METHOD AND APPARATUS FOR STATE ANALYSIS

Abstract: A method for analyzing a state of an element in a speci­ men comprises the steps of applying an exciting source to the element, detecting the intensity of characteristic X-rays gen­ erated from measurement points at two wavelengths pre­ viously selected depending on the state of the element to be analyzed, comparing the intensity ratio of the characteristic X-rays at the two wavelengths to detect some measurement points providing the detected intensity ratio falling within a range selected depending on the state of the element, and outputting state detection signals detected only at said some measurement points to obtain a line analysis or a two-­ dimensional scanning image.

Description: Field of the Invention The present invention relates to an apparatus for analyzing the chemical bonding state of an element, e. g. for analyzing whether Si or SiO₂ is present. Description of the Prior Art An article by R. G. Hurley and E.W. Shite in Analytical Chemistry, Vol. 46, Nr. 14, December 1974, pages 2234-2237 with the title "New Soft X-Ray Method for Determining the Chemical Forms of Sulfur in Coal" describes an apparatus having the following features: exciting means for exciting the emission of characteristic X-rays from an element, spectrometer means for measuring with a single spectrometer the intensities of the characteristic X-rays at four predetermined wavelengths, one after the other, and evaluating means for calculating intensity ratios of the signals as measured by said spectrometer means at said wavelengths, for determining the chemical bonding state from the ratios. Whereas the just mentioned apparatus performs measurements at the four predetermined wavelengths one after the other, an apparatus as described in an article by H. Rehme and E. Wolfgang in Siemens-Zeitschrift 49(1975), Vol. 11, pages 732-739 with the title "Spektroskopische Methoden zur Mikroanalyse im Rasterelektronenmikroskop" acquires a complete spectrum by use of an energy dispersive spectrometer. However, the authors mention that the resolution of an energy dispersive spectrometer is only sufficient for distinguishing different elements from each other; it is not sufficient to distinguish different bonding states of a single element. A similar apparatus, however not for analyzing the chemical bonding state of an element, is described in US-A-3,909,612. It uses a plurality of spectrometers, one for each predetermined wavelength. The apparatus serves for detecting the presence of different elements in a probe. For to decide whether e.g. two predetermined metals are present, two wavelengths are predetermined, whereby each of the two wavelengths is set to a maximum emission wavelength of one of the two metals. The ratio between intensities of signals of the first and second wavelength, respectively, is high in regions where the first metal is present, whereas it is low in regions where the second metal is present. A special realization of a wavelength dispersive spectrometer is the so-called PSD(Position Sensitive Detector)-spectrometer. One kind of such spectrometer is described in an article by H. Ebel et al. in X-RAY SPECTROMETRY, Vol. 12, No. 1, 1983, pages 47-49 under the title "An X-Ray Spetrometer with a Position-Sensitive Wire Detector (PSD)". It is the object of the present invention to provide a simply contructed apparatus for analyzing the chemical bonding state of an element on an extended sample in real-time. The apparatus of claim 1 realizes the object of the invention. Due to the scanning means and the simultaneous measurement at two predetermined wavelengths, line analysis or two-dimensional analysis of the chemical bonding state of an element can be performed in real-time. The present invention will become more fully understood from the detailed description given herein below illustrated by the accompanying figures in which: Figs. 1 through 4 are graphs of spectra of characteristic X-rays used for explaining a method of the present invention; FIG.5 is a schematic arrangement of a state analysis apparatus according to a first preferred embodiment of the present invention; FIGS.6 through 8 are block diagrams of the state analysis apparatus of FIG.5 to process state detection signals; FIG.9 is a schematic arrangement of a state analysis apparatus according to a second preferred embodiment of the present invention; and FIG.10 is a block diagram of the state analysis apparatus of FIG.9 to process state detection signals. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS.1 through 4 are graphs of spectra of characteristic X-rays used for explaining a method of the present invention. FIG.1 shows spectra of characteristic X-ray of Si element or SiO₂, for example, contained in the specimen. The changing from Si to SiO₂ enables the shift of the peak wavelength in the spectra of the characteristic X-rays. When the element of Si is in a first state to be metallic Si, it provides spectra 1 of FIG. 1 as the inherent characteristic X-rays. In the spectra 1, the peak wavelength value is λ₁. A wavelength value far from λ₁, at about a half of half width (at most at the peak half width) is λ₂. Since the values of λ₁ and λ₂ are previously known depending on an element to be analyzed, two spectrometers are set to the wavelengths λ₁ and λ₂, respectively. When the two spectrometers detect the spectra, the intensity detected is given to he I₁ and I₂. It is assumed that they satisfy the following relation. I₁ ≧ αβ₁I₂ (1) α is an inherent factor so that the sensitivity of a first spectrometer for measuring