X-ray measurement device

Abstract

To improve the accuracy of calculating a film thickness.SOLUTION: Provided is an X-ray measurement device 1 for measuring a film thickness for a sample 2 on the surface of which a film is formed. The X-ray measurement device 1 comprises: an acquisition unit for acquiring the diffraction ring of an X-ray with which the sample 2 is irradiated; an identification unit for identifying peak intensity for each of a plurality of α angles in the diffraction ring; a Fourier unit for performing Fourier series expansion on the distribution of peak intensities for α angles; and a calculation unit for calculating the film thickness of the film on the basis of a Fourier coefficient calculated by Fourier series expansion.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an X-ray measurement device. [Background technology]

[0002] By irradiating a sample with X-rays, the thickness (film thickness) of a film formed on the surface of the sample can be measured. For example, in Patent Document 1, a sample is irradiated with X-rays, and the amount of fluorescent X-rays emitted is measured to calculate the film thickness. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-128042 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when calculating the film thickness based on the attenuation of X-rays such as the dose of irradiated X-rays, it is considered that only the intensity of one specific α angle in the diffraction ring diffracted by the sample is used. In this case, if the detected value varies depending on the α angle, the accuracy of the film thickness calculation may decrease.

[0005] In view of the above-mentioned problems, an object of the present invention is to provide an X-ray measuring apparatus capable of improving the accuracy of calculating a film thickness. [Means for solving the problem]

[0006] In order to solve the above problems, the X-ray measurement device of the present invention is an X-ray measurement device that measures the film thickness of a sample having a film formed on its surface, and includes an acquisition unit that acquires a diffraction ring of X-rays irradiated to the sample, an identification unit that identifies peak intensities for each of a plurality of α angles in the diffraction ring, a Fourier unit that performs a Fourier series expansion on the distribution of the peak intensities for the α angles, and a calculation unit that calculates the film thickness of the film based on the Fourier coefficients calculated by the Fourier series expansion.

[0007] In the X-ray measurement device, the Fourier coefficient is a zeroth-order coefficient in the Fourier series expansion.

[0008] In the X-ray measurement apparatus, the calculation unit calculates the film thickness of the film from the Fourier coefficients based on correction information in which the Fourier coefficients are represented as an exponential function of the film thickness.

[0009] In the X-ray measurement device, the correction information is set based on a plurality of reference diffraction rings obtained by irradiating X-rays onto respective reference samples having different film thicknesses.

[0010] In the X-ray measurement device, the correction information is set based on a distribution state of peak intensity with respect to the α angle obtained by the plurality of reference diffraction rings. Effect of the Invention

[0011] According to the X-ray measuring device of the present invention, alignment can be performed while suppressing the complexity of the mechanism. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing an example of the configuration of an X-ray measurement apparatus according to an embodiment of the present invention. [Diagram 2] 2 is a block diagram showing an example of various functions in a processing unit in FIG. 1. [Diagram 3] 2 is a diagram showing an example of a diffraction ring detected by a detection unit in FIG. 1. [Figure 4]2 is a flowchart showing an example of the flow of a film thickness calculation process by a processing unit in FIG. [Diagram 5] 2 is a diagram showing an example of a case where a reference sample is irradiated with X-rays by the X-ray measurement device of FIG. 1. [Figure 6] FIG. 4 is a diagram showing an example of the relationship between peak intensity and α angle. [Figure 7] FIG. 13 is a diagram illustrating an example of the relationship between the Fourier coefficient and the film thickness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted as appropriate.

[0014] === Implementation form === <Overall composition> 1 is a diagram showing an example of the configuration of an X-ray measurement apparatus 1 according to this embodiment. The X-ray measurement apparatus 1 irradiates a sample 2 with X-rays and detects the X-rays diffracted by the sample 2 to perform X-ray measurement.

[0015] The sample 2 is an object to be analyzed, and may be, for example, an automobile part such as a gear, a crankshaft, a shaft, or other part. The sample 2 may be, for example, a steel material. In particular, the sample 2 has a film formed on its surface. The film may be, for example, a coating such as paint on a substrate. Parameters of the sample 2 to be analyzed may be, for example, the film thickness t and stress of the sample 2.

