JP2004093521A - Apparatus and method for x-ray reflectance measuring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for X-ray reflectance measuring capable of accurately evaluating an extremely thin film by allowing the measuring of reflected X-ray in wide angle. <P>SOLUTION: This X-ray reflectance measuring apparatus comprises a light source radiating X-ray, an optical system leading the X-ray radiated from the light source to the surface of specimen, a specimen position adjusting means adjusting the position of the specimen relative to the X-ray radiated from the light source, a detector detecting the intensity of the reflected X-ray reflected on the surface of the specimen, and an absorbing plate disposed on the front stage of the detector. The absorbing plate comprises a first absorbing end near the energy of the X-ray and on the high-energy side. The absorbing plate also comprises a second absorbing end near the harmonic energy of the X-ray and on the lower energy side of the harmonic energy. The detector measures the intensity of the reflected X-ray for each divided measuring area formed by dividing a specified measuring area into a plurality of measuring areas. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray reflectivity measuring apparatus and a measuring method, and more particularly, to an X-ray reflectivity measuring apparatus and a measuring method capable of measuring a reflected X-ray at a wide angle.
[0002]
[Prior art]
The X-ray reflectivity method is a method of analyzing the thickness of a thin film, the unevenness of a surface or an interface, the film density, and the like from an interference pattern of X-rays reflected from a thin film sample. The X-ray reflectivity method is characterized in that it can evaluate even an optically opaque metal thin film or an amorphous (amorphous) film, and can also evaluate an ultrathin film. It is used for evaluation of advanced thin film materials such as evaluation and evaluation of multilayer films of magnetic heads.
[0003]
In the X-ray reflectivity measurement, when a thin film having a thickness t is present on the substrate, the intensity of the reflected X-ray appearing at an angle 2θ is measured while changing the incident angle (θ) of the X-ray to the thin film surface. Here, the incident angle (θ) is, as shown in FIG. 1B, the angle formed by the incident light with respect to the surface of the sample 103, and 2θ is the angle of the reflected light reflected by the surface of the sample 103. , With respect to the optical axis A of the incident light.
[0004]
When the sample 103 is irradiated with X-rays, as shown in FIG. 1A, the reflected light l′ ref reflected on the surface of the thin film 102 having a thickness t and the reflected light reflected on the interface with the substrate 101. The light lref interferes and the reflected X-ray intensity oscillates. By measuring the intensity of the reflected X-ray (interference wave) at the corresponding 2θ position while changing the incident angle θ, the period of oscillation of the reflected X-ray intensity can be obtained. The period of the oscillation of the reflected X-ray intensity is a function of the film thickness t, and from the obtained period and intensity, the film thickness of the thin film 102, unevenness of the surface or interface, density, and the like can be evaluated nondestructively.
[0005]
At this time, there is a configuration in which an X-ray absorber is installed in the X-ray path and the X-ray intensity incident on the sample is adjusted so that the X-ray intensity does not exceed the measurement limit (for example, see Patent Document 1). .
[0006]
[Patent Document 1]
JP-A-9-105726 (FIGS. 1 and 2)
[Problems to be solved by the invention]
The oscillation period Δ2θ of the reflected interference light appearing at the angle 2θ is inversely proportional to the film thickness t, and is expressed by Δ2θ (radian) = λ / t. Here, λ is the wavelength of the X-ray. When the film thickness t is small, for example, when measuring an extremely thin film of about 1 nm, it is necessary to measure the interference light up to a relatively large 2θ angle. However, the intensity of the reflected X-ray is 1 / θ ⁴ Therefore, at a large 2θ angle, the background noise overlaps with the signal, and the measurement becomes difficult. For this reason, it was difficult to evaluate an extremely thin film.
[0007]
Therefore, an object of the present invention is to provide an X-ray reflectivity measuring apparatus and a measuring method capable of measuring interference X-rays at a relatively wide angle and accurately evaluating an ultrathin film.
[0008]
[Means for Solving the Problems]
In order to enable the measurement of the reflected X-ray at a wide angle, the following method is conceivable.
(1) Increasing the intensity (luminous flux density) of incident X-rays.
(2) Divide the measurement range into a plurality of regions, optimize each region so as not to exceed the maximum number of detectors, perform divided measurement, and link the measurement results.
(3) Efficiently remove the background from the measured intensity to enable measurement of weak reflected X-rays at a wide angle.
[0009]
To realize these methods, the following configuration is proposed.
(1) X-rays from a light source are condensed in both the vertical and horizontal directions by a mirror or a curved crystal to increase the intensity of incident X-rays incident on the sample surface. Alternatively, synchrotron radiation X-rays are used.
(2) Absorbing plates having different thicknesses are inserted according to each of the divided measurement regions, and the reflected X-rays are attenuated to an optimum intensity that can be measured in each measurement region. This makes it possible to obtain an appropriate measurement result for each divided measurement region even if the measurement range is set wide.
(3-1) As an absorption plate, an absorption plate having an absorption edge energy in the vicinity of the irradiated X-ray energy and on the high energy side, or in the vicinity of the harmonic energy of the irradiated X-ray and lