JPH07122222A - Element analyzing method - Google Patents

Abstract

PURPOSE:To grasp the distribution of minute quantity of impurities in Si in the contact part with good reliability by setting the spectral intensity ratio so as to correspond to either of three regions, and performing analysis. CONSTITUTION:Ti and W are entered by an input device 3, and the energy position of each element is checked on the basis of the characteristic X-ray peak profile for element accommodated in a memory 6. A computational processing device 4 determines the noise intensity N in the same energy range as the integral intensity in the specified energy region, and the ratio S/N is obtained. If this ratio exceeds 1.8, the As concentration is calculated using a program for concentration conversion accommodated in the memory 6-if below 1.8, judgement is passed that As exists qualitatively. When the ratio S/N is smaller than 1.4, it is judged that As is below the sensibility limit. Similar processing is made for Al, Si, Ti, W, and the results are displayed by a display device 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantitative elemental analysis using a spectrum unique to each element, and more particularly, to a characteristic X-ray characteristic of each element for concentration of an element. It relates to a method for quantitatively analyzing.

[0002]

2. Description of the Related Art Conventionally, in order to quantitatively analyze the elements contained in a sample using characteristic X-rays, first, from the energy position of the peak of the obtained energy dispersive characteristic X-ray spectrum, A method is employed in which identification is performed, and then the peak intensity of each identified element is obtained, and the concentration is converted from the value. Since the energy position of the characteristic X-ray generated from each element is not one, the peak positions from different elements may be very close or may overlap. In such a case, the individual peak intensities can be obtained from the overlapping spectra by approximating the shape of each peak by a Gaussian distribution and using a deconvolution operation using a computer. Then, the peak intensity (k
It is possible to calculate the concentration of each element from the spectrum obtained from an unknown sample by previously obtaining the value).

[0003]

When quantifying an element that may be present in a sample from the obtained characteristic X-ray spectrum, if the element has a minute concentration close to the detection limit, the peak intensity is increased. Is susceptible to noise,
The concentration may be overestimated. Similarly, when the peak due to the element of minute concentration overlaps with the peaks of other elements, the concentration may be overestimated. When performing quantitative analysis using characteristic X-rays in this way, when the concentration of the element to be measured is minute, not only the reliability is poor, but also the quantitative value that is far from the expected value is shown. There is even a case of losing sex.

An object of the present invention is to provide an elemental analysis method using characteristic X-rays, which is intended to improve the reliability of quantitative analysis.

[0005]

According to the present invention, in the method of quantitative elemental analysis using characteristic X-rays, the peak intensity of the actually measured spectrum is set in advance. Elemental analysis method and elemental analysis characterized by performing analysis in correspondence with one of an intensity region to be performed, (b) an intensity region that qualitatively shows the existence of an element, and (c) an intensity region that is below the detection limit. It is a device.

[0006]

In the characteristic X-ray spectrum, the quantification is possible when the peak intensity is sufficiently large. However, when the peak intensity approaches the noise level, it is certain that the element due to the energy position exists, but the spectral shape deviates greatly from the Gaussian distribution. Therefore, quantification is inherently difficult, especially when there is spectral overlap. Therefore, it is considered that the correct method is to qualitatively indicate the existence of the element. Therefore, the peak intensity of the actually measured characteristic X-ray spectrum is set to a preset intensity region for quantitative analysis, an intensity region for qualitatively indicating the presence of an element, and an intensity region for indicating that it is below the detection limit. By performing analysis in accordance with any of the above, it becomes possible to prevent the elements contained in the sample at concentrations close to the detection limit from being estimated at excessive concentrations, and to improve the reliability of quantitative analysis. . In addition, this method and apparatus can be generally applied to elemental analysis using a spectrum derived from elemental concentration, for example, a mass spectrometer, ion chromatography, etc. Similarly, the measured spectrum intensity can be quantitatively, qualitatively, The reliability of quantitative analysis can be improved by performing analysis in correspondence with one of the detection limits and below.

The operation of the present invention will be described in more detail below. In the following description, the description will be divided into a) a single spectrum and b) an overlapping spectrum.

A) Single spectrum As shown in FIG. 3A, in the conventional method, when the spectrum intensity is S and the noise intensity is N, the ratio of the spectrum intensity to the noise intensity (S / N). Is larger than 1.5, for example, N is subtracted from S to obtain a peak intensity k for a known concentration in advance, and the peak intensity k is divided by this value.
Suppose that the value of N) / k is the element concentration due to this peak, and S
When / N was smaller than 1.5, it was supposed that there was no peak in this region. However, in reality, S / N
When becomes smaller than about 1.8, the shape of the spectrum is disturbed and it is difficult to quantify. Furthermore, the S / N is about 1.
If it is 4 or more, it can be considered that a peak exists in this region. Therefore, in the present invention, i) when S / N ≧ 1.8, the density is calculated from the k value as in the conventional method. ii)
When 1.4 ≦ S / N <1.8, it is difficult to quantify, so only the existence of elements originating from this region is qualitatively shown. iii) When S / N <1.4, it means that the value is below the detection limit.

