JP2000241593A - Multilayer film spectral element for analyzing fluorescent x rays of carbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film spectral element for analyzing fluorescent X rays of carbon that enables highly accurate analysis of fluorescent X rays of carbon (C). SOLUTION: Iron (Fe) and carbon (C) are used for a reflecting layer 31 and a spacer 32 respectively, a period length is set at between 7.0 nm and 10.0 nm inclusive and the number of pairs of layers is fixed at between 18 and 25 inclusive. A multilayer spectral element 3 where the outermost surface of the multilayers ends with a carbon (C) layer 32 ensures the strength of analysis that is almost equal to that of a conventional Ni/C multilayer spectral element in comparison of the former with the latter, and makes it possible to obtain the improvement in a ratio of measurement strength (P) to background strength (B) by about 70% and the about 86% increase in a half-value width.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer spectroscopic element which is formed by laminating a large number of layer pairs comprising a reflective layer and a spacer layer on a substrate and is used for X-ray fluorescence analysis of carbon.

[0002]

2. Description of the Related Art Boron (B), carbon (C), nitrogen (N)
In a so-called soft X-ray region including fluorescent X-rays such as those described above, since the wavelength is relatively long, about several nm, there is no natural suitable crystal capable of utilizing Bragg reflection. It was a major challenge in the field. On the other hand, with the recent development of the film forming technology by vacuum deposition, a multilayer film element formed by alternately laminating different substances has been found to be very useful as a soft X-ray spectroscopic element. Practical use has been attempted over a wide area including hard X-rays.

FIG. 10 shows an example of an X-ray fluorescence analyzer using the above-mentioned multilayer film spectroscopic element. In the figure, an X-ray tube 1
The sample 2 is irradiated with primary X-rays B1 from the sample 2, and the fluorescent (secondary) X-rays B2 generated in the sample 2 are irradiated by the multilayer spectroscopic element 3 at a predetermined wavelength λ satisfying the Bragg equation (1). Only the fluorescent X-ray B2 is Bragg reflected at the same reflection angle θ as the incident angle θ. The other fluorescent X-rays B2 are emitted from the multilayer spectroscopic element 3
Hardly reflected from 2d · sin θ = mλ (1) (where d is the cycle length, m is the order of reflection 1, 2, 3,...) Then, the reflected X-rays B3 from the multilayer film spectral element 3 are made incident on the detector 4. The analyzer 6 obtains a reflection peak profile of an X-ray to be analyzed. The solar slit 5 is X
This is to make the lines parallel light.

In a fluorescent X-ray analysis of carbon (C), a Ni / C multilayer film is conventionally considered to be useful as a spectroscopic element, and the multi-layer spectroscopic element is used in most analyzers. Also, a multilayer spectroscopic element having a high reflectance characteristic near the same wavelength has been studied and studied from a theoretical or experimental standpoint. For example, C or Ca is used as a spacer layer, and V, Cr is used as a reflective layer. , Mn, F
It has been proposed to use substances such as e, Co, Ni, Re.

[0005]

Generally, in the X-ray fluorescence analysis of light elements such as B, C, and N, the fluorescent X
Since the line intensity is originally very weak, in particular, in order to accurately perform a trace analysis in a thin film, a high reflectance (the intensity of the reflected X-ray B3 relative to the intensity of the incident X-ray B2) and the measured intensity ( P) and the ratio of background intensity (B) (P /
(B ratio) is required as much as possible. The P / B ratio is accurately represented by the ratio of (P−B) / B. In particular, in analysis using a multilayer spectroscopic element, high-order Bragg reflection lines of fluorescent X-rays of other elements often appear as interference peaks in the vicinity of the analysis peak of the element to be measured, which deteriorates the analysis accuracy. Therefore, some countermeasures are required.

To meet these requirements, a Ni / C multilayer spectroscopic element conventionally used for X-ray fluorescence analysis of carbon (C) can obtain a relatively high reflection intensity, but still has a P / B ratio. In the case of carbon (C) analysis of a sample which is not sufficient, and particularly contains oxygen (O),
There is also a drawback that the device is strongly affected by interference due to higher-order Bragg reflection lines in the fluorescent X-ray analysis.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multilayer X-ray spectroscopic element for carbon X-ray fluorescence analysis capable of solving the above-mentioned problems and performing high-precision X-ray fluorescence analysis of carbon (C).

