TWI827060B - Total reflection fluorescence X-ray analysis device - Google Patents

Abstract

An object of the present invention is to provide a total reflection fluorescence X-ray analysis device with high analysis sensitivity and fast analysis speed. The total reflection fluorescence X-ray analysis device of the present invention has: size; a spectroscopic element, the effective width of which is greater than the focus of the electron beam in the aforementioned orthogonal direction, and has a surface curved along the aforementioned irradiation direction; and a plurality of detectors, which are arranged in a plurality of arrays along the aforementioned orthogonal direction, and measure the self-irradiation efficiency The intensity of the fluorescent X-ray emitted by the sample of the primary X-ray collected by the aforementioned spectroscopic element.

Description

Total reflection fluorescence X-ray analysis device

The invention relates to a total reflection fluorescence X-ray analysis device.

As a device for analyzing elements contained in a sample, a fluorescent X-ray analyzer is known. The fluorescent X-ray analysis device irradiates the sample with X-rays once and performs analysis based on the intensity and energy of the fluorescent X-rays emitted from the sample. In particular, in order to analyze trace contamination on the sample surface, a total reflection fluorescence X-ray analyzer is used that irradiates the sample surface with X-rays once at a total reflection critical angle or less.

In recent years, pollution management in the semiconductor industry has become more advanced, and in order to quickly determine the contamination of extremely small amounts of impurities, improvements in analysis sensitivity and analysis speed have been pursued. As one of the methods for improving the analysis sensitivity and analysis speed, there is a method of increasing the intensity of the primary X-ray irradiated onto the surface of the sample.

For example, the following Patent Document 1 discloses that primary X-rays emitted from a point light source are concentrated at an artificial multilayer film lattice having a concave surface, and the primary X-rays with high intensity of the collected light are irradiated to the sample.

Furthermore, the following Patent Documents 2 to 7 disclose that by using a plurality of detectors or a detector with a wide detection area to measure fluorescent X-rays generated from a specific area, the detectable amount per unit time can be improved. The intensity of the fluorescent X-rays emitted. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Laid-Open No. 6-82400 [Patent Document 2] Japanese Patent Application Publication No. 8-5584 [Patent Document 3] U.S. Patent No. 5742658 Specification [Patent Document 4] Japanese Patent Application Publication No. 2001-165875 [Patent Document 5] Japanese Patent Application Laid-Open No. 9-61382 [Patent Document 6] Japanese Patent Application Publication No. 11-40632 [Patent Document 7] Japanese Patent No. 2921910

[Problem to be solved by the invention]

The total intensity of fluorescent X-rays generated from the sample depends on the intensity of the primary X-ray irradiated to the sample and the detection area. Therefore, studies have been conducted to increase the amount of fluorescent X-rays detected by increasing the detection area as in Patent Documents 2 to 7. In addition, the analysis sensitivity and analysis speed can be further improved by increasing the intensity of the primary X-ray irradiated to the sample.

However, when the X-ray source is a point light source like the above-mentioned Patent Document 1, if the current flowing through the electron beam source, such as a filament, is increased, there is a risk of evaporation, deformation, and melting of the filament due to heat, which affects the life of the filament. become shorter. It is known that even if a cold cathode type electron source is used, if the current flowing through it is increased, the lifespan will be shortened. In addition, the target may be damaged due to the increase in current, and there is a risk of melting.

The present invention was made in view of the above-mentioned problems, and an object thereof is to provide a total reflection fluorescence X-ray analyzer with high analysis sensitivity and fast analysis speed. [Technical means to solve the problem]

The total reflection fluorescence X-ray analysis device of claim 1 is characterized by having: an X-ray source having an electron beam focus, the effective width of the electron beam focus in a direction parallel to the sample surface and orthogonal to the The size of the aforementioned X-ray irradiation direction; the spectroscopic element, the effective width of which is parallel to the aforementioned sample surface and orthogonal to the aforementioned X-ray irradiation direction is greater than the effective width of the aforementioned electron beam focus, and includes the sum of the aforementioned X-ray irradiation directions The sample surface has a curved cross section in a plane perpendicular to the surface; and a plurality of detectors are arranged toward the sample surface in a direction orthogonal to the X-ray irradiation direction, and measure the self-irradiation effect by collecting light through the spectroscopic element. The intensity of the fluorescent X-ray generated by the previous X-ray and the above-mentioned sample.

