of trace contaminants (hereinafter referred to as samples) on the surface of coating films, papers, films, thin films, and silicon wafers. The commonly used ATR method uses a sample and an infrared region having a higher refractive index (measurement wavelength region).
This is a method in which a transparent medium (prism) is brought into contact with the sample, the incident angle is set to be larger than the critical angle, and total reflection occurs inside the prism for measurement. At this time, the light penetrates into the sample slightly to a certain depth and then is totally reflected, so that an infrared absorption spectrum of the sample surface is obtained. By analyzing this spectrum, the structure analysis and qualitative quantitative analysis of the sample are performed. Can be performed. The ATR analysis method is described in Koichi Nishida and Reikichi Iwamoto, Material Analysis by Infrared Method, Vol.
Page-page 199 (Kodansha Scientific, 1991
Year issuance).

In this method, referring to FIG. 3, the number of multiple reflections N determined by the length L of the prism 100, the thickness t, and the incident angle θ of the incident light 2 emitted from the light source 1 is determined by sampling the sample 101. The number almost coincides with the number of times, and the higher the number of times of sampling, the higher the sensitivity of the analysis. Outgoing light 3
Is detected by the detector 4.

[0004]

In the manufacture of a VLSI, hundreds of processes are required in several hundred days. During this long process, the VLSI is subjected to various types of contamination due to transportation and standing between processes. Minimizing these contaminations increases device yield, process reliability,
The reproducibility can be significantly improved. As a countermeasure against contamination, it is important to clarify the contaminants on the silicon wafer surface and to eliminate the source of the contamination based on this knowledge.

As a method for clarifying contaminants on the surface of a silicon wafer, the above-mentioned A, which is a kind of infrared spectroscopy, is used.
The TR method is known. For this, for example, Pr
oc. Semiconductor Pure Water Chem. conf., (199
5) It is described in detail on pages 260-275.

However, when the amount of contaminants adhering to the silicon wafer surface is a small amount of a monolayer or less, or when the absorption coefficient of the contaminants is small, the conventional ATR method has insufficient sensitivity and cannot always be analyzed. . For this reason, referring to FIG. 3, it has been considered to reduce the thickness t of the prism. However, it is very difficult to process the prism for forming an angle on the end face, and the prism itself becomes thin. However, it was not always practical because it was difficult to secure the target strength. In addition, when the sample length is short, it is not possible to simply use a long prism, and as a result, it is not always possible to ensure sufficient sensitivity by analysis using an existing prism, so that the obtained peak is very small. This makes analysis difficult.

The present invention has been made to solve the above problems, and has as its object to provide an improved high-sensitivity ATR analysis method capable of realizing high-sensitivity analysis. .

Another object of the present invention is to provide a prism used for such a highly sensitive ATR analysis method.

[0009]

The invention according to claim 1 is
The present invention relates to ATR analysis in which incident light having an incident angle equal to or greater than a critical angle with respect to the prism is introduced into the prism, and the sample is analyzed by causing total reflection at the prism-sample interface. It is characterized in that incident light is made to travel back and forth inside the prism at least three times while being reflected multiple times inside the prism.

According to the present invention, since the incident light is made to travel back and forth inside the prism at least three times while being reflected multiple times inside the prism, the number of times of sampling of the sample is increased, and high-sensitivity analysis is performed. Can do it.

The invention according to claim 2 relates to a prism used for a high-sensitivity ATR analysis method. The device is characterized in that the incident light can travel back and forth in the prism three or more times while being internally reflected multiple times.

According to the present invention, the incident light travels back and forth in the prism three or more times while being internally reflected multiple times, so that the number of times of sampling is increased and high-sensitivity analysis can be performed.

According to the third aspect of the present invention, the prism for use in ATR analysis has a first end face and a second end face which do not come into contact with a sample which receives or emits light. The first
A reflection film is provided on a part of each of the second end face and the second end face.

According to the present invention, since the incident light is almost reflected by the reflection film, the effective luminous length is increased, and multiple reflections are caused three or more times in the prism. As a result, higher sensitivity of the obtained spectrum is achieved.

According to the prism used for high-sensitivity ATR analysis according to claim 4, a reflection film is provided on the entire first end face,
A reflection film is provided on a part of the second end face for inputting and outputting light.

According to the present invention, the incident light is almost reflected by the reflection film, so that the effective luminous length is increased, and multiple reflection is caused three or more times in the prism. As a result, higher sensitivity of the obtained spectrum is achieved.

In the prism according to the fifth aspect, the reflection film is formed of an Au film or a laminated film of Cr and Au. When the reflection film is formed of Au, a prism having a good infrared light reflectance can be obtained. Further, when Cr is used as the Au underlayer, the adhesion is improved, so that the mechanical reliability is improved.

