JP2002243671A - X-ray filter and x-ray fluorescence analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray filter of which the thickness can be easily altered finely, and an X-ray fluorescence analyzer. SOLUTION: An X-ray fluorescence analyzer 100 is an energy dispersion type total reflection X-ray fluorescence analyzer and equipped with a synchrotron(SR) radiation source 101, a slit 102 for narrowing the continuous light 1 emitted from the SR radiation source 101, and X-ray filter 103 made of silicon for making continuous light 1 quasi-monochromatic to convert the same to X-rays 2, having to irradiate a sample S and a detector 104 for detecting fluorescent X-rays 3 generated from the sample S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray filter and an X-ray fluorescence analyzer.

[0002]

2. Description of the Related Art An X-ray fluorescence spectrometer can simultaneously analyze non-destructive multi-elements, but cannot be said to be highly sensitive to so-called light elements having an atomic number lower than that of titanium. However, the analysis of light elements is also important for the analysis of impurities in semiconductor wafers and the research of cutting-edge materials, and it is expected that the detection limit of light elements will be improved in fluorescent X-ray analyzers.

According to a conventional X-ray fluorescence analyzer, a sample is irradiated with X-rays generated from an X-ray source as monochromatic light by an X-ray filter. As a result, the elements of the sample irradiated with the X-rays are excited to generate fluorescent X-rays, and the spectrum of the fluorescent X-rays is detected and analyzed by a detector to perform qualitative or quantitative analysis of the elements in the sample. . When light elements are to be analyzed, a series of optical paths from the X-ray source to the detector are placed in a vacuum system.

Generally, the lower limit of detection of an X-ray fluorescence analyzer is:
It is determined by the ratio (S / N ratio) between the signal intensity of the detection target element among the fluorescent X-rays generated from the sample and the background intensity such as other fluorescent X-rays and scattered X-rays. Since the intensity of the fluorescent X-ray generated from the sample increases in proportion to the X-ray intensity applied to the sample, if the thickness of the X-ray filter is reduced, the signal intensity increases with the X-ray intensity. On the other hand, increasing the X-ray intensity also increases the background intensity. Therefore, instead of simply reducing the thickness of the X-ray filter, using an X-ray filter having an optimum thickness that maximizes the S / N ratio improves the lower detection limit.

[0005]

(Equation 1) Equation (1) is for calculating the detection lower limit LD,
The concentration of C _X is to be detected element, N _P is the measured fluorescence X
Of line spectrum (FIG. 8), the peak value (signal intensity) to be detected element, N _B is the background value. Than this, the peak value _{N P} and background values _{N B}
The difference between the large and more background value N _B is small, it can be seen that the detection limit LD decreases.

However, in order to make the X-ray filter have an optimum thickness, X-ray filters having a plurality of thicknesses are prepared and the fluorescent X-ray filter is used.
The X-ray filter in the vacuum system of the X-ray analyzer is replaced with another X-ray filter after the vacuum system is once returned to the atmospheric pressure, and the S / N ratio is calculated after returning to the vacuum again. You have to repeat the task several times, which is very troublesome.

In order to simplify such operations, a method of attaching a plurality of X-ray filters having different thicknesses to a rotatable disk and changing the thickness of the X-ray filter by rotating the disk is described. Has been devised.

[0008]

According to the above method, X
In order to replace the line filter, it is not necessary to return the vacuum system of the X-ray fluorescence analyzer to the atmospheric pressure, and the replacement operation becomes easy. However, since the disk and its driving source need to be placed in the vacuum system. Considering the size of the entire apparatus, the size of the disk is limited, for example, such that four types of X-ray filters are mounted on a disk having a diameter of about 5 cm. For this reason, the thickness of each X-ray filter is also limited, and when analyzing a certain sample, the four types of mounted X-ray filters do not always include those having the optimum thickness. That is, there is a problem that an optimum S / N ratio cannot always be realized, and the improvement of the detection lower limit is also limited.

[0009] The present invention has been made in view of these points, and the present invention provides an X-type device that can easily change a minute thickness.
It is an object to provide a line filter and a fluorescent X-ray analyzer.

[0010]

According to a first aspect of the present invention, there is provided an X-ray filter comprising a material having a predetermined X-ray absorption edge. The thickness of the X-ray transmitting portion is changed stepwise.

According to a second aspect of the present invention, there is provided an X-ray filter made of a material having a predetermined X-ray absorption end, wherein the thickness of the X-ray transmitting portion of the X-ray filter is continuously reduced. It has been changed.

Further, according to the present invention (claim 3), in the X-ray filter according to claim 1, the change in thickness of the X-ray transmitting portion per step is in a range of 5 micrometers to 100 micrometers. belongs to.