B) When the spectra overlap each other As shown in FIG. 3B, the S / N of the A or B region
The value of is divided into three as in the case of a), but since the uncertainty increases, i) When S / N ≧ 2, peak separation (deconvolution) is performed. ii) When 1.5 ≦ S / N <2, only qualitatively indicates existence. iii) When S / N <1.5, it is below the detection limit. Similarly, the result of the peak separation performed in i) is divided into three, and each peak is quantified when i) S / N ≧ 2. ii), iii)
And so on.

As described above, the spectral intensity ratio is made to correspond to one of the three regions to perform analysis,
It is possible to show highly reliable analysis results.

[0011]

【Example】

Example 1 FIG. 2 shows an example of an elemental analyzer using characteristic X-rays for carrying out the method of the present invention. In the figure, 1 is an X-ray spectroscope,
Reference numeral 2 is a central control device for performing various control processes, 3 is an input device for inputting registered element names and the like, 4 is a calculation processing device for performing calculation processes such as integration of characteristic X-ray peak intensity, and 5 is a display of calculation results etc. Display device. In the first memory of No. 6, the characteristic X
Profiles of line peaks and various programs are stored, and a second memory 7 stores a database for peak intensity region determination. The third memory 8 stores temporarily the measured characteristic X-ray data and the processed data.

Next, the elemental analysis method of the present invention is used to measure the impurities in the Si substrate of the semiconductor, and the energy dispersive X-ray analyzer (ED) attached to the transmission electron microscope (TEM) is used.
X) will be described with reference to the flowchart of FIG. In order to investigate the distribution of impurities in Si at the contact portion with the wiring, a cross-sectional TEM sample aiming at the contact portion was prepared. Point analysis is performed at an acceleration voltage of 200 kV, a probe diameter of 20 nm, and a characteristic X-ray acquisition time of 200 seconds to obtain a characteristic X-ray spectrum at each measurement point (step (a)). Next, the names of elements that may be contained in the sample, in this case, As that is ion-implanted, Al that is the wiring material, and Ti and W that are used to prevent reaction between Al and Si are input devices. 3 is input (step (b)), and the energy position of each element is confirmed based on the characteristic X-ray peak profile of each element stored in the first memory 6 (step (c)). In this case, the energy position of each element is As-1.282 keV (Lα), A
l-1.486 keV (Kα), Si-1.739 keV
(Kα), Ti-4.508 keV (Kα), W-8.396
keV (Lα), and there is no problematic overlap of energy positions (step (d)). Therefore, the process proceeds to step (Y). First, for As (Lα), the arithmetic processing unit 4 calculates the integrated intensity S in the energy region of 1.22 keV to 1.34 keV and the noise intensity N in the same energy range.
Is obtained, and the value of the ratio (S / N) is obtained. The following operation is performed based on this S / N value. If the value of S / N is 1.8 or more, the process proceeds to step (T) to calculate the concentration of As using the concentration conversion program stored in the first memory 6. If the S / N value is less than 1.8, step
Go to (R) and check if this value is 1.4 or more. If the value of S / N is 1.4 or more, the process proceeds to step (so), and As is determined to be qualitatively present.
If the S / N value is less than 1.4, step (T)
Then, it is determined that As is below the detection limit. Al and S entered in step (b) for operations after step (yo)
The process is repeated for i, Ti, and W, and finally the result is displayed by the display device 5 (step (ne)). By using such a method, it is possible to reliably investigate the distribution of a trace amount of impurities in Si at the contact portion with the wiring.

As shown in FIG. 3B, the case where the spectrum has overlapping peaks consisting of the elements A and B will be described with reference to the flowchart of FIG. If there are overlapping peaks in the spectrum, the process proceeds from step (d) to step (e) to check whether the ratio of the overlapping peak intensity Sab to the noise intensity N (Sab / N) is 2 or more. Find out. When Sab / N is 2 or more, go to step (f) to separate peaks (deconvolution)
I do. For each of the separated peaks, the ratio of the intensity of A to noise Sa / N, the ratio of the intensity of B to noise Sb
The value of / N is obtained, and the operation following step (g) is performed. First, with respect to the element A, when Sa / N 2 is 2 or more, the process proceeds to step (h), and the concentration of the element A is calculated using the concentration conversion program stored in the first memory 6. Sa /
When N is less than 2, proceed to step (re),
Further, it is checked whether Sa / N is 1.5 or more.
When Sa / N is 1.5 or more, the process proceeds to step (nu), and it is determined that the element A exists qualitatively. Sa / N
When is less than 1.5, the process proceeds to step (l), and it is determined that the element A is below the detection limit. Similarly, for the element B, the operations following step (G) are performed.

