JP2000147199A - Multilayer film spectral element for x-ray fluorescence analysis of beryllium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make accurately analyzable in a short time by multiply layering on a substrate using ruthenium on a reflection layer and beryllium on a spacer layer and constituting with a specific periodic length and a layer number. SOLUTION: A layer body consisting of a reflection layer 31 and a spacer layer 32 is multiply layering in constitution on a substrate 7 such as silicon wafer. For the reflection layer 31, ruthenium is used, for the spacer layer 32, beryllium is used and a film is made by ion beam sputtering method, for example. The periodic length (d) is desired to be 7 to 10 nm from a theoretical calculation and experience for gaining a constant reflection intensity and reducing the background. The layer number is obtained from the theoretical calculation corresponding to the periodic length (d) and desired to be 20 to 40. However, the periodic length (d) and the layer number is desired to be selected and used according to the purpose and usage. For example, when the periodic length (d) is 7 nm, 10 nm and 15 nm, the layer number corresponding to the periodic numbers (d) to be 30 to 50 layers, 25 to 40 layers and 20 to 40 layers are used.

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 consisting of a reflective layer and a spacer layer on a substrate and is used for X-ray fluorescence analysis of beryllium.

[0002]

2. Description of the Related Art In the so-called soft X-ray region including fluorescent X-rays of beryllium (Be), since the wavelength is as long as 10 nm or more, an appropriate spectral crystal that can utilize Bragg reflection naturally exists. Without this, it has been a major issue in the field of soft X-ray spectroscopy. On the other hand, with the recent progress in film forming technology by vacuum deposition, a multilayer film element in which different materials are alternately laminated as a reflective layer and a spacer layer is very useful as a soft X-ray spectroscopic element. It has been found, and its practical use has been attempted over a wide area including hard X-rays.

FIG. 9 shows an example of an X-ray fluorescence analyzer using the above-mentioned multilayer film spectroscopic element. In the figure, a sample 2 is irradiated with a primary X-ray B1 from an X-ray tube 1, and a fluorescent (secondary) X-ray B2 generated in the sample 2 is
Only the fluorescent X-ray B2 having a predetermined wavelength λ that satisfies the Bragg equation (1) is Bragg reflected at the same reflection angle θ as the incident angle θ. The other fluorescent X-rays B <b> 2 are hardly reflected from the multilayer spectral element 3. 2d · sin θ = nλ (1) (where d is the cycle length, n 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.

The following requirements (a) to (c) are known as requirements for obtaining a multilayer spectral device having excellent spectral characteristics in the target X-ray region. (A) The material constituting the multilayer film has an appropriate optical constant in the target X-ray region. (B) The constituent material can form a flat and continuous ultrathin film in units of 0.1 nm. (C) The constituent materials can form a steep interface without being mutually diffused at the lamination interface.

The Be-Kα ray to be analyzed (wavelength: 11.4)
From the viewpoint of the above requirement (a), it is known that the use of Be as the spacer layer material is theoretically optimal for a multilayer film element having high reflection performance at a wavelength near (nm). However, Be is a toxic substance also specified as a specific chemical substance, and its handling requires sufficient safety management. Therefore, as a multilayer element using Be that has been actually manufactured and evaluated up to now, W / B
e, Ti / Be, Ge / Be, Al / Be, etc., but there have been reports only on very limited combinations, but recently, the Mo / Be multilayer film is very high around the wavelength. It has been reported that the measured reflectivity is exhibited, and the usefulness of the Be spacer layer has been confirmed again.

Further, even if the requirement (a) is satisfied, the performance according to the theoretical calculation cannot be obtained in most cases due to the imperfection of the structure when the multilayer structure is actually laminated.
Investigations on so-called "interface roughness" regarding the main factors (b) and (c) are also being conducted. This is evaluated, for example, by actually fabricating a multilayer film and measuring the X-ray reflectance. That is, when the theoretically predicted reflectance of the ideal structure of the multilayer film (interface roughness = 0) is I ₀ , the measured reflectance of the actual multilayer film is I, the interface roughness is σ, and the period length is d, approximation is performed. It is expressed by the following equation (2). Here, the reflectance refers to the reflected X-ray B3 with respect to the intensity of the incident secondary X-ray B2 in the multilayer film.
(Hereinafter referred to as reflection intensity). I = I ₀ · exp [− (2πσ / d) ² ] (2)

Based on the equation (2), the theoretical predicted reflectance I ₀
Is obtained by theoretical calculation, and the measured reflectance I and the period length d are experimentally obtained, whereby the interface roughness σ can be obtained. As a result, in most multilayer films, about 0.1.
It is clear that an interface roughness σ of 3 nm or more exists.