According to a fourth aspect of the present invention, there is provided an X-ray fluorescence analyzer comprising: an X-ray source for irradiating a sample with X-rays; and a detector for detecting X-ray fluorescence generated from the sample. An X-ray fluorescence analyzer according to claim 1, wherein the X-ray filter according to claim 1 or 2 has an optical path from the X-ray source to the sample, wherein the thickness of the X-ray transmitting portion changes with respect to the optical path. As described above.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an X-ray fluorescence analyzer 100 according to an embodiment of the present invention will be specifically described with reference to the drawings. As shown in FIG. 1, the present X-ray fluorescence analyzer 100
Is a synchrotron (SR) radiation source 101 and a slit 102 for narrowing the continuous light 1 generated from the SR radiation source 101.
A silicon X-ray filter 103 that converts the continuous light 1 into a quasi-monochromatic X-ray 2 to be irradiated on the sample S, and a detector 104 that detects fluorescent X-rays 3 generated from the sample S. Things.

The SR radiation source 101 bends high-energy electrons by a magnetic field in the electron storage ring and emits continuous light 1 in a wide area generated in a tangential direction of the electron storage ring. (SSD).
The optical path from the SR radiation source 101 to the SSD 104 is in a vacuum system.

As shown in FIG. 2A, the X-ray filter 103 has a stepped concave portion (X-ray transmitting portion) 31 formed at the center of a silicon substrate 30 of about 30 mm square and 400 μm thick. As shown in FIG. 2 (b), the concave notch 31 is concavely notched in eight steps, the width of one step is about 1.2 mm, and the thickness of the thinnest part. Is 40 μm, and the thickness change per step is in the range of 20 μm to 100 μm.

The range of the thickness of the concave portion 31 of the X-ray filter 103 depends on the intensity of the X-ray transmitted through the X-ray filter and is not particularly limited. Thus, the SR of critical energy 844 eV
When using the radiation source 101, 5 μm to 400 μm
Is preferably within the range. X-ray filter 103
When the thickness is more than 400 μm, the X-ray intensity near the K-absorption edge decreases, and a desired increase in sensitivity cannot be realized.

The number of recesses 31 is not limited to eight, and may be set arbitrarily. However, the number of recesses 31 is set so that the X-ray intensity near the K-absorption edge is evenly divided at desired intervals. It is preferable to set the number of steps of the notch 31 and the change in thickness per step. Further, the concave notch 31 for transmitting X-rays
Is not limited to the center of the X-ray filter 103, but may be provided at an arbitrary position such as near the lower end.

The X-ray filter 103 has a slit 10
3, the optical path of the continuous light 1 is provided so as to transmit through the concave portion (X-ray transmitting portion) 31. As shown in FIG. The frame 32 is fixed to be in the horizontal direction, and the frame 32 can be moved up and down by an adjustment knob 33 provided outside the vacuum system. Thus, the X-ray filter 103 placed in a vacuum system
Can be moved with respect to the continuous light 1 such that its thickness changes.

Note that the present invention also includes another configuration that can be relatively moved with respect to the continuous light 1 so that the thickness of the X-ray filter 103 changes. For example, the X-ray filter 103 may be moved with respect to the continuous light 1 by a driving source such as a motor, or the X-ray filter 103 may be moved.
May be fixed, and the SR radiation source 101 may be moved by well-known moving means.

As shown in FIG. 4, the critical energy of continuous light 1 generated from SR radiation source 101 in the present embodiment is 844 eV, and X-ray filter 10 made of silicon is used.
3 is quasi-monochromatic, and becomes X-ray 2 having an X-ray intensity peak at about 10 keV. FIG. 4 shows the X-ray filter 103 having a thickness of 380 μm.

In X-ray fluorescence analysis, analysis cannot be performed unless X-rays having a higher energy than the K absorption edge of the element to be analyzed are used. In addition, the excitation efficiency of an element is higher as the X-ray having an intensity peak on the high energy side near the K absorption edge peculiar to the element is excited. For example, when analyzing calcium (K absorption edge = 4.038 keV),
When the peak is excited by 5 keV X-ray, the peak becomes 6 keV
Analysis can be performed with higher sensitivity than when excited by V X-rays. Therefore, the X-ray 2 is sodium (K absorption edge = 1.08)
The analysis conditions are considerably poor for light elements such as keV).

On the other hand, by moving the X-ray filter 103 to reduce the thickness of the concave portion 31 for transmitting the continuous light 1, as shown in FIG. The X-ray intensity near the end (1.838 keV) increases. Therefore, an element having a K absorption edge smaller than the K absorption edge, for example, sodium, magnesium (K
The sample S is irradiated with X-rays 2 adjusted so that the S / N ratio is maximized with respect to the absorption edge = 1.303 keV) and aluminum (K absorption edge = 1.559 keV). improves.

