1. Field of the Invention
The present invention relates to apparatus and method for analyzing a sample by X-ray spectroscopy by irradiating the sample with an electron beam or X-rays and spectrally resolving and detecting characteristic X-rays emitting from the sample by a wavelength-dispersive X-ray spectrometer (WDS). More specifically, the invention relates to apparatus and method for analyzing the chemical state in a sample by making use of variations in and among characteristic X-ray spectra.
2. Description of Related Art
An electron probe microanalyzer (EPMA) is an X-ray analyzer for analyzing a sample by irradiating it with an electron beam and spectrally resolving and detecting characteristic X-rays emitting from the sample by a wavelength-dispersive X-ray spectrometer.
The X-ray spectrometer of
L=2R×sin θ (1)
where θ is the angle of incidence of X-rays on the center C of the diffraction plane (i.e., the angle that a straight line C1 passing through the center C of the diffraction plane and circumscribing the Rowland circle RC makes to the straight-line segment SC).
Meanwhile, for the diffraction conditions for the analyzing crystal, it can be seen from the Bragg's condition that the following relationship holds:
2d×sin θ=n×λ (2)
where λ is the wavelength of X-rays and d is the spacing of planes in the analyzing crystal. n is a diffraction order assuming a positive integer. Diffraction lines with n equal to or greater than 2 are generally referred to as higher-order diffraction lines or simply as higher-order lines. Eqs. (1) and (2) lead to
L=(2R/2d)×n×λ (3)
It is possible to know the wavelength λ of the diffracted characteristic X-rays by measuring the spectral position L. Because characteristic X-rays have wavelengths intrinsic to each element, the elements contained in the sample can be identified from the wavelengths λ. Furthermore, the concentrations of the elements contained in the sample can be known from the measured intensities of the characteristic X-rays.
A dispersion element that is not strictly a crystal, such as a Langmuir-Blodgett (LB) film or an artificial multilayer film (artificial superlattice), is used in a practical WDS. In the present specification, all of them are conveniently referred to as analyzing crystals. Dispersion elements referred to herein embrace all analyzing crystals, diffraction gratings, and so on which spectrally resolve X-rays based on the Bragg's condition.
Species of characteristic X-rays released from elements constituting a sample have many kinds for each element, including Kα-line, Kβ-line, Lα-line, Lβ-line, Mα-line, and Mβ-line. Furthermore, a spectrum spectrally resolved with WDS contains many higher-order lines. A technique for facilitating identifying elements by analyzing such complex spectra is disclosed, for example, in JP-B-6-97213. In this technique, with respect to characteristic X-rays of a specified element, markers are displayed at spectral positions where higher-order lines appear, as well as at the positions of the first-order diffraction lines.
In elemental analysis, higher-order lines hinder observation of the first-order lines used for analysis and, thus, are to be eliminated. For example, JP-A-2002-357571 discloses a technique for a wavelength-dispersive X-ray fluorescence analyzer to remove the background arising from higher-order lines by the use of a multichannel pulse height analyzer.
JP-A-2006-58015 discloses a technique for removing higher-order lines by making use of a multichannel analyzer (MCA) equipped to an energy-dispersive X-ray spectrometer (EDS).
A known method uses a spectrum of characteristic X-rays released from a sample to analyze the chemical state in elements constituting a substance. Where the chemical state in an element of interest is analyzed (hereinafter may be abbreviated “chemical state analysis” or “state analysis”) using a spectrum of characteristic X-rays, the analysis is performed utilizing variations in spectral wavelength (energy) and spectral waveform due to different chemical states, as well as variations in intensity between plural characteristic X-ray species. For example, JP-A-2003-75376 discloses a technique for analyzing the chemical state in tungsten based on the intensities of W-Mα line and Mβ-line of the characteristic X-rays from tungsten measured by an electron probe microanalyzer (EPMA).