On the other hand, as a multilayer film element having relatively good spectral performance for use in X-ray fluorescence analysis of beryllium (Be), a multilayer film element combining molybdenum (Mo) and boron carbide (B ₄ C) is known. has been found to be useful, currently, Mo / B ₄ C multilayer film is used mainstream manner.

[0009]

[0006] However, the conventional beryllium multilayer film spectral element Mo / B ₄ C multilayer film which are used, the use of the B ₄ C as a material of the spacer layer, a suitable optical It cannot be said that it is sufficient from the viewpoint of the requirement (a) of having a constant.

In addition, since the reflection intensity of Be-Kα ray is relatively small, in order to perform the quantitative analysis of beryllium (Be) component with high accuracy in the Mo / B ₄ C multilayer film, the analysis time is required. It needs to be very long, and there is a demand for the practical use of a multilayer spectroscopic element having higher intensity reflection performance.

Further, for example, zinc (Z
n) When a transition metal such as copper (Cu) or the like is contained, the fluorescent X-rays such as Zn-Kα ray and Cu-Kα ray have wavelengths that are about two orders of magnitude shorter than Be-Kα rays. From
It passes through the multilayer film 3A of FIG. 7B and reaches the surface (cut surface) 7a of the substrate 7. Zn-Kα ray or C reaching surface 7a
The u-Kα ray is diffracted as indicated by a broken line on the lattice plane 7c of the crystal of the substrate 7 and is transmitted to the detector 4 (FIG. 9) as a diffracted X-ray B4 of an element which becomes an interference spectrum with respect to the spectrum of the analysis element Be. Incident, and as shown in FIG.
It overlaps with the Kα ray. As a result, the analysis accuracy of the beryllium (Be) component was reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a beryllium fluorescent X-ray analysis multilayer film spectroscopic element capable of high-accuracy and short-time fluorescent X-ray analysis of beryllium (Be). I have.

[0013]

According to the present invention, there is provided, according to the present invention, a structure in which a plurality of layer pairs each including a reflective layer and a spacer layer are laminated on a substrate, and the beryllium ( Be) A multilayer spectroscopy element used for the fluorescent X-ray analysis of Be), wherein ruthenium (Ru) is contained in the reflection layer;
Beryllium (Be) is used for the spacer layer, the period length is 7 nm or more, and the number of layer pairs is 20 or more.

According to the above configuration, the reflection intensity of the beryllium fluorescent X-ray is increased about twice or more as compared with the conventional Mo / B ₄ C multilayer spectroscopic element, and the beryllium fluorescent X-ray can be obtained with higher accuracy and in a shorter time. Line analysis becomes possible.

Preferably, the substrate is provided with the diffraction element so that diffraction X-rays of another element contained in the sample, which becomes an interference spectrum with respect to the spectrum of beryllium (Be) as an analysis element, do not enter the detector. It is composed of a crystalline substrate or an amorphous substrate in which the lattice plane of the crystal that reflects X-rays is inclined with respect to the surface of the substrate. Therefore, when a transition metal or the like is contained in the sample, beryllium fluorescent X-ray analysis can be performed with higher accuracy without being affected by diffracted X-rays that interfere with the transition metal or the like.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a structure of a multilayer spectroscopic element 3 for beryllium fluorescent X-ray analysis according to one embodiment of the present invention. In this multilayer film spectroscopic element 3, a layer pair composed of the reflective layer 31 and the spacer layer 32 is formed of silicon (S
i) Ruthenium (Ru), which is formed by laminating a large number on a substrate 7 such as a wafer and has excellent reflectivity as the reflective layer 31, and beryllium (Be) as the spacer layer 32. The multilayer spectroscopic element 3 is formed by, for example, an ion beam sputtering method. Thus, a multilayer spectroscopic element 3 having excellent reflectivity is obtained. The multilayer spectroscopic element 3 generates a diffracted X-ray B3 by diffracting the fluorescent X-ray B2 of beryllium (Be) contained in the sample.

