JP4738189B2 - X-ray source and fluorescent X-ray analyzer - Google Patents

Description

  The present invention relates to an X-ray source that emits characteristic X-rays and a fluorescent X-ray analyzer using the X-ray source.

  In a general X-ray source, braking X-rays and characteristic X-rays peculiar to a target are emitted by making electrons accelerated by a high voltage incident on a target that is an anode (see, for example, 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. 11 shows an example of a general configuration of a high-resolution X-ray fluorescence analyzer that utilizes the characteristic X-rays described above. 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 results in an increase in cost, which is a factor that strengthens restrictions on diffusion. For example, see Non-Patent Document 1. ).

FIG. 12 shows total reflection fluorescent X-ray analysis (TXRF), which has been used for the purpose of surface contamination inspection of a semiconductor wafer as a sample 6 in recent years. For example, a sheet beam shape including a fan-shaped fan beam is suitable because it needs to be incident on the surface at a constant angle as much as possible and at a very shallow angle of 0.1 ° or less.
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

  In a high-resolution X-ray fluorescence analyzer, in addition to being able to generate characteristic X-rays efficiently, the emitted X-ray spectrum should not contain unnecessary noise components as much as possible, and more Providing an X-ray source from which characteristic X-rays can be selected is the most important issue.

  In particular, there is a need for an X-ray source capable of obtaining low noise, that is, high monochromaticity, a sheet-like X-ray beam required for high-resolution total reflection fluorescent X-ray analysis that is remarkably popular in the semiconductor field.

  The present invention has been made in view of the above points, and can emit characteristic X-rays with high efficiency, can suppress the mixing of noise components into the emitted characteristic X-rays, and, for example, totally reflected fluorescence X It is an object of the present invention to provide an X-ray source and a fluorescent X-ray analyzer that can easily obtain characteristic X-rays having a sheet beam shape suitable for X-ray analysis.

  The X-ray source according to the present invention includes a vacuum container, an electron gun that generates an electron beam in the vacuum container, a wall section that defines the inside of the vacuum container, and an electron that is provided on the wall section and is generated by the electron gun. A partition part having an electron beam passage hole through which the beam passes, a primary target provided in the partition part and emitting an X-ray upon incidence of an electron beam that has passed through the electron beam passage hole, and provided in the partition part And a secondary target that emits characteristic X-rays when X-rays emitted from the primary target are incident, and characteristic X-rays that are provided in the vacuum vessel facing the partition and are emitted from the secondary target And an X-ray transmission window for emitting the light to the outside.

  In addition, an X-ray fluorescence analyzer of the present invention excites elements on the surface of the sample by the X-ray source according to any one of claims 1 to 7 that irradiates the sample with characteristic X-rays and the irradiation with the characteristic X-rays. And an X-ray detector for detecting fluorescent X-rays emitted.

  According to the present invention, an X-ray source capable of emitting characteristic X-rays with high efficiency by incorporating a primary target and a secondary target in a vacuum vessel, and mixing noise components into the emitted characteristic X-rays And a characteristic X-ray having a sheet beam shape suitable for, for example, total reflection fluorescent X-ray analysis can be easily obtained.

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

  1 to 3 show 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 on one end side of the vacuum container 12.

  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. A filament 16 is provided. The filament 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 box-shaped X-ray generation unit 21 is partitioned and formed on one end side in the vacuum vessel 12. In the X-ray generator 21, a partition portion 23 is formed by a wall portion 22 that partitions the inside of the vacuum vessel 12. The surface of the wall portion 22 facing the electron gun 14 is a slit-shaped electron beam passage hole through which the electron beam 15 can easily pass in correspondence with the shape of the line-shaped electron beam 15 generated by the electron gun 14. 24 is formed. An X-ray transmission window 13 is disposed on a surface intersecting with the surface where the electron beam passage hole 24 of the partition portion 23 is provided.

  A primary target 26 is provided on the inner surface of the partition 23 facing the electron beam passage hole 24, and a box-shaped secondary target 27 is formed on the inner surface of the partition 23 except for the primary target 26. Is provided.

