Thickness measuring method, x-ray analysis device, information processing device, and computer program

Abstract

Provided are a thickness measuring method, an X-ray analysis device, an information processing device, and a computer program that can measure the thicknesses of more multilayer samples as compared to conventional means.　This thickness measuring method comprises: irradiating a sample including a first layer and a second layer which are laminated, with X-rays such that the X-rays transmit through the first layer and the second layer in the stated order; detecting fluorescent X-rays generated from the first layer; detecting transmitting X-rays that have transmitted through the sample; identifying the density of the first layer and the absorption coefficient of X-rays at the first layer through elementary analysis based on the fluorescent X-rays; and calculating the thickness of the first layer on the basis of the absorption coefficient and the density, and the intensities of the transmitting X-rays at two different energies.

Description

Thickness measurement method, X-ray analysis device, information processing device, and computer program

[0001] The present invention relates to a thickness measurement method for measuring the thickness of a specific layer included in a multi-layer sample, an X-ray analysis apparatus, an information processing apparatus, and a computer program.

[0002] It is sometimes desirable to measure the thickness of each layer contained in a multilayer sample. For example, it is sometimes desirable to measure the thickness of a coating covering a substrate. One method for measuring the thickness of each layer of a multilayer sample involves irradiating the multilayer sample with X-rays, detecting fluorescent X-rays emitted from the multilayer sample, and measuring the thickness of each layer based on the fluorescent X-rays. Another method involves detecting transmitted X-rays that have passed through the multilayer sample and measuring the thickness of each layer based on the transmitted X-rays. Patent Document 1 discloses a technique for measuring the thickness of a sample based on transmitted X-rays.

[0003] Japanese Patent Application Publication No. 11-287643

[0004] In thickness measurement methods based on fluorescent X-rays, the detected intensity of fluorescent X-rays generated from areas far from the surface is low, so there is a limit to the thickness that can be measured. Information about transmitted X-rays that have passed through a multilayer sample is a superposition of information about multiple layers. Therefore, in thickness measurement methods based on transmitted X-rays, the composition of each layer must be known. As such, conventional methods are limited in the samples whose thickness can be measured. The present invention has been made in consideration of these circumstances, and its purpose is to provide a thickness measurement method, an X-ray analysis apparatus, an information processing apparatus, and a computer program that can measure the thickness of more multilayer samples than conventional methods.

[0005] A thickness measurement method according to one aspect of the present invention includes irradiating a sample including a stacked first layer and a second layer with X-rays so that the X-rays penetrate the first layer and then the second layer, detecting fluorescent X-rays generated from the first layer, detecting transmitted X-rays that have passed through the sample, identifying an absorption coefficient of the X-rays in the first layer and a density of the first layer by elemental analysis based on the fluorescent X-rays, and calculating a thickness of the first layer based on the intensities of the transmitted X-rays at two different energies, the absorption coefficient, and the density.

[0006] In one aspect of the present invention, a sample including a stacked first layer and a second layer is irradiated with X-rays, fluorescent X-rays and transmitted X-rays are detected, and the X-ray absorption coefficient and density of the first layer are identified based on the fluorescent X-rays. Furthermore, the thickness of the first layer is calculated based on the intensities of the transmitted X-rays at two energies and the X-ray absorption coefficient and density of the first layer. By utilizing the detection results of both the fluorescent X-rays and the transmitted X-rays, it becomes possible to measure the thickness of the first layer for samples that are different from conventional methods. By calculating the thickness of the first layer using the characteristics of the first layer analyzed based on the detection results of the fluorescent X-rays, it becomes possible to measure the thickness of the first layer even for samples whose composition is unknown.

[0007] In a thickness measurement method according to one aspect of the present invention, the difference between the two energies is within a predetermined range.

[0008] In one aspect of the present invention, the intensities of transmitted X-rays at two energies are used to calculate the thickness of the first layer, and the two energies are specified so that the difference between the two energies falls within a predetermined range. Because the difference between the two energies is small, the intensities of the X-rays irradiated to the sample at each energy become approximately the same, and the equation for calculating the thickness of the first layer can be approximated so that the intensity ratio of the two energies of the X-rays irradiated to the sample, which is included in the equation, can be omitted.

[0009] In a thickness measurement method according to one aspect of the present invention, an absorption edge of an element contained in the second layer is not included in an energy range between the two energies.

[0010] In one embodiment of the present invention, the difference between the two energies is small, and the position of the absorption edge of the element contained in the second layer is not included in the energy range between the two energies. Therefore, the X-ray absorption coefficients in the second layer are approximately the same. The formula for calculating the thickness of the first layer can be approximated so as to omit the term obtained by multiplying the difference between the X-ray absorption coefficients of the two energies in the second layer by the density and thickness of the second layer. By using the approximated formula, it is possible to calculate the thickness of the first layer even if the composition or thickness of the second layer is unknown.

[0011] A thickness measurement method according to one aspect of the present invention is characterized in that the two energies are identified by elemental analysis based on the fluorescent X-rays so that an absorption edge of an element contained in the first layer is included in an energy range between the two energies.

[0012] In one aspect of the present invention, the energy range between the two energies includes the position of the absorption edge of the element contained in the first layer. Therefore, the difference in the intensities of transmitted X-rays at the two energies becomes large, and the difference in the absorption coefficients of X-rays at the two energies in the first layer also becomes large. The equation for calculating the thickness of the first layer includes the ratio between the logarithm of the ratio of the intensities of transmitted X-rays at the two energies and the difference in the absorption coefficients of X-rays at the two energies in the first layer. The calculation result of the equation is not inaccurate, and the thickness of the first layer can be calculated accurately.

[0013] An X-ray analysis apparatus according to one aspect of the present invention includes an irradiation unit that irradiates a sample including stacked first and second layers with X-rays so that the X-rays penetrate the first layer and then the second layer; an X-ray fluorescence detector that detects fluorescent X-rays generated from the first layer; a transmission X-ray detector that detects transmitted X-rays that have transmitted through the sample; and an analysis unit, wherein the analysis unit identifies the X-ray absorption coefficient of the first layer and the density of the first layer by elemental analysis based on the fluorescent X-rays, and calculates the thickness of the first layer based on the intensities of the transmitted X-rays at two different energies, the absorption coefficient, and the density.