the intensity I₁ at the wavelength λ₁ becomes equal to that of a second spectrometer for measuring the intensity I₂ at the wavelength λ₂. The factor α is defined according to the spectrometers. β₁ is a factor represetative of the wavelength shift amount in the characteristic X-ray spectra, the factor being defined with corresponding to the specific state of the element to be analyzed. In a second state of the Si element, it is a compound of, for example, SiO₂. The spectra of the Si element in this second state is shifted toward the shorter wavelengths due to the effect of oxygen to be spectra 2, far from spectra 1. The peak wavelength value of the spectra 2 is thereby shifted toward the shorter wavelengths. When the two spectrometers set to the wavelengths λ₁ and λ₂ are used to detect the characteristic X-ray spectra in the second state, the intensity I₁ and I₂ satisfy the following relation. I₁ < αβ₁I₂ (2) Therefore, the characteristic X-rays of the element to be analyzed are detected based on the wavelengths λ₁ and λ₂ previously selected in order to compare the detected intensity data with each other. To detect the first state of the element S₁, state detection signals are outputted in connection with only some measurement points providing the intensity ratio for satisfying the relation (1), so that a line analysis or a two-dimensional scanning image in the first state can be displayed. To detect the second state of the combination of Si with O, namely SiO₂, state detection signals are outputted from only some measurement points providing the intensity ratio for satisfying the inequality (2), so that the line analysis or the two-dimensional scanning image in the second state can be displayed, also. FIG. 2 shows a graph of spectra of the characteristic X-rays where the intensity ratio of the related peaks are changed depending on the specific state such as the chemical bonding, for example, in the case of Lα and Lβ of Fe or α₃ and α₄ of K satellites. Two spectrometers are set to peak wavelengths λ₃ and λ₄ of the two related peaks 3 and 4. In the first state, the detected intensity data I₁ and I₂ of the characteristic X-rays at the selected wavelengths λ₃ and λ₄ are assumed to satisfy the following relation. I₁ ≧ αβ₂I₂ (3) In the second state, the intensity data I₁ and I₂ are assumed to satisfy the following relation. I₁ < αβ₂I₂ (4) β₂ is a factor representative of the intensity ratio of the related peaks. The line analysis or the two-dimensional scanning image specific to the states can be given by determining whether the spectra of the characteristic X-rays at the measurement points belong to either of the relations (3) and (4). FIG. 3 shows a graph of spectra of the characteristic X-rays wherein symmetry in the spectra is changed depending on the change of the state such as the chemical bonding states. The two spectrometers are set to wavelengths λ₅ and λ₆, respectively, which are, for example, about a half of the half width, at the longer and shorter wavelength sides. It is detected whether the intensity data of the characteristic X-rays at the selected wavelengths λ₅ and λ₆ satisfy one of the following relations. I₁ > αβ₃I₂ (5) I₁ < αβ₃I₂ (6) I₁ < αβ₃I₂ (7) β₃ is a factor representative of asymmetry in the spectra of the characteristic X-rays. By detecting one of the relations, the line analysis or the two-dimensional scanning image specific to the state to which the spectra belong can be obtained. FIG. 4 shows a graph of spectra of the characteristic X-rays where the half width in the spectra of the characteristic X-rays can be altered depending on the changes of the state such as the chemical bonding state. Then it is assumed that the spetra are altered as shown in spectra 5 and 6 depending on the changes of the state, the wavelengths of the two spectrometers should be selected to be λ₁ of the peak wavelength and λ₂ far from λ₁ at about a half of the half width as shown in FIG. 1. The line analysis or the two-dimensional scanning image can be given in the same method as in FIG.1 because the detected intensity ratio can be changed at the selected wavelength if the peak half width of the spectra is changed. FIG. 5 is a schematic representation of a state analysis apparatus according to a first preferred embodiment of the present invention. An electron beam 12 emitted from an electron gun 11 is incident upon a measurement point on a sample 10 to be analyzed with a condenser lens 13 and an objective lens 14. A scanning coil 15 is provided for enabling the scanning on the sample 10. In response to the application of the electron beam 12, a characteristic X-ray 16 and secondary electrons are emitted from the sample 10. In the first preferred embodiment of the present invention, a first and second wavelength dispersive spectrometers are provided to detect the characteristic X-ray 16. The first wavelength dispersive spectrometer comprises a spectroscopic crystal 17 as a wavelength dispersion means and a detector 18. The second wavelength dispersive spectrometer comprises a spectroscopic crystal 19 as a wavelength dispersion means and a detector 20. The two spectrometers with the same sensitivity can detect the characteristic X-rays having the wavelengths specified in FIGS.1 through 4; i.e., one of them is set to λ₁, λ₃, or λ₅, while another to λ₂, λ₄, or λ₃, respectively. The detectors 18 and 20 may be proportional counters, position sensitive detectors, etc. It is preferable that both spectrometers are positioned adjacently to each other to make a measurement condition similar. The characteristic X-rays 16 emitted from the