In state analysis using variations in characteristic X-ray spectra, it is advantageous to select measurement conditions under which the spectral wavelength or energy resolution is optimized. Therefore, in available methods, an analyzing crystal providing a high wavelength resolution or an analyzing crystal having a plane spacing maximizing the measured diffraction angle of characteristic X-rays is selected. One method of these measuring techniques is to use higher-order diffraction lines. For example, Japanese Patent No. 2,759,922 discloses a technique employing higher-order reflections from an analyzing crystal in EXAFS spectroscopy using X-ray fluorescence analysis. EXAFS spectroscopy is a technique of performing a structural analysis using an absorption spectrum obtained near an X-ray absorption end. One of the reasons why higher-order diffractions are used is the same as why characteristic X-rays of higher-order diffractions are used in order to improve the wavelength resolution for state analysis.
As shown in
One example of substance undergoing a state analysis using higher-order lines is magnesium.
An X-ray analysis apparatus, such as EPMA or X-ray fluorescence spectrometer, is used, first of all, for elemental analysis, such as elemental identification (qualitative analysis) or quantitative analysis. State analysis, especially a method using higher-order diffraction lines, is one mode of usage of the apparatus but is less popular than elemental analysis. Therefore, these X-ray analysis apparatus are so devised that priority is placed on efficient implementation of element analysis in both hardware and software. For example, in many highly computerized apparatus operated under computer control, if the name of an element to be analyzed and characteristic X-ray species used for analysis are specified, analytical conditions are so set that an analyzing crystal is automatically set to the wavelength position of the first-order line.
Furthermore, the wavelength range in which a spectrum is acquired (scanning range of the analyzing crystal) must be widened according to the order of diffraction of a higher-order line. Therefore, if a second-order line is used, for example, to perform a state analysis, it is necessary to find a wavelength of twice of that of the first-order line and the scanning range of the analyzing crystal by manual computations.
In addition, an apparatus capable of highly automated element analysis may be equipped with a function of automatically setting a pulse height analyzer (PHA) equipped to the WDS, based on the energy value of the first-order line corresponding to the position of the spectral wavelength so as to remove higher-order lines. Where higher-order lines are used for analysis, the PHA must be set such that the first-order line diffracted at that wavelength position is removed, contrary to the case of elemental analysis.
However, where second-order lines are used for state analysis, the gain for electrical pulses and the window (see
It is relatively rare that a second-order line is used for a state analysis and a first-order line of another element is close to the used second-order line as in the example of
As described previously, in order to use higher-order lines for analysis, various operations must be performed manually. For example, analytical conditions different from analytical conditions under which elemental analysis is performed are set. These operations are cumbersome for the operator to perform. In addition, there is the possibility that incorrect settings are made.
Of course, where a spectrum of higher-order lines is displayed, it is displayed as a spectrum having double wavelength if the higher-order lines are second-order lines. However, where higher-order lines are used for state analysis, the purpose is only to improve the wavelength resolution or energy resolution of the spectrum. The absolute wavelength of the spectral position of a higher-order line or an energy corresponding to a first-order line of that wavelength is meaningless. In any case, in order to obtain information about the chemical state from the obtained spectrum, it is necessary that the wavelength or energy of a higher-order line be converted into a wavelength or energy of the original first-order line and displayed. However, this function is not necessary for elemental analysis, per se. Therefore, the conventional instrument does not have such a function of automatic conversion and display. Operations for reconverting the wavelengths of spectra into the wavelengths of first-order lines according to the orders of higher-order lines and displaying the wavelengths are cumbersome for the operator to perform. In addition, these manual operations tend to be carried out incorrectly.
It is an object of the present invention to provide a technique of automatically setting an X-ray analyzer to analytical conditions different from analytical conditions under which a general elemental analysis is performed to thereby permit measurements of higher-order lines to be performed efficiently when a state analysis is performed after spectra of the higher-order lines are acquired by a wavelength-dispersive X-ray spectrometer.
