JPH0682400A - Total reflection x-ray fluorescence analyser - Google Patents

Abstract

PURPOSE:To enhance analyzing accuracy by increasing the intensity of diffraction X-rays by preventing the lowering of the intensity of X-rays at the time of spectral diffraction of X-rays in total reflection X-ray fluorescence analysis. CONSTITUTION:X-rays from an X-ray source P are made monochromatic by an artificial multilayered membrane lattice 1 to be allowed to be incident on a sample at a minute incident angle alpha. The artificial multilayered membrane lattice 1 diffracts the X-rays B1 made incident at an incident angle thetaN from the X-ray source P on the reflecting surface 1a of the lattice 1 at a diffraction angle thetaN. The cycle of the lattice surface intervals of the artificial multilayered membrane lattice 1 is set so as to continuously become large along the reflecting surface 1a. The cycle is set so as to become large as going away from the X-ray source P as shown by an arrow 10 in the relation with the X-ray source P.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a surface of a sample with a primary X-ray at a minute incident angle to cause fluorescence X from a surface layer of the sample.
The present invention relates to a total reflection X-ray fluorescence analyzer for analyzing rays.

[0002]

2. Description of the Related Art Conventionally, a total reflection X-ray fluorescence analyzer is
It is used as a device for detecting impurities adhering to the surface layer of a sample (see, for example, JP-A-63-78056). An example of this type of device is shown in FIG.

In FIG. 5, an X-ray B1 emitted from an X-ray source (light source) P of an X-ray tube 5 goes to a Johansson type dispersive crystal (dispersive element) 1A through a slit 5a. X-ray B
The characteristic X-ray having a predetermined wavelength of 1 is diffracted by the dispersive crystal 1A, and the monochromatic diffracted X-ray (primary X-ray) B2 is incident on the surface 2a of the sample 2 at a small incident angle α (for example, 0.05 °). ~ 0.
It is irradiated at about 20 °). Diffracted X-ray B incident on sample 2
Part 2 is totally reflected to become a reflected X-ray B4, and the other part excites the sample 2 as a primary X-ray to generate a fluorescent X-ray B5 specific to the element forming the sample 2. The fluorescent X-ray B5 is the X-ray detector 3 arranged so as to face the sample surface 2a.
Incident on. The X-ray detector 3 detects the X-ray intensity of the incident fluorescent X-rays B5, and then the target X-rays are detected by the multiple wave height analyzer 4 based on the detection signal a from the X-ray detector 3. A spectrum is obtained.

In this type of total reflection X-ray fluorescence analyzer, since the incident angle α of the diffracted X-ray (first-order X-ray) B2 is minute, the reflected X-ray B4 and the scattered X-ray are transmitted to the X-ray detector 3. Fluorescent X-ray B5 which is difficult to enter and is detected by the X-ray detector 3.
There is an advantage that the noise is smaller than the output level of. In other words, a large S / N ratio can be obtained, so that there is an advantage that the analytical sensitivity is high and, for example, a trace amount of impurities can be detected. Therefore, this analysis method
It is effective as an analysis method of surface contamination of silicon wafers and is widely adopted.

Further, in this prior art, since the primary X-ray B1 is monochromated by using the dispersive crystal 1A, the intensity of scattered X-rays and the like is reduced, so that the analysis accuracy is further improved. On the other hand, when the X-ray B1 is monochromated, the intensity of the diffracted X-ray B2 is significantly reduced. Therefore, the curved X-ray B1 is used to focus the diffracted X-ray B2 on the sample surface 2a to generate the excitation X-ray. The intensity of the X-ray (diffracted X-ray) B2 is recovered.

[0006]

However, the total reflection fluorescence X
Unlike the usual fluorescent X-ray analysis, in the X-ray analysis apparatus, even if the curved type dispersive crystal 1A is used, the intensity of the excitation X-ray (diffraction X-ray) B2 can be sufficiently increased for the following reason. Can not.

That is, in this type of optical system, the divergence angle Ωo of the divergent X-ray B1 incident on the dispersive crystal 1A from the X-ray source P.
And the angle at which the bundle of diffracted X-rays B2 converges (hereinafter referred to as “convergence angle”) becomes equal. On the other hand, in the total reflection X-ray fluorescence analysis, it is necessary to set the incident angle α to a small angle range of about 0.05 ° to 0.20 ° as described above, and therefore it is necessary to set the convergence angle Ω to about 0.1 °. Therefore, there is no choice but to reduce the divergence angle Ωo of the divergent X-ray B1 before being monochromatic. Therefore, the intensity of the diffracted X-ray (excited X-ray) B2 is also weakened, and the analysis accuracy is not improved yet.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a total reflection X-ray fluorescence analyzer capable of increasing the intensity of diffracted X-rays and improving the accuracy of analysis. And