[0014] In one aspect of the present invention, an X-ray analysis device irradiates X-rays onto a sample including a stacked first layer and a second layer, detects fluorescent X-rays and transmitted X-rays, and identifies the X-ray absorption coefficient and density of the first layer through elemental analysis based on the fluorescent X-rays. The X-ray analysis device also calculates the thickness of the first layer based on the intensities of the transmitted X-rays at two energies, the X-ray absorption coefficient of the first layer, and the density of the first layer. By calculating the thickness of the first layer using the characteristics of the first layer analyzed based on the results of the fluorescent X-ray detection, it becomes possible to measure the thickness of the first layer even for samples whose composition is unknown.

[0015] In one embodiment of the X-ray analysis apparatus of the present invention, the analysis unit calculates the thickness of the first layer by elemental analysis based on the fluorescent X-rays, without using the detection results of the transmitted X-rays.

[0016] In one aspect of the present invention, the X-ray analysis device can measure the thickness of a first layer contained in a sample based on the detection results of only fluorescent X-rays, without using the detection results of transmitted X-rays. When the thickness of the first layer is relatively small, the X-ray analysis device can simply measure the thickness of the first layer based on the detection results of only fluorescent X-rays. When the thickness of the first layer is relatively large, the X-ray analysis device can measure the thickness of the first layer by using the detection results of both fluorescent X-rays and transmitted X-rays.

[0017] An information processing device according to one aspect of the present invention is characterized by comprising: an acquisition unit that acquires detection results of fluorescent X-rays generated from the first layer and detection results of transmitted X-rays that have passed through the sample by irradiating a sample including stacked first and second layers with X-rays so that the X-rays pass through the first layer and the second layer in that order; an identification unit that identifies the absorption coefficient of the X-rays in the first layer and the density of the first layer by elemental analysis based on the detection results of the fluorescent X-rays; and a calculation unit that calculates the thickness of the first layer based on the intensities of the transmitted X-rays at two different energies, the absorption coefficient, and the density.

[0018] A computer program according to one aspect of the present invention causes a computer to execute a process of: irradiating a sample including stacked first and second layers with X-rays so that the X-rays penetrate the first layer and the second layer in that order; identifying an absorption coefficient of the X-rays in the first layer and a density of the first layer by performing elemental analysis based on a detection result of fluorescent X-rays generated from the first layer; and calculating a thickness of the first layer based on the intensities of the transmitted X-rays at two different energies included in a detection result of the transmitted X-rays that have passed through the sample, the absorption coefficient, and the density.

[0019] In one aspect of the present invention, an X-ray absorption coefficient and a density of the first layer are identified by information processing based on fluorescent X-rays detected by irradiating X-rays onto a sample including a stacked first layer and a second layer. Furthermore, a thickness of the first layer is calculated by information processing based on the intensities of the detected transmitted X-rays at two energies and the X-ray absorption coefficient and the density of the first layer. By calculating the thickness of the first layer using the characteristics of the first layer analyzed based on the results of fluorescent X-ray detection, it becomes possible to measure the thickness of the first layer even for samples whose composition is unknown.

[0020] The present invention makes it possible to measure a larger thickness than conventional methods, and also makes it possible to measure the thickness of the first layer even in samples where the composition of the first layer is unknown. Therefore, the present invention has excellent effects, such as making it possible to measure the thickness of the first layer contained in more multilayer samples than conventional methods.

[0021] FIG. 1 is a block diagram showing an example of the functional configuration of an X-ray analysis apparatus; FIG. 2 is a block diagram showing an example of the internal configuration of an analysis unit; FIG. 3 is a schematic cross-sectional view of a sample; FIG. 4 is a graph showing an example of a spectrum of transmitted X-rays; FIG. 5 is a flowchart showing an example of a processing procedure for measuring the thickness of a first layer performed by an X-ray analysis apparatus; and FIG. 6 is a flowchart showing an example of a processing procedure for measuring the thickness of a first layer based on fluorescent X-rays performed by an X-ray analysis apparatus according to a second embodiment.

[0022] The present invention will be described in detail below with reference to the drawings illustrating embodiments. <Embodiment 1> Fig. 1 is a block diagram showing an example of the functional configuration of an X-ray analysis apparatus 100. The X-ray analysis apparatus 100 includes an irradiation unit 21 that irradiates a sample 3 with X-rays, an X-ray fluorescence detector 22 that detects fluorescent X-rays generated from the sample 3 irradiated with X-rays, and a transmission X-ray detector 23 that detects transmitted X-rays that have passed through the sample 3. The sample 3 is a multilayer sample including multiple stacked layers. The X-ray analysis apparatus 100 executes a thickness measurement method for measuring the thicknesses of the layers included in the sample 3. The irradiation unit 21 includes an X-ray source that generates X-rays. The X-ray source is, for example, an X-ray tube. In Fig. 1, arrows indicate the X-rays, fluorescent X-rays, and transmitted X-rays irradiated to the sample 3.

[0023] The X-ray fluorescence detector 22 and the transmission X-ray detector 23 are radiation detectors having radiation detection elements made of semiconductors. For example, the X-ray fluorescence detector 22 and the transmission X-ray detector 23 are silicon drift detectors (SDDs). The X-ray fluorescence detector 22 is disposed so as to face the surface of the sample 3 that is irradiated with X-rays. When X-rays are irradiated onto the sample 3 from the irradiation unit 21, fluorescent X-rays are generated in the sample 3. The fluorescent X-rays are emitted from the surface of the sample 3 and enter the X-ray fluorescence detector 22. The X-ray fluorescence detector 22 detects the incident fluorescent X-rays and outputs a signal with an intensity corresponding to the energy of the fluorescent X-rays.