The total reflection fluorescence X-ray analysis device of claim 2 is the total reflection fluorescence X-ray analysis device of claim 1, wherein the X-ray irradiation width on the sample surface in a direction orthogonal to the X-ray irradiation direction is is more than 60 mm.

The total reflection fluorescence X-ray analysis device of claim 3 is the total reflection fluorescence X-ray analysis device of claim 1 or 2, wherein the direction of the aforementioned spectroscopy is parallel to the aforementioned sample surface and orthogonal to the aforementioned X-ray irradiation direction. The effective width of the component is more than 30 mm.

The total reflection fluorescence X-ray analysis device of claim 4 is the total reflection fluorescence X-ray analysis device of any one of claims 1 to 3, wherein the The effective width of the aforementioned electron beam focus is 15 mm or more.

The total reflection fluorescence X-ray analysis device of claim 5 is the total reflection fluorescence X-ray analysis device of any one of claims 1 to 4, wherein the total reflection fluorescence X-ray analysis device is parallel to the sample surface and orthogonal to the X-ray irradiation direction The cross section of the reflective surface of the aforementioned light splitting element is a straight line.

The total reflection fluorescence X-ray analysis device of claim 6 is the total reflection fluorescence X-ray analysis device of any one of claims 1 to 5, wherein the plurality of detectors include detectors with different characteristics.

The total reflection fluorescence X-ray analysis device of claim 7 is the total reflection fluorescence X-ray analysis device of claim 6, wherein the aforementioned characteristics are detection area, energy resolution, spatial resolution, or energy sensitivity.

The total reflection fluorescence X-ray analysis device of claim 8 is the total reflection fluorescence X-ray analysis device of any one of claims 1 to 7, wherein the plurality of detectors are relative to the sum of the X-ray irradiation directions. The aforementioned specimen surfaces are arranged symmetrically with respect to the vertical surfaces. [Effects of the invention]

According to the inventions of claims 1 to 8, a total reflection fluorescence X-ray analysis device with high analysis sensitivity and fast analysis speed can be realized.

As shown in FIG. 1 , the total reflection fluorescence X-ray analyzer 100 irradiates the surface of a sample 110 such as a silicon substrate with X-rays once at a total reflection critical angle or less. Then, the total reflection fluorescence X-ray analysis device 100 obtains a spectrum indicating the relationship between the intensity and energy of the emitted fluorescent X-rays. The total reflection fluorescence X-ray analyzer 100 analyzes elements contained in the sample 110 using this spectrum. Specifically, for example, the total reflection fluorescence X-ray analysis device 100 includes an X-ray source 102, a spectroscopic element 104, a sample stage 106, and a detection unit 108.

The X-ray source 102 generates one X-ray. Hereinafter, the direction orthogonal to the irradiation direction of the generated primary X-ray (center direction of irradiation) and parallel to the surface of the sample 110 is referred to as the y-axis direction. In addition, let the direction parallel to the surface of the sample 110 and orthogonal to the y-axis be the x-axis direction. Furthermore, let the direction perpendicular to the surface of the sample 110 be the z-axis direction. For example, as shown in FIG. 2 , the X-ray source 102 includes an electron beam source 202 , a target 204 , and a power supply 208 .

Specifically, for example, when the X-ray source 102 is a hot cathode type, the electron beam source 202 is a filament, and a negative voltage is applied from the power supply 208 to generate the electron beam 203 . A positive voltage is applied to the target 204 by a power supply 208, and the electron beam 203 generated from the electron beam source 202 is irradiated. From the electron beam focus 201 on the target 204 irradiated with the electron beam 203, primary X-ray 205 is generated. As the material of the target 204, a material that generates primary X-rays with high excitation efficiency is appropriately selected according to the energy of the absorption end of the measurement element. The filament and target 204 are disposed inside a vacuum-evacuated housing. The housing has an opening if necessary, and the opening is covered with a film made of a material that transmits primary X-rays. The film is formed of beryllium, for example. However, when the absorption of the window material becomes a problem due to the wavelength of the X-rays used, the X-ray source 102, the optical element 104 and the sample 110 can be placed in the same vacuum chamber, and the window material can be omitted. In the example shown in FIG. 2 , the primary X-ray 205 generated from the target 204 is extracted at an appropriate extraction angle and emitted in the direction in which the spectroscopic element 104 is arranged.

Here, the electron beam focus 201 on the target 204 generates X-rays in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction (ie, the y-axis direction). The effective width is larger than the size of the X-ray irradiation direction. Specifically, for example, when the electron beam source 202 is a filament, the tungsten filament is spirally wound with the y-axis direction as the central axis of the winding axis. The target 204 is formed such that the size of the x-axis and the y-axis are larger than the size of the filament, and the electron beam 203 generated from the electron beam source 202 is irradiated to an area with a length of, for example, 15 mm in the y-axis direction.

The effective width of the spectroscopic element 104 for splitting X-rays in the direction parallel to the sample surface and orthogonal to the X-ray irradiation direction (that is, the y-axis direction) is greater than the effective width of the electron beam focus 201, and has a curved shape along the irradiation direction. noodle. Specifically, description will be made using, for example, FIG. 3(a) and FIG. 3(b). FIG. 3(a) is a diagram for explaining the optical path of primary X-rays, and is a diagram viewed from the upper side of the sample 110 (that is, in the z-axis direction). FIG. 3(b) is a diagram for explaining the optical path of the primary X-ray, and is a diagram viewed from the side of the sample 110 (that is, in the y-axis direction).

As shown in FIGS. 3(a) and 3(b) , the spectroscopic element 104 is a concave curved crystal having a curved cross section in a plane perpendicular to the sample surface including the X-ray irradiation direction. The curved surface is a part of an ellipse on the xz plane. One focus of the ellipse is the X-ray source 102 and the other focus is the measurement position on the sample 110 . An artificial multi-layer film is formed on the curved surface, which only reflects X-rays of specific wavelengths through the interference of the multi-layer films. The spectroscopic element 104 may not be a multi-layer film, but may be a Johnson-type curved crystal or a logarithmic spiral curved crystal whose curved surface is a logarithmic spiral curve. Furthermore, in the example shown in FIG. 3(a) , the measurement position is an area having a certain length in the y-axis direction with the center of the disc-shaped substrate as the center.

In addition, the effective width of the spectroscopic element 104 in the direction parallel to the sample surface and orthogonal to the X-ray irradiation direction (ie, the y-axis direction) is larger than the effective width of the electron beam focus. Thereby, the component of the primary X-ray emitted from the X-ray source 102 that expands in the y-axis direction can be reflected by the spectroscopic element 104 and irradiated to the surface of the sample 110 . The length of the y-axis direction of the spectroscopic element is, for example, 40 mm. Furthermore, it is ideal that the effective width of the spectroscopic element in the direction parallel to the sample surface and orthogonal to the X-ray irradiation direction is 30 mm or more. Thereby, as shown in FIG. 3(a) , X-rays of sufficient intensity are irradiated over a wide range of the sample 110 . For example, it is ideal that the X-ray irradiation width in the direction orthogonal to the X-ray irradiation direction on the sample surface is 60 mm or more.

In fact, the length of the measurement area in the y-axis direction can be expanded to about 80 mm, and the total intensity of primary X-rays irradiated to the surface of the sample 110 can be increased. Previously, because the lengths of the electron beam focus 201 and the spectroscopic element 104 in the y-axis direction were short, the X-ray irradiation area on the sample surface in the y-axis direction was limited to near the center of the sample 110 . Therefore, on the surface of the sample, the area with X-rays is irradiated with sufficient intensity, for example, about 20 mm to 30 mm. As will be described later, according to this embodiment, it is possible to irradiate an area approximately three times wider with one X-ray while keeping the X-ray intensity unchanged compared to the conventional method.

Furthermore, the spectroscopic element 104 may also have a cylindrical shape in which the cross section of the reflection surface in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction (ie, the y-axis direction) becomes a straight line.

The sample table 106 places the sample 110 to be analyzed. Specifically, for example, the sample stage 106 places a silicon substrate used for manufacturing semiconductor products. Furthermore, the sample stage 106 moves the substrate so that the measurement position is located directly below the detector 302 . There is a risk that impurities such as Ni may adhere to silicon substrates in semiconductor factories where silicon substrates are manufactured or processed. The sample stage 106 moves the silicon substrate, thereby irradiating X-rays once to a plurality of positions on the silicon substrate. Thereby, the total reflection fluorescence X-ray analysis device 100 can analyze whether impurities are attached to the surface of the silicon substrate.

The detection unit 108 includes a detector 302 and a counter. The detector 302 is, for example, a semiconductor detector such as an SDD (Silicon Drift Detector) detector. A plurality of detectors 302 are opposed to the surface of the sample and arranged in a direction orthogonal to the irradiation direction, and measure fluorescent X-rays ( Fluorescent X-rays or scattered rays) intensity. Furthermore, the detector 302 outputs a pulse signal having a peak value corresponding to the measured energy of the fluorescent X-ray. Furthermore, in the example shown in Figure 3(a), the X-ray irradiation width in the direction orthogonal to the X-ray irradiation direction on the sample surface is 60 mm or more. Since the area irradiated with a certain X-ray intensity is long in the y-axis direction, three detectors 302 are arranged in an array along the y-axis direction. In this way, multiple locations can be detected at the same time. In the example shown in Figure 3(a), fluorescent X-rays from three locations can be detected at the same time, thereby greatly increasing the throughput of pollution analysis.

The counter counts the pulse signal output from the detector 302 corresponding to the peak value. Specifically, for example, the counter is a multi-channel analyzer, which counts the output pulse signal of the detector 302 for each channel corresponding to the energy, and outputs it as the intensity of the fluorescent X-ray. The detection unit 108 acquires the output of the counter as a spectrum.

The operations of the sample stage 106, the X-ray source 102, and the detection unit 108 are controlled by a control unit (not shown). Specifically, for example, the control unit is a personal computer. The control unit controls the operations of the sample stage 106, the X-ray source 102, and the detection unit 108 by sending and receiving instructions to and from each component. Furthermore, the control unit analyzes the sample 110 based on the spectrum output from the detection unit 108 .

As described above, according to this embodiment, primary X-rays are generated from a region having a certain length along the y-axis direction. Therefore, the total intensity of primary X-rays generated by the X-ray source 102 can be increased. Furthermore, as shown in FIG. 3(a) , by using the spectroscopic element 104 that generates X-rays from a certain length and has a wide width in the y-axis direction, primary X-rays of a certain intensity can be irradiated to a wide range on the sample. And the total intensity of X-rays irradiated onto the sample can be further increased. Furthermore, in FIG. 3(a) , the primary X-ray irradiated to a point on the sample 110 corresponding to the center of the field of view detected by each detector 302 is schematically shown, but in fact, it is irradiated to a point in the y-axis direction. It is a long continuous area.

In addition, the primary X-ray is emitted from a local area in the xz plane. That is, in the xz plane, the X-ray source 102 can be regarded as a point light source. Therefore, as shown in FIG. 3(b) , the components diverging in the xz plane of the primary X-ray can be collected by the spectroscopic element 104 having a curved surface in the irradiation direction. Thereby, the intensity of one X-ray per unit area irradiated to the surface of the sample 110 can be increased.

The higher the intensity of the primary X-ray irradiated to the sample 110, the higher the intensity of the fluorescent X-ray generated from the sample 110. According to this embodiment, by not only increasing the intensity of one X-ray per unit area irradiated to the surface of the sample 110 but also increasing the area on the sample irradiated with the increased intensity, it is possible to improve the analysis sensitivity and shorten the measurement time. .

