JP4349146B2 - X-ray analyzer - Google Patents

Description

  The present invention relates to an electron beam probe microanalyzer, a scanning electron microscope, a transmission electron microscope, a fluorescent X-ray analyzer, etc., which emits intrinsic X-rays from a sample using an electron beam or X-ray as an excitation ray and analyzes the X More particularly, the present invention relates to an X-ray analyzer suitable for analyzing a very small area on a sample.

  The electron probe microanalyzer (EPMA) irradiates a sample with an electron beam having high energy as an excitation beam, and thereby emits intrinsic X-rays emitted to the outside when the inner electrons of the components contained in the sample are excited. By analyzing, the element is identified and quantified, and the distribution of the element is examined. On the other hand, a fluorescent X-ray analyzer irradiates a sample with primary X-rays as excitation rays, and thereby analyzes intrinsic X-rays (fluorescent X-rays) emitted from the sample in the same manner as EPMA.

  In addition, as a method for analyzing the characteristic X-rays of such an analyzer, the characteristic X-rays are dispersed with a spectroscopic crystal, and only the diffracted X-rays having a specific wavelength (energy) among the various diffracted X-rays dispersed are used as a detector. Wavelength dispersion method (WDS) to be introduced and detected, and inherent X-rays are directly introduced into a semiconductor detector, and a pulse signal having a wave height proportional to the wavelength (energy) of the X-rays is generated. There is an energy dispersive method (EDS) in which the wave height value is detected and detected by electrical wavelength separation.

  In micro-partial analysis using such an X-ray analyzer, in recent years, a polycapillary (Polycapillary) that has a point focus on the incident side and a parallel beam on the output side between the sample emitting the intrinsic X-ray and the detector is used. What was inserted is known (for example, refer nonpatent literature 1 etc.). A polycapillary has a basic structure in which a large number of thin glass tubes (fibers) that guide X-rays are bundled, and X-rays emitted from an X-ray source that can be regarded as almost a point can be expressed at a large solid angle on the entrance side. The parallel beam is emitted from the exit side on the opposite side. Therefore, by disposing the polycapillary between the sample and the detector, the characteristic X-rays emitted from the sample in all directions can be efficiently collected and guided to the detector.

  Although the size of the point focus on the incident side of the polycapillary depends on the type of sample element, it is generally a very small size of about several tens of μm. However, especially in the case of electron beam excitation, the electron beam has a very small diameter. It is possible to make the size of the X-ray emission region on the aperture and the sample even smaller than the size of the point focal region of the polycapillary. Furthermore, it is also possible to scan the irradiation position of the electron beam in the point focal region. Therefore, the minute portion for detecting the characteristic X-ray in the point focal region is sequentially shifted, and the distribution of the X-ray intensity values in the point focal region can be acquired at high speed. By combining such scanning of the electron beam and horizontal movement of the sample itself, fine element mapping within an arbitrary range on the sample becomes possible.

  However, the polycapillary has different intensities (sensitivities) of X-rays guided between the central portion and the peripheral portion in the point focal region. This is because X-rays emitted from the vicinity of the central portion are taken into the polycapillary more efficiently than X-rays emitted from the peripheral portion. Therefore, even if specific X-rays having the same intensity are emitted from any position in the point focal region, the X-ray detection values (X-ray intensity values) in the range corresponding to that region are not uniform. For these reasons, there is a problem that accurate mapping cannot be performed even if element mapping is performed by scanning the irradiation position of the electron beam within the point focal region on the sample.

“Focusing Polycappillary Optics Ultra-High-Resolution EDS Detectors”, [Online], X-Ray Optical Systems, Inc. (X-Ray Optical) Systems, Inc.), February 12, 2004 search, Internet <URL: http://www.xrayoptics.com/appnotes/app102.pdf>

  The present invention has been made to solve such a problem, and an object of the present invention is to enable microanalysis without sensitivity unevenness regardless of the X-ray emission position in the point focal region of the polycapillary. Is to provide a simple X-ray analyzer.