As described above, according to the fluorescence analyzer 100 according to the present embodiment, the X-ray filter 103 having the concave notch 31 whose thickness is changed stepwise is provided, and the X-ray filter 103 transmitting the continuous light 1 is provided. By changing the thickness of the line filter 103 easily and stepwise, the intensity of the X-rays 2 irradiating the sample S is changed stepwise, and the X-ray having the optimum intensity to maximize the S / N ratio is obtained. Line 2 can be obtained, and the detection limit of light elements can be improved.

Hereinafter, modifications of the above embodiment will be described with reference to the drawings. In the present modification, an X-ray filter 10 as shown in FIG.
3a, and the other configuration of the X-ray fluorescence analyzer is the same as that of the above embodiment.

As shown in the figure, the X-ray filter 103a is formed by forming a slope-shaped concave portion 31a having a thickness continuously changed from 400 μm to 40 μm in the center of a silicon substrate 30. is there. Note that the X-ray filter 103a also has a slit
The optical path of the continuous light 1 is provided so as to pass through the concave notch 31a, and can be moved with respect to the continuous light 1 such that its thickness changes.

As described above, according to this modification, the continuous light 1
Since the thickness of the X-ray filter 103a that transmits X-rays can be changed easily and continuously, the intensity of the X-rays 2 irradiating the sample S is continuously changed, so that the S / N ratio is maximized. Intense X-rays 2 can be obtained, and the lower limit of detection of light elements can be improved.

In the above-described embodiment and the modified example, the thickness of the concave notches 31 and 31a is reduced in a step shape or a slope from one end thereof in one direction. The shape of is not limited to this, for example,
The shape may be such that it becomes thinner in a step-like or slope-like manner from both ends toward the center.

Further, in addition to the silicon X-ray filters shown in the above-described embodiment and modified examples, titanium (K absorption edge = 4.964 keV) and aluminum X-ray filters having the same structure are used. An X-ray filter to be used may be arranged in series and an X-ray filter to be used is selected from the three types of X-ray filters according to an element to be analyzed. As a result, the detection lower limit of calcium, potassium, chlorine, sulfur, phosphorus, and silicon is improved when using a titanium X-ray filter, and magnesium, sodium, and fluorine are used when using an aluminum X-ray filter. Is improved.

Further, in the above-described embodiment and the modified examples, the description has been given of the fluorescent X-ray analyzer which converts the SR radiation source into quasi-monochromatic X-rays for irradiating the sample. For example, even in a fluorescent X-ray analyzer that irradiates a sample with primary X-rays from a tube as secondary X-rays using an appropriate target, the X-ray filter 1
03, 103a, the same effect can be obtained.

[0031]

EXAMPLE (Preparation of X-ray filter) After nickel / chromium was vacuum-deposited on a silicon substrate having a thickness of 400 μm,
A resist was applied. After exposing and developing the silicon substrate, the deposited nickel / chromium was etched, the resist was further removed, and silicon etching was performed to form one step of a concave notch. This operation was repeated to form an eight-step concave portion, and the remaining nickel and chromium were removed, washed, and dried to obtain an X-ray filter having a thickness changing to eight steps. The measured value of the thickness of each step of the recess is 3
70 μm, 345 μm, 305 μm, 269 μm, 23
8 μm, 188 μm, 134 μm, 42 μm,
The width per step was about 1.2 mm. Note that a plate-shaped X-ray filter having a thickness of 380 μm was used as an object.

(Measurement Sample and Measurement Conditions)
0 ng / ml, 50 ng / ml of aluminum, and 50 ng / ml of magnesium in each of three aqueous standard samples.
A sample of 0 μl, which was dropped on a silicon wafer (30 × 30 mm ² ) and dried, was used as a sample. The measurement was performed in the total reflection mode, the incident angle of the incident X-ray was set near 1 mrad, the thickness of the X-ray filter and the slit width (0.9 mm,
(0.65 mm, 0.4 mm, 0.25 mm). The atmosphere in the sample chamber is about 2 × 10 ^−3.
At Torr, the measurement time is 500 s.