  The primary target 26 receives the electron beam 15 that has passed through the electron beam passage hole 24 and emits continuous X-rays 28 as X-rays as primary X-rays toward the secondary target 27.

  The secondary target 27 receives continuous X-rays 28 emitted from the primary target 26 and emits characteristic X-rays 29 as K-rays which are secondary X-rays. The secondary target 27 is formed with a slit-shaped electron beam passage hole 30 that allows the electron beam 15 to easily pass in correspondence with the shape of the line-shaped electron beam 15 generated by the electron gun 14. An X-ray passage hole 31 that emits characteristic X-rays 29 is formed on a surface that intersects the surface on which the beam passage hole 30 is formed and that faces the X-ray transmission window 13. The X-ray passage hole 31 is formed in an elongated slit-like hole shape so that continuous X-rays 28 are not mixed and a characteristic X-ray 29 having a sheet beam shape can be taken out.

  The secondary target 27 has a narrow shape in the passing direction of the electron beam 15 and in the opposing direction of the primary target 26 and the secondary target 27, and the distance from the electron beam passing hole 30 to the primary target 26 is short. Shall. With this configuration, continuous X-rays 28 emitted from the primary target 26 can be incident on the secondary target 27 at a wide angle, and the excitation efficiency of the secondary target 27 can be increased.

  The primary target 26 is also formed in an elongated line shape in accordance with the shape of the electron beam 15 passing through the electron beam passage hole 30 of the secondary target 27, and a cathode equipped with a water cooling jacket 32 is used for high-intensity electron beam incidence. The primary target 26 is attached to the structure so that heat can be removed.

  The electron beam 15 emitted by applying a voltage from the drive power source 17 to the electron gun 14 passes through the electron beam passage hole 30 of the box-shaped secondary target 27 and is placed opposite to the primary beam. Incident on the target 26. At this time, by irradiating the secondary target 27 facing the continuous X-rays 28 emitted from the primary target 26, the secondary target 27 is excited and emits characteristic X-rays 29. Only the characteristic X-ray 29 component emitted from the surface of the secondary target 27 at a shallow angle passes through the X-ray passage hole 31 and is emitted to the outside through the X-ray transmission window 13.

  In this way, it is possible to provide the X-ray source 11 from which the characteristic X-ray 29 having a sheet beam shape in which mixing of noise components other than the characteristic X-ray 29 to be used is suppressed can be obtained.

  The box-shaped secondary target 27 does not need to use all the constituent materials as secondary target materials. For example, a general material such as stainless steel is used as a main constituent material, and continuous X-rays 28 are incident. It is possible to cope with the case where the foil of the secondary target material is pasted or coated only on the surface portion.

  Next, FIG. 4 shows a second embodiment.

  In this embodiment, in the X-ray source 11 of the first embodiment, the primary targets 26a, 26b, and 26c are configured using a plurality of materials (elements), and are simultaneously opposed to receive continuous X-rays 28. A plurality of materials (atoms) are used for the secondary targets 27a, 27b, and 27c.

  When using excitation by X-rays, primary targets 26a to 26c that emit continuous X-rays 28 that excite the secondary target 27 use an element that is about 2 larger in atomic number than the secondary targets 27a to 27c. Utilizing the characteristic X-rays 29 emitted thereby makes it possible to excite the secondary target 27 most efficiently.

  Therefore, in order to obtain the target characteristic X-ray 29, when using a plurality of secondary targets 27a to 27c, it is necessary to select primary targets 26a to 26c of elements that are optimal for exciting the respective elements. is there.

  As an example, secondary targets 27a to 27c are titanium (Ti: characteristic X-ray Kα energy 4.5 keV), and primary targets 26a to 26c are chromium (Cr: characteristic X-ray Kα energy 5.4 keV), and secondary target is molybdenum. Rhodium (Rh: characteristic X-ray Kα energy 20.2 keV) as primary target 26a-26c for (Mo: characteristic X-ray Kα energy 17.5 keV), gadolinium (Gd: characteristic X-ray Kα) as secondary targets 27a-27c As the primary targets 26a to 26c with an energy of 43 keV), a combination of tantalum (Ta: characteristic X-ray Kα energy 57.5 keV) or the like can be adopted, and as a result, three characteristic X-rays of Cr, Mo, and Gd are obtained. An X-ray beam containing (4.5 keV, 17.5 keV, 43 keV) 29 at the same time can be emitted.

