JPH083475B2 - Sample holder for X-ray fluorescence analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses X-rays or synchrotron radiation to detect trace elements or thicknesses on the surface of a sample electrode from several tens to several tens.
The present invention relates to a sample holder used in a fluorescent X-ray analyzer for nondestructive analysis of a trace amount of elements in a 100 Å ultrathin film.

(Prior Art) In a conventional X-ray fluorescence analyzer, X-rays are incident on a sample surface at about 60 °, and the incident X-rays generate fluorescent X-rays peculiar to the elements in the sample. The constituent elements of the sample were clarified by detecting. However, in this case, the X-ray penetrates into the sample by 2-3 μm, so several tens of
~ Detecting trace elements in ultra-thin films with a thickness of several hundred Å, which is two to three orders of magnitude less than the X-ray penetration depth, fluorescent X-rays from other than the ultra-thin film of interest are the major part. However, since the background is too high, it is extremely difficult, and the detection amount is limited to several 10 ppm to several 1000 ppm. To analyze trace elements in the ultra-thin film that adheres to the sample electrode surface or has a thickness of several tens of liters, X-rays can penetrate only several tens of liters into the sample.
Utilizing total internal reflection was more effective than conventional X-ray fluorescence analysis. However, since the X-ray incident angle used for X-ray total reflection is usually about 0.05 to 0.1 degrees, the irradiation area of the X-ray beam is widened and the intensity per unit area is weakened. Moreover, since the X-ray beam spreads too much, only a part of the X-ray beam is incident on the sample.

Further, since the fluorescent X-rays from the sample are emitted from the entire irradiation surface, in the case of a sample having a surface shape of several tens of mm square, the fluorescent X-rays generated by using a detector having a normal detection window of about 1 inch diameter. Receiving all lines at the detector is not possible if the detector window is smaller than the sample geometry. For example, if the X-ray beam shape is 1 mm in length × 10 mm in width and the sample is irradiated at an angle of 0.05 °, the shape of the irradiation surface is 1146 mm × 10 mm.
Becomes Since the sample is usually several mm to several tens of mm long,
Most of the X-rays are applied to the area other than the sample surface. That is, the amount of fluorescent X-rays generated from the sample is small, and the detection efficiency is poor because the size of the detection window of the detector is limited.

Furthermore, when total reflection X-rays are used, the X-rays penetrate only about 50Å, so the accuracy of elemental analysis of samples having a thickness of about 50Å or more decreases. At present, a laboratory-level X-ray apparatus has a detection sensitivity of several thousand ppb for heavy elements. There is a secondary ion mass spectrometry method for the analysis of other trace elements, and the maximum detection sensitivity reaches several tens ppb depending on the sample, but this method has a drawback that the sample is destroyed.

(Problems to be Solved by the Invention) The present invention efficiently utilizes incident X-rays for the generation of fluorescent X-rays and reduces the amount of scattered X-rays mixed in the fluorescent X-ray detector. It is an object of the present invention to provide a sample holder for a fluorescent X-ray analyzer capable of increasing the fluorescent X-ray detection sensitivity.

(Means for Solving the Problem) The sample holder for an X-ray fluorescence analyzer of the present invention is characterized in that a light element thin film and a heavy element thin film are alternately laminated on a holding table.

Conventional sample holders use simple substances such as single metals, alloys, glass, etc., and do not use laminated materials of different materials.

FIG. 2 shows a schematic diagram of the structure of the multilayer thin film. In FIG. 2, 1 is a heavy element layer and 2 is a light element layer. When this multi-layered thin film is irradiated with X-rays, most of the X-rays pass through the light element layer and are partially reflected on the surface of each heavy element layer, and then proceed to the deeper part. =
λ, where d is the thickness obtained by adding one heavy element layer and one light element layer, θ is the incident angle, and λ is the wavelength of the X-ray. The principle of this diffraction is shown in FIG. In FIG. 3, 3 is an incident X-ray, 4 is a diffracted X-ray, 5
Indicates an X-ray incident angle, and 6 indicates an X-ray diffraction angle. Further, FIG. 4 shows an example of the X-ray diffraction profile from the multilayer thin film. The vertical axis represents the X-ray intensity represented by the ratio of the diffracted X-ray intensity I and the incident X-ray intensity I _O, and the horizontal axis represents the diffraction angle. This example is a diffraction profile from a multi-layer thin film in which W (tungsten) is a heavy element and C (carbon) is a light element, and W layers are alternately stacked 40 times with a thickness of about 16Å and a thickness of about 24Å. The dotted line is the calculated value,
The solid line shows the measured value. The film thickness in this example is such that when the wavelength λ of the X-ray used is 1.54Å, the incident angle θ of the X-ray is about 1.1.
The above-mentioned Bragg equation is satisfied when In the case of this example, when the incident angle is about 1.1 degrees, the reflectance can be increased to about 70%. FIG. 5 is a diagram showing the relationship between the X-ray reflection intensity of the multilayer thin film and the number of layers. This example shows the wavelength λ
Shows the result of actually measuring the reflection intensity from a multilayer thin film in which W layers are alternately laminated with a thickness of about 33 Å and C layers with a thickness of about 54 Å using 1.54Å X-rays. According to this figure, the reflectance is about 20 layers.
It has reached 80%. The number of layers in which the reflectance is saturated depends on the X-ray transmission capacity, but in the case of X-rays with a wavelength λ of 1.54Å, the total thickness of the W layer that mainly reflects X-rays is approximately 700Å
This corresponds to the case of (20 × 33Å). In this case,
The Bragg equation is satisfied when the incident angle θ is about 0.6 degrees.