Next, the effects of this embodiment will be described together with the experimental results. Sample 110 is a disc-shaped silicon substrate with Ni as a trace impurity attached to the center portion of the substrate. The substrate is arranged so that the center of the primary X-ray irradiation area is located at the center of the silicon substrate. The primary X-ray reflected by the spectroscopic element 104 is irradiated at an incident angle of 0.1 degrees with respect to the surface of the substrate. Figures 4 and 5 are diagrams showing the distribution of the net intensity of the Si-Kα line (Figure 4) and Ni-Kα line (Figure 5) measured under the measurement conditions. The circular line represents the outline of the 8-inch diameter silicon substrate. The primary X-ray is incident from the x-direction and centered on the x=0 line. Furthermore, the graph on the left side of Figure 4 shows the intensity distribution of the x=0 section of the Si-Kα line and the Ni-Kα line, and the graph on the upper side shows the intensity distribution of the y=0 section.

As shown in FIGS. 4 and 5 , by using the spectroscopic element 104 to concentrate primary X-rays into a narrow area in the x-axis direction, a higher intensity of fluorescent X-rays can be obtained. Furthermore, by using the X-ray source 102 that has a longer electron beam focus 201 in the y-axis direction because the electron beam source 202 is longer in the y-axis direction, a wider area can be obtained in the y-axis direction. High fluorescent X-ray intensity. Specifically, fluorescent X-rays having sufficient intensity for analysis are measured in an area of 30 mm in the x-axis direction and 80 mm in the y-axis direction, centered on the center of the substrate. Furthermore, fluorescent X-rays having sufficient intensity for analysis are appropriately set depending on the purpose of analysis and the elements contained in the sample 110 . Here, in order to analyze Ni, which is a trace impurity, a sufficient net intensity is set to 2300.

The present invention is not limited to the above-described embodiment, and various changes can be made. The configuration of the total reflection fluorescence X-ray analyzer 100 described above is an example and is not limited thereto. Replacement can be made if it is a structure that is substantially the same as the structure shown in the above-mentioned embodiment, a structure that exhibits the same function and effect, or a structure that achieves the same purpose.

For example, in the above-mentioned embodiment, the case where three detectors 302 are arranged along the y-axis direction has been described, but the layout of the plurality of detectors 302 is not limited to this. FIGS. 6(a) to 6(k) are diagrams showing variations in the layout of the detector 302 when viewed from the upper side of the sample 110 in the same manner as in FIG. 3(a) . Furthermore, each circle in FIG. 6(a) to (k) is the detection area of one detector 302. In addition, the left and right directions in the drawings of FIGS. 6(a) to (k) are the x-axis direction, and the up and down directions in the drawings are the y-axis direction.

Specifically, for example, as shown in FIGS. 6(a) to (c) , the number of detectors 302 arranged along the y-axis direction may be any one from 2 to 4. In addition, the number may be four or more.

In addition, as shown in FIGS. 6(d) to (f), the detectors 302 may be arranged in two rows in the x-axis direction. At this time, by arranging the detector 302 on the left row and the detector 302 on the right row by 1/2 in the y-axis direction in the figure, the gap between the detection areas can be reduced. Furthermore, the detectors 302 may be arranged in two or more rows along the x-axis direction.

In addition, the plurality of detectors 302 may include detectors 302 with different characteristics. Specifically, for example, the characteristic is detection area, energy resolution, spatial resolution, or energy sensitivity. As shown in Figure 6 (g) to (k), the plurality of detectors 302 may include detectors 302 (large circles in the figure) with large detection areas and high sensitivity, but low energy resolution and spatial resolution, and detection areas. The detector 302 is small and has low sensitivity but high energy resolution and spatial resolution (small circle in the figure). Furthermore, it may also include a detector with high energy sensitivity for high-energy X-rays and a detector with high energy sensitivity for low-energy X-rays.