  As a result, in the X-ray fluorescence analysis, when excited by single energy X-rays, the types of elements that can be excited thereby are limited, but a plurality of low energy to high energy regions are covered. X-rays containing a single-color energy component can be used, and a wide area of elemental analysis can be taken.

  In this way, it is possible to provide an X-ray source 11 that can emit characteristic X-rays 29 having a small noise component and including a plurality of characteristic X-ray spectra of energy.

  Next, FIG. 5 shows a third embodiment.

  In this embodiment, in the X-ray source 11 of the second embodiment, the operation of the X-ray source 11 including a combination of a plurality of primary targets 26a to 26c and a plurality of secondary targets 27a to 27c. Is about the method.

  When continuous X-rays 28 emitted from the primary targets 26a to 26c try to excite the secondary targets 27a to 27c selected as a combination most efficiently, the electron beam 15 irradiating the primary targets 26a to 26c is 1 It is important that the next target 26a to 26c has sufficient energy to emit continuous X-rays 28 sufficiently.

  In general, when excited by an electron beam 15 having an energy 2 to 3 times the K-ray energy of the primary targets 26a to 26c, continuous X-rays 28 of the primary targets 26a to 26c can be emitted most efficiently. As a result, the characteristic X-rays 29 of the secondary targets 27a to 27c are also emitted most efficiently.

  Conversely, if the continuous X-rays 28 from the primary targets 26a to 26c do not reach the K-shell absorption edge energy of the secondary targets 27a to 27c, the characteristic X-rays 29 are emitted from the secondary targets 27a to 27c. become unable.

  By utilizing such characteristics, an operation method is possible in which the acceleration voltage of the electron beam 15, that is, the energy of the electron beam 15, is adjusted in accordance with the energy of the characteristic X-ray 29 to be selected.

  FIGS. 5A, 5B, 5C, and 5D show a method for controlling the spectral distribution of the characteristic X-rays 29 to be emitted. When the power supply voltage is increased and excitation is performed with a high-energy electron beam 15, the primary targets 26a to 26c having a high atomic number are excited most efficiently as shown in the target D and the secondary target 27a. The intensity of the characteristic X-ray 29 emitted from .about.27c can be increased. Conversely, as shown in the target A, the continuous X-ray 28 emitted from the primary targets 26a to 26c having a low atomic number is Since the intensity is lowered, the intensity of the characteristic X-ray 29 from the combined secondary targets 27a to 27c is lowered.

  By reducing the power supply voltage, the spectral intensity of the characteristic X-ray 29 on the high energy side decreases as shown in targets D and C, and the low energy side as shown in targets C and B. The spectral intensity of the characteristic X-ray 29 increases. As the power supply voltage continues to decrease, the spectrum on the high energy side disappears as shown in targets D and C, and the X-ray spectrum only on the low energy side is emitted as shown in targets B and A. be able to.

  In X-ray fluorescence analysis, by controlling the distribution of such X-ray spectra, the X-ray fluorescence signals from samples containing from low atomic number elements to high atomic number elements are discriminated, and accurate This is effective for obtaining analysis results.

  As described above, the X-ray source 11 having a small noise component and capable of emitting the characteristic X-ray 29 including the characteristic X-ray spectra of a plurality of energies can adjust the spectrum distribution of the characteristic X-ray 29 to be emitted. Source 11 can be provided.

  Next, FIGS. 6 and 7 show a fourth embodiment.

  In the X-ray source 11 of the second embodiment, characteristic X-rays 29 from a plurality of primary targets 26a to 26c and secondary targets 27a to 27c can be emitted simultaneously. Since the distributed number of primary targets 26a to 26c is irradiated, it is disadvantageous in increasing the intensity of each characteristic X-ray 29.

  In the fourth embodiment, a plurality of X-ray generation units 21a to 21d, which are a plurality of sets of combinations of primary targets 26a to 26d and secondary targets 27a to 27d, are used and rotated by a rotation mechanism 41. To be installed on the same circumference of the turntable 42 to be operated. It is possible to change the characteristic X-ray 29 to be emitted by selecting an arbitrary X-ray generator 21a to 21d by the rotating mechanism 41 and moving it to the electron beam incident position where the electron beam 15 is incident. It is.