[0016] 1, the X-ray measurement device 1 has a main body 10, and its main components are a tube 11, a collimator 12, a substrate 13, and a detection unit 14. The X-ray measurement device 1 also has a processing unit 15.

[0017] The tube 11 functions as an irradiation unit that generates X-rays and irradiates the generated X-rays toward the sample 2. The tube 11 is made of a material such as glass or metal.

[0018] Collimator 12 has a function of adjusting the irradiation range of the X-rays generated by tube 11. Collimator 12 is provided below (on the substrate side) of tube 11, and extends toward substrate 13. The X-rays generated by tube 11 pass through collimator 12 and are irradiated onto sample 2.

[0019] The substrate 13 is a plate-like member, and is provided with a detection unit 14, which will be described later. A hole is provided in the substrate 13, and a collimator 12 extending from the bulb 11 side protrudes from this hole to the sample 2 side.

[0020] The detector 14 has, for example, a rectangular shape, and is provided on the substrate 13 on the side of the sample 2 (the side opposite to the tube 11). The detector 14 detects X-rays diffracted from the sample 2. Specifically, the detector 14 detects a diffraction ring, which is a ring-shaped diffraction image of the diffracted X-rays. The diffraction ring is also called a Debye ring or a Debye-Scherrer ring. The detector 14 is an imaging element for imaging the diffraction ring, and is, for example, an SOI (Silicon on Insulator) sensor. For example, the detector 14 is composed of two chips provided on either side of the collimator 12. The number of chips is not limited.

[0021] The processing unit 15 is an information processing device that measures the film thickness t of the sample 2. The processing unit 15 may also perform other X-ray measurements such as stress measurements.

[0022] The processing unit 15 includes, for example, a control device 20, a communication device 21, and a storage device 22. The control device 20 is mainly configured with a CPU (Central Processing Unit) 25 and a memory 26. In the control device 20, the CPU 25 executes a predetermined program stored in the memory 26 or the storage device 22, etc., thereby functioning as various functional configurations described below. The communication device 21 includes a communication interface for communicating with an external device, etc. The storage device 22 includes a hard disk, etc., and stores various programs and various information required for executing the processing in the control device 20, as well as information on the processing results. The processing unit 15 may be configured with a single information processing device or multiple information processing devices. Also, FIG. 1 shows only a part of the main hardware configuration of the processing unit 15, and the processing unit 15 may include other configurations such as an operation device and a display device.

[0023] <Functional configuration> 2 is a block diagram showing an example of various functions in the processing unit 15 of the X-ray measuring device 1. The position correction process is executed by the function in each block.

[0024] As shown in FIG. 2, the processing unit 15 mainly includes an acquisition unit 31, a specification unit 32, a Fourier unit 33, and a calculation unit .

[0025] The acquisition unit 31 acquires the diffraction ring detected when X-rays are irradiated onto the sample 2. Specifically, the acquisition unit 31 acquires the diffraction ring detected by the detection unit .

[0026] FIG. 3 is a diagram showing an example of a diffraction ring detected by the detection unit 14. X-rays irradiated to the sample 2 are detected as a diffraction ring, for example, as shown as C in FIG. 3. The angle of the diffraction ring in the circumferential direction is the α angle. Parts of the diffraction ring are detected by each of the two chips constituting the detection unit 14. In other words, the α angle is the central angle of the diffraction ring on the detection plane of the detection unit 14. A part of the diffraction ring may be detected, or the entire circumference (whole) of the diffraction ring may be detected. Returning to FIG. 2, the diffraction ring acquired by the acquisition unit 31 is output to the identification unit 32.