(Measurement Results) FIG. 7A is a fluorescent X-ray spectrum obtained by optimizing the thickness of the X-ray filter.
On the other hand, FIG. 7B shows a fluorescent X-ray spectrum when an X-ray filter having a uniform thickness of 380 μm is used. As shown in the figure, when the X-ray filter according to the present example was used, a sensitizing effect was clearly observed, and the lower limit of detection (LD) calculated by equation (1) was 5 times for sodium and 5% for magnesium. 4 times, and aluminum twice. Note that the sample of the comparative example shown in FIG.
/ Ml, 50 ng / ml of aluminum, and 50 ng / ml of magnesium, each of which is 30 µ
1, which was dropped on a silicon wafer (30 × 30 mm ² ) and dried.

[0034]

As described above, according to the X-ray filter of the present invention, in the X-ray filter made of a material having a predetermined X-ray absorption edge, the thickness of the X-ray transmitting portion of the X-ray filter is reduced. The thickness of the X-ray filter through which the X-rays pass can be easily and gradually changed by moving the X-ray transmitting portion relatively with respect to the optical path of the X-rays. Can be changed to

According to the X-ray filter of the present invention, in the X-ray filter made of a material having a predetermined X-ray absorption end, the thickness of the X-ray transmitting portion of the X-ray filter is continuously changed. Therefore, the thickness of the X-ray filter through which the X-ray passes can be easily and continuously changed by relatively moving the X-ray transmitting portion with respect to the optical path of the X-ray. .

The X-ray fluorescence analyzer according to the present invention comprises an X-ray source for irradiating a sample with X-rays, and a detector for detecting X-ray fluorescence generated from the sample. In the X-ray fluorescence spectrometer, the X-ray filter is provided in an optical path from the X-ray source to the sample so as to be relatively movable with respect to the optical path so that the thickness of the X-ray transmitting portion changes. Therefore, by changing the thickness of the X-ray filter that transmits X-rays easily and stepwise, X-
By changing the intensity of the line in a stepwise manner, it is possible to obtain an X-ray having an optimum intensity so that the S / N ratio becomes maximum. Thereby, the detection lower limit of the light element of the X-ray fluorescence analyzer is improved.

[Brief description of the drawings]

FIG. 1 is an X-ray fluorescence analyzer 1 according to an embodiment of the present invention.
It is a schematic diagram which shows the structure of 00.

FIGS. 2A and 2B are a front view and a cross-sectional view illustrating a configuration of an X-ray filter 103. FIGS.

FIG. 3 is a schematic perspective view showing an external configuration of an X-ray filter 103 fixed to a frame 32.

FIG. 4 is a diagram illustrating an SR spectrum transmitted through an X-ray filter.

FIG. 5 is a diagram illustrating a relationship between a thickness of an X-ray filter and an SR spectrum.

FIG. 6 is a front view and a cross-sectional view illustrating a configuration of an X-ray filter 103a.

FIG. 7 is a diagram showing a fluorescent X-ray spectrum obtained in an example.

FIG. 8 is a diagram showing signal intensity and background intensity.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 X-ray fluorescence analyzer 101 SR radiation source 103 X-ray filter 104 SSD 2 X-ray 3 X-ray fluorescence 31 Concave portion

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshiyuki Toriyama 1-1-1, Nojihigashi, Kusatsu-shi, Shiga Ritsumeikan University Inside the Faculty of Science and Engineering (72) Inventor Haruki Haruki Shiraishi 1, Nojihigashi-1, Kusatsu-shi, Shiga 1-1 Ritsumeikan University Biwako / Kusatsu Campus Faculty of Science and Technology (72) Inventor Shinjiro Hayakawa 1-4-1 Kagamiyama, Higashihiroshima-shi, Hiroshima F-term Hiroshima University Faculty of Engineering F-term (reference) 2G001 AA01 AA09 BA04 BA11 BA13 CA01 EA06 EA20 FA09 JA01 JA11 JA14 KA01 LA02 NA04 NA05 NA06 NA07 NA09 NA15 NA16 NA17 RA04

Claims (4)

[Claims] 1. An X-ray filter comprising a material having a predetermined X-ray absorption edge, wherein the thickness of an X-ray transmitting portion of the X-ray filter is changed stepwise. filter. 2. An X-ray filter comprising a material having a predetermined X-ray absorption edge, wherein the thickness of an X-ray transmitting portion of the X-ray filter is continuously changed. filter. 3. The X-ray filter according to claim 1, wherein a change in thickness of the X-ray transmitting portion per one step is in a range of 5 μm to 100 μm. 4. An X-ray source for irradiating a sample with X-rays,
An X-ray fluorescence analyzer comprising: a detector for detecting X-ray fluorescence generated from a sample. The X-ray filter according to claim 1 or 2, wherein an X-ray filter according to claim 1 or 2 is provided in an optical path from the X-ray source to the sample. An X-ray fluorescence analyzer provided so as to be relatively movable with respect to the optical path so that the thickness of the X-ray transmitting portion changes.