In the multilayer spectroscopy element 3, a combination of ruthenium (Ru) for the reflective layer 31 and a combination of beryllium (Be) for the spacer layer 32 will be described below.

[I] Reason for Combining Ru for Reflective Layer and Be for Spacer Layer First, from the viewpoint of the requirement (a) that the optical layer has an appropriate optical constant, a Be-Kα ray (wavelength: 11. 4n
With respect to the constituent materials in the multilayer spectroscopic element for m), optimization of the combination was examined. In general, it is known that the optical characteristics (scattering and absorption) of a substance with respect to X-rays are represented by a physical property parameter called an atomic scattering factor. (Henke) et al. And reported in the literature. Furthermore, the reflection and absorption phenomena that occur when X-rays are incident on a flat material surface are calculated using the complex refractive index calculated from the above factors.
It can be expressed as a Fresnel reflection amplitude coefficient. This coefficient is a value generally represented by a complex number, and the real part is a value corresponding to the reflection intensity and the imaginary part is a value corresponding to the absorption.

FIG. 2 shows the Fresnel reflection amplitude coefficients of the main elements at a wavelength of 11.4 nm. The horizontal axis represents the real part, and the vertical axis represents the imaginary part. Be and Si are in the negative region due to transmission by the resonance phenomenon. Here, as the most suitable combination as the constituent material of the multilayer film, it is desirable that a material pair having the largest possible optical contrast and the smallest possible absorption loss in the material in order to cause efficient reflection at each layer interface is desirable. Are known. That is, in FIG. 2, it can be said that a substance pair that is as far away from each other as possible in the horizontal axis direction and that both substances are as close as possible to the horizontal axis is optimal. From the figure, it can be seen that a substance pair that meets these conditions is a combination of Ru and Be. Therefore, Ru is used for the reflective layer and B is used for the spacer layer.
The combination of e is optimal. In other combinations, it is clear that conventionally used Mo and B ₄ C, for example, are at least insufficient in optical constants.

In the multilayer film spectroscopic element 3,
[II] The period length d is 7 nm or more, and the number of [III] layer pairs is 20 or more.
] Will be described.

[II] Reason for setting the period length d to be 7 nm or more First, for the Ru / Be multilayer film, the change in the reflection intensity of Be fluorescent X-rays when the period length d is slightly changed is obtained from the above equation (2). Is used to determine the interface roughness σ of the Ru / Be multilayer film. As a result, the interface roughness σ of the Ru / Be multilayer film is about 1 nm. A method for easily obtaining the interface roughness σ will be described later. Therefore, a reflection intensity of about 45% or more of the theoretical reflection intensity predicted in an ideal case (interface roughness σ = 0), that is, at least about twice or more of the conventional Mo / B ₄ C multilayer film is obtained. Therefore, it is necessary to set the period length d to 7 nm or more from the calculation of the equation (2).

On the other hand, it is desirable that the upper limit of the cycle length d be smaller. That is, according to the Bragg equation (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 S / N ratio is larger in d1. Empirically,
It is appropriate that the period length d be about 15 nm or less. Therefore, the range of the period length d of the multilayer film spectral element 3 according to the present invention is 7 to 15 nm, preferably 7 to 10 nm.

Here, a method for easily obtaining the interface roughness σ of the multilayer film using the above equation (2) will be described. As shown in FIG. 4, two artificial multilayer spectroscopic elements having slightly different cycle lengths d1 and d2 are formed, and the measured reflectivity of the spectroscopic element having the cycle length d1 is I ₁ , and the measured reflectivity of the spectroscopic element having the cycle length d2 is set as If I ₂ , the following equations (3) and (4) are established from the above equation (2). I ₁ / I ₀ = exp [− (2πσ / d1) ² ] (3) I ₂ / I ₀ = exp [− (2πσ / d2) ² ] (4) Both sides of the above equations (3) and (4) By dividing
The following equation is obtained. I ₁ / I ₂ = exp [− (2πσ) ² (1 / d1 ² −1 / d2 ² )] (5) In equation (5), the ratio of two measured reflectances, that is, the ratio I of two reflection intensities ₁ / I ₂ can be easily obtained from an actual measurement. Also, in the Bragg equation (1), d is obtained from the incident angle θ by d.
Since 1 and d2 are obtained, the interface roughness σ is obtained. As a result, in the Ru / Be, Mo / Be multilayer film according to the present invention and the conventional Mo / B ₄ C multilayer film, the interface roughness σ is approximately the same at about 1 nm.