[0027] The determination unit 32 determines peak intensities for a plurality of α angles in the diffraction ring. The plurality of α angles are set, for example, at equal intervals in the circumferential direction. In this embodiment, it is assumed that N α angles are set. The determination unit 32 determines peak intensities for each of the profiles (diffraction profiles) corresponding to the plurality of α angles. The profile indicates the radial intensity distribution of the diffraction ring at a particular α angle. For example, the profile is shown as a distribution of radial positions (e.g., pixels) based on the center of the diffraction ring on the vertical axis and the horizontal axis. For example, in the profile, the intensity is high at radial positions where the diffraction ring is detected, and the intensity is low at positions where the diffraction ring is not detected. The peak intensity is obtained as a peak value by fitting the profile with a Gaussian function. Note that the peak intensity is not limited to the peak value of the Gaussian function, and may be, for example, the maximum intensity in the profile. In this manner, the determination unit 32 obtains peak intensities corresponding to each of the N α angles.

[0028] The Fourier unit 33 performs a Fourier series expansion on the distribution of peak intensity with respect to the α angle. For example, the Fourier unit 33 performs a second-order Fourier series expansion. That is, the Fourier unit 33 calculates, as Fourier coefficients, a0 of the zeroth order coefficient in the Fourier series expansion, a1 of the first-order cosine wave (cosα), a1 of the first-order sine wave (sinα), a2 of the second-order cosine wave (cos2α), and a2 of the second-order sine wave (sin2α). The Fourier unit 33 outputs the calculated Fourier coefficient a0, which is the zeroth order coefficient, to the calculation unit 34. Note that other coefficients of the Fourier series expansion may be used as the Fourier coefficients.

[0029] The calculation unit 34 calculates the film thickness t of the sample 2 based on the Fourier coefficient a0 calculated by the Fourier series expansion. Specifically, the calculation unit 34 calculates the film thickness t from the Fourier coefficient a0 based on the correction information.

[0030] The correction information corresponds to the Fourier coefficient a0 as an exponential function of the film thickness t, as shown in the following formula (1).

[0031]

number

[0032] As shown in formula (1), the Fourier coefficient a0 and the film thickness t correspond to each other as an exponential function with the Napier's number (the base of natural logarithms) as the base. The coefficients m and n in formula (1) are set in advance. The calculation unit 34 converts the calculated Fourier coefficient a0 into the film thickness t using the correction information.

[0033] <Processing flow> 4 is a flow chart showing an example of the flow of the film thickness calculation process according to the present embodiment. Each process in the following steps is started, for example, after irradiating the sample 2 to be measured with X-rays. Note that the order and contents of each step in the following steps can be changed as appropriate.

[0034] (Step SP10) The acquiring unit 31 acquires a diffraction ring of the X-rays irradiated onto the sample 2. The diffraction ring is output to the identifying unit 32. Then, the process proceeds to step SP11.

[0035] (Step SP11) The identifying section 32 identifies peak intensities corresponding to each of the N α angles for the acquired diffraction ring. The peak intensities are output to the Fourier section 33. Then, the process proceeds to step SP12.

[0036] (Step SP12) The Fourier section 33 performs Fourier series expansion on the distribution of peak intensity with respect to the α angle, and then the process proceeds to step SP13.

[0037] (Step SP13) The Fourier section 33 sets the zeroth-order coefficient in the Fourier series expansion as the Fourier coefficient a0. The Fourier coefficient a0 is output to the calculation section 34. Then, the process proceeds to step SP14.

[0038] (Step SP14) The calculation unit 34 calculates the film thickness t from the Fourier coefficient a0 based on the correction information.

[0039] In this manner, the thickness t is calculated from the diffraction ring, and the calculated thickness t is notified to, for example, the user.

[0040] In addition, parameters such as stress may be calculated based on the diffraction ring used to calculate the film thickness t. When calculating stress, a profile without the coating may be calculated and stress calculation may be performed based on this profile. In this way, it is possible to obtain multiple measurement results of film thickness t and stress from one obtained diffraction ring.

[0041] <Correction information settings> Next, the setting of the correction information will be described. The correction information is set in advance for X-ray measurement. A reference sample 2s is used as the sample 2 to set the correction information. A plurality of reference samples 2s are prepared, each having the same base material but different film thicknesses t. Note that the film thickness t may be changed for one base material.