When Sab / N is smaller than 2 in step (e), the process proceeds to step (wo) and Sab
Check whether / N is 1.5 or more. When Sab / N is 1.5 or more, the process proceeds to step (wa), and it is determined that the elements A and B are qualitatively present. When Sab / N is smaller than 1.5, the process proceeds to step (f), and it is judged that the elements A and B are below the detection limit. Finally, the result obtained by such a procedure is displayed on the display device 5 (step (ne)).

In the above-mentioned embodiment, determination of three intensity regions below the quantitative, qualitative and detection limits was carried out by using the ratio of the spectral intensity S of the element to the noise intensity N, S / N.
The three intensity regions may differ depending on each element. Therefore, by performing the intensity determination using the peak intensity region determination database for each element stored in the second memory 7, it is possible to perform a more reliable quantitative analysis.

Further, the analyzer and the analyzing method can be similarly applied to the elemental analysis which generally utilizes the spectrum caused by each element, such as mass spectrometry and ion chromatography. In this case, the X-ray spectroscopic device 1 of FIG. 2 is a measuring device for obtaining a spectrum, for example, a mass spectrometer or an ion chromatograph device,
Each of the three memories stores the spectrum data corresponding to the device.

Example 2 In this example, in elemental analysis using characteristic X-rays, four regions in which the peak intensity of the actually measured spectrum was set in advance, namely, (a) intensity region for quantitative analysis, ) When the analysis is performed in correspondence with any of the intensity region that qualitatively indicates the existence of an element, c) the intensity region that is below the detection limit, and d) the region where the result cannot be obtained (unknown). is there. In elemental analysis using characteristic X-rays, light elements such as hydrogen and helium cannot be analyzed due to the nature of the detector. Therefore, it is unclear if these element names are entered as contained elements. indicate.

[0018]

As described above, according to the present invention, the characteristic X
In elemental analysis using lines, it is possible to improve the reliability of quantitative analysis. In addition, in elemental analysis that generally uses a spectrum caused by each element, such as mass spectrometry and ion chromatography, the reliability of quantitative analysis can be similarly improved.

[Brief description of drawings]

FIG. 1 is a flow chart of an elemental analysis method using characteristic X-rays of the present invention.

FIG. 2 is a diagram showing an elemental analysis apparatus using characteristic X-rays for carrying out the method of the present invention.

FIG. 3 is a diagram showing a method of dividing a spectrum intensity.

[Explanation of symbols]

1 ... X-ray spectroscopic device, 2 ... Central control device, 3 ... Input device,
4 ... Arithmetic processing device, 5 ... Display device, 6 ... First memory, 7
... second memory, 8 ... third memory.

Claims (5)

[Claims] 1. In a method for quantitative elemental analysis using a unique spectrum caused by each element, the peak intensity of the actually measured spectrum is set in advance,
An elemental analysis method, characterized in that analysis is performed in correspondence with one of an intensity region in which a quantitative analysis is performed, an intensity region in which the presence of an element is qualitatively indicated, and an intensity region in which an element is below a detection limit. 2. A peak intensity of an actually measured spectrum in a method of performing quantitative elemental analysis using characteristic X-rays,
The feature is that analysis is performed in correspondence with one of the preset intensity region for quantitative analysis, the intensity region for qualitatively indicating the presence of an element, and the intensity region for indicating that it is below the detection limit. And elemental analysis method. 3. A method for quantitative elemental analysis using a unique spectrum derived from each element, and when the actually measured spectrum has overlapping peaks, at least one peak intensity constituting the overlapping peaks is An elemental analysis method, characterized in that analysis is performed in correspondence with one of an intensity region for quantitative analysis, an intensity region for qualitatively indicating the presence of an element, and an intensity region for indicating that the element is below the detection limit. 4. In the method for quantitative elemental analysis using characteristic X-rays, when the actually measured spectrum has overlapping peaks, at least one peak intensity constituting the overlapping peaks is the intensity for quantitative analysis. An elemental analysis method, characterized in that analysis is performed in correspondence with either a region, an intensity region that qualitatively indicates the presence of an element, or an intensity region that is below a detection limit. 5. A method for performing quantitative elemental analysis using characteristic X-rays, in the case where the actually measured spectrum has overlapping peaks, at least one peak intensity constituting the overlapping peaks is intensity for performing quantitative analysis. The feature is that the analysis is performed in correspondence with one of the region, the intensity region that qualitatively shows the existence of the element, the intensity region that is below the detection limit, and the region where the result cannot be obtained (unknown). And elemental analysis method.