  In addition, the vacuum vessel 12 is provided with a target exchange port 43 that can exchange the X-ray generators 21a to 21d, and a vacuum pump 44 that exhausts the inside of the vacuum vessel 12. For this reason, even when the required X-ray energy changes, the X-ray generation units 21a to 21d can be replaced and used.

  By adopting this configuration, the emitted characteristic X-rays 29 can be selected and used in order. In the fluorescent X-ray analysis, performing the analysis by irradiating the characteristic X-rays 29 one by one in this way is effective in accurately identifying the element in the sample.

  As described above, it is possible to provide the X-ray source 11 that can arbitrarily select and extract a plurality of characteristic X-rays 29 having a low noise component and high intensity.

  Next, FIG. 8 shows a fifth embodiment.

  In this embodiment, in the X-ray source 11 of the second embodiment, the electrons in the electron beam passage hole 24 in the wall portion 22 of the partition 23 that is the anode and the electrons in the electron beam passage holes 30 in the secondary targets 27a to 27c. The deflecting magnet 52 of the electron beam deflecting means 51 is installed upstream of the beam passing direction.

  In this configuration, when an electromagnet is applied as the deflecting magnet 52, the trajectory of the electron beam 15 can be changed to an electron beam 15a, an electron beam 15b, and an electron beam 15c by controlling the magnetic field strength. Different primary targets 26a to 26c can be irradiated.

  When a permanent magnet is applied as the deflecting magnet 52, the trajectory can be changed similarly to the electron beams 15a to 15c by changing the energy of the passing electron beam 15.

  When the voltage of the drive power supply 17 is lowered and the low energy electron beam 15 is used, the same primary magnetic field intensity is set as the electron beam 15c, and the target primary target 26c is installed at the end thereof. Similarly, with respect to the high energy electron beam 15, the degree of deflection of the orbit becomes small as in the case of the electron beam 15b and the electron beam 15a, and the primary targets 26b and 26a are installed at the respective ends. By adopting such a configuration, it is possible to irradiate primary targets having different electron beams according to the voltage of the drive power supply 17, so that the intensity is higher than the configuration of the second embodiment in which several types of primary targets are irradiated simultaneously. High continuous X-rays 28 can be emitted. Therefore, the distribution of the X-ray spectrum obtained by controlling the voltage shown in the third embodiment can be further emphasized.

  In this way, it is possible to provide the X-ray source 11 that has a small noise component and can be extracted while controlling the spectral distribution including the plurality of characteristic X-rays 29 by the voltage.

  Next, FIG. 9 shows a sixth embodiment.

  In this embodiment, in the configuration of the X-ray source 11 of the fifth embodiment, the X-ray generators 21a to 21a, which are independent units for the primary targets 26a to 26c and the secondary targets 27a to 27c one by one. The structure is divided into 21c. The electron beam 15 has its trajectory bent by the deflecting magnet 52 and is incident on the primary targets 26a to 26c of the arbitrary X-ray generators 21a to 21c.

  For example, when the energy of the electron beam 15a and the magnetic field strength of the deflecting magnet 52 are set so that the electron beam 15a is incident on the primary target 26a of the X-ray generator 21a, the primary target of the X-ray generator 21a is set. The continuous X-ray 28 incident on 26a excites the independent box-shaped secondary target 27a, and does not enter / excite the secondary targets 27b and 27c of the other X-ray generation units 21b and 21c. As a result, when the characteristic X-ray 29 is emitted from any one of the X-ray generators 21a to 21c, the other characteristic X-rays 29 are not emitted and the single characteristic X-ray 29 is emitted. It becomes possible to use only.

  Therefore, in the fluorescent X-ray analysis, the characteristic X-rays 29 from low energy to high energy can be irradiated and excited in order, so that the elements in the sample can be easily identified.

  As described above, it is possible to provide the X-ray source 11 which has a small noise component and can arbitrarily take out a plurality of characteristic X-rays 29 one by one by controlling the voltage and the magnetic field strength.