[0024] The transmission X-ray detector 23 is disposed at a position facing the irradiation unit 21. With the sample 3 disposed between the irradiation unit 21 and the transmission X-ray detector 23, X-rays are irradiated from the irradiation unit 21 to the sample 3. A portion of the X-rays irradiated from the irradiation unit 21 to the sample 3 are transmitted through the sample 3. The X-rays that have transmitted through the sample 3 are called transmitted X-rays. The transmitted X-rays are incident on the transmission X-ray detector 23. The transmission X-ray detector 23 detects the incident transmitted X-rays and outputs a signal with an intensity corresponding to the energy of the transmitted X-rays.

[0025] A first signal processing unit 24 is connected to the fluorescent X-ray detector 22, and a second signal processing unit 25 is connected to the transmission X-ray detector 23. The first signal processing unit 24 and the second signal processing unit 25 are connected to the analysis unit 1. The analysis unit 1 is configured using a computer. A display unit 27 such as a liquid crystal display or an EL display (Electroluminescent Display) is connected to the analysis unit 1. The irradiation unit 21, the first signal processing unit 24, the second signal processing unit 25, and the analysis unit 1 are connected to a control unit 26.

[0026] The control unit 26 controls the operations of the irradiation unit 21, the first signal processing unit 24, the second signal processing unit 25, and the analysis unit 1. The control unit 26 is configured using a computer including a calculation unit that executes calculations to control each unit. The control unit 26 may be configured to receive operations from a user and control each unit of the X-ray analysis apparatus 100 in accordance with the received operations. The control unit 26 and the analysis unit 1 may be configured integrally.

[0027] The X-ray fluorescence detector 22 outputs a signal having an intensity corresponding to the energy of the fluorescent X-rays, and the first signal processing unit 24 receives the signal output by the X-ray fluorescence detector 22. The first signal processing unit 24 detects the intensity of the received signal, thereby detecting a signal value corresponding to the energy of the fluorescent X-rays detected by the X-ray fluorescence detector 22. The first signal processing unit 24 counts the signals for each signal value, and outputs data indicating the relationship between the signal value and the count number to the analysis unit 1.

[0028] The transmission X-ray detector 23 outputs a signal having an intensity corresponding to the energy of the transmitted X-ray, and the second signal processing unit 25 receives the signal output by the transmission X-ray detector 23. The second signal processing unit 25 detects the intensity of the received signal to detect a signal value corresponding to the energy of the transmitted X-ray detected by the transmission X-ray detector 23. The second signal processing unit 25 counts the signals for each signal value and outputs data indicating the relationship between the signal value and the count number to the analysis unit 1.

[0029] The analysis unit 1 receives data indicating the relationship between the signal value and the count number output by the first signal processing unit 24. The analysis unit 1 generates a spectrum of the fluorescent X-rays detected by the fluorescent X-ray detector 22 based on the data from the first signal processing unit 24. The signal value corresponds to the energy of the fluorescent X-rays, and the count number corresponds to the number of times the fluorescent X-rays are detected, i.e., the intensity of the fluorescent X-rays. Therefore, a spectrum of the fluorescent X-rays indicating the relationship between the energy and intensity of the fluorescent X-rays can be obtained from the relationship between the signal value and the count number.

[0030] The analysis unit 1 also receives data indicating the relationship between the signal value and the count number output by the second signal processing unit 25. The analysis unit 1 generates a spectrum of the transmitted X-rays detected by the transmitted X-ray detector 23 based on the data from the second signal processing unit 25. The signal value corresponds to the energy of the transmitted X-rays, and the count number corresponds to the number of times the transmitted X-rays are detected, i.e., the intensity of the transmitted X-rays. Therefore, the spectrum of the transmitted X-rays indicating the relationship between the energy and intensity of the transmitted X-rays can be obtained from the relationship between the signal value and the count number.

[0031] The process of counting the signals output by the X-ray fluorescence detector 22 and the X-ray transmission detector 23 by signal value may be performed by the analysis unit 1, rather than by the first signal processing unit 24 and the second signal processing unit 25. The generation of the fluorescent X-ray spectrum may be performed by the first signal processing unit 24, and the generation of the transmitted X-ray spectrum may be performed by the second signal processing unit 25. The analysis unit 1 stores spectral data representing the fluorescent X-ray spectrum and spectral data representing the transmitted X-ray spectrum. The display unit 27 displays the spectrum of the fluorescent X-ray or the transmitted X-ray. The user can check the spectrum of the fluorescent X-ray from the sample 3 or the spectrum of the transmitted X-ray that has passed through the sample 3. The analysis unit 1 also performs information processing based on the spectra of the fluorescent X-ray and the transmitted X-ray. More specifically, the analysis unit 1 performs information processing to measure the thickness of layers included in the sample 3. The analysis unit 1 corresponds to an information processing device that performs information processing to measure the thickness of layers included in the sample 3.

[0032] FIG. 2 is a block diagram showing an example of the internal configuration of the analysis unit 1. The analysis unit 1 is configured using a computer such as a personal computer. The analysis unit 1 includes a calculation unit 11, a memory 12, a reading unit 13, a storage unit 14, and an operation unit 15. The calculation unit 11 is configured using, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a multi-core CPU. The calculation unit 11 may also be configured using a quantum computer. The memory 12 stores temporary data generated during calculation. The memory 12 is, for example, a RAM (Random Access Memory). The reading unit 13 reads information from a recording medium 10 such as an optical disk or a portable memory. The storage unit 14 is nonvolatile, for example, a hard disk or nonvolatile semiconductor memory. The operation unit 15 accepts input of information such as text by accepting operations from a user. The operation unit 15 is, for example, a touch panel, a keyboard, or a pointing device. The user operates the operation unit 15 to input various instructions to the analysis unit 1. The analysis unit 1 accepts the instructions input using the operation unit 15.

[0033] The calculation unit 11 causes the reading unit 13 to read the computer program 141 recorded on the recording medium 10, and stores the read computer program 141 in the storage unit 14. The calculation unit 11 executes the processing required for the analysis unit 1 in accordance with the computer program 141. The computer program 141 may be downloaded from outside the analysis unit 1. Alternatively, the computer program 141 may be pre-stored in the analysis unit 1. In these cases, the analysis unit 1 does not need to include the reading unit 13. The analysis unit 1 may be composed of multiple computers.