Conventionally, the reflectivity was determined from the ratio of the incident intensity to the reflected intensity using a reflectometer, and the interface roughness σ was determined.
According to this method, the interface roughness σ can be obtained simply and relatively inexpensively by measuring the ratio of the two reflection intensities of the spectral element without using an expensive reflectometer.

[III] Reason why the number of layer pairs is 20 or more FIG. 5 shows that the period length d of the Ru / Be multilayer film is 7 nm.
In the case of, the change in the reflection intensity of the Be fluorescent X-ray with respect to the layer logarithm is shown by a theoretical calculation. The horizontal axis represents the number of layers, and the vertical axis represents the normalized reflectance obtained by normalizing the reflectance in a saturated state to 1. As is apparent from FIG.
The u / Be multilayer film has almost reached a saturation value in about 30 layer pairs or more, and in order to obtain sufficient reflection performance of this multilayer film, the number of layer pairs should be about 30 layer pairs or more. In addition, 5
The reflectance is saturated at the zero layer pair. Similarly, when the period length d is 15 nm, the saturation value is almost reached at about 20 layer pairs or more. Therefore, the range of the layer logarithm of the multilayer spectral element 3 according to the present invention is 20 to 50 layer logarithms, preferably 2
The logarithm is 0 to 40 layers.

Based on the above [II] and [III], it is preferable that the period length d and the number of layers of the multilayer spectral element 3 are appropriately selected and used according to the purpose and application. For example, the following are selected. When the period length d is 7 nm, the number of layer pairs is 50 when the number of layer pairs is 30 or more.
When the period length d is 10 nm and the number of layer pairs is 25 or more,
0 layer pair or less When the period length d is 15 nm, the number of layer pairs is 4 for 20 layer pairs or more.
0 layer pair or less

When a sample containing impurities such as a transition metal such as Zn or Cu in addition to Be is to be measured, the surface (cut surface) 7a of the crystalline substrate 7 such as a silicon wafer is As shown in FIG. 7A, the crystal is inclined by an angle α with respect to the lattice plane (for example, (100) plane) 7c of the crystal. Therefore, the lattice plane 31 of the multilayer film spectral element 3
a is also inclined by an angle α with respect to the lattice plane 7c of the crystal. As the angle α, the diffraction X-ray B4 of an element (heavy element) such as a transition metal such as Zn or Cu, which becomes an interference spectrum with respect to the spectrum of Be as an analysis element, is obtained by the detector 4 shown in FIG.
May be set so as not to be incident on the lens, and is generally set to about 5 °. In the case of a sample that does not contain a transition metal or the like, the above-described inclination need not be provided.

The fluorescent light X passing through the multilayer film 3A shown in FIG.
Line B2 is diffracted at the lattice plane 7c of the crystal. However, the lattice plane 31a of the multilayer film 3A is different from the lattice plane 7a of the crystal.
Since c is inclined, the angle of incidence θ of the multilayer film 3A with respect to the lattice plane 3a and the angle of incidence θ1 with respect to the lattice plane 7c of the crystal are different from each other, so that the analytical X-ray (Be-K
α-ray) The emission direction of B3 and the diffracted X-ray (Zn-
(Kα line, Cu-Kα line) B4 are different from each other. Accordingly, by setting the inclination angle α to an appropriate value, it is possible to prevent the diffracted X-rays that interfere with the detector 4 in FIG. 9 from being incident.

The substrate 7 is not a crystalline substrate as described above, but a Zn-Kα ray or Cu
An amorphous substrate made of amorphous silicon, glass, or the like that does not diffract -Kα rays may be used.