[0009]

The structure and principle of the present invention for achieving the above object will be described with reference to FIG. 1 showing an embodiment. In the present invention, the artificial multilayer film grating 1 is used as the spectroscopic element. In FIG. 1 (a), the artificial multilayer film grating 1 has an X-ray B incident from the X-ray source P at an incident angle θ.
1 is diffracted at the diffraction angle θ on the reflecting surface 1a to be monochromatic. Period d of the lattice spacing in this artificial multilayer lattice 1
Is set to continuously increase along the surface of the reflecting surface 1a. In relation to the X-ray source P, the cycle d is set to be larger as the distance from the X-ray source P increases as indicated by an arrow 10.

Here, the shape of the vertical cross section of the reflecting surface 1a in the artificial multilayer film grating 1 is preferably set by polar coordinates represented by the following equation (1).

[0011]

[Equation 2]

[0012]

The X-ray diffraction condition is given by the following Bragg equation as is well known. 2d · sin θ = nλ θ: incident angle and diffraction angle in the artificial multilayer film grating λ: wavelength of X-rays n: order of reflection The angle between X-ray B1 and diffracted X-ray B2 (hereinafter referred to as “reflection angle”). If Ψ _N , then the Bragg equation is represented by the following equation (2). 2d · sin {(π−Ψ _N ) / 2} = nλ (2) Further, this equation (2) can be converted into the following equation (3). 2d · cos (Ψ _N / 2) = nλ (3)

From the equation (3), when the period d becomes large, that is, at the reflection point far from the X-ray source P in the artificial multilayer film lattice 1, the reflection angle Ψ _N becomes large and Ψ ₁ <Ψ ₂ . Now, focusing on ΔPLO and ΔQRO, the corner LOP
= Angle ROQ and Ψ ₁ <Ψ ₂ , the convergence angle Ω becomes smaller than the divergence angle Ωo. Therefore, the X-ray B1 emitted toward the artificial multilayer lattice 1 with a large divergence angle Ωo.
Can be made incident on the sample 2 with a small convergence angle Ω. Therefore, it is possible to suppress the decrease in the intensity of the diffracted X-ray B2 and increase the intensity as compared with the conventional one while maintaining the range of the predetermined small incident angle α. it can.

Incidentally, as a prior art in which the lattice plane spacing in the artificial multi-layered film lattice is changed along the surface, Japanese Patent Laid-Open No.
3-61200, RKSmither "New method
for focusing x rays and gamma rays '' REVIEW OF SCIEN
TIFIC INSTRUMENTS.VOL.53 (2), Fed.1982, American
There is an Institute of physics. However, in these prior arts, by applying the total reflection X-ray fluorescence analysis,
No mention is made of the fact that such an effect occurs.

By the way, as a general dispersive crystal in which the period d of the lattice spacing is constant, a Johann type spectroscope, a Johansson type spectroscope and a log spiral type spectroscope are known. Among these spectroscopes, the Johan-type spectroscope is used only when the length of the crystal is short due to its performance, and the Johansson-type spectroscope and the log spiral spectroscope are generally used. However, the Johansson spectrometer
Since a part of the crystal is polished, it is difficult to apply it to the artificial multilayer lattice 1 having an extremely thin lattice layer. Therefore, in the total reflection X-ray fluorescence analyzer of the present invention, it is preferable to use a log spiral spectroscope.

Here, in FIG. 2, the general log-spiral equation is given by the following equation (4) because the incident angles θ _N are equal at any point of the reflecting surface 1a.
Therefore, the distance (radius) r from the X-ray source P to the reflecting surface 1a at the tilt angle φ is expressed by the following equation (5).

[0017]

[Equation 3]