[0042] 5 is a diagram showing an example of a case where a reference sample 2s is irradiated with X-rays at a predetermined incident angle φ0. Using the reference sample 2s, diffraction rings with different patterns of the film thickness t of the reference film 36 are obtained. The diffraction ring for the reference sample 2s is taken as the reference diffraction ring. For example, if there are W types of film thickness t patterns, W reference diffraction rings are obtained.

[0043] Then, based on each reference diffraction ring, a distribution of peak intensity with respect to the α angle is obtained corresponding to each of the multiple film thicknesses t. FIG. 6 is a diagram showing an example of the distribution of peak intensity with respect to the α angle. In FIG. 6, the vertical axis represents the peak intensity, the horizontal axis represents the α angle, and the distribution is shown for each film thickness t. As an example, the film thickness t has six patterns of film thickness t1, film thickness t2, film thickness t3, film thickness t4, film thickness t5, and film thickness t6, and the film thickness t increases from film thickness t1 to film thickness t6. Then, the distributions corresponding to film thickness t1, film thickness t2, film thickness t3, film thickness t4, film thickness t5, and film thickness t6 are shown as distribution L1, distribution L2, distribution L3, distribution L4, distribution L5, and distribution L6, respectively.

[0044] By expanding each distribution into a Fourier series, we obtain the Fourier coefficient a0 corresponding to distribution L1, the Fourier coefficient a0 corresponding to distribution L2, the Fourier coefficient a0 corresponding to distribution L3, the Fourier coefficient a0 corresponding to distribution L4, the Fourier coefficient a0 corresponding to distribution L5, and the Fourier coefficient a0 corresponding to distribution L6. In other words, we obtain the Fourier coefficient a0 corresponding to each film thickness t.

[0045] FIG. 7 is a diagram showing an example of the distribution of the Fourier coefficient a0 with respect to the film thickness t. In FIG. 7, the vertical axis represents the Fourier coefficient a0, and the horizontal axis represents the film thickness t. When the plotted distribution is approximated by an exponential function M1, formula (1) is obtained. In this manner, the correction information (particularly the coefficients m and n) is set based on the reference sample 2s.

[0046] By setting equation (1) in this way and using it as correction information in calculation unit 34, it becomes possible to calculate film thickness t from Fourier coefficient a0 based on the detected diffraction ring.

[0047] <Action and effect> As described above, in this embodiment, the X-ray measuring apparatus 1 is an X-ray measuring apparatus 1 that measures the film thickness t of a sample 2 having a film formed on its surface, and includes an acquisition unit 31 that acquires a diffraction ring of X-rays irradiated to the sample 2, an identification unit 32 that identifies the peak intensity for each of a plurality of α angles in the diffraction ring, a Fourier unit 33 that performs a Fourier series expansion on the distribution of peak intensity for the α angle, and a calculation unit 34 that calculates the film thickness t of the film based on the Fourier coefficients calculated by the Fourier series expansion.

[0048] According to this configuration, the film thickness t can be calculated based on the multiple α angles of the obtained diffraction ring, which improves the accuracy of the calculation of the film thickness t.

[0049] For example, when calculating the film thickness t using the reflected light of a light source such as an LED, the reflected light may be difficult to detect due to the reflectance of the film, but the effect of reflectance can be suppressed by using a diffraction ring produced by irradiating X-rays. Also, when calculating the film thickness t using the attenuation of the intensity of a specific α angle, the calculation accuracy of the film thickness t may deteriorate due to the variation in peak intensity for each α angle, but the calculation accuracy can be improved by using the peak intensities of multiple α angles.

[0050] In addition, since the angle of incidence of the X-rays on the sample 2 is not limited to the normal direction of the sample 2, it is possible to perform other X-ray measurements such as stress, and it becomes possible to analyze multiple parameters such as film thickness t and stress in parallel from one diffraction ring. For example, for the sample 2 that has been ground or heat-treated and then painted, it is possible to detect grinding burns and uneven heat treatment while measuring the film thickness t, and in the manufacture of semiconductor chips, it may be possible to detect deformation due to residual stress generated during chip molding while measuring the film thickness t.