It is another object of the present invention to provide a technique of automatically reconverting the wavelength axis of a spectrum of higher-order lines acquired at high wavelength resolution for state analysis into values of the original first-order lines and displaying the values, thus permitting quick analysis of the chemical state.
A first embodiment of the present invention that achieves the foregoing objects provides an X-ray analysis apparatus for analyzing the chemical state in a sample by irradiating the sample with an electron beam and spectrally resolving and detecting characteristic X-rays emitting from the sample by a wavelength-dispersive X-ray spectrometer. The X-ray spectrometer has: specifying means for specifying an element to be analyzed in terms of the chemical state, a species of characteristic X-rays used for the analysis of the element, and its order of diffraction; setting means for setting measurement conditions under which a spectrum of the characteristic X-rays specified by the specifying means is measured; and storage means in which parameters necessary to set the measurement conditions are stored. The setting means reads out the parameters stored in the storage means based on the species of the characteristic X-rays specified by the specifying means and on its diffraction order and sets the measurement conditions under which the spectrum of the characteristic X-rays is measured.
A second embodiment of the present invention is based on the first embodiment and further characterized in that at least (i) energy and/or wavelength of the characteristic X-rays specified by the specifying means, (ii) a kind of X-ray analyzing crystal capable of measuring a spectrum of the characteristic X-rays specified by the specifying means, and (iii) a plane spacing of the X-ray analyzer is stored in the storage means.
A third embodiment of the present invention is based on the first or second embodiment and further characterized in that the setting means has means for setting a pulse height analyzer of an X-ray detection system for detecting the characteristic X-rays in such a way as to detect only diffraction lines of the second or higher order specified by the specifying means when the characteristic X-rays specified by the specifying means are diffraction lines of the second or higher order.
A fourth embodiment of the present invention is based on the first embodiment and further characterized in that the X-ray analysis apparatus further includes: conversion means for converting the wavelengths of a characteristic X-ray spectrum measured under the above-described measurement conditions into wavelengths of a spectrum of first-order diffraction lines; and display means for displaying the spectrum obtained by the conversion.
A fifth embodiment of the present invention provides an X-ray analysis apparatus for analyzing the chemical state in a sample by irradiating the sample with an electron beam and spectrally resolving and detecting characteristic X-rays emitting from the sample by a wavelength-dispersive X-ray spectrometer. The X-ray analysis apparatus has: specifying means for specifying an element to be analyzed in terms of the chemical state, a species of characteristic X-rays used for the analysis of the element, and its order of diffraction; conversion means for converting wavelengths of a characteristic X-ray spectrum measured based on the species of characteristic X-rays and order of diffraction specified by the specifying means into wavelengths of a spectrum of first-order diffraction lines; and display means for displaying the spectrum obtained by the conversion.
A sixth embodiment of the present invention provides a method of X-ray analysis for analyzing the chemical state in a sample by irradiating the sample with an electron beam and spectrally resolving and detecting characteristic X-rays emitting from the sample by a wavelength-dispersive X-ray spectrometer. This method starts with specifying an element to be analyzed in terms of the chemical state, a species of characteristic X-rays used for the analysis of the element, and its order of diffraction. Measurement conditions under which a spectrum of the specified characteristic X-rays is measured are set. Parameters necessary to set the measurement conditions are read from storage means, based on the specified species of characteristic X-rays and diffraction order, and then the measurement conditions under which a spectrum of the characteristic X-rays is measured are set.
A seventh embodiment of the present invention also provides a method of X-ray analysis for analyzing the chemical state in a sample by irradiating the sample with an electron beam and spectrally resolving and detecting characteristic X-rays emitting from the sample by a wavelength-dispersive X-ray spectrometer. This method starts with specifying an element to be analyzed in terms of the chemical state, a species of characteristic X-rays used for the analysis of the element, and its order of diffraction. The wavelengths of the characteristic X-ray spectrum measured based on the specified species of characteristic X-rays and order of diffraction are converted into wavelengths of a spectrum of first-order diffraction lines. The spectrum obtained by the conversion is displayed.