sample 10 are dispersed to different wavelengths with the spectroscopic crystals 17 and 19 and are detected by the detectors 18 and 20 at the same time for each scanned position, and sequentially for consecutive scanned positions. It is assumed that the detected intensity of the two detectors 18 and 20 is I, and I₂, respectively. The intensity I₂ is changed to "αβI₂" with an α set means 21 and a βi ( i=1, 2, or 3 ) set means 22 as FIG. 6 shows. A comparison means 23 is provided for comparing I₁, with αβiI₂ so as to determine whether any specific state is specified. While a plurality of measurement points are scanned with displaying the state detection in a real time on a display, a line analysis or a two-dimensional scanning image can be displayed. As FIG. 7 shows, the output signals from the detectors 18 and 20 are stored in memories 24 and 25 in the form of the data I₁ and αβiI₂, respectively, together with the position information of the measurement point. Thereafter, a computer 26 is operated to compare the data with each other. Otherwise, as FIG.8 shows, the intensity data I₁ and I₂ from the detectors 18 and 20 are directly stored in memories 27 and 28 together with the position information of the measurement point. Thereafter, a computer 29 is operated to add the two coefficients α and βi and compare the resultant data with each other so as to display the result. FIG. 9 is a schematic illustration of a state analysis apparatus according to a second preferred embodiment of the present invention. The state analysis apparatus of FIG. 9 is different from that of FIG. 5 in that a single wavelength dispersive spectrometer is provided which comprises a position sensitive detector 30 and a spectroscopic crystal 31 and that the intensity data by the position sensitive detector 30 are detected at two positions; respectively, corresponding to one selected wavelength ( λ₁ for example ) and another selected wavelength ( λ₂ for example ). In case where the two independent spectrometers are provided for measuring the intensity data at the two selected wavelengths λ₁ and λ₂, each of them can be placed in a completely spectroscopic condition. On the other hand, in case where only the single spectrometer with the position sensitive detector is provided for simultaneously measuring the intensity data for each scanned position of the sample at two positions of the detector corresponding to the wavelengths λ₁ and λ₂, a spectroscopic condition is approximated. This is, however, no problem in practice to compare the intensity data between the adjacent wavelengths. In the second preferred embodiment, as FIG. 10 shows, two portions of the single position sensitive detector 30 provide the intensity data I₁ and I₂ in the two different selected wavelengths, simultaneously or sequentially. In FIG. 10, the intensity data I₁ and I₂ are processed in a real time. Otherwise they are processed after stored within the memories 24, 25, 27, and 28 as shown in FIGS. 7 and 8. A line analysis or a two-dimensional scanning image at the specific state can be thereby displayed. As described above, in accordance with the present invention, in case where the state of an element contained in a specimen is altered depending on the chemical bonding state, the characteristic X-ray spectra are correspondingly altered in a condition in which a point analysis mode can be applied to analyze the spectra. In such a case, the characteristic X-ray spectra can be effectively separated and altered. A line analysis or a two-dimensional scanning image of a composition distribution in the specimen to be analyzed can be displayed, having the same real time as the conventional case. The capability of the EPMA can be highly expanded beyond the conventional capability only for analyzing the element, in that according to the present invention, the EPMA can afford the important information of the state analysis in analyzing a material.

Claims: An apparatus for analyzing the chemical bonding state of an element of a sample, comprising exciting means (11) for exciting the emission of characteristic X-rays from the element, spectrometer means for measuring the intensities of the characteristic X-rays at predetermined wavelengths within the spectrum of the characteristic X-rays generated by said element in a first bonding state, and evaluating means for calculating the intensity ratio of the signals as measured by the spectrometer means at said wavelengths, for comparing said calculated intensity ratio with predetermined ratios, and for outputting state detection signals indicating the chemical bonding state depending on the comparison result, characterized in that the predetermined wavelengths are two wavelenghts; said spectrometer means is arranged to measure the intensities at said both wavelengths simultaneously by a wavelength dispersive arrangement; and a scanning means (15) is provided for scanning the samples to perform line analysis or two-dimensional analysis of the sample. An apparatus according to claim 1, characterized in that said spectrometer means comprises two spectrometers. An apparatus according to claim 1, characterized in that said spectrometer means comprises a wave length dispersive spectrometer having a position sensitive detector (30) and a spectroscopic crystal (31), which spectrometer measures said both intensities simultaneously at two position of said position sensitive detector approximated for the both wavelengths.

Inventors: SOEZIMA, HIROYOSHI
Applicants: SHIMADZU CORPORATION
Application year: 1985
Main classification: G01N23
IPC codes: G01N23, H01J37