The present invention, which has been made to solve the above problems, analyzes a sample after irradiating the sample with excitation rays and condensing the X-rays emitted from the sample by a polycapillary having a point focal point on the incident side. X-ray analyzer
a) storage means for preliminarily storing the sensitivity distribution of the polycapillary in the point focal region of the polycapillary on the sample;
b) position detection means for detecting the irradiation position of the excitation beam on the sample at the time of analysis execution;
acquires sensitivity information for the position from the storage means in response to the excitation beam irradiation position information obtained by c) said position detecting means, so that the sensitivity GaHitoshi one at the point focal region with a sensitive index information And a correction calculation means for correcting the detected value of the X-ray with respect to the excitation beam irradiation position,
It is characterized by having.

  Specifically, as one aspect of the present invention, the storage means uses, as a parameter, the distance between the X-ray emission point in the polyfocal point focal point region on the sample and the central point of the point focal point region. The sensitivity distribution of the polycapillary can be stored in advance. This sensitivity distribution may be obtained by calculation, but it is preferable to actually measure each device (polycapillary).

  In the present invention, the excitation beam is not particularly limited, such as an electron beam, a proton beam, an α ray, a γ ray, and an X ray, but at least the size of the irradiation region is smaller than the size of the point focal region of the polycapillary on the sample. The irradiation diameter can be narrowed down. Further, the excitation line itself can be scanned so that the irradiation position of the excitation line moves within the point focal region of the polycapillary. When an excitation ray with such a small diameter hits the sample during analysis, specific X-rays are emitted from the irradiation position and the vicinity thereof. The polycapillary efficiently collects the X-rays and sends them to the subsequent X-ray analysis unit. The X-ray analysis unit includes a spectral crystal and an X-ray detector in the wavelength dispersion method, and includes a semiconductor detector in the energy dispersion method. By these X-ray analysis units, intensity values of X-rays collected by the polycapillary can be obtained.

On the other hand, the position detection means detects the irradiation position of the excitation beam on the sample. Specifically, the position detection means detects, for example, secondary electrons or reflected electrons coming from the sample, forms an electron image of the sample based on the detection signal, and information on the irradiation position of the excitation beam in the electron image. The structure which calculates | requires can be taken. The correction calculation means obtains sensitivity information at the position in light of the excitation ray irradiation position information in light of the sensitivity distribution stored in the storage means. As a sensitivity GaHitoshi one in point focus area, to correct the detection value of the X-rays obtained as described above the (X-ray intensity values). For example, when the sensitivity of the position (usually the center point) with the highest sensitivity in the point focus area is 1 and the sensitivity of other positions is expressed as a relative sensitivity, the reciprocal of this sensitivity information is detected as a correction coefficient. If the value is multiplied, the above correction can be performed.

  According to the X-ray analyzer according to the present invention, the sensitivity unevenness caused by the sensitivity distribution of the polycapillary is automatically corrected regardless of the position of the X-ray emission position in the point focal region of the polycapillary. The sensitivity characteristic is substantially uniform. Therefore, when scanning the excitation line within the focal region of the polycapillary and detecting X-rays at each position on the scanning locus, an accurate detection value is obtained by removing the influence of the sensitivity distribution of the polycapillary. Can do. Thereby, for example, element mapping in the point focal region can be performed accurately.

  An electron beam probe microanalyzer according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a main part of an electron beam probe microanalyzer according to the present embodiment. In this analyzer, a wavelength dispersion method (WDS) is adopted as an X-ray analysis unit.