In the example shown in FIG. 6(g) , the detector 302 with a large detection area is arranged in the center, and the detectors 302 with a small detection area are arranged adjacent to each other in the y-axis direction. In the example shown in FIG. 6(h) , the detector 302 with a large detection area is arranged in the center, and the detectors 302 with small detection areas are arranged at four oblique positions. In the example shown in FIG. 6(i) , three detectors 302 with a large detection area are arranged along the y-axis direction, and detectors with a small detection area are respectively arranged at four positions in the diagonal direction of the detector 302 arranged in the center. Detector 302. In the example shown in FIG. 6(j) , the detector 302 with a small detection area is arranged in the center, and the detectors 302 with a large detection area are arranged adjacent to each other in the y-axis direction. In the example shown in FIG. 6(k) , the detector 302 with a small detection area is arranged in the center, and the detectors 302 with a large detection area are arranged at four oblique positions.

As described above, it is desirable that the detector 302 is arranged so that the entire detection area formed by the plurality of detectors 302 covers an area in which fluorescent X-rays of sufficient intensity are emitted for analysis. For example, it is desirable that the plurality of detectors 302 be arranged in line symmetry with a line segment passing through the center of the spectroscopic element 104 and parallel to the irradiation direction being the axis of symmetry. According to the X-ray source 102 and the spectroscopic element 104 having the above-described configuration, one X-ray is irradiated to a region symmetrical along the symmetry axis of the sample 110 . Therefore, in the examples shown in FIGS. 6(a) to 6(k) (except FIG. 6(f) ), the entire detection area formed by a plurality of detectors 302 can effectively cover the entire area for analysis. An area that emits fluorescent X-rays of sufficient intensity.

100: Total reflection fluorescence X-ray analysis device 102:X-ray source 104:Spectral element 106: Sample table 108:Testing Department 110:Sample 201: Electron beam focus 202: Electron beam source 203:Electron beam 204:Target 205: 1 X-ray 208:Power supply 302:Detector x, y, z: axis direction

FIG. 1 is a diagram probabilistically showing the overall structure of the total reflection fluorescence X-ray analysis device. Figure 2 is a diagram schematically showing an X-ray source. Figure 3 is a diagram showing the path of one X-ray. Figure 4 is a diagram showing an example of experimental results. Figure 5 is a diagram showing an example of experimental results. Figures 6 (a) to (k) are diagrams showing the layout of the detector.

100: Total reflection fluorescence X-ray analysis device 102:X-ray source 104:Spectral element 106: Sample table 108:Testing Department 110:Sample x, y, z: axis direction

Claims (8)

A total reflection fluorescence X-ray analysis device, characterized by: An X-ray source has an electron beam focus, and the effective width of the electron beam focus in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction is greater than the size of the aforementioned X-ray irradiation direction; The effective width of the spectroscopic element in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction is greater than the effective width of the electron beam focus, and in a plane perpendicular to the sample surface including the X-ray irradiation direction, Has a curved cross-section; and A plurality of detectors are arranged facing the surface of the sample in a direction orthogonal to the irradiation direction of the X-ray, and measure fluorescent X-rays generated by the sample since the X-rays are collected by the spectroscopic element. intensity. The total reflection fluorescence X-ray analysis device of claim 1, wherein the X-ray irradiation width on the surface of the sample in a direction orthogonal to the X-ray irradiation direction is 60 mm or more. A total reflection fluorescence X-ray analysis device as claimed in claim 1 or 2, wherein the effective width of the spectroscopic element in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction is 30 mm or more. The total reflection fluorescence X-ray analysis device of claim 1 or 2, wherein the effective width of the electron beam focus in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction is 15 mm or more. The total reflection fluorescence X-ray analysis device of claim 1 or 2, wherein the section of the reflective surface of the spectroscopic element in a direction parallel to the sample surface and orthogonal to the X-ray irradiation direction is a straight line. The total reflection fluorescence X-ray analysis device of claim 1 or 2, wherein the plurality of detectors include detectors with different characteristics. Such as the total reflection fluorescence X-ray analysis device of claim 6, wherein the aforementioned characteristics are detection area, energy resolution, spatial resolution, or energy sensitivity. The total reflection fluorescence X-ray analysis device of claim 1 or 2, wherein the plurality of detectors are arranged symmetrically with respect to a plane perpendicular to the sample surface including the X-ray irradiation direction.