  Next, FIG. 10 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 a characteristic X-ray 29 having a sheet beam shape 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 29 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 energy spectrum of the X-ray source 11 applied to the fluorescent X-ray analyzer 61 is mainly composed of the characteristic X-rays 29 of the secondary targets 27 and 27a to 27d. It is possible to analyze the elemental composition by capturing fluorescent X-rays 63 emitted when the element is excited.

  At this time, the spectrum of the characteristic X-ray 29 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 29 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 explaining the relationship between the electron gun of an X-ray source same as the above, and an X-ray generation part. It is explanatory drawing explaining the relationship between an electron gun and an X-ray generation part seeing from a 90-degree different direction with respect to FIG. 2 of an X-ray source same as the above. It is explanatory drawing of the X-ray source which shows the 2nd Embodiment of this invention. FIG. 9 is an explanatory diagram showing the relationship between the energy and intensity of an electron beam according to the third embodiment of the present invention, as shown in (a) to (d). It is explanatory drawing of the X-ray source which shows the 4th Embodiment of this invention. It is explanatory drawing of the target of X-ray source same as the above. 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. It is explanatory drawing of the conventional total reflection fluorescent-X-ray-analysis method.

Explanation of symbols

11 X-ray source
12 Vacuum container
13 X-ray transmission window
14 electron gun
15, 15a ~ 15d Electron beam
21a-21d X-ray generator
22 Wall
23 compartment
24 Electron beam passage hole
26, 26a-26d Primary target
27, 27a-27d Secondary target
28 Continuous X-ray as X-ray
29 Characteristic X-ray
30 Electron beam passage hole
31 X-ray passage hole
51 Electron beam deflection means
61 X-ray fluorescence analyzer
62 samples

Claims (8)

A vacuum vessel;
An electron gun for generating an electron beam in the vacuum vessel;
A wall section partitioning the inside of the vacuum vessel, and a partition section provided on the wall section and having an electron beam passage hole through which an electron beam generated by the electron gun passes,
A primary target that is provided in the partition and that emits an X-ray upon incidence of an electron beam that has passed through the electron beam passage hole;
A secondary target that is provided in the partition and that emits characteristic X-rays upon incidence of X-rays emitted from the primary target;
An X-ray source, comprising: an X-ray transmission window that is provided in a vacuum vessel facing the partition and that emits characteristic X-rays emitted from the secondary target to the outside. The secondary target has a box shape and is provided with an electron beam passage hole through which an electron beam passes, and an X-ray passage hole through which characteristic X-rays are emitted in a sheet beam shape. Item 2. The X-ray source according to Item 1. 3. The X-ray according to claim 1, wherein a plurality of primary targets and secondary targets are provided using different kinds of materials so that characteristic X-rays having a plurality of spectral distributions can be emitted. source. 4. The X-ray source according to claim 3, wherein the spectral distribution of characteristic X-rays emitted from the secondary target is controlled by adjusting an acceleration voltage of an electron beam generated by the electron gun. An electron beam that includes a plurality of X-ray generation units in which a plurality of primary targets and a plurality of secondary targets using different types of materials are combined, and an electron beam is incident on the plurality of X-ray generation units from the electron gun. The X-ray source according to any one of claims 1 to 3, wherein the X-ray source is movable with respect to an incident position, and characteristic X-rays are emitted from an X-ray generation unit disposed at the electron beam incident position. The X-ray according to claim 3, further comprising electron beam deflecting means for deflecting an electron beam generated by the electron gun so as to be incident on an arbitrary primary target among the plurality of primary targets. source. A plurality of X-ray generators comprising a combination of a plurality of primary targets and a plurality of secondary targets using different types of materials;
The electron beam deflecting means for deflecting an electron beam generated by the electron gun so as to be incident on an arbitrary X-ray generation unit among the plurality of X-ray generation units is provided. X-ray source. The X-ray source according to claim 1, which irradiates the sample with characteristic X-rays;
An X-ray fluorescence analyzer comprising: an X-ray detector that detects fluorescent X-rays generated by excitation of elements on the surface of the sample by irradiation with the characteristic X-rays.

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