  In FIG. 1, an electron beam as an excitation beam emitted from an electron gun 1 is two-dimensionally bent by a magnetic field formed by a deflection coil 2 and irradiated onto a sample 3. Part of the intrinsic X-rays emitted from the electron irradiation position on the sample 3 and the vicinity thereof are incident on the polycapillary 4 which is an X-ray lens. be introduced. The spectroscopic crystal 5 splits the incident X-rays into a spectrum having a wavelength component corresponding to each element, and the X-rays having a specific wavelength component (energy) among the diffracted X-rays is passed through a solar slit or the like (not shown). Introduced to the X-ray detector 6. A pulse signal which is a detection signal from the X-ray detector 6 is input to the counting unit 8 through the wave height selecting unit 7 and a value corresponding to the X-ray intensity is obtained by counting the pulse signals obtained per unit time.

  The signal processing unit 9 receives this X-ray intensity value, performs qualitative analysis and quantitative analysis, obtains an X-ray intensity distribution, and further calculates an element intensity distribution and an element content distribution (element mapping) from the X-ray intensity distribution. ) Etc. is performed to obtain derivative information. In order to perform correction processing of the X-ray intensity value as will be described later in the process of performing such signal processing, a sensitivity distribution information storage unit 92 that stores sensitivity distribution information in advance as described later and the sensitivity distribution information are used. And a sensitivity correction calculation unit 91 that executes a calculation for correcting the X-ray intensity value.

  On the other hand, secondary electrons and reflected electrons are also generated from the sample 3 by the electron beam irradiation. These electrons are detected by the detector 10, and based on the detection signal, the image forming processing unit 11 generates an electronic image related to the sample 3. Form. The irradiation position recognizing unit 12 identifies the irradiation position of the electron beam in the electronic image and recognizes the position information, and provides the position information to the signal processing unit 9 following the scanning of the irradiation position. The control unit 13 controls each unit of the apparatus. For example, the control unit 13 controls the deflection coil 2 to scan the electron beam. Although not shown in FIG. 1, the spectroscopic crystal 5 is placed at the center of the goniometer and the X-ray detector 6 is arranged on the circumference of the goniometer so that the spectroscopic crystal 5 and the X-ray detector 6 By rotating while maintaining the angular relationship, the wavelength of the diffracted X-ray introduced into the X-ray detector 6 can be appropriately changed or scanned.

  In the above configuration, the size of the point focal region on the incident side of the polycapillary 4 (defined by the half-value width of sensitivity from the center point) depends on the wavelength of the X-ray to be detected, that is, the type of element. Is about 50 μm. On the other hand, the irradiation diameter of the excitation electron beam can be reduced to 0.1 μm or less. The region that emits intrinsic X-rays on the sample 3 upon receiving this electron beam irradiation becomes larger than the irradiation diameter of the electron beam due to the diffusion of electrons inside the sample 3, but it is appropriate to suppress the acceleration voltage of the electron beam. By appropriate control, it can be suppressed to about 1 μm. Therefore, as shown in FIG. 2, the irradiation position of the electron beam with a very small diameter can be obtained by appropriately irradiating the electron beam by the deflection coil 2 within the point focal region A of the polycapillary 4 on the sample 3. It is possible to scan along an appropriate trajectory. As a result, the X-ray intensity distribution of each minute portion having a size of about 1 μm or smaller in the point focal region A can be obtained, and element mapping or the like can be performed using the result.

  In the case of performing analysis over a range that exceeds the point focal region A of the polycapillary 4, a sample table (not shown) on which the sample 3 is placed is moved in the horizontal direction so that the sample 3 The position of the point focal region and the center irradiation position of the electron beam (irradiation position when not deflected) are moved.

  In order to eliminate the influence of the nonuniformity of the sensitivity distribution due to the transmission characteristics of the polycapillary 4 when the X-ray intensity distribution is obtained by performing the electron beam scanning in the point focal region A as described above, The apparatus according to the embodiment executes characteristic signal processing as described below.