According to the prism of the sixth aspect, the reflection film
With Al film or Al and MgF_TwoIs formed with a laminated film. Anti
If an Al film is used as the emitting film, not only infrared light but also ultraviolet light
It can be used for analysis using light and visible light. Ma
Also, thin MgF on the surface of Al _TwoBy providing a membrane,
Oxidation can be suppressed, and a decrease in reflectance can be prevented.

According to the prism of the present invention, the reflection film is formed of Ag. When Ag is used, the reflectance increases, and it can also be used for visible light.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a conceptual diagram of a prism according to Embodiment 1.
(A) shows a sectional view of the prism, and (B) shows a sectional view of the prism.
It is a figure which shows the 1st end surface of a prism, (C) is a figure which shows the 2nd end surface of a prism. In the prism according to the first embodiment, since the film 5 capable of reflecting light is provided on a part of the first and second end faces, light reciprocates while being multiple-reflected inside the prism as illustrated. And sample 10
The number N of multiple reflections of light on one surface increases. For this reason, light absorption proceeds, and as a result, high sensitivity of the obtained spectrum can be achieved.

Referring to FIG. 1, a reflecting film 5 for reflecting light is provided on a part of the end face of the prism 100 by a metal vapor deposition method or the like, except for a part of a window through which light enters and exits. This was processed so that infrared light could be reflected. The light 2 is made to enter the prism from the part of the entrance window 6 where the reflection film 5 is not attached, and the light 3 emitted from the exit window 7 after being totally reflected in the prism several times is introduced into the detector 4. An absorption spectrum of the sample 101 arranged on the surface 100 is obtained. Since the incident light 2 is almost reflected by the reflection film 5, the effective optical path length becomes long, and causes multiple reflections in the prism 100 three or more times. Therefore, the sampling frequency N
Increases, light absorption proceeds, and as a result, high sensitivity of the obtained spectrum is achieved. As the background spectrum at this time, the sample 101 was
The light 3 can be obtained by making the light incident on the prism 100 in the same manner without contact with the prism 100 and introducing the emitted light 3 into the detector 4. As shown in FIG. 1, the sample 101 may be placed on the upper surface or the lower surface of the prism 100, or the sample 101 may be contacted on both the upper surface and the lower surface.

Second Embodiment FIG. 2 is a conceptual diagram of a prism used for ATR analysis according to a second embodiment. (A) is a sectional view of a prism,
(B) is a diagram showing a first end face of the prism, (C)
FIG. 4 is a view showing a second end face of the prism.

According to the prism of the second embodiment, the reflection film 5 is provided on the entire one end surface 11 of the prism 100 and a part of the other end surface 10 so that the incident light 2 and the reflected light 3 are the same. Take out from the side. Even with such a configuration, since light reciprocates in the prism 100 while being multiply reflected, the number N of multiple reflections of light on the surface of the sample 101 increases. For this reason, light absorption proceeds, and as a result, high sensitivity of the obtained spectrum can be achieved.

In the above embodiment, the reflection film 5
Any material can be used as long as it reflects light.

In the case of using infrared light, Au is particularly preferable as a material having a high infrared light reflectance. In addition, Au
When Cr is used for the underlayer, the adhesion is improved, and the mechanical reliability is improved.

As the prism material, for example, KRS-5, Ge or Si is preferable for infrared light, and glass is preferable for visible / ultraviolet light.

Al is an inexpensive material having a high reflectivity. If Al is used, it can be used for analysis using not only infrared light but also ultraviolet light and visible light. It should be noted that Al is oxidized with time and the reflectance is reduced. In particular, there is a problem that this reduction is severe in an ultraviolet light region.
By providing a thin MgF ₂ film on the surface of Al, oxidation can be suppressed and a decrease in reflectance can be prevented.

Further, Ag is preferable as a material having a high reflectance. Ag has the advantage that it can also be used for visible light.

[0030]

Embodiments of the present invention will be described below.

Embodiment 1 This embodiment is a specific example in which the present invention is applied to the analysis of organic substances attached to the surface of a silicon wafer. Since the refractive index of Si is 3.4, with reference to FIG. 1, the prism 100 needs to be a material having a higher refractive index. For this reason, the prism 100 used was made of germanium crystal having a refractive index of 4.0. A commercially available germanium prism having an end face of 60 ° was used, and Al was deposited on a part of both end faces of the germanium prism by about 100 nm to provide a reflection film 5. A part of one end face is used as an incident window 6 for the incident light 2, Al is vapor-deposited on the other end face part 8, and a part of the other end face is used as an exit window 7 for outgoing light. A on the end face part 9
1 was deposited.

Using a Fourier transform infrared analyzer as an infrared spectrometer, infrared light 2 was incident, and the outgoing light 3 was analyzed by a high sensitivity MCT detector 4. At this time, since the critical angle is 58 ° based on the refractive index of Ge and the refractive index of Si, the angle of incidence on the sample surface must be larger than 58 °.
The analysis surface of the silicon wafer as the sample 101 is prism 1
The measurement was carried out with a strong adhesion to 00. As a background spectrum for measurement, a spectrum measured under the same conditions without bringing the sample 101 into close contact with the prism 100 was used.