On the other hand, in the present invention, the distance d from the X-ray source P on the reflecting surface 1a of the artificial multilayer film grating 1 becomes larger, so that the period d of the lattice plane interval becomes larger, so that the incident angle θ _N on the artificial multilayer film grating 1 is increased. Needs to be small. Therefore, the present inventor has conducted earnest research on the cross-sectional shape of the reflecting surface 1a of the artificial multilayer film lattice 1, and as the tilt angle φ in FIG. 2 increases, the radius vector r is obtained from r given by the equation (5). It has been found that the incident angle θ _N becomes smaller as the value becomes larger.
Completed the invention of. That is, as in the above formula (1),
By expressing the radius vector r by a higher-order exponential function of the tilt angle φ, the incident angle θ _N becomes smaller as the tilt angle φ becomes larger. Therefore, according to the polar coordinates represented by the above formula (1), the artificial multilayer film grating 1 applied to the total reflection X-ray fluorescence analyzer of the present invention.
Can be obtained.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1A, the artificial multilayer film grating 1 which constitutes a part of the irradiation device 11 has an incident angle θ from the X-ray source P.
_The X-ray B1 incident at _N is diffracted at the reflection surface 1a at the diffraction angle θ _N to be monochromatic. As shown in FIG. 3C, the period d _N of the lattice plane spacing in the artificial multilayer film lattice 1 is
It is set so as to continuously increase along the surface of the reflecting surface 1a. The period d _N is the X-ray source P of FIG.
In relation to, the distance is set larger as the distance from the X-ray source P increases as shown by arrow 10. For example, if the length of the artificial multilayer lattice 1 in the direction of arrow 10 is 40 mm, the left end 1
In L, d = 50Å, and in the right end 1R, d = 72Å.

In the artificial multi-layered film lattice 1, the reflecting surface 1a is formed by a gentle concave surface, and as shown in FIG.
It has a barrel-shaped (toroidal) reflecting surface 1a curved in the 0 direction and a direction orthogonal thereto, and collects the X-ray B1 also in the direction orthogonal to the paper surface. The diffracted X-ray B2 diffracted by the reflection surface 1a of FIG.
The light is incident on the condensing point Q on the sample (for example, a silicon wafer) 2 at (for example, 0.05 ° to 0.20 °). A part of the incident diffracted X-ray (excited X-ray) B2 is totally reflected to become a reflected X-ray B4, and another part excites the sample 2 and a fluorescent X-ray specific to the element constituting the sample 2. B5 is generated. The fluorescent X-ray B5 is the X-ray detector 3 arranged so as to face the sample surface 2a.
Incident on. The X-ray detector 3 detects the X-ray intensity of the incident fluorescent X-ray B5, and then the target X-ray is detected by the multiple wave height analyzer 4 based on the detection signal a from the X-ray detector 3. A spectrum is obtained. Other configurations are the same as the above-mentioned conventional example, and detailed description thereof will be omitted.

As described above, in the total internal reflection X-ray fluorescence analyzer, the incident angle α is set to an extremely small angle, so that the convergence angle Ω is allowed.
It must be set smaller than the range. Here, in the conventional curved type dispersive crystal 1A of FIG. 5, since the convergence angle Ω and the divergence angle Ωo are equal, the divergence angle Ωo also needs to be small. Therefore, the excitation X-ray (diffraction X
The strength of line B2 becomes weak. On the other hand, in this embodiment, the period d _N of the lattice plane spacing in the artificial multilayer film lattice 1 of FIG. 1 is continuously set to be larger as the distance from the X-ray source P is increased along the surface of the reflecting surface 1a. As described in the section of [Operation] of, the divergence angle Ωo is larger than the convergence angle Ω. For example, for a divergence angle Ωo = 1 °, a convergence angle Ω =
It can be set to about 0.1 °, and therefore, the excitation X-ray (diffraction X-ray) B
The strength of 2 can be increased. As a result, the analysis accuracy of the sample 2 is improved.

Next, a method for determining the period d of the lattice plane spacing of the artificial multilayer film lattice 1 will be described. First, the incident angle α and the convergence angle Ω are determined from the range exhibiting the phenomenon of total reflection, and the wavelength λ of the monochromatic light (diffracted X-ray) B2 to be used is determined. Then, the reflection angles Ψ ₁ and Ψ ₂ at both ends of the artificial multilayer film grating 1 are determined, and the period d at the L point and the R point at both ends is determined.
Define ₁ and d ₂ . Between the L point and the R point, the value of the incident angle θ in the Bragg's equation is generally small. Therefore, if it is changed approximately linearly, the diffracted X-ray B2 can be converted to the converging point Q with sufficient accuracy. Converge.

Next, the cross-sectional shape of the reflecting surface 1a of the artificial multilayer film grating 1 will be described. In FIG. 2, the reflecting surface 1a
The cross-sectional shape of is set, for example, by the following equation (6).

[0024]

[Equation 4]

As described above, by expressing the radius vector r by a high-order exponential function of the tilt angle φ, the concave surface of the reflecting surface 1a of the artificial multilayer film grating 1 used in the present invention can be obtained. At this time, Since the period d _N of the lattice plane intervals may be changed linearly, the artificial multilayer film lattice 1 can be easily obtained by the following manufacturing method.