[0008]

In order to achieve the above object, a multilayer spectroscopic element for carbon X-ray fluorescence analysis according to claim 1 is provided.
A multilayer spectroscopic element for use in X-ray fluorescence analysis of carbon (C) contained in a sample, comprising a plurality of layer pairs composed of a reflective layer and a spacer layer laminated on a substrate. Using carbon (C) as the spacer layer, iron (Fe) has a period length of 7.0 nm or more and 10.0 nm or less, the number of layer pairs is 18 or more and 25 or less, and the outermost surface of the multilayer film is made of carbon. (C) Termination at layer.

According to the above configuration, iron (Fe) is added to the reflection layer.
Using carbon (C) for the spacer layer, and setting the period length to 7.
0 nm or more and 10.0 nm or less, the number of layer pairs is 18 layer pairs or more and 2
With a multilayer spectroscopic element having 5 or less layers and the outermost surface of the multilayer film terminated with a carbon (C) layer, the analysis intensity is almost equal to that of a conventional Ni / C multilayer spectroscopic element, and
An approximately 1.7-fold improvement in measured intensity (P) / background intensity (B) (P / B ratio) and an improvement in half-width of about 86% can be obtained. Here, the half width represents the resolution of the measured spectrum, and refers to the spread of the spectrum at a half intensity position of the measured spectrum.

According to a second aspect of the present invention, the film thickness ratio between the reflective layer and the spacer layer is set to 1: 3 or 1: 1. Therefore, in a fluorescent X-ray analysis of carbon (C) of a sample containing oxygen (O), higher-order reflection lines of O can be suppressed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged sectional view showing a multilayer spectroscopic element 3 for carbon (C) X-ray fluorescence analysis according to an embodiment of the present invention. This multilayer film spectroscopic element 3 includes a reflective layer 3
1 and a spacer layer 32, a large number of layer pairs are laminated on a substrate 7 such as a silicon wafer, and iron (Fe) is used as the reflection layer 31 and carbon (C) is used as the spacer layer 32. .

The outermost surface of the multilayer film is terminated by a C layer 32. This is because, in general, if a Fe thin film is left in the air as it is, it reacts with moisture and oxygen in the air and changes to an oxide film, so in a multilayer film whose outermost surface is terminated with an Fe layer, This is because it will have a significant effect on its performance. The lowermost layer of the multilayer film, that is, the layer corresponding to the adhesive layer between the multilayer film and the substrate 7 is also formed of the C layer 32. This is because the surface of the Fe layer is generally rough, whereas the surface of the C layer is smooth and suitable for an adhesive layer. The Fe / C multilayer film spectral element 3 is formed by, for example, an ion beam sputtering method. The above Fe
/ C multilayer film spectroscopic element 3 is composed of carbon (C) contained in the sample.
The reflected X-ray B2 is generated by Bragg reflection of the fluorescent X-ray B2.

In the Fe / C multilayer film spectroscopic element 3 according to the present invention, the [I] cycle length d is set to 7.0 nm or more and 10.0 n or more.
m and the number of [II] layer pairs is from 18 layer pairs to 25 layer pairs. The period length d and the number of layer pairs will be described below.

[I] Regarding the Period Length d It is known that the reflection performance of a multilayer spectroscopic element is generally greatly affected by the disturbance of the laminated interface (interface roughness σ), and the actually obtained reflection intensity (I) Is approximately expressed by the following equation with respect to the reflection intensity (I ₀ ) in an ideal case without disturbance. I = I ₀ · exp [− (2πmσ / d) ² ] (2) where d represents the period length of the multilayer film spectroscopic element, and m
Is the Bragg reflection order, which is 1 in this case. As is clear from this equation, the reflection performance of the multilayer spectroscopic element is generally
It tends to deteriorate as the cycle length d decreases.

On the other hand, when the Fe / C multilayer spectroscopic element is used as a spectroscopic element for carbon analysis replacing the conventional Ni / C multilayer spectroscopic element, considering the continuity with the conventional analysis, It is desirable that the analysis intensity is at least 90% or more of the conventional intensity. When the interface roughness σ of the Fe / C multilayer film spectroscopic element according to the present invention was evaluated from the change in the reflection intensity when the period length d was changed, using Expression (2),
It was found to be about 0.8 nm. Therefore, in order to secure the analysis intensity of 90% or more of the conventional Ni / C multilayer film spectroscopic element, it is necessary to obtain the period length d of about 7 nm or more from the equation (2).
It should be understood that

On the other hand, it is desirable that the upper limit of the period length d be smaller. That is, according to Bragg's formula (1), the smaller the period length d is, the larger the incident angle θ is.
2 having different wavelengths λ like the reflection peak profile of
For one fluorescent X-ray, d1 having a small cycle length and d having a large cycle length
In the case of No. 2, the separation of the reflection peak of d1 having a small cycle length becomes large, and high-precision analysis becomes possible. FIG.
As shown in (b), the total reflection intensity of the multilayer film decreases as the incident angle θ increases, and the total reflection intensity overlaps with the reflection peak as a background. Therefore, the period length is small (the incident angle θ is large). D) The background is smaller and the P / B ratio is larger for d1. Empirically,
It is appropriate that the period length d be about 10 nm or less. Therefore, it is desirable that the range of the period length d of the multilayer film spectral element 3 according to the present invention is not less than 7.0 nm and not more than 10.0 nm. Preferably, it is not less than 8.0 nm and not more than 9.0 nm.