[0034] The analysis unit 1 is connected to a display unit 27, a first signal processing unit 24, a second signal processing unit 25, and a control unit 26. The display unit 27 displays an image. The analysis unit 1 outputs information necessary for information processing by displaying an image including information on the display unit 27. The analysis unit 1 receives signals from the first signal processing unit 24 and the second signal processing unit 25, and receives a control signal from the control unit 26. The analysis unit 1 and the control unit 26 may be configured as the same computer.

[0035] The memory unit 14 stores an element database that records data necessary for elemental analysis. The element database records information representing the characteristics of multiple elements. For example, the element database records the positions of peaks included in the fluorescent X-ray spectrum of each element, the intensity ratio of multiple peaks, the positions of absorption edges, the mass absorption coefficient, and the density. The positions of the peaks and the positions of the absorption edges are expressed in terms of X-ray energy. The element database may be provided outside the analysis unit 1. For example, the element database is stored in a storage device connected to the analysis unit 1 via a communication network. The element database may also be configured using the cloud. The calculation unit 11 accesses the element database via the communication network and performs processing to reference the data recorded in the element database.

[0036] FIG. 3 is a schematic cross-sectional view of the sample 3. The sample 3 includes a first layer 31 and a second layer 32 stacked together. The thickness of the first layer 31 is t1, and the thickness of the second layer 32 is t2. For example, the second layer 32 is a base material, and the first layer 31 is a coating covering the base material. For example, the sample 3 is part of a plate-shaped material. The analysis unit 1 performs information processing to measure the thickness of the first layer 31 included in the sample 3. As shown in FIG. 3, X-rays are irradiated onto the sample 3 so that the X-rays pass through the first layer 31 and then the second layer 32 in that order. Fluorescent X-rays are generated from the irradiated first layer 31. The fluorescent X-rays detected by the X-ray fluorescence detector 22 are mainly fluorescent X-rays generated from the first layer 31. The fluorescent X-rays generated from the second layer 32 are absorbed by the first layer 31 and are hardly detected by the X-ray fluorescence detector 22.

[0037] FIG. 4 is a graph showing an example of a spectrum of transmitted X-rays. The horizontal axis of FIG. 4 represents the energy of the transmitted X-rays, and the vertical axis represents the intensity of the transmitted X-rays. For example, the X-ray intensity is expressed as the number of counts per unit time. Two different energies of the transmitted X-rays from which the spectrum was obtained are designated E1 and E2. Both of the energies E1 and E2 are different from the peak energy of the spectrum of the fluorescent X-rays generated from the first layer 31. Furthermore, both of the energies E1 and E2 are different from the absorption edge of the elements contained in the first layer 31 or the second layer 32.

[0038] As shown in Fig. 3, the intensity of the X-rays irradiated onto the sample 3 at energy E1 is defined as I0(E1), and the intensity at energy E2 is defined as I0(E2). The X-ray intensities I0(E1) and I0(E2) are the intensities before the X-rays are incident on the sample 3. The intensity of the detected fluorescent X-rays at energy E1 is defined as I F (E1), and the intensity at energy E2 is I F The intensity of the detected transmitted X-ray at energy E1 is defined as I T (E1), and the intensity at energy E2 is I T Let (E2).

[0039] The mass absorption coefficient of the X-rays of the first layer 31 at energy E1 is μ1(E1), and the mass absorption coefficient of the X-rays at energy E2 is μ1(E2). The mass absorption coefficient of the X-rays of the second layer 32 at energy E1 is μ2(E1), and the mass absorption coefficient of the X-rays at energy E2 is μ2(E2). The density of the first layer 31 is ρ1, and the density of the second layer 32 is ρ2. The transmittance of the X-rays of the sample 3 at energy E1 is T(E1), and the transmittance of the X-rays at energy E2 is T(E2). The transmittances T(E1) and T(E2) are expressed by the following equations (1) and (2): ln(T(E1))=ln(I T (E1) / I0 (E1)) = -μ1 (E1)ρ1t1 -μ2 (E1)ρ2 t2...(1) ln(T(E2)) = ln(I T(E2) / I0 (E2)) = -μ1 (E2)ρ1t1 -μ2 (E2)ρ2t2...(2)

[0040] By subtracting equations (1) and (2), the following equation (3) is obtained: ln(T(E1)) - ln(T(E2)) = ln(I T (E1) / I0 (E1))-ln(I T (E2 ) / I0 (E2 )) = - (μ1 (E1 ) ρ1t1 + μ2 (E1 ) ρ2 t2 ) + (μ1 (E2 ) ρ1t1 + μ2 (E2 ) ρ2 t2 ) ln (T (E1 ) / T (E2 )) = ln ({I T (E1) / I T (E2)}・{I0 (E2) / I0 (E1)} = (μ1 (E2) - μ1 (E1)) ρ1 t1 + (μ2 (E2) - μ2 (E1)) ρ2 t2 ... (3)

[0041] Here, E2 = E1 + ΔE and ΔE ≈ 0. That is, it is assumed that energy E2 is a value very close to energy E1. In this case, the intensities of the X-rays irradiated onto the sample 3 at energies E1 and E2 are almost the same, and I0(E1) ≈ I0(E2). It is also assumed that the absorption edge of the element contained in the second layer 32 is not included in the energy range between energy E1 and energy E2. In this case, the mass absorption coefficients of the X-rays at energies E1 and E2 of the second layer 32 are almost the same, and μ2(E1) ≈ μ2(E2). From equation (3), the following equation (4) is obtained. ln(T(E1) / T(E2)) ≈ ln(I T (E1) / I T (E2 )) ≒ (μ1 (E2) - μ1 (E1)) ρ1 t1 …(4)

[0042] From equation (4), the following equation (5) is obtained as an equation for calculating the thickness t1 of the first layer 31: t1 ≈ ln(I T (E1) / I T (E2)) / {(μ1(E2)−μ1(E1))ρ1}…(5)

[0043] By using equation (5), the thickness t1 of the first layer 31 can be calculated. T (E1) and I T (E2) is obtained from the spectrum of the transmitted X-ray. When the absorption edge of the element contained in the first layer 31 is included in the energy range between the energy E1 and the energy E2, the intensity I of the transmitted X-ray is T (E1) and I T (E2) becomes larger, and the difference between the X-ray mass absorption coefficients μ1 (E2) and μ1 (E1) of the first layer 31 also becomes larger.