  First, sensitivity distribution characteristics in the point focal region A of the polycapillary 4 are obtained by actual measurement or calculation, and the sensitivity distribution characteristics are converted into data and stored in the sensitivity distribution information storage unit 92 in advance. Most preferable from the viewpoint of correction accuracy, sensitivity distribution information (that is, three-dimensional information) on a two-dimensional plane is acquired by measuring the sensitivity to each minute portion in the point focal region A, and all of these are data. It is to make it. According to this, for example, it is possible to obtain a sensitivity distribution reflecting the non-uniformity of the diameter and shape of each X-ray waveguide on a concentric circle around the central axis of the polycapillary. Therefore, when the storage capacity of the sensitivity distribution information storage unit 92 can be sufficiently secured, such three-dimensional sensitivity distribution data may be stored. However, in this case, since the data amount becomes considerably large, generally approximate sensitivity distribution data is held as follows.

  That is, since the difference in sensitivity is substantially small on a concentric circle around the central axis of the polycapillary, the sensitivity is considered to be constant on the concentric circle. Under such conditions, only sensitivity distribution data on a straight line corresponding to the radius of the circular point focal region A may be stored in the sensitivity distribution information storage unit 92. For example, it is assumed that a sensitivity distribution on a straight line passing through the center point B of the point focal region A with respect to the intrinsic X-ray of a certain element C is obtained as shown by a solid curve in FIG. This sensitivity distribution is relative sensitivity when the sensitivity at the center point is 1.0, and the range where the sensitivity is 0.5 or more is the point focal region A. As described above, when the sensitivity is constant on the concentric circles, the sensitivity distribution curve is line-symmetric with respect to the center point B. Therefore, in practice, as shown in FIG. The sensitivity distribution may be converted into data using the distance from the center point B as a parameter.

  As described above, after actually measuring the three-dimensional sensitivity information in the point focal region A, appropriate arithmetic processing such as taking an average value of sensitivity on a concentric circle is performed, and finally the point focal region as described above. Sensitivity distribution data corresponding to the radius of A may be acquired and stored in the sensitivity distribution information storage unit 92. In addition, as described above, the sensitivity distribution on a certain straight line passing through the center point B of the point focus area A may be measured, and an average value may be calculated on both sides of the center point B.

  The sensitivity distribution characteristic of the polycapillary depends on the component (element) to be analyzed. For example, the sensitivity distribution of the element D different from the element C is as shown by a dashed-dotted curve in FIG. Therefore, for this element D, it is necessary to retain sensitivity distribution data such as a one-dot chain line curve in FIG. Accordingly, for all components (elements) to be analyzed, such sensitivity distribution data is stored with the distance from the center point B as a parameter. Actually, the sensitivity distribution information does not need to be measured by the user who installed the device, but the device manufacturer actually measures it during the adjustment process, and stores the sensitivity distribution data based on the measured data in a nonvolatile memory such as a ROM. You can let it go.

  When actually performing the analysis, the signal processing unit 9 detects X-rays emitted from the sample 3 as described above, so that the signal processing unit 9 performs X-rays for a certain minute portion in the point focal region on the sample 3. An intensity value is obtained. On the other hand, the image formation processing unit 11 creates an electronic image based on secondary electrons generated from the sample 3. When the irradiation position recognition unit 12 receives the electron image on the sample 3, for example, as shown in FIG. 3C, the irradiation position recognition unit 12 recognizes the irradiation position of the electron beam, and determines the distance between the position and the center point B of the point focal region. Obtained as the irradiation position information. In the example of FIG. 3C, the distance d is electron beam irradiation position information, which is given to the signal processing unit 9.