Next, an example of a method for manufacturing the above-mentioned artificial multilayer film lattice 1 will be described with reference to FIG. First, for example, a substrate 1b having a flat surface such as a silicon wafer is prepared, and a vapor deposition base material 6w made of tungsten and a vapor deposition base material 6 made of silicon are provided immediately below the right end 1R thereof.
install si. Subsequently, as shown in FIG. 3A, the tungsten vapor deposition base material 6w is evaporated in a vacuum to form the base material 1b.
A tungsten thin film 1w is formed on the surface of. Then,
As shown in FIG. 3B, the silicon evaporation substrate 6si is evaporated in a vacuum, and the silicon thin film 1si is vacuum evaporated on the tungsten film 1w. By alternately repeating the vapor deposition of tungsten and silicon, the artificial multilayer film lattice 1 of FIG. 3C is obtained.

Here, since the vapor deposition base materials 6w and 6si shown in FIGS. 2A and 2B are both installed right below the right end 1R, the thin films 1w and 1si become thicker at the right end 1R. ,
It becomes thinner at the left end 1L. Therefore, as shown in FIG. 2C, the period d _N of the lattice spacing becomes continuously larger along the surface of the reflecting surface 1 a as it goes to the right. Although the reflecting surface 1a is slightly convex, it is made concave by bending the artificial multilayer film lattice 1.

Next, another example of the method for manufacturing the artificial multilayer film lattice 1 will be described with reference to FIG. This example uses a method called Chemical Vapor Deposition,
Only the main points will be described. In FIG. 4, a mask 7 having minute slits 7a is installed on the lower surface of a substrate 1b made of a silicon wafer so as to be horizontally movable. Mask 7
A gas mixture of a compound of gallium Ga and a compound of arsenic As is sealed in the gas chamber 8 below. While the mask 7 is gradually moved to the left side and the gas chamber 8 is exhausted, a compound of indium In is supplied to the gas chamber 8. As a result, a thin film is formed by atoms having different diameters, and the ratio of gallium to indium in the In-Ga-As compound attached to the substrate 1b gradually changes from the right end 1R to the left end 1L (In _X Ga _1-X As), and the period d ₂ of the lattice spacing at the right end 1R becomes larger than the period d _{1 at the} left end 1L, for example.

[0029]

As described above, according to the present invention, in a total reflection X-ray fluorescence analyzer in which the incident angle is set in a small range, the primary X-rays are diffracted by the artificial multilayer film grating and the artificial multilayer film is used. Since the period of the lattice plane intervals in the film lattice is changed, the intensity of the diffracted X-ray can be increased while keeping the incident angle on the sample within a predetermined minute range, so that the analysis accuracy is improved.

According to the second aspect of the invention, since the lattice plane spacing d of the artificial multi-layered film lattice may be changed linearly, the manufacture of the artificial multi-layered film lattice is facilitated.

[Brief description of drawings]

1A is a schematic configuration diagram of a total reflection X-ray fluorescence analyzer showing an embodiment of the present invention, and FIG. 1B is a perspective view of an artificial multilayer film lattice 1.

FIG. 2 is a side view showing the shape of a reflecting surface of an artificial multilayer film grating.

FIG. 3 is a process drawing showing an example of a method for manufacturing an artificial multilayer film lattice.

FIG. 4 is a front view showing another example.

FIG. 5 is a schematic configuration diagram of a conventional total reflection X-ray fluorescence analyzer.

[Explanation of symbols]

1 ... Artificial multilayer film grating, 1a ... Reflective surface, 2 ... Sample, 2a ...
Sample surface, 3 ... X-ray detector, 11 ... Irradiation device, B1 ... X
Line, B2 ... Diffracted X-ray, B5 ... Fluorescent X-ray, d _N ... Period, P
... X-ray source, α ... angle of incidence.

Claims (2)

[Claims] 1. An X-ray from an X-ray source is diffracted by a spectroscopic element to collect monochromatic primary X-rays toward a sample surface, and the primary X-rays are irradiated onto the sample surface at a minute incident angle. An irradiation device and an X-ray detector that faces the sample surface and detects fluorescent X-rays from the sample that has received the primary X-rays are provided, and the fluorescent X-rays are detected based on the detection result of the X-ray detector.
In a total reflection X-ray fluorescence analyzer for analyzing rays, the spectroscopic element is composed of an artificial multi-layered film lattice, and the period of the lattice plane intervals in the artificial multi-layered film lattice is along the surface of the reflection surface of the artificial multi-layered film lattice. An X-ray fluorescence analyzer for total internal reflection, which is set to be continuously large as the distance from the X-ray source increases. 2. The total reflection X-ray fluorescence analyzer according to claim 1, wherein the shape of the vertical cross section of the reflecting surface of the artificial multilayer film lattice is set by polar coordinates represented by the following formula (1). [Equation 1]