[0044] When calculating the thickness t1 of the first layer 31 using equation (5), the intensities I0(E1) and I0(E2) of the X-rays irradiated onto the sample 3 are not used in the calculation. Therefore, there is no need to acquire the X-rays irradiated onto the sample 3. Furthermore, the X-ray mass absorption coefficients μ2(E1) and μ2(E2) of the second layer 32, the density ρ2 of the second layer 32, and the thickness t2 of the second layer 32 are not used in the calculation. Therefore, even if the composition or thickness t2 of the second layer 32 is unknown, the thickness t1 of the first layer 31 can be calculated.

[0045] 5 is a flowchart showing an example of the processing procedure for measuring the thickness t1 of the first layer 31 executed by the X-ray analysis apparatus 100. Hereinafter, steps are abbreviated as S. The analysis unit 1 executes processing by having the calculation unit 11 execute information processing in accordance with the computer program 141. The irradiation unit 21 generates X-rays and irradiates the sample 3 with the X-rays (S101). The sample 3 is held in the X-ray analysis apparatus 100 so that the X-rays pass through the first layer 31 and then the second layer 32. Fluorescent X-rays are generated from the first layer 31 by the irradiation of the X-rays. The fluorescent X-ray detector 22 detects the fluorescent X-rays (S102). The transmission X-ray detector 23 detects the transmitted X-rays that have passed through the sample 3 (S103).

[0046] The fluorescent X-ray detector 22 outputs a signal having an intensity corresponding to the energy of the fluorescent X-rays to the first signal processing unit 24, which counts the signals for each signal value and outputs data indicating the relationship between the signal value and the count number to the analysis unit 1. The transmitted X-ray detector 23 outputs a signal having an intensity corresponding to the energy of the transmitted X-rays to the second signal processing unit 25, which counts the signals for each signal value and outputs data indicating the relationship between the signal value and the count number to the analysis unit 1. The analysis unit 1 receives data from the first signal processing unit 24 and the second signal processing unit 25, thereby acquiring detection results of the fluorescent X-rays and transmitted X-rays (S104). The analysis unit 1 generates spectra of the fluorescent X-rays and transmitted X-rays and stores the spectral data in the storage unit 14. The processing of S104 corresponds to the acquisition unit.

[0047] The analysis unit 1 performs elemental analysis based on the fluorescent X-ray spectrum to identify the elements contained in the first layer 31 (S105). In S105, for example, the calculation unit 11 identifies the peak positions and intensity ratios of the multiple peaks contained in the fluorescent X-ray spectrum, and identifies the elements by searching an element database for elements whose peak positions and intensity ratios match. If the first layer 31 contains multiple elements, the calculation unit 11 identifies the multiple elements.

[0048] The analysis unit 1 identifies two energies E1 and E2 (S106). In S106, the calculation unit 11 identifies E1 and E2 as energies different from the positions of peaks included in the fluorescent X-ray spectrum. The calculation unit 11 identifies the energies E1 and E2 so that the positions of the absorption edges of the elements included in the first layer 31 recorded in the element database are included in the energy range between E1 and E2. The calculation unit 11 also identifies the energies E1 and E2 so that the difference between the two energies E1 and E2 is included in a predetermined range. The predetermined range is a small range in which the intensities I0(E1) and I0(E2) of the X-rays irradiated to the sample 3 are approximately the same. For example, the calculation unit 11 identifies the energies E1 and E2 so that the absolute value of the difference between E1 and E2 is equal to or less than a predetermined threshold. The threshold is stored in advance in the storage unit 14.

[0049] In S106, the calculation unit 11 specifies energies E1 and E2 in the highest possible energy range. The higher the X-ray energy, the easier the X-ray penetrates the sample 3, and the greater the intensity of the transmitted X-ray. T (E1) and I T (E2) becomes larger, and the signal-to-noise ratio becomes larger.

[0050] When the elements contained in the second layer 32 are known, the calculation unit 11 specifies the energies E1 and E2 so that the position of the absorption edge of the element contained in the second layer 32 is not included in the energy range between E1 and E2. In this case, the position of the absorption edge of the element contained in the second layer 32 is stored in the memory unit 14. Alternatively, information indicating the elements contained in the second layer 32 is stored in the memory unit 14, and the calculation unit 11 specifies the position of the absorption edge by referring to an element database. The user may operate the operation unit 15 to input the position of the absorption edge of the element contained in the second layer 32 or information indicating the elements contained in the second layer 32 to the analysis unit 1.

[0051] In S106, the calculation unit 11 identifies the two energies E1 and E2 by selecting two energies E1 and E2 that meet the conditions from the energies of the detected transmitted X-rays. Combinations of the two energies E1 and E2 may be stored in advance in the storage unit 14, and the calculation unit 11 may identify the two energies E1 and E2 by selecting a combination that meets the conditions from a plurality of stored combinations. The values ​​of the two energies E1 and E2 may be input by a user operating the operation unit 15, and the calculation unit 11 may identify the two energies E1 and E2 by acquiring the input values ​​of E1 and E2.

[0052] The analysis unit 1 identifies the X-ray mass absorption coefficients μ(E) and μ(E) of the first layer 31 and the density ρ of the first layer 31 by elemental analysis (S107). If the first layer 31 contains a single element, in S107 the calculation unit 11 obtains the mass absorption coefficients μ(E) and μ(E) and the density ρ of the element contained in the first layer 31 from the element database.

[0053] If the first layer 31 contains multiple elements, in S107, the calculation unit 11 determines the content ratio of the multiple elements based on the fluorescent X-ray spectrum. For example, the calculation unit 11 determines the content ratio of the multiple elements based on the intensity ratio of peaks attributed to each element. By determining the content ratio of the multiple elements, the calculation unit 11 determines the composition of the first layer 31. The calculation unit 11 determines the mass absorption coefficients at energies E and E and the density of the first layer 31 according to the composition of the first layer 31. For example, the calculation unit 11 calculates the X-ray mass absorption coefficients μ(E) and μ(E) of the first layer 31 by calculating a weighted average of the mass absorption coefficients at energies E and E of the multiple elements recorded in the element database according to the content ratio of the multiple elements. Similarly, the calculation unit 11 calculates the density ρ of the first layer 31 by calculating a weighted average of the densities of the multiple elements recorded in the element database according to the content ratio of the multiple elements. Alternatively, the calculation unit 11 may identify the density ρ by acquiring the density associated with the composition of the first layer 31 from a database in which the composition and density of a substance are associated. The process of S107 corresponds to the identifying unit.

[0054] The analysis unit 1 measures the intensity I of transmitted X-rays at two energies E and E. T (E1) and I T In S108, the calculation unit 11 determines the intensity I of the transmitted X-ray by reading out the intensities of the transmitted X-ray at the energies E1 and E2 from the spectrum of the transmitted X-ray. T (E1) and I T (E2) is identified. The processes of S105 to S108 may be performed in a different order.

[0055] The calculation unit 11 calculates the thickness t1 of the first layer 31 (S109). In S109, the calculation unit 11 calculates the mass absorption coefficients μ1(E1) and μ1(E2) of the X-rays of the first layer 31, the density ρ1 of the first layer 31, and the intensity I of the transmitted X-rays. T (E1) and I T By substituting (E2) into equation (5) and performing the calculation expressed by equation (5), the thickness t1 of the first layer 31 is calculated. The process of S109 corresponds to the calculation unit. Through the processes of S101 to S109, the X-ray analysis apparatus 100 measures the thickness t1 of the first layer 31.

[0056] The analysis unit 1 outputs the calculated thickness t1 of the first layer 31 (S110). In S110, the calculation unit 11 outputs the calculated value of the thickness t1 of the first layer 31 by displaying the value on the display unit 27. The calculation unit 11 stores the thickness t1 of the first layer 31 in the storage unit 14. After S110 is completed, the analysis unit 1 ends the process for measuring the thickness t1 of the first layer 31.

[0057] As described above in detail, the X-ray analysis apparatus 100 irradiates the sample 3 with X-rays, detects fluorescent X-rays and transmitted X-rays, and calculates the thickness t1 of the first layer 31 using the X-ray mass absorption coefficient and density of the first layer 31 determined based on the fluorescent X-rays, and the intensity of the transmitted X-rays. Conventional techniques that utilize only the detection results of fluorescent X-rays have limitations on the thickness that can be measured. In contrast, the present embodiment utilizes the detection results of fluorescent X-rays and transmitted X-rays to enable measurement of larger thicknesses. Furthermore, the present embodiment analyzes the characteristics of the first layer 31, such as the X-ray mass absorption coefficient, based on the detection results of fluorescent X-rays, and calculates the thickness t1 of the first layer 31 using the analyzed characteristics of the first layer 31. This makes it possible to measure the thickness of the first layer 31 of a sample 3 whose composition is unknown. Therefore, it is possible to measure the thickness of the first layer 31 of more multilayer samples than before.

[0058] In this embodiment, the intensities of transmitted X-rays at two energies E1 and E2 are used, and the energies E1 and E2 are specified so that the difference between the two energies E1 and E2 falls within a small predetermined range. Because the difference between the two energies E1 and E2 is small, the intensities I(E1) and I(E2) of the X-rays irradiated onto the sample 3 become approximately the same. Therefore, equation (3) for calculating the thickness t1 of the first layer 31 can be approximated so that I(E2) / I(E1) included in equation (3) can be omitted. This simplifies the calculation of the thickness t1 of the first layer 31, and it is not necessary to measure the intensities I(E1) and I(E2) before the X-rays are incident on the sample 3. Therefore, the measurement of the thickness t1 of the first layer 31 is simplified.

[0059] In this embodiment, the absorption edge of the element contained in the second layer 32 is not included in the energy range between the two energies E1 and E2. Because the difference between the two energies E1 and E2 is small and the absorption edge of the element contained in the second layer 32 is not included between E1 and E2, the X-ray mass absorption coefficients μ(E1) and μ(E2) in the second layer 32 are approximately equal. Therefore, equation (3) for calculating the thickness t1 of the first layer 31 can be approximated to omit the term obtained by multiplying the difference between μ(E1) and μ(E2) by the density ρ of the second layer 32 and the thickness t2 of the second layer 32. As a result, the thickness t1 of the first layer 31 can be calculated using equation (5), which is an approximation of equation (3). By using equation (5), the thickness t1 of the first layer 31 can be calculated regardless of the characteristics of the second layer 32. Therefore, even if the composition or thickness of the second layer 32 is unknown, the thickness t1 of the first layer 31 can be measured.

[0060] In this embodiment, the absorption edge position of the element contained in the first layer 31 is included in the energy range between the two energies E1 and E2. T (E1) and I TWhen the absorption edge position is not included between the energies E1 and E2, the difference between the mass absorption coefficients μ(E2) and μ(E1) of the X-rays of the first layer 31 increases. T (E1) and I T (E2) are almost the same, and the mass absorption coefficients μ1(E2) and μ1(E1) are also almost the same. In this case, equation (5) divides a value close to zero by a value close to zero, and the calculation result of equation (5) may be inaccurate. In this embodiment, the intensity I of the transmitted X-rays is T (E1) and I T Since the difference between the mass absorption coefficients μ(E2) and μ(E1) is large, and the difference between the mass absorption coefficients μ(E2) and μ(E1) is also large, the calculation result of equation (5) is accurate, and the thickness t1 of the first layer 31 can be accurately calculated using equation (5).

[0061] In this embodiment, the two energies E1 and E2 are in the high energy range. The higher the energy of the X-rays, the easier they are to transmit through the sample 3, so it is possible to detect the transmitted X-rays even if the sample 3 is thick. Therefore, even if the sample 3 is thick, it is possible to measure the thickness t1 of the first layer 31. In addition, because the energies E1 and E2 are in the high energy range, the intensity I of the transmitted X-rays T (E1) and I T By utilizing the intensity of the transmitted X-rays with a large S / N ratio, the thickness t1 of the first layer 31 can be measured with high precision.

[0062] Although the first embodiment mainly illustrates an example in which the thickness t of the first layer 31 is calculated using equation (5), the X-ray analysis apparatus 100 may be configured to calculate the thickness t of the first layer 31 using another equation. For example, the X-ray analysis apparatus 100 may be configured to calculate the thickness t of the first layer 31 using equation (3). In this configuration, the composition and thickness of the second layer 32 are known, and the X-ray mass absorption coefficients μ(E) and μ(E), the density ρ of the second layer 32, and the thickness t of the second layer 32 are stored in the memory unit 14. The analysis unit 1 uses the information stored in the memory unit 14 to calculate the thickness t of the first layer 31 according to equation (3). In this configuration, the difference between the two energies E and E does not need to be within a predetermined range. In this embodiment, the energy range between the two energies E1 and E2 may include the position of the absorption edge of the element contained in the second layer 32, or may not include the position of the absorption edge of the element contained in the first layer 31. The X-ray analysis apparatus 100 can also perform processing using two energies E1 and E2 in a relatively low energy range.

[0063] In the first embodiment, the sample 3 includes the first layer 31 and the second layer 32. However, the X-ray analysis apparatus 100 may measure the thickness of the first layer 31 included in a sample 3 including three or more stacked layers. For example, if the first layer 31 is covered with a thinner surface layer, the X-ray analysis apparatus 100 may calculate the thickness of the surface layer and perform elemental analysis of the first layer 31 based on the fluorescent X-ray detection results, and measure the thickness t1 of the first layer 31. For example, if the first layer 31 is stacked on multiple layers, the X-ray analysis apparatus 100 may measure the thickness t1 of the first layer 31 by calculation using equation (5) or equation (3) including terms related to layers other than the first layer 31 and the second layer 32. The X-ray analysis apparatus 100 may measure the thickness t1 of the first layer 31 by calculation using equation (3) or equation (5), assuming that multiple layers other than the first layer 31 correspond to the second layer 32.

[0064] <Embodiment 2> The functional configuration of the X-ray analysis apparatus 100 and the analysis unit 1 according to embodiment 2 is the same as that of embodiment 1. In embodiment 2, the X-ray analysis apparatus 100 calculates the thickness t1 of the first layer 31 included in the sample 3 based on the fluorescent X-rays. When the thickness t1 of the first layer 31 is relatively small, the thickness t1 can be calculated based on the fluorescent X-rays without using the detection results of the transmitted X-rays.

[0065] 6 is a flowchart showing an example of a processing procedure executed by the X-ray analysis apparatus 100 according to the second embodiment for measuring the thickness t1 of the first layer 31 based on fluorescent X-rays. The irradiation unit 21 irradiates the sample 3 with X-rays (S21), and the X-ray fluorescence detector 22 detects the fluorescent X-rays (S22). The X-ray fluorescence detector 22 outputs a signal having an intensity corresponding to the energy of the fluorescent X-rays to the first signal processing unit 24. The first signal processing unit 24 counts the signals for each signal value and outputs data indicating the relationship between the signal value and the count number to the analysis unit 1. The analysis unit 1 acquires the detection result of the fluorescent X-rays by receiving data from the first signal processing unit 24 and the second signal processing unit 25 (S23). The analysis unit 1 generates a spectrum of the fluorescent X-rays and stores the spectrum data in the storage unit 14.

[0066] The analysis unit 1 calculates the thickness t1 of the first layer 31 contained in the sample 3 by performing elemental analysis based on the fluorescent X-ray spectrum (S24). In S24, the calculation unit 11, as in the first embodiment, identifies the elements contained in the first layer 31 by performing elemental analysis based on the fluorescent X-ray spectrum. The calculation unit 11 also calculates the thickness t1 of the first layer 31 based on the fluorescent X-rays using conventional technology. For example, the calculation unit 11 calculates the thickness t1 of the first layer 31 in accordance with the intensity of a peak contained in the obtained fluorescent X-ray spectrum, in accordance with the relationship between the intensity of a peak attributable to a specific element contained in the fluorescent X-ray spectrum and the thickness t1. The relationship between the peak intensity and the thickness t1 is determined in advance and stored in the storage unit 14.

[0067] The analysis unit 1 outputs the calculated thickness t1 of the first layer 31 (S25). In S25, the calculation unit 11 outputs the calculated value of the thickness t1 of the first layer 31 by displaying the value on the display unit 27. The calculation unit 11 stores the thickness t1 of the first layer 31 in the storage unit 14. After S25 is completed, the analysis unit 1 ends the process for measuring the thickness t1 of the first layer 31.

[0068] The X-ray analysis apparatus 100 can execute both the processes of S101 to S110 and the processes of S21 to S24. The X-ray analysis apparatus 100 can switch between the processes of S101 to S110 and the processes of S21 to S24 as the processes to be executed. For example, the user operates the operation unit 15 to input a process switching instruction to the analysis unit 1, and the analysis unit 1 switches the process to be executed in accordance with the switching instruction.

[0069] When the thickness t1 of the first layer 31 is relatively small, the X-ray analysis apparatus 100 can easily measure the thickness t1 of the first layer 31 by performing the processes of S21 to S25. When the thickness t1 of the first layer 31 is relatively large, the X-ray analysis apparatus 100 can more accurately measure the thickness t1 of the first layer 31 by performing the processes of S101 to S110. In this way, in the second embodiment, the thickness t1 of the first layer 31 can be measured by an appropriate method depending on the size of the thickness t1 of the first layer 31.

[0070] In the first and second embodiments, the thickness t1 of the first layer 31 is measured using the mass absorption coefficient of X-rays. However, the X-ray analysis apparatus 100 may be configured to measure the thickness t1 of the first layer 31 using the linear absorption coefficient as the absorption coefficient of X-rays.

[0071] In the first and second embodiments, the X-ray fluorescence detector 22 and the transmission X-ray detector 23 are radiation detectors having radiation detection elements formed using semiconductors. However, the X-ray fluorescence detector 22 and the transmission X-ray detector 23 may be radiation detectors having radiation detection elements other than those formed using semiconductors. The X-ray fluorescence detector 22 and the transmission X-ray detector 23 may be detectors having multiple channels. For example, the X-ray fluorescence detector 22 and the transmission X-ray detector 23 may be strip detectors, pixel array detectors, or line sensors, or may be configured by arranging multiple detectors. Using a detector having multiple channels enables measurement at a higher count rate than using a detector having a single channel.

