JP2008016339A - X-ray source and fluorescent x-ray analysis device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray source 11 capable of easily emitting a plurality of kinds of characteristic X-rays 25 by easily enabling replacement of a secondary target 26. <P>SOLUTION: An electron gun 14 generating an electron beam 15, and a primary target 20 emitting a primary X-ray 21 by entering the electron beam 15 are arranged in a vacuum vessel 12 having an X-ray transmissive window 13 of a vacuum vessel 12. The primary X-ray 21 permeates the X-ray transmissive window 13. A box-shaped secondary target body 23 is detachably attached by surrounding the outside of the X-ray transmissive window 13 of the vacuum vessel 12. The secondary target body 23 is provided with the secondary target 26 emitting a characteristic X-ray 25 by entering the primary X-ray 21 permeating the X-ray transmissive window 13 therein. The secondary target body 23 is provided with a characteristic X-ray extraction window 27 emitting the characteristic X-ray 25 to the outside. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an X-ray source that emits characteristic X-rays and an X-ray fluorescence analyzer.

  It is known that a general X-ray source emits a mixture of braking X-rays and characteristic X-rays peculiar to a target when electrons accelerated by a high voltage are incident on a target that is an anode. For example, see Patent Document 1).

  The bremsstrahlung X-ray is a continuous energy spectrum composed of white, and its spectral distribution changes depending on the incident electron energy, whereas the characteristic X-ray does not depend on the electron energy. It is a monochromatic energy distribution. X-ray fluorescence analysis measures the energy distribution of fluorescent X-ray signals emitted when characteristic X-rays are incident on a sample, and identifies the type and amount of elements in the sample. Various X-ray sources devised to enhance are used.

  In a fluorescent X-ray analyzer, by exciting a sample using characteristic X-rays having a known spectrum, it becomes easier to separate fluorescent X-ray signals and noise components that are scattered incident X-rays. Since elemental analysis at the S / N ratio is possible, attempts have been made to make the X-ray spectrum emitted from the X-ray source close to a single color, and some of them have been put into practical use.

  FIG. 9 shows an example of a general configuration of a high-resolution X-ray fluorescence analyzer utilizing the above characteristic X-rays. Here, using a general X-ray source 1, continuous X-rays 2 that are primary X-rays of a continuous energy spectrum emitted from the X-ray source 1 are incident on the secondary target 3, and characteristic X-rays 4 Is emitted to the sample 6 through the collimator 5 installed outside, and the X-ray detector 8 detects the fluorescent X-rays 7 emitted by exciting the elements on the surface of the sample 6.

In the emission method of the characteristic X-ray 4 in this configuration, the X-ray source 1 and the secondary target 3 must be installed apart from each other. Since the continuous X-ray 2 is emitted in the 4π direction, which is the entire circumferential direction, and its intensity decreases in inverse proportion to the square of the distance, in the conventional configuration, the secondary X-ray 2 emitted from the X-ray source 1 is secondary. In order to increase the intensity of the characteristic X-ray 4 emitted from the secondary target 3 because the efficiency of irradiating the target 3 is low, it is necessary to provide a high-power X-ray source 1, thereby high-resolution X-ray fluorescence analysis This increases the size of the apparatus, increases the power consumption, increases the scale of X-ray shielding, and consequently increases the cost, which is a factor that strengthens restrictions on diffusion (see, for example, Non-Patent Document 1).
JP 2004-28845 A (page 4-5, FIG. 1-2) Current Status and Prospect of X-ray Fluorescence Analysis Izumi Nakai Applied Physics Vol. 74 No. 4 (2005) pp. 455-456

  As described above, a high-resolution X-ray fluorescence analyzer can generate characteristic X-rays efficiently, and provide an X-ray source that contains as little unwanted noise components as possible in the emitted X-ray spectrum. This is an important issue.

