JPS60237349A - Fluorescent x-ray structural analysis apparatus - Google Patents

Abstract

PURPOSE:To measure fluorescent X-rays within a short time with good accuracy without requiring re-measurement and long-time measurement, by providing a variable filter for attenuating the intensity of X-rays incident on a specimen and measuring the intensity of X-rays incident on the specimen. CONSTITUTION:X-rays generated from an X-ray source 1 passes through an evacuated X-ray route 2 by a vacuum pump 12 and reflected by the crystal 7 arranged in a spectroscopic converging crystal chamber 3 and X-rays with desired energy are selected to irradiate the specimen 15 in a specimen chamber 19 through a filter selector 6 having an X-ray attenuating filter 6a arranged thereto and a slit 13. The position of the hole provided to the filter selector 6 is selected by an X-ray intensity adjusting mechanism 9 to select the proper intensity of X-rays. The intensity of X-rays irradiating the specimen is measured by an incident X-ray intensity measuring counter 14 and the intensity of fluorescent X-rays generated from the specimen 15 is measured by a fluorescent X-ray intensity measuring counter 16. The measured value is inputted to a data processing apparatus 18 where a fluorescent X-ray spectrum is analyzed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a fluorescent X-ray structure analysis device for analyzing the structure of a substance at the atomic level, and in particular, to a structure analysis of an amorphous thin film formed on a substrate. The present invention relates to a fluorescent X-ray structure analysis device suitable for.

[Background of the invention]

Fluorescent X-ray structure analysis equipment irradiates a sample with X-rays from an X-ray source while changing the wavelength within a certain range, and observes the fluorescent X-rays generated by the irradiation to determine the structure of the target object. It is for analysis. An electron beam excitation type X-ray generator is often used as an X-ray source. In order to utilize this technology, the device is constructed with a highly sensitive X-ray optical system. However, the electron beam excitation type Xf5! In addition to the low-intensity continuous X-rays mentioned above, the generator also generates very high-intensity characteristic X-rays (line spectrum). Since the input X-ray intensity of the radiation measuring device is too large, the measurement accuracy deteriorates significantly. For this reason, the conventional method has been to reduce the power input to the X-ray generator and perform the measurement again after completing the continuous spectrum measurement. In addition, conventional equipment scanned by changing the X-ray wavelength at fixed energy (or wavelength) intervals using an X-ray monochromator, but in order to obtain sufficient resolution in the low energy region, the energy interval was changed. If this setting is made, the energy interval becomes unnecessarily small in the high-energy region, the number of extra measurement points increases, the measurement takes a long time, and there are problems with the reliability of the data due to the stability of the device.

[Purpose of the invention]

An object of the present invention is to provide a fluorescent X-ray structure analysis device that uses an electron beam excitation type X-ray worm generator but can perform measurements with high accuracy in a short time without requiring remeasurements or long-term measurements. It is in.

[Summary of the invention]

The present invention provides a variable filter that attenuates the intensity of X-rays incident on the sample, and measures the intensity of X-rays incident on the sample so that the intensity falls within a range that does not deteriorate the measurement accuracy of the X-ray intensity measuring device. In addition to providing a mechanism to automatically adjust the variable filter mentioned above, we focused on the fact that when processing fluorescence data emitted from a sample, analysis is performed by converting it into a spectrum with the wave number of the scattered electron waves inside the sample as a unit. The scanning step width of the X-ray wavelength is not the conventional constant energy width,
It is characterized by being pressed to perform the wave number width steps at a constant wave number width.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows the operating principle of the spectral convergence type curved crystal used in the fluorescent X-ray structure analysis apparatus of this example. X-ray diffraction by a crystal is defined by Bragg's law as shown in the following equation.

2dIdflθ=nλ Song interval, song, listen (1) Here, d
is the spacing between the crystal planes, and θ is the crystal plane contributing to diffraction and the incident X
The diffraction angle formed by the line, λ is the wavelength of the diffracted X-ray, and n is the order (integer) of diffraction.