[0072] The X-ray fluorescence detector 22 and the transmission X-ray detector 23 are not limited to energy dispersive detectors, but may be any detector capable of detecting the intensities of X-rays with specific energies E1 and E2. For example, the X-ray fluorescence detector 22 and the transmission X-ray detector 23 may be configured using a CCD (Charge Coupled Device) photosensor or a CMOS (Complementary Metal-Oxide-Semiconductor) photosensor, or may be configured using a combination of a photomultiplier tube and a scintillator. Such detectors may be used in combination with a filter that transmits X-rays of a specific energy or an element that focuses X-rays of a specific energy by diffraction.

[0073] In the first and second embodiments, the horizontal axis of the X-ray spectrum represents energy, but the X-ray analysis apparatus 100 may be configured to handle a spectrum in which the horizontal axis represents a value other than energy, such as wavelength or wave number. In this configuration, the analysis unit 1 may perform processing to calculate the thickness t1 of the first layer 31 using two wavelengths or wave numbers corresponding to two energies.

[0074] The X-ray analysis apparatus 100 may be configured with a mechanism capable of adjusting the intensity of the transmitted X-rays. If the intensity of the transmitted X-rays is too high, the number of X-rays incident on the transmission X-ray detector 23 increases, increasing the probability that signals corresponding to the incident X-rays will overlap, resulting in a longer detection dead time or a risk of the transmission X-ray detector 23 failing. It is desirable to be able to adjust the intensity of the transmitted X-rays in order to accommodate various samples 3 with different thicknesses or to prevent failure of the transmission X-ray detector 23. For example, the X-ray analysis apparatus 100 may include an adjustment mechanism that adjusts the intensity of the transmitted X-rays when the intensity of the detected transmitted X-rays exceeds a predetermined threshold or when the dead time exceeds a predetermined threshold. For example, the adjustment mechanism adjusts the intensity of the X-rays irradiated by the irradiation unit 21 by adjusting the current flowing through the X-ray tube. For example, the adjustment mechanism may include a collimator disposed between the irradiation unit 21 and the sample 3, and adjust the intensity of the X-rays irradiated to the sample 3 by changing the size of the collimator or by switching between collimators of multiple sizes. For example, the adjustment mechanism adjusts the distance between the sample 3 and the transmission X-ray detector 23 to adjust the intensity of the transmission X-rays.

[0075] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. In other words, embodiments obtained by combining technical means modified appropriately within the scope of the claims are also included in the technical scope of the present invention.

[0076] The matters described in each embodiment can be combined with each other. Furthermore, the independent claims and dependent claims described in the claims can be combined with each other in any and all combinations, regardless of the reference format. Furthermore, the claims use a format in which a claim references two or more other claims (multiple claim format), but this is not limited to this. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used.

[0077] REFERENCE SIGNS LIST 100 X-ray analysis apparatus 1 Analysis unit 10 Recording medium 141 Computer program 21 Irradiation unit 22 X-ray fluorescence detector 23 Transmission X-ray detector 3 Sample 31 First layer 32 Second layer

Claims

1. A thickness measurement method comprising: irradiating a sample including a stacked first layer and a second layer with X-rays so that the X-rays penetrate the first layer first, then the second layer; detecting fluorescent X-rays generated from the first layer; detecting transmitted X-rays that have penetrated the sample; identifying the X-ray absorption coefficient of the first layer and the density of the first layer by elemental analysis based on the fluorescent X-rays; and calculating the thickness of the first layer based on the intensities of the transmitted X-rays at two different energies, the absorption coefficient, and the density.

2. The thickness measurement method according to claim 1, characterized in that the difference between the two energies is within a predetermined range.

3. The thickness measurement method according to claim 2, characterized in that the absorption edge of the element contained in the second layer is not included in the energy range between the two energies.

4. A thickness measurement method according to any one of claims 1 to 3, characterized in that the two energies are specified by elemental analysis based on the fluorescent X-rays so that the absorption edge of the element contained in the first layer is included in the energy range between the two energies.

5. An X-ray analysis apparatus comprising: an irradiation unit that irradiates a sample including a stacked first layer and a second layer with X-rays so that the X-rays penetrate the first layer and then the second layer; an X-ray fluorescence detector that detects fluorescent X-rays generated from the first layer; a transmission X-ray detector that detects transmitted X-rays that have penetrated the sample; and an analysis unit, wherein the analysis unit identifies the X-ray absorption coefficient of the first layer and the density of the first layer by elemental analysis based on the fluorescent X-rays, and calculates the thickness of the first layer based on the intensities of the transmitted X-rays at two different energies, the absorption coefficient, and the density.

6. The X-ray analysis apparatus according to claim 5, characterized in that the analysis unit calculates the thickness of the first layer by elemental analysis based on the fluorescent X-rays, without using the detection results of the transmitted X-rays.

7. An information processing device comprising: an acquisition unit that acquires detection results of fluorescent X-rays generated from the first layer and detection results of transmitted X-rays that have passed through the sample by irradiating a sample including stacked first and second layers with X-rays so that the X-rays pass through the first layer and the second layer in that order; an identification unit that identifies the absorption coefficient of the X-rays in the first layer and the density of the first layer by elemental analysis based on the detection results of the fluorescent X-rays; and a calculation unit that calculates the thickness of the first layer based on the intensities of the transmitted X-rays at two different energies, the absorption coefficient, and the density.

8. A computer program that causes a computer to execute the following processing: Identifying the absorption coefficient of X-rays in the first layer and the density of the first layer by performing elemental analysis based on the detection results of fluorescent X-rays generated from the first layer when a sample including stacked first and second layers is irradiated with X-rays so that the X-rays penetrate the first layer and then the second layer; and calculating the thickness of the first layer based on the intensities of the transmitted X-rays at two different energies contained in the detection results of the transmitted X-rays that have passed through the sample, the absorption coefficient, and the density.