[II] Regarding the Number of Layer Logs In general, the spectral performance of a multilayer film spectroscopic element is affected by the number of laminated layers in addition to the above-described period length d. That is, if the number of layer pairs is too small, the number of layers contributing to reflection is insufficient, and as a result, the reflection intensity becomes weak,
In addition, the half-value width also increases. The half width represents the resolution of the measured spectrum, and refers to the spread of the spectrum at a half intensity position of the measured spectrum. On the other hand, when the number of layers is increased, the spectral performance is saturated at a certain number of layers or more. It should be noted that, in some cases, the interface roughness σ is amplified together with the number of layers, and if the number of layers exceeds a certain number, the spectral performance may be deteriorated. Therefore, it is necessary to determine the optimum layer logarithm for efficiently obtaining the best spectral performance.

Then, as a result of examining the spectral performance of the Fe / C multilayer film spectroscopic element while changing the number of laminated layer pairs, as shown in FIG. 4, a sufficiently large reflectance was obtained with 18 layer pairs and saturation was observed with almost 20 layer pairs. , And its performance hardly changed even when the number of layers was further increased to 30. In FIG. 4, the horizontal axis represents the layer logarithm, and the vertical axis represents the normalized reflectance obtained by normalizing the reflectance in a saturated state to 1. Therefore, it has been found that the optimum number of layer pairs necessary for obtaining the best spectral performance in the multilayer spectral element 3 according to the present invention is 20 to 25 layer pairs.

Further, in this embodiment, the thickness ratio between the reflective layer and the spacer layer is set to 1: 3.
This is the same as the / C multilayer spectroscopic element. FIG. 5 shows the relationship between the peak intensity (solid line), the half width (dotted line), the background (dashed line) of the measured spectrum, and the film thickness ratio between the reflective layer and the spacer layer. As is clear from this figure, as the thickness of the reflective layer is made relatively thinner than the thickness of the spacer layer,
The half width is small, that is, the resolution is high.

FIG. 6 shows a case where graphite is used as a sample, and in the Fe / C multilayer spectroscopy device 3 as shown in FIG. 1, the period length d is 8.0 nm, the number of layers is 20 pairs, and the reflection (Fe) layer 3 is used.
7 shows an analysis peak of fluorescent X-rays (C-Kα) from graphite when the thickness ratio of 1 to the spacer (C) layer 32 is 1: 3. For comparison, the results of a conventional Ni / C multilayer film spectral element having the same configuration are also shown. As is apparent from these results, in the Fe / C multilayer spectroscopy device, the peak intensity is kept almost the same value as the conventional one, and the background intensity is reduced to about 60%. From this, it is understood that a performance improvement of about 1.7 times as a P / B ratio is realized. In addition, the half-value width related to the resolution of adjacent analysis peaks has a sharper peak shape of about 86%.

In the X-ray fluorescence analysis of carbon (C), it is often problematic to analyze a sample containing oxygen (O). The secondary) reflection peaks overlap as disturbing lines,
This would lead to a large deterioration in analysis accuracy. Even in such a case, the Fe / C multilayer spectroscopy device 3 according to the present invention has a smaller size than the conventional Ni / C multilayer spectroscopy device.
The analysis performance of C can be improved.

FIG. 7 shows that, using a carbon (C) thin film on a glass plate as a sample, the period length d of the Fe / C multilayer film spectroscopic element was 8.0 nm, the number of layers was 20, and The analysis peak of the fluorescent X-ray (C-Kα) when the film thickness ratio is 1: 3 is shown. As is apparent from this figure, it is very difficult to separate the reflection peaks of C and O (secondary reflection) in the conventional Ni / C multilayer spectroscopic element, but in the Fe / C multilayer spectroscopic element 3, , O (secondary reflection), the peak intensity is reduced by half, the separation state of each peak is also improved, and the analysis performance of C is greatly improved.