According to the first embodiment of the present invention, when chemical states in an element are analyzed using higher-order diffraction lines, measurement conditions which are suitable for measurement of a spectrum of the higher-order diffraction lines and which are different from measurement conditions adapted for measurement of a spectrum of first-order diffraction lines can be set easily, the latter measurement conditions being used for normal elemental analysis. Consequently, a high wavelength-resolution spectrum using higher-order diffraction lines can be efficiently measured.
According to the second embodiment of the present invention, parameters necessary to find the measurement conditions are read from storage means. Measurement conditions suitable for measurement of a spectrum of higher-order diffraction lines can be easily established. Therefore, a high wavelength-resolution spectrum using higher-order diffraction lines can be measured efficiently.
According to the third embodiment of the present invention, the pulse height analyzer can be set to operative conditions suitable for measurement of a spectrum of higher-order diffraction lines differently from the operative conditions of the pulse height analyzer suitable for measurement of a spectrum of first-order diffraction lines used for normal elemental analysis. Consequently, a high wavelength-resolution spectrum using higher-order diffraction lines can be measured efficiently.
According to the fourth embodiment of the present invention, a high wavelength-resolution spectrum obtained by higher-order diffractions can be easily converted into wavelengths of the original first-order diffraction lines or energy-axis and be displayed. In consequence, the chemical state can be analyzed quickly.
According to the fifth embodiment of the present invention, a high wavelength-resolution spectrum obtained by higher-order diffractions can be easily converted into wavelengths of the original first-order diffraction lines or energy axis and be displayed. Hence, the chemical state can be analyzed quickly.
According to the sixth embodiment of the invention, when chemical states in an element are analyzed using higher-order diffraction lines, measurement conditions which are suitable for measurement of a spectrum of higher-order diffraction lines and which are different from measurement conditions suitable for measurement of a spectrum of first-order diffraction lines used for normal elemental analysis can be established easily. Consequently, a high wavelength-resolution spectrum using higher-order diffraction lines can be efficiently measured.
According to the seventh embodiment of the invention, a high wavelength-resolution spectrum obtained by higher-order diffractions can be easily converted into wavelengths of the original first-order diffraction lines or energy axis and be displayed. Hence, the chemical state can be analyzed quickly.
Other objects and features of the invention will appear in the course of the description thereof, which follows.
Embodiments of the present invention are hereinafter described with reference to the accompanying drawings. It is to be noted, however, that the technical scope of the invention is not limited thereby. In the various figures, those components operating identically or similarly are indicated by the same reference numerals and their repeated detailed description will be omitted.
The position (i.e., analysis point) of the electron beam EB on the sample 2 placed on a sample stage 9 can be moved in the X- and Y-directions (horizontal directions) and in the Z-direction (heightwise direction) by a sample stage drive mechanism 10. The WDS measurement system 8 and sample stage drive mechanism 10 are connected with the measurement control unit 11, which, in turn, provides control and acceptance of signals necessary for measurements. A pulse height analyzer (PHA) identical in structure with the PHA already described is incorporated in the WDS measurement system 8. Input devices 12 including a keyboard and a computer mouse are connected with the measurement control unit 11. Furthermore, a display device (such as a liquid crystal display) 13 and a storage device 14 are connected with the measurement control unit 11. The characteristic X-ray wavelengths and/or energy values of various elements are stored in the storage device 14, as well as PHA measurement conditions. Parameters necessary for analysis and display of spectra (such as analyzing crystal plane spacings) are also stored in the storage device.
Actual instrumentation includes many other components, such as a vacuum pumping system for maintaining the inside of the electron optical system to a high degree of vacuum (of the order of 10−3 Pa), a secondary electron detector, a backscattered electron detector, a power supply, a digital-to-analog converter, and an analog-to-digital converter, but they are not directly associated with the understanding of the present invention and so they are neither shown nor described.