  In the signal processing unit 9, the sensitivity correction calculation unit 91 is in light of sensitivity distribution data regarding the component to be analyzed (detected) at that time among various sensitivity distribution data stored in the sensitivity distribution information storage unit 92. Sensitivity data corresponding to the distance as electron beam irradiation position information is read. Specifically, as shown in FIGS. 3B and 3C, when the analysis target is the element C, the sensitivity p is read out corresponding to the distance d. Therefore, the sensitivity correction calculation unit 91 performs sensitivity correction by multiplying the X-ray intensity value acquired for the minute portion by the correction coefficient using the reciprocal 1 / p of the read sensitivity p as a correction coefficient. For example, when the sensitivity p is 0.8, the X-ray intensity value is multiplied by the reciprocal of 1.25 as a correction coefficient.

  When scanning the electron beam in the point focal region A and measuring the X-ray intensity values of different minute portions sequentially, sensitivity data corresponding to the electron irradiation position is obtained for each measurement, as described above. Perform sensitivity correction. As a result, the non-uniformity of the sensitivity of the polycapillary 4 can be removed for any minute portion, and an X-ray intensity value can be obtained under a substantially constant sensitivity condition. The signal processing unit 9 executes element mapping processing using such corrected X-ray intensity values. Therefore, elemental mapping is required in a state in which the non-uniformity of sensitivity due to the polycapillary 4 is almost completely eliminated, so that accurate mapping is possible.

  In the above description, the wavelength dispersion type configuration is used as the X-ray analysis unit that detects the intrinsic X-rays collected by the polycapillary 4, but the energy dispersion type configuration, that is, the intrinsic X-rays collected by the polycapillary 4 is used. It is clear that wavelength separation may be achieved by directly introducing the signal into the semiconductor detector to generate a pulse signal having a peak value corresponding to the wavelength (energy) and separating the pulse signal for each peak value. It is.

  In addition, an electron beam probe microanalyzer that emits an electron beam to a sample and emits intrinsic X-rays from the sample has been described as an example. However, as an excitation beam to be irradiated to a sample, at least a point focal region of a polycapillary is used. As long as the size of the irradiation region of the excitation beam is smaller than the size and the excitation beam can be scanned, the type is not particularly limited, and X-rays, proton rays, α rays, γ rays are not limited. In addition to particle beams such as, radiation light may be used.

  In addition, it is obvious that any modification, correction, or addition that is appropriately made within the scope of the present invention is included in the scope of the claims of the present application.

The block diagram of the principal part of the electron beam probe microanalysis apparatus by one Example of this invention. FIG. 2 is an enlarged perspective view in the vicinity of a point focal region in FIG. 1. The figure for demonstrating the sensitivity correction | amendment processing operation | movement in the electron beam probe microanalyzer of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electron gun 2 ... Deflection coil 3 ... Sample 4 ... Polycapillary 5 ... Spectral crystal 6 ... X-ray detector 7 ... Wave height selection part 8 ... Counting part 9 ... Signal processing part 91 ... Sensitivity correction calculation part 92 ... Sensitivity distribution information Storage unit 10 ... Detector 11 ... Image formation processing unit 12 ... Irradiation position recognition unit 13 ... Control unit A ... Point focal region B of polycapillary ... Center point of point focal region

Claims (2)

An X-ray analyzer that irradiates a sample with an excitation beam and analyzes X-rays emitted from the sample according to the sample after being collected by a polycapillary having a point focus on the incident side,
a) storage means for preliminarily storing the sensitivity distribution of the polycapillary in the point focal region of the polycapillary on the sample;
b) position detection means for detecting the irradiation position of the excitation beam on the sample at the time of analysis execution;
acquires sensitivity information for the position from the storage means in response to the excitation beam irradiation position information obtained by c) said position detecting means, so that the sensitivity GaHitoshi one at the point focal region with a sensitive index information And a correction calculation means for correcting the detected value of the X-ray with respect to the excitation beam irradiation position,
An X-ray analysis apparatus comprising:
  The storage means stores in advance the sensitivity distribution of the polycapillary in advance by using the distance between the X-ray emission point and the center point of the point focal region in the polycapillary point focal region on the sample as a parameter. The X-ray analyzer according to claim 1.

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