  Furthermore, providing an X-ray source from which a plurality of types of characteristic X-rays can be selected according to the analysis target is also an important issue. As an example, in the high-resolution total reflection X-ray fluorescence analysis that is remarkably popular in the semiconductor field, it is required to analyze a large number of target elements from ultra trace amounts of light elements to heavy elements. Therefore, a plurality of X-ray sources having different primary and secondary targets that can emit a plurality of types of characteristic X-rays must be used, and the X-ray source must be switched according to the X-ray energy region to be used. .

  The present invention has been made in view of the above points, and can emit characteristic X-rays with high efficiency, suppresses the mixing of noise components into the emitted characteristic X-rays, and is suitable for, for example, total reflection fluorescent X-ray analysis. An X-ray source and a fluorescent X-ray analyzer that can easily obtain characteristic X-rays with a simple sheet beam shape, can easily exchange secondary targets, and can easily emit multiple types of characteristic X-rays The purpose is to provide.

  The X-ray source of the present invention includes a vacuum vessel having an X-ray transmission window, an electron gun that generates an electron beam in the vacuum vessel, and an electron beam that is provided in the vacuum vessel and is generated by the electron gun. A primary target that emits X-rays, and a box that is detachably attached to the outside of the X-ray transmission window of the vacuum vessel, and is emitted from the primary target to be used as the X-ray extraction window. A secondary target that emits characteristic X-rays upon incidence of transmitted X-rays, and a secondary target body having a characteristic X-ray extraction window that emits characteristic X-rays emitted from the secondary target to the outside. It is what.

  An X-ray fluorescence analyzer of the present invention excites an element on the surface of the sample by irradiation with the X-ray source according to any one of claims 1 to 6 and irradiating the sample with the characteristic X-ray. And an X-ray detector for detecting fluorescent X-rays emitted.

  According to the present invention, X-rays emitted from the primary target in the vacuum vessel penetrate the X-ray extraction window of the vacuum vessel and enter the box-shaped secondary target body surrounding the outside of the X-ray transmission window. Since the characteristic X-rays incident on the secondary target and emitted from the secondary target are emitted to the outside from the characteristic X-ray window of the secondary target body, the characteristic X-rays can be emitted with high efficiency and emitted. Mixing of noise components into X-rays can be suppressed, and characteristic X-rays having a sheet beam shape suitable for, for example, total reflection fluorescent X-ray analysis can be easily obtained. Moreover, since the secondary target body can be attached to and detached from the vacuum vessel side, it can be easily replaced with different types of secondary targets, and an X-ray source that can easily emit a plurality of types of characteristic X-rays can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment.

  The X-ray source 11 has a vacuum container 12 in which the inside is held in vacuum, and an X-ray transmission window 13 for emitting X-rays to the outside is disposed on a side surface near one end of the vacuum container 12. The X-ray transmission window 13 is formed of a material such as Be (beryllium), for example, and plays a role of keeping airtightness.

  An electron gun 14 is disposed at the other end of the vacuum vessel 12, and is an emitter that emits an electron beam 15 toward one end of the vacuum vessel 12 at the end of the electron gun 14 located in the vacuum vessel 12. An electron source 16 is provided. The electron source 16 is formed in a line shape and can emit an elongate line-shaped electron beam 15. The electron gun 14 generates and accelerates an electron beam 15 by a driving power source 17.

  A primary target 20 is disposed in the vacuum container 12 so as to face the electron gun 14. The primary target 20 is irradiated with an electron beam 15 and emits primary X-rays 21, which are continuous X-rays as X-rays, toward the X-ray transmission window 13.

  A box-shaped secondary target body 23 covering the outside of the X-ray transmission window 13 is detachably attached to the outer surface of the vacuum vessel 12 where the X-ray transmission window 13 is provided. An X-ray passage port 24 through which the primary X-ray 21 that passes through the X-ray transmission window 13 passes through the secondary target body 23 is formed on the surface of the secondary target body 23 facing the vacuum vessel 12. A secondary target 26 that emits characteristic X-rays 25 that are secondary X-rays when primary X-rays 21 are incident is formed on at least the inner surface of the secondary target body 23.

  The secondary target 26 is formed only on the inner surface portion of the secondary target body 23 where the primary X-rays 21 of a main component formed in a box shape with a general material such as stainless steel are incident. This can be achieved by attaching a material foil or by coating the material of the secondary target 26. Alternatively, the secondary target body 23 may be formed from the material of the secondary target 26.

  The secondary target body 23 has a characteristic X-ray 25 at a position that intersects the opposing surface 23a facing the X-ray transmission window 13 and the X-ray passage opening 24 and is along the opposing surface 23a. A characteristic X-ray extraction window 27 for emission is formed. The characteristic X-ray extraction window 27 is formed in an elongated slit-like opening shape along the facing surface 23a so that the primary X-ray 21 is not mixed and the characteristic X-ray 25 having a sheet beam shape can be extracted.

  The anode side, which is the primary target 20 side, is set to the ground potential, and a negative high voltage is applied to the cathode side, which is the electron gun 14 side.

  In addition, the primary target 20 uses an element having an atomic number about 2 larger than that of the secondary target 26 and uses the primary X-ray 21 emitted thereby to excite the secondary target 26 most efficiently. be able to.

  Then, the electron beam 15 emitted by applying a voltage from the driving power source 17 to the electron gun 14 is incident on the primary target 20, and the primary X-ray 21 emitted from the primary target 20 becomes the X-ray transmission window 13. To the secondary target body 23. The primary X-rays 21 transmitted into the secondary target body 23 mainly enter the secondary target 26 on the facing surface 23 a of the secondary target body 23, and the characteristic X-rays 25 are emitted from the secondary target 26. Only the component of the characteristic X-ray 25 emitted from the surface of the secondary target 26 of the opposing surface 23a of the secondary target body 23 at a shallow angle passes through the characteristic X-ray extraction window 27, and the sheet is placed outside the secondary target body 23. Beam characteristic X-rays 25 are emitted.

  In this way, it is possible to provide the X-ray source 11 that can obtain the characteristic X-ray 25 having a sheet beam shape in which mixing of noise components other than the characteristic X-ray 25 to be used is suppressed.

  Further, by adopting this configuration, the characteristic X-ray 25 does not pass through the solid X-ray transmission window 13 and therefore is not subjected to an attenuation action at the time of transmission. This is advantageous when trying to obtain 25. Furthermore, there is no need to worry about the generation of Compton scattering components when passing through the solid X-ray transmission window 13, and this makes it possible to ensure X-ray intensity and ensure high spectral monochromaticity.

  Moreover, since the secondary target body 23 can be attached to and detached from the vacuum vessel 12 side, a plurality of types of secondary target bodies 23 having a plurality of types of secondary targets 26 from which characteristic X-rays 25 to be used can be obtained are prepared. Thus, the X-ray source 11 that can easily emit a plurality of types of characteristic X-rays 25 can be provided by replacing the secondary targets 26 with different types.

  Next, FIG. 2 shows a second embodiment.

  In this embodiment, in the X-ray source 11 of the first embodiment, the anode side which is the primary target 20 side is set to the ground potential, and a negative high voltage is applied to the cathode side which is the electron gun 14 side. In contrast, the reverse configuration is adopted, that is, the cathode side on the electron gun 14 side is set to the ground potential, and the anode side on the primary target 20 side is set to the high voltage potential.

  FIG. 3 is a diagram for explaining the influence of whether the cathode or the anode is set to the ground potential.

  As shown in FIG. 3B, in the case of anode grounding, the primary target 20 that emits the primary X-ray 21 and the X-ray transmission window 13 have the same ground potential, so there is no need to consider the insulation distance. It is possible to shorten the distance between them and increase the irradiation efficiency of the primary X-rays 21 to the secondary target 26. On the other hand, recoil electrons 29, which are high energy components in the primary X-rays 21 emitted from the primary target 20, collide with the X-ray transmission window 13 without damaging the energy and cause damage. . In general, Be (beryllium) having a small X-ray attenuation rate is used for the X-ray transmission window 13, and when a low energy component is extracted, a very thin one having a thickness of 1 mm or less is used. However, considering the damage caused by the recoil electrons 29, it is difficult to reduce the window thickness.

  As shown in FIG. 3A, in the opposite configuration, that is, when the cathode is set to the ground potential, most of the recoil electrons 29 emitted from the primary target 20 return to the primary target 20. Therefore, it does not reach the X-ray transmission window 13 and give an impact. As a result, a very thin X-ray transmission window 13 can be used, which is advantageous in efficiently extracting low-energy X-rays. On the other hand, the primary target 20 and the X-ray transmission window 13 need to secure a certain distance L to ensure insulation, and therefore the distance to the secondary target 26 increases, and the primary X-ray 21 2 This is disadvantageous in increasing the irradiation efficiency to the next target 26.

  Therefore, if the energy of the characteristic X-ray 25 of the target secondary target 26 is low, it is effective to adopt the cathode grounding configuration as in the second embodiment.

  Next, FIG. 4 shows a third embodiment.

  In this embodiment, in the X-ray source 11 of the first embodiment, electron sources 16a and 16b that can be operated independently of the electron gun 14 and primary targets 20a and 20b made of different materials (elements) are used. It is composed. The electron beam 15a from one electron source 16a is irradiated to one primary target 20a, and the electron beam 15b from the other electron source 16b is irradiated to the other primary target 20b. Further, the acceleration energy of the electron sources 16a and 16b can be easily changed by a single drive power source 17.

  Furthermore, it is possible to obtain two or more types of characteristic X-rays 25 by combining a secondary target body 23 having different types of secondary targets 26 with the primary targets 20a and 20b.

  When the X-ray excitation method is used, it is effective to select primary X-rays 21a and 21b having energy capable of efficiently emitting characteristic X-rays 25 of the secondary target 26. Therefore, in order to obtain a target characteristic X-ray 25, when replacing a plurality of secondary targets 26, it is necessary to select primary targets 20a and 20b of elements most suitable for exciting each element. is there.

  An example of the optimal combination is titanium (Ti: characteristic X-ray Kα energy 4.5 keV) as a secondary target 26 and primary target 20a, 20b as chromium (Cr: characteristic X-ray Kα energy 5.4 keV), secondary The target 26 is molybdenum (Mo: characteristic X-ray Kα energy 17.5 keV), the primary target 20a, 20b is rhodium (Rh: characteristic X-ray Kα energy 20.2 keV), the secondary target 26 is gadolinium (Gd: characteristic X As the primary targets 20a and 20b for the line Kα energy 43 keV), a combination of tantalum (Ta: characteristic X-ray Kα energy 57.5 keV) or the like can be adopted.

  In addition, in the secondary target 26, an element having an atomic number of about 2 smaller than the primary target 20a, 20b gives the highest excitation efficiency, but if the primary target 20a, 20b having a smaller atomic number is also incorporated at the same time, Even when the secondary target 26 having an atomic number smaller than the optimum value is selected, the characteristic X-ray 25 can be emitted from the secondary target 26 with high excitation efficiency.

  As a result, characteristic X-rays 25 including a plurality of monochromatic energy components from high energy to low energy can be emitted, and a wide element analysis area can be taken.

  As described above, the X-ray source 11 capable of emitting a plurality of characteristic X-rays 25 from high energy to low energy by simply selecting the electron sources 16a and 16b of one electron gun 14 or replacing the secondary target 26 side. Can be provided.

  Next, FIG. 5 shows a fourth embodiment.

  In this embodiment, an X-ray transmission window 13 facing the electron gun 14 is formed at one end of the vacuum vessel, and a primary target 20 is formed on the inner surface of the X-ray transmission window 13 by coating. The thickness of the primary target 20 is assumed to be thicker than the range of accelerated electrons.

  A box-shaped secondary target body 23 covering the outer side of the X-ray transmission window 13 is detachably attached to one end surface of the vacuum vessel 12 where the X-ray transmission window 13 is provided.

  Then, the electron beam 15 generated by the electron gun 14 enters the primary target 20, and the primary X-ray 21 emitted from the primary target 20 is transmitted through the X-ray transmission window 13 into the secondary target body 23. . The primary X-rays 21 transmitted into the secondary target body 23 mainly enter the secondary target 26 on the facing surface 23 a of the secondary target body 23, and the characteristic X-rays 25 are emitted from the secondary target 26. Only the component of the characteristic X-ray 25 emitted from the surface of the secondary target 26 of the opposing surface 23a of the secondary target body 23 at a shallow angle passes through the characteristic X-ray extraction window 27, and the sheet is placed outside the secondary target body 23. Beam characteristic X-rays 25 are emitted.

  Thus, by integrating the X-ray transmission window 13 which is a vacuum partition and the primary target 20, the irradiation angle of the primary X-ray 21 to the secondary target 26 can be increased, and the primary X-ray is obtained. 21 utilization efficiency can be increased.

  Further, when the primary X-ray 21 that transmits through the primary target 20 is used, there is no shielding to the secondary target 26, and other constituent materials are excited and emitted by the primary X-ray 21. The configuration is such that emission of noise components is easily suppressed. Thereby, the structure from the primary target 20 to the characteristic X-ray extraction window 27 can be reduced in size, and the X-ray source 11 can be reduced in size.

  Also in this case, it is possible to provide the X-ray source 11 that can emit a plurality of characteristic X-rays 25 by simply replacing the secondary target 26 side, can be used efficiently, and can be miniaturized.

  Next, FIG. 6 shows a fifth embodiment.

  In this embodiment, in the X-ray source 11 of the fourth embodiment, electron sources 16a and 16b that can be operated independently of the electron gun 14 and primary targets 20a and 20b made of different materials (elements) are used. It is composed. The electron beam 15a from one electron source 16a is irradiated to one primary target 20a, and the electron beam 15b from the other electron source 16b is irradiated to the other primary target 20b. Further, the acceleration energy of the electron sources 16a and 16b can be easily changed by a single drive power source 17.

  Furthermore, it is possible to obtain two or more types of characteristic X-rays 25 by combining a secondary target body 23 having different types of secondary targets 26 with the primary targets 20a and 20b.

  In this way, it is possible to provide the X-ray source 11 capable of emitting a plurality of types of characteristic X-rays 25 from high energy to low energy simply by replacing the secondary target 26 side.

  Next, FIG. 7 shows a sixth embodiment.

  In this embodiment, in the X-ray source 11 of the fifth embodiment, the trajectories of the electron beams 15a and 15b emitted from the electron gun 14 are deflected to arbitrarily select one of a plurality of types of primary targets 20a and 20b. A deflecting electromagnet 32 is provided as an electron beam deflecting means 31 for entering any one of the above. In the case of deflecting electrons, an electric field may be used.

  Further, the acceleration energy of the electron gun 14 can be easily changed by operating the drive power source 17.

  Furthermore, it is possible to obtain two or more types of characteristic X-rays 25 by combining a secondary target body 23 having different types of secondary targets 26 with the primary targets 20a and 20b.

  In this way, multiple types of characteristic X-rays 25 can be emitted from high energy to low energy simply by selecting the electron sources 16a and 16b of one electron gun 14 or replacing the secondary target 26 side, thus increasing output. Alternatively, the X-ray source 11 that can be miniaturized can be provided.

  Next, FIG. 8 shows a fluorescent X-ray analyzer 61 using the X-ray source 11 of each of the above embodiments.

  The X-ray fluorescence analyzer 61 irradiates the sample 62 with the characteristic X-ray 25 in the form of a sheet beam emitted from the X-ray source 11, and the fluorescent X-ray 63 emitted from the surface element of the sample 62 is excited. This is a configuration in which elemental analysis is performed by the detector 65.

  For the purpose of surface contamination inspection of the semiconductor wafer as the sample 62, the characteristic X-rays 25 need to be incident on the semiconductor wafer surface at a constant angle as much as possible and at a very shallow angle of 0.1 ° or less. Therefore, for example, a sheet beam shape including a fan-shaped fan beam is used.

  The X-ray source 11 applied to the fluorescent X-ray analyzer 61 has its energy spectrum mainly composed of the characteristic X-rays 25 of the secondary target 26, thereby exciting the elements on the surface of the sample 62. By capturing the fluorescent X-rays 63 emitted, the elemental composition can be analyzed.

  At this time, the spectrum of the characteristic X-ray 25 to be excited is stored in advance in the analytical instrument, and if the relationship between the fluorescence signal / excitation intensity obtained thereby is grasped, the element on the surface of the sample 62 is determined from the fluorescence signal intensity. Quantitative analysis can be performed with high accuracy.

  As described above, the X-ray source 11 capable of efficiently emitting the characteristic X-ray 25 having the sheet beam shape can provide the high-resolution fluorescent X-ray analyzer 61.

It is explanatory drawing of the X-ray source which shows the 1st Embodiment of this invention. It is explanatory drawing of the X-ray source which shows the 2nd Embodiment of this invention. It is explanatory drawing explaining the influence of the grounding potential of an X-ray source, showing cathode grounding in (a) and anode grounding in (b). It is explanatory drawing of the X-ray source which shows the 3rd Embodiment of this invention. It is explanatory drawing of the X-ray source which shows the 4th Embodiment of this invention. It is explanatory drawing of the X-ray source which shows the 5th Embodiment of this invention. It is explanatory drawing of the X-ray source which shows the 6th Embodiment of this invention. It is explanatory drawing of the fluorescent-X-ray-analysis apparatus using the X-ray source of this invention. It is explanatory drawing of the conventional fluorescent X ray analyzer.

Explanation of symbols

11 X-ray source
12 Vacuum container
13 X-ray transmission window
15, 15a, 15b Electron beam
20, 20a, 20b Primary target
21, 21a, 21b Primary X-ray as X-ray
23 Secondary target body
25 Characteristic X-ray
26 Secondary target
27 Characteristic X-ray extraction window
31 Electron beam deflection means
61 X-ray fluorescence analyzer
62 samples
63 X-ray fluorescence
65 X-ray detector

Claims (7)

A vacuum vessel having an X-ray transmission window;
An electron gun that generates an electron beam in the vacuum vessel;
A primary target provided in the vacuum vessel and emitting an X-ray upon incidence of an electron beam generated by the electron gun;
It is provided in a box shape that is detachably attached to the outside of the X-ray transmission window of the vacuum vessel, and X-rays emitted from the primary target and transmitted through the X-ray extraction window are incident to generate characteristic X-rays. An X-ray source comprising: a secondary target to be emitted; and a secondary target body having a characteristic X-ray extraction window for emitting characteristic X-rays emitted from the secondary target to the outside. The X-ray source according to claim 1, wherein the electron gun side is at ground potential and the primary target side is at high voltage potential. The X-ray source according to claim 1, comprising a plurality of types of primary targets that emit a plurality of types of X-rays. The X-ray source according to any one of claims 1 to 3, wherein the primary target is coated on the X-ray transmission window so as to be thicker than an electron range. The X-ray source according to claim 3, wherein the electron gun includes a plurality of electron sources that generate an electron beam for each of a plurality of types of primary targets. An electron beam deflecting means for deflecting an orbit of an electron beam generated by one electron gun so as to be incident on an arbitrary primary target among a plurality of types of primary targets is provided. 3. The X-ray source according to 3. The X-ray source according to any one of claims 1 to 6, wherein the sample is irradiated with characteristic X-rays;
An X-ray fluorescence analyzer comprising: an X-ray detector for detecting fluorescent X-rays generated by the excitation of the element on the surface of the sample by irradiation with the characteristic X-rays.

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