A method for implementing the present invention in the EPMA having the structure shown in
In step S1, the operator enters the name of an element that will undergo a state analysis, a species of characteristic X-ray(s) used for the analysis, and diffraction order(s) used for the analysis, using the input devices 12. In step S2, the measurement control unit 11 reads data about the wavelengths of first-order lines from the storage device 14 in accordance with the characteristic X-ray species of the specified element and finds the actual spectral wavelength positions and range of measured wavelengths according to the diffraction order(s). Additionally, the control unit finds the energies from the wavelengths of the first-order lines. Furthermore, the control unit 11 sets the pulse height analyzer within the WDS measurement system 8 such that only X-ray signals of the specified diffraction order(s) are selected.
In step S3, the WDS driver system 7 scans the analyzing crystal 5 within the range of measured wavelengths and measures an X-ray spectrum under control of the measurement control unit 11. In step S4, the operator selects a method of displaying the measured spectra. One choice of the method of display is selection of the horizontal axis (such as wavelength, energy, or unit of representation). Another choice is to determine whether or not wavelengths are converted into the values of first-order lines. If a method of converting wavelengths into the values of the first-order lines is selected in step S5, control goes to step S6, where the wavelengths on the horizontal axis are converted into the values of the first-order lines in accordance with the diffraction order. Where the wavelengths are not converted into the values of the first-order lines, control directly proceeds to step S7.
In step S7, the measurement control unit 11 displays the measured spectrum on the display device 13 in accordance with the selected method of display. In step 8, the operator makes a decision as to whether the method of displaying a spectrum should be varied. If the method should be varied, control returns to step S4. Where the method should not be varied, the processing is terminated.
The procedure of implementing the present invention has been described so far. In the above procedure, a method of displaying a spectrum is selected by the operator after measurement of the spectrum. For example, before the measurement is started, a method of display may be selected. Alternatively, wavelengths may be automatically converted into values of first-order lines and displayed without user selections. If necessary, the operator is allowed to modify the method of display. In addition, the measurement conditions set in step S2 may be stored in the storage device 14. If only the name of an element is specified, a chemical state analysis of the element will be immediately performed.
Another embodiment of the present invention in which an EPMA is taken as an example is next described by referring to
The EPMA 200 has a dispersion element 25, such as a diffraction grating, and a wavelength-dispersive X-ray spectrometer (WDS) 24. The WDS 24 consists of a CCD detector 26 capable of detecting multiple wavelengths of X-rays at the same time. The WDS 4 equipped to the EPMA 100 shown in
In the EPMA 200, the range of measured spectra may be kept constant. Alternatively, in the same way as in the case of the EPMA 100, if the name of an element subjected to a chemical analysis, a species of characteristic X-ray, and a diffraction order are specified, optimum dispersion element and range of measured wavelengths complying with the purpose of analysis may be selected.
With respect to the spectrum acquired by the WDS 24, the horizontal axis is a wavelength axis. X-ray intensity is plotted on the vertical axis when the spectrum is displayed on the display device 13. Where higher-order lines are used for measurements, the measured spectral wavelengths are converted into values of first-order lines automatically or according to the manipulator's choice and spectra are displayed, in the same way as in the embodiment using the EPMA 100.
As described previously, when a state analysis is performed using X-ray spectra measured by a wavelength-dispersive X-ray spectrometer, higher-order diffraction lines have been heretofore often employed. However, there is the problem that where an X-ray spectrometer more automated to make measurements in elemental analysis is used, it is more cumbersome to perform a state analysis utilizing higher-order diffraction lines.
According to the present invention described above, when a state analysis is performed using higher-order diffraction lines, an X-ray spectrometer is automatically set to analytical conditions different from analytical conditions under which a general elemental analysis is performed. Thus, spectra can be measured efficiently. Furthermore, wavelengths of higher-order spectra can be automatically converted into wavelengths of the original first-order lines and displayed. Consequently, the chemical state can be analyzed quickly.
Having thus described my invention with the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.
Number | Date | Country | Kind |
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2007-214740 | Aug 2007 | JP | national |