As for the size of the entrance window 6 and the exit window 7 on which no reflecting film is provided on the end face of the prism, the CH peak intensity of the organic substance increases as the size decreases. At this time, the light amount decreased as the window became smaller, and the S / N ratio became worse.
The improvement was achieved by increasing the number of times of measurement integration, using a high-luminance light source, or condensing the incident light 2 on the window 6. A comparison of the peak intensity of the peak at around 2900 cm ⁻¹ based on the stretching vibration of the C—H ₂ bond between the method of the present invention and the conventional method without the reflective film on the end face shows that the peak intensity is remarkably large in the present method. And increased sensitivity was achieved.

Example 2 As shown in FIG. 2, Au was deposited as a reflective film 5 on the entirety of one end face 11 of the germanium prism 100 and a part of the other end face 10. When only Au was vapor-deposited, the adhesion between the prism 100 and Au was poor. Therefore, when the Cr was first vapor-deposited thinly on the prism 100, and then Au was vapor-deposited, the reflection film 5 having good adhesion could be formed. As shown in FIG. 2, in order to separate the incident light 2 and the outgoing light 3, the position at the time of vapor deposition on a part of one end face 10 is defined as an entrance window 6 of the incident light 2 above the end face, and The lower part is an emission window 7 for the emitted light 3. As a result, the incident light 2 and the output light 3 could be separated. Further, when the size of the entrance window 6 and the exit window 7 is reduced, separation becomes easier. Further, the CH peak intensity of the organic substance was increased, and high sensitivity was achieved. But,
Although the amount of light decreased and the S / N ratio deteriorated, it could be improved by increasing the number of measurement integrations, using a high-luminance light source, or condensing the incident light 2 on the window 6. . It was also found that the sensitivity was slightly different by changing the incident angle.

As in Example 1, the present invention is applied to the analysis of organic substances adhering to the Si wafer surface,
^A comparison of the peak intensity of the peak near the ⁻¹ based on the stretching vibration of the C—H ₂ bond with that of the conventional method revealed that the peak intensity was remarkably increased in the present method, and high sensitivity was achieved.

Example 3 A 2 mm thick glass plate was coated with 100 n of Au, Al and Ag.
Approximately m, deposit infrared light, ultraviolet light, and visible light using an infrared spectrophotometer and an ultraviolet / visible spectrophotometer, measure the reflected light intensity, and compare the reflectance between each material. did. Note that A
Regarding u, since the adhesion between the Au deposited film and the glass was poor, when Cr was thinly deposited on the glass and Au was deposited thereon, good adhesion was obtained. As a result, in the ultraviolet light range, the reflectance was Al >> Au, in the Ag visible light range, the reflectance was Ag>Al> Au In the infrared light range, the reflectance was Au>Al> Ag.

Therefore, Al is a good reflection film over a wide range, Ag is good in the visible light range, and Au is good in the infrared light range. Therefore, it was found that these materials should be selected according to the wavelength to be measured. .

[0038]

According to the present invention, the number of times of multiple reflection of light can be increased by using a prism provided with a reflection film on a part or the whole of the end face, so that the number of times of sampling can be increased. As an effect, it has become possible to analyze materials with even higher sensitivity.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of an ATR method according to Embodiment 1.

FIG. 2 is a conceptual diagram showing an example of an ATR method according to a second embodiment.

FIG. 3 is a conceptual diagram of a conventional ATR method.

[Explanation of symbols]

2 incident light, 3 outgoing light, 100 prism, 101
sample.

Claims (7)

[Claims] 1. An ATR analysis method in which incident light having an incident angle greater than a critical angle with respect to a prism is introduced into the prism and total reflection is caused at a prism-sample interface to analyze the sample. A high-sensitivity ATR analysis method, wherein the laser beam is moved back and forth inside the prism at least three times while being reflected multiple times inside the prism. 2. While the incident light is internally reflected multiple times,
A prism used for high-sensitivity ATR analysis, characterized in that the prism can be moved back and forth inside the prism three or more times. 3. A method according to claim 1, further comprising a first end face and a second end face that do not come into contact with a sample for light incidence or light emission, and a reflection film provided on a part of each of the first and second end faces. The high sensitivity AT according to claim 2,
Prism used for R analysis. 4. A reflection film is provided on the entire first end face,
3. The prism for use in a high-sensitivity ATR analysis method according to claim 2, wherein a reflection film is provided on a part of the second end face for inputting and outputting light. 5. The reflection film is made of an Au film or Cr and A
The prism used in the high-sensitivity ATR analysis method according to claim 2, which is formed of a laminated film of u. 6. The prism for use in a high-sensitivity ATR analysis method according to claim ₂ , wherein the reflection film is formed of an Al film or a laminated film of Al and MgF ₂ . 7. The prism for use in a high-sensitivity ATR analysis method according to claim 2, wherein the reflection film is made of Ag.