Further, in the Be analysis of a sample containing a light element other than the heavy element, the Be
X-rays of light elements whose wavelengths are close to the X-rays are mainly reflected by the reflective layer 31, and the reflected X-rays of light elements appear as disturbing lines near the reflection peak of Be, causing deterioration of analysis accuracy. There is a problem. For this reason, the film thickness ratio between the reflective layer 31 and the spacer layer 32 of the multilayer film spectral element 3 is, for example, when the tertiary reflection line becomes an obstruction line, the reflection layer: spacer layer = 1: 2.
It is preferred that By setting the film thickness ratio of the reflective layer 31 and the spacer layer 32 to 1: 2, the multilayer spectroscopic element 3 can be used for the tertiary reflection line of the light element other than the heavy element, which is an obstacle.
The reflected X-rays reflected by each of the reflective layers 31 have a phase in which the reflected X-rays cancel each other, and this disturbing line is removed.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a multilayer film spectroscopic element 3 is formed by laminating a large number of layer pairs composed of, for example, a reflective layer 31 using Ru and a spacer layer 32 using Be on a substrate 7 of a Si wafer. The period length d is about 9 nm, the number of layer pairs is 30, and the thickness ratio between the reflective layer 31 and the spacer layer 32 is 1: 2.

A Ru / Be multilayer spectroscopic element according to the present invention,
For the conventional Mo / Be multilayer spectroscopic element and Mo / B ₄ C multilayer spectroscopic element, for example, a measurement sample is
The reflection peak profile of Be-Kα ray in the case of a Be thin film having a thickness of about 1 (μm) formed thereon is measured.
FIG. 8 shows a reflection peak profile of Be-Kα ray by each multilayer spectroscopic element. Referring to FIG.
The solid line in the case of the u / Be multilayer spectroscopic element, the conventional Mo / B
The case of the e multilayer film spectral element and the case of the Mo / B ₄ C multilayer spectral element are indicated by a dashed line and a broken line, respectively. Since the period length d is different for each spectral element, the peak incident angles of the respective profiles are slightly shifted from each other.

As is clear from this figure, the conventional Mo /
Ru / B for the case of using a B ₄ C multilayer spectroscopic element
When the e-multilayer spectroscopy element is used, the reflection intensity of the Be-Kα ray increases about 2.7 times. As a result, high-accuracy beryllium fluorescent X-ray analysis can be performed in a short time.

[0034]

According to the present invention, since the reflective layer is made of ruthenium (Ru) and the spacer layer is made of beryllium (Be), the period length is 7 nm or more and the number of layer pairs is 20 or more. The reflection intensity of beryllium fluorescent X-rays is more than doubled as compared with the conventional Mo / B ₄ C multilayer spectroscopy element, so that beryllium fluorescent X-ray analysis can be performed with higher accuracy and in a shorter time.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing a multilayer spectroscopic element for beryllium fluorescent X-ray analysis according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a distribution of Fresnel reflection amplitude coefficients of elements.

FIGS. 3A and 3B are characteristic diagrams showing a fluorescent X-ray reflection peak profile.

FIG. 4 is a characteristic diagram showing a fluorescent X-ray reflection peak profile.

FIG. 5 is a characteristic diagram showing a relationship between a layer logarithm of the multilayer element and a normalized reflectance.

6A is a characteristic diagram showing a beryllium fluorescent X-ray reflection peak profile of the multilayer device, and FIG. 6B is a characteristic diagram of a conventional multilayer device.

FIG. 7A is an enlarged sectional view showing the multilayer film element,
(B) is an enlarged sectional view showing a conventional multilayer element.

FIG. 8 is a characteristic diagram showing a beryllium (Be) fluorescent X-ray reflection peak profile of each multilayer element.

FIG. 9 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 spectroscopy element used for X-ray fluorescence analysis of beryllium (Be) contained in a sample, comprising a plurality of layer pairs composed of a reflective layer and a spacer layer laminated on a substrate. Using ruthenium (Ru) for the reflective layer and beryllium (Be) for the spacer layer, and having a period length of 7 nm or more;
Beryllium fluorescence X having 20 or more layer pairs
Multi-layer spectroscopic element for X-ray analysis. 2. The substrate according to claim 1, wherein the substrate does not receive a diffracted X-ray of another element contained in the sample, which becomes an interference spectrum with respect to a spectrum of beryllium (Be) as an analysis element, to the detector. Thus, a beryllium fluorescent X-ray analysis multilayer film spectroscopic element comprising a crystalline substrate or an amorphous substrate in which the lattice plane of the crystal that reflects the diffracted X-rays is inclined with respect to the surface of the substrate.