Now, as shown in Figure 1, the lattice plane of the spectroscopic crystal C has a radius of 2.
When the crystal is mechanically bent along the circle R and the inside of the crystal is shaped along the radius R, the divergence from X# source S becomes X11.
! Of these, only the X-rays with wavelengths that reach the crystal C and satisfy the condition of equation (1) converge on AP located on the same circumference with radius R. Therefore, if a slit is installed at this point P, the energy E of the X-rays passing through the slit can be expressed by the following equation from the relationship between the wavelength of the electromagnetic wave and the energy.

Here, J and c are a blank constant and the speed of light, respectively. In equation (2), n=1 is the fundamental wave, n≧2
These are called harmonics, but the material and crystal structure of the spectroscopic crystal,
By appropriately selecting the surface index, it is possible to set the diffraction to occur strongly only when n = 1, and to make the diffraction weak when n≧2, making it possible to converge monochromatic X-rays to P. Therefore, desired X-rays can be focused and used.

Therefore, by changing various spectroscopic crystals with different d, θ, etc., it is possible to perform fluorescence measurements with various wavelengths (energy).

However, when an electron beam excitation type X# generator is used as the X-ray source S, in addition to continuous X-rays with low intensity as mentioned above, special energy (wavelength) with high intensity (number of counts per unit time) is generated. X-rays are incident on crystal C. Therefore,
As shown in Figure 2, an example in which tungsten (W) is used as the anticathode material, the intensity of the X-rays passing through the slit also fluctuates significantly, and as a result, as described in the conventional equipment, the X-ray generator It was necessary to significantly reduce the input power and re-measure. Note that the characteristic X-rays (X-ray line spectrum) with high intensity are determined by the metal material used for the anticathode, and if the atomic number of the material for the anticathode is selected to be small, this characteristic X-ray can be suppressed to some extent. It is possible to reduce the intensity, but as the atomic number is reduced, the intensity decreases to that of continuous X-rays, so it is essentially impossible to avoid it.

Therefore, in the present invention, by using an apparatus configuration as shown in FIG. 3 as an embodiment, it is possible to automatically measure the entire measurement range without reducing the accuracy of the X-ray measurement system and without re-measuring. This method reduces the time required for measurement by removing unnecessary measurement points. In Figure 3, X-ray source 1
The X-rays generated at The X-rays are selected and irradiate the sample 15 in the sample chamber 19 through the filter selector 6 equipped with the X-ray attenuation filter 6a and the slit 13. Here, each filter 6a has an X-ray intensity of about 115 in the desired measurement energy (wavelength) range, and 0 filters are installed in each of the four holes of the filter selector 6. The X-ray intensity adjustment mechanism 9 selects the position of the hole and selects an appropriate X-ray intensity. The energy (wavelength) of the X-ray is determined by equation (2), but in this example, the diffraction angle θ is determined by the crystal position control device 4, slit and sample position control device 5, and the interplanar spacing d of the crystal is Crystal exchange mechanism 8
Determined by selecting the spectrally convergent crystal 7,
The desired X-ray energy (wavelength) is obtained by these θ and d.

The intensity of X-rays irradiating the sample 15 is measured by an incident X-ray intensity measuring counter 14, and the intensity of fluorescent X-rays generated from the sample 15 is measured by a fluorescent X-ray intensity measuring counter 16. These measured values are transmitted through the interface 17 to the data processing device 18, where the fluorescent X-ray spectrum is analyzed, and various parts are controlled for automatic measurement.

FIG. 4 is a flowchart showing a method of controlling the above-mentioned apparatus. First, in step 100, the X-ray energy E
(wavelength). This determination method will be described in detail later, and here it is assumed that a certain value E is set. continue,
In step IQ1, the filter selector 6 is set to one of the filters.
Place the empty hole in a position where the X-rays will pass through. (This position is said to be reset as the initial state).

In step 102, the intensity of each X-ray is measured for 1/m second. That is, the counter 14 measures the incident X# intensity Io1, and the counter 16 measures the fluorescent X-ray intensity 1. Measure. However, 1/m second is the time at which the count value of the incident X-ray intensity Io+ can be obtained with sufficient accuracy. Then step 103
Now, it is determined whether the incident X# intensity I01 just measured does not exceed the maximum X-ray intensity that does not deteriorate the measurement accuracy. Assuming that gas flow type proportional counters are used as the X-ray intensity measurement counters i4 and 16, the maximum X-ray intensity mentioned above is approximately 20,000 counts/sec, so the number of counts IoX for 17 msec is 20,000/sec. Since measurement is possible if the count is less than m, the filter selector 6 is left as is and the process proceeds to the next step. Therefore, if the intensity of the continuous spectrum part of the X-ray source and the counting time of 1/msec in step 102 are set to satisfy these conditions, characteristic ) is selected in step 100, the process does not return to step 104, but when the energy of the line spectrum is selected, the condition of step 103 is usually not satisfied, and therefore, the process does not return to step 104. Then, a command is issued to the adjusting mechanism 9 to drive the filter selector 6 so that the incident X-rays pass through only one filter 6a. This increases the incident X-ray intensity by 115 times, and in this state steps 102 and 10
3 is executed again, and if the condition of step 103 is still not satisfied, the process returns to step 104 and the number of filters 6a is set to two. In this way, the incident X-ray intensity is maximum (1
15)' Since it is possible to attenuate up to 1/625 times (when using 4 sheets), even in the case of normal characteristic The process can proceed to step 105. In step 105, the incident X-ray intensity I02 and the fluorescence
) seconds.

Here, Ir is the count number of the counter 16 necessary to measure the fluorescent X-ray intensity with sufficient accuracy. Since the fluorescent X-ray intensity is smaller than the normal incident X-ray intensity, step 102
The X-ray intensity I obtained in step 1 is smaller than g, so step 1
Ir/(mI 1) seconds (greater than 1/m seconds) at 05
When a further measurement is performed, since the count value is proportional to the measurement time, the output of the counter 16 becomes Ir or more, and the fluorescent X-ray intensity is measured with sufficient accuracy. As a result, the counter 14 calculates the incident X-ray intensity at steps 102 and 105 by -(1+Ir/
x1)/m seconds to obtain a total intensity (count number) of Io+ + IO2, and the counter 16 counted for 1 second for the same time to obtain a total fluorescent X-ray intensity (count number) of I++I2. Therefore, the ratio of the fluorescent X-ray intensity to this incident intensity, that is, the fluorescent X-ray yield at the target energy E (E) = '(11+I2) /
(IO1+IO2) is calculated in step 106. Next, in step 107, it is checked whether the measurement in the required energy range has been completed, and if not, the process returns to step 100, the energy E is changed, and the step 9 below is executed. As described above, since the intensity of characteristic X-rays is automatically attenuated by a filter to a value that can be measured with high precision before measurement is performed, the required fluorescence You can increase the rate.

Next, the X-ray energy (
The method for selecting wavelength) E will be described.

Fluorescence X-ray structure analysis has a higher energy constraint than the fluorescence excitation energy of a specific element.The fluorescence yield spectrum X between 1 keV
(E). This is a method to calculate the radial distribution by Fourier transforming the change in fluorescence yield caused by the scattering of slow electron spherical waves in a material centered around a specific element by surrounding elements. In the analysis, the wave number R of the slow electron spherical wave is analyzed as a unit. Therefore, the required data can be obtained by measuring the fluorescence yield spectrum When me is the energy E
There is the following relationship between

Therefore, the wave number R and the energy E are not in a proportional relationship, and when R is set at equal intervals R1, R2, etc., the energy E also changes as EI + E2... No. For example, EO = 1835eV (S
i's fluorescence X-ray excitation energy), and the interval of wave numbers R is Δ
If R=0.03, then R=2.8 (E=E.

ΔE near 130eV is 07ev, R-16(E=
ΔE near EO (11000 eV) is 4.1 eV
becomes. Therefore, in order to maintain an interval of ΔR=0.05, in the case of a conventional device that scans at constant energy intervals, ΔE=
It must be kept constant at around 0.7 eV. However, in this case, in the high energy region around R=16, measurements are performed at intervals of about 1/6 of the required interval of 4.1 eV. Expressing this in terms of the number of measurement points is ΔE == 0.7
In constant ΔE measurement at 6V, for approximately 1400 measurement points, ΔR=
A constant Δλ measurement of 0.03 means that measurement at measurement point 440 can be performed with equivalent accuracy. Therefore, in the present invention, the setting value of the energy E in step 100 of FIG. 4 is determined as follows. In other words, the value of the wave number R is expressed as RII+R at equal intervals.
2r...+R1+... is defined. Formula (2).

From (3), we get: E - heat sea (morning) 2 + Eo (4), so R on the right side of this equation is R1 + 1 ''' + 2
The energy Ei obtained by substituting +... is (m, ,'
*E.

is given in advance as a constant), and this energy El +
The crystal position control device 4, slit and sample position control device 5, shown in FIG.
The crystal exchange mechanism 8 is controlled to set the diffraction angle θ and the crystal spacing d. By selecting the X-ray energy E and scanning so that the wave numbers R are equally spaced in this manner, the number of measurement points can be reduced to 440/1400 x 1/3 in the above example.

〔Effect of the invention〕

According to the present invention, even if an electron beam excitation type X-ray source is used,
Since there is no need to re-measure characteristic X-rays and the fluorescent X-ray yield is measured using only the minimum number of measurement points necessary for the required measurement accuracy, the measurement time can be significantly reduced compared to conventional methods. effective.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a spectroscopic crystal for separating and converging divergent X-rays, Fig. 2 is a diagram showing an example of the spectrum of electron beam-excited X-rays, and Fig. 3 is a diagram showing an embodiment of the present invention. , 4th
This figure is a flowchart showing a method of adjusting and measuring the incident Xi intensity in the embodiment of FIG. 1... X-ray source, 4... Crystal position control device, 5...
- Slit and sample position control device, 6... Filter selection machine, 7... Spectral focusing crystal, 8... Crystal exchange mechanism, 9... X-ray intensity adjustment mechanism, 13... Slit, 14. ... Incident X-ray intensity measurement counter, 15... Sample, 16... Fluorescent X-ray intensity measurement counter, 18... Data processing device. Figure 1 Figure 7 Figure 2 Figure 3 (Ao) Figure 4

Claims (1)

[Claims] Incident X-ray wavelength determination in which the wavelength of the incident X-ray is determined for each measurement point so that the wave number of the slow electron spherical wave generated in the sample when the X-ray is incident changes in a predetermined constant step width. means, and X, I of the wavelength determined by the incident X@wavelength determination means among the X-rays output from the X-ray generator.
an incident X-ray wavelength control means for controlling only J to irradiate the sample as selectively incident X@; a first measuring means for measuring the intensity of the selectively incident X-ray; and attenuating the intensity of the selectively incident X-ray. a filter whose attenuation rate can be variably set; and X-ray intensity control means for controlling the attenuation rate of the filter so that the measured value of the first measuring means falls within a predetermined reference intensity. , a second measuring means for measuring the intensity of fluorescent X-rays emitted from the sample corresponding to the selected incident X-rays;
A fluorescent X-ray structure analysis apparatus comprising: calculation means for calculating the fluorescent X-ray yield of the sample from the X-ray intensity measurements by the first and second measuring means.