[0051] Moreover, in the X-ray measurement apparatus 1 according to this embodiment, the Fourier coefficient a0 is the zeroth-order coefficient in the Fourier series expansion.

[0052] According to this configuration, the film thickness t can be calculated with high accuracy by using the Fourier coefficient a0.

[0053] Moreover, in the X-ray measurement apparatus 1 according to this embodiment, the calculation unit 34 calculates the film thickness t of the film from the Fourier coefficients based on correction information in which the Fourier coefficients are represented as an exponential function of the film thickness t.

[0054] According to this configuration, the Fourier coefficients are based on correction information expressed as an exponential function of the film thickness t, so that the film thickness t can be calculated with high accuracy from the Fourier coefficients.

[0055] Moreover, in the X-ray measurement apparatus 1 according to this embodiment, the correction information is set based on a plurality of reference diffraction rings acquired by irradiating X-rays onto each of the reference samples 2s having different film thicknesses t.

[0056] According to this configuration, the accuracy of the correction information can be improved by using the correction information based on the reference samples 2s having different film thicknesses t.

[0057] Moreover, in the X-ray measurement apparatus 1 according to this embodiment, the correction information is set based on the distribution state of the peak intensity with respect to the α angle obtained by a plurality of reference diffraction rings.

[0058] According to this configuration, the correction information can be set based on the distribution state of the peak intensity with respect to the α angle obtained from the reference diffraction ring, regardless of a specific α angle.

[0059] <Modification> The present invention is not limited to the above-described embodiment. In other words, the above-described specific example may be modified by a person skilled in the art as appropriate, and the modifications may be included in the scope of the present invention as long as they include the features of the present invention. In addition, the elements of the above-described embodiment and the following modifications may be combined to the extent technically possible, and the combinations of these may be included in the scope of the present invention as long as they include the features of the present invention.

[0060] For example, in the above embodiment, a case has been described in which the processing unit 15 is provided separately from the main body unit 10, but the processing unit 15 is not limited to being provided separately from the main body unit 10, and may be mounted on the main body unit 10.

[0061] For example, in the above embodiment, the identifying unit 32 identifies the peak intensity, but the integrated intensity may be used. The integrated intensity may be calculated by fitting the profile with a Gaussian function and calculating the product of the peak value of the Gaussian distribution and the width parameter σ, or may be a value obtained by integrating the entire profile (or a part of it).

[0062] In addition, in the above embodiment, the formula shown in Equation (1) is used as the correction information, but other types of formulas may be used, and the correction information is not limited to a formula but may be in the form of, for example, a graph or a table. [Explanation of symbols]

[0063] 1:X-ray measuring device 2: Sample 26: Memory 31: Acquisition part 32: Specific part 33: Fourier section 34: Calculation section a0: Fourier coefficient t: Film thickness

Claims

1. An X-ray measurement apparatus for measuring a film thickness of a sample having a film formed on its surface, comprising: an acquisition unit that acquires a diffraction ring of X-rays irradiated onto the sample; an identifying unit that identifies a peak intensity for each of a plurality of α angles in the diffraction ring; a Fourier section that performs a Fourier series expansion on the distribution of the peak intensity with respect to the α angle; a calculation unit that calculates a thickness of the film based on the Fourier coefficients calculated by the Fourier series expansion; An X-ray measuring device comprising:

2. The Fourier coefficient is a zero-order coefficient in the Fourier series expansion.

2. The X-ray measurement device according to claim 1.

3. the calculation unit calculates the film thickness from the Fourier coefficients based on correction information in which the Fourier coefficients are represented as an exponential function of the film thickness; 3. The X-ray measuring device according to claim 1 or 2.

4. the correction information is set based on a plurality of reference diffraction rings obtained by irradiating X-rays onto respective reference samples having different film thicknesses; 4. The X-ray measurement device according to claim 3.

5. the correction information is set based on a distribution state of peak intensities with respect to α angles obtained by a plurality of the reference diffraction rings.

5. The X-ray measurement apparatus according to claim 4.

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