In general, in a multilayer spectroscopic element, by adjusting the thickness ratio between the reflective layer and the spacer layer,
It is possible to suppress certain higher-order Bragg reflections.
For example, when the film thickness ratio is H: L (H and L are positive integers), higher-order reflection lines that are integral multiples of H + L are suppressed. Therefore, as one countermeasure against the disturbing line caused by the secondary reflection line of the fluorescent X-ray of oxygen (O), the film thickness ratio is set to 1: 1 by utilizing this property of the multilayer spectroscopic element.
By doing so, a method of suppressing the above interference line is considered. However, since the spectral performance of the multilayer spectroscopic element tends to deteriorate as the thickness of the reflective layer becomes relatively thick, it is very difficult to use, for example, a conventional Ni / C multilayer spectroscopic element. There was a disadvantage that it would. In such a case, the Fe / C multilayer film spectral element 3 according to the present invention can improve spectral performance.

FIGS. 8 and 9 show that the graphite / carbon (C) thin film on the glass plate was used as the sample, the period length d and the number of layers of the Fe / C multilayer film spectroscopic element were the same as above, and the film thickness ratio was set. The measurement result of the C fluorescent X-ray analysis peak in the case of 1: 1 is shown. As is clear from these results, the conventional N
Compared to the i / C multilayer spectroscopic element, the peak intensity is about 1.
1 time, about 88% in half width, about 6 in background intensity
A significant performance improvement of 5% and a P / B ratio of about 1.7 times was obtained, which proves to be very effective as a countermeasure for the above-mentioned interference line.

The long-term stability of the multilayer spectroscopy device 3 of FIG. 1 in which the outermost surface was terminated by the C layer 32 was examined. As a result, it was found that even after being left in the air for about three years, the reflection performance was hardly changed. In addition, by terminating the outermost surface with the C layer, there was obtained an advantage that the background intensity was reduced by half compared to the Fe layer termination.

As described above, in the fluorescent X-ray analysis of carbon (C), iron (Fe) is applied to the reflective layer 31 and the spacer layer 32
, Using carbon (C) for the period length of 7.0 nm or more and 1
0.0 nm or less, the number of layer pairs is 18 or more and 25 or less, and the outermost surface of the multilayer film is Fe / terminated with a carbon (C) layer 32.
While the C multilayer spectroscopic element 3 ensures almost the same analysis intensity as the conventional Ni / C multilayer spectroscopic element,
It became possible to improve the P / B ratio by about 1.7 times and the half width by about 86%.

[0027]

According to the present invention, the P / B ratio is about 1.7 times and the P / B ratio is about 86%, while the analysis intensity is almost equal to that of the conventional Ni / C multilayer film spectroscopic element. The half width can be improved, and high-accuracy X-ray fluorescence analysis can be performed.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view illustrating a multilayer spectroscopic element for carbon X-ray fluorescence analysis according to an embodiment of the present invention.

FIGS. 2A and 2B are characteristic diagrams showing a fluorescent X-ray reflection peak profile.

FIG. 3 is a characteristic diagram showing a fluorescent X-ray reflection peak profile.

FIG. 4 is a characteristic diagram showing a relationship between a layer logarithm of a multilayer film spectral element and a normalized reflectance.

FIG. 5 is a characteristic diagram showing a relationship between a peak intensity, a half width, a background, and a film thickness ratio.

FIG. 6 is a characteristic diagram showing a carbon fluorescent X-ray analysis peak of a graphite sample.

FIG. 7 is a characteristic diagram showing a carbon fluorescent X-ray analysis peak of a carbon thin film sample on a glass plate.

FIG. 8 is a characteristic diagram showing a carbon fluorescent X-ray analysis peak of a graphite sample.

FIG. 9 is a characteristic diagram showing a carbon fluorescent X-ray analysis peak of a carbon thin film sample on a glass plate.

FIG. 10 is a side view showing an X-ray fluorescence analyzer using a multilayer spectroscopic element.

[Explanation of symbols]

3 ... multilayer spectroscopic element, 7 ... substrate, 31 ... reflective layer, 32 ...
Spacer layer, B2: X-ray fluorescence, B3: X-ray diffraction.

Claims (2)

[Claims] 1. A multilayer spectroscopic element used for X-ray fluorescence analysis of carbon (C) contained in a sample, comprising a multiplicity of layer pairs comprising a reflective layer and a spacer layer laminated on a substrate. Using iron (Fe) for the reflection layer and carbon (C) for the spacer layer, the period length is set to 7.0 nm or more and 10.0 n.
m, the number of layer pairs is 18 to 25, and the outermost surface of the multilayer film is terminated with a carbon (C) layer. 2. The method according to claim 1, wherein the thickness ratio between the reflective layer and the spacer layer is set to 1: 3 or 1: 3.
2. A multilayer spectroscopic element for X-ray fluorescence analysis of carbon.