As described above, in the multilayer thin film, when the incident X-ray is set at a certain specific angle, the reflectance can be about 80% or more. That is, when the multilayer thin film is used as the sample holder, incident X-rays pass through the sample and are then reflected by the multilayer thin film by about 80%, and the reflected X-rays are incident on the sample again. That is, assuming that the X-ray dose before reflection on this sample is I _O , the X-ray that actually enters the sample reaches as high as about 1.8 I _O. In addition, since the incident angle is several times to several tens times the total reflection angle (about 0.05 ° to 0.1 °), there is an advantage that the density of incident X-rays is several times to several tens times larger than that in the case of total reflection.

In addition, about 80% of the incident X-rays are emitted at the same diffraction angle as the incident angle, so the X-ray dose mixed in the detector, that is, the scattered X-ray dose, is greater than that of the fluorescent X-ray analysis method using a normal sample holder. 70-80% reduction, detection sensitivity is improved. As described above, the sample holder of the present invention can detect a trace substance with extremely high sensitivity by applying an optimum condition between the incident angle of X-rays, that is, the density of X-rays on the sample surface and the thickness of each layer of the multilayer film. It becomes possible to do.

FIG. 1 is a block diagram of a fluorescent X-ray analyzer using the sample holder of the present invention, where 3 is an incident X-ray, 4 is a diffracted X-ray, and 5 is.
Indicates an X-ray incident angle, and 6 indicates an X-ray diffraction angle. Reference numeral 7 is an X-ray source, 8 is a sample, 9 is a multilayer thin film holder, 10 is a multilayer thin film, 11 is a multilayer thin film holder, 12 is fluorescent X-rays generated, 13 is a semiconductor detector, and 14 is a measuring circuit. .

(Example) The fluorescent X-ray analyzer having the configuration shown in FIG. 1 was used. X
The line generation voltage and current are 50 Kv and 300 mA, respectively. The multilayer thin film holder used has the X-ray reflection characteristics shown in FIG. This multilayer thin film holder is produced by alternately stacking W layers of about 16Å and C layers of about 24Å on Si 40 times.

The intensity of the first-order diffraction peak was 73% of the incident X-ray _IO . Therefore, when the angle 2θ = 2.2 degrees at which this peak appears is set, the sample is irradiated with X-rays of about 1.7 times the incident X-ray dose I _O. A Nb thin film sample having a surface shape of 50 mm × 20 mm and a thickness of about 100 Å was formed on the multilayer thin film holder by the sputtering method and analyzed at an X-ray incident angle of 2θ = 2.2 degrees. At this time, the X-ray irradiation area was about 1/22 as compared with the case of using total reflection, so the irradiation density was about 22 times. Moreover, the ratio of the X-ray dose I _OS incident on the sample and the irradiated X-ray I _O I _OS / I
_O was about 19 times higher in the method of the present invention than in the total reflection method. About 30% of the incident X-ray dose affects the background, but the detection sensitivity improved by about one digit due to the significant increase in I _OS / I _O. This analysis showed that the sample contained approximately 650 ppb Zn.
Contaminant was detected. This value is 2 for the same sample
About 570p of the value obtained by destructive analysis using a secondary ion mass spectrometer
It was about the same as pb.

In addition, in this embodiment, an example in which the sample is formed as a thin film on the sample holder of the present invention having a multilayer thin film in which heavy elements and light elements are alternately laminated is described. The same effect can be obtained by forming a sample thin film on the sample holder and mounting it on the sample holder of the present invention.

(Effects of the Invention) As described above, the X-ray fluorescence analyzer of the present invention is
Incident X on the sample compared to X-ray fluorescence analyzer using total internal reflection
Since the dose can be increased, it is possible to increase the fluorescent X-rays from the atoms in the sample.
Since the background is greatly reduced as compared with the line analyzer, nondestructive and highly sensitive trace substance analysis becomes possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an X-ray fluorescence analyzer used in an embodiment of the present invention, FIG. 2 is a schematic diagram of a structure of a multilayer thin film, FIG. 3 is a principle diagram of X-ray diffraction by the multilayer thin film, and FIG. Is a diagram showing an example of an X-ray diffraction profile by a multilayer thin film, and FIG. 5 is a diagram showing a relationship between the number of pairs of layers of the multilayer thin film and the intensity of diffracted X-rays. 1 ... Heavy element layer, 2 ... Light element layer 3 ... Incident X-ray, 4 ... Diffracted X-ray 5 ... X-ray incident angle, 6 ... X-ray diffraction angle, 7 ... X-ray source, 8 ... … Sample thin film 9 …… Multilayer thin film holder, 10 …… Multilayer thin film 11 …… Multilayer thin film holder, 12 …… Generated fluorescent X-ray 13 …… Semiconductor detector, 14 …… Measuring circuit

Claims (1)

[Claims] 1. A sample holder for an X-ray fluorescence analyzer, wherein light element thin films and heavy element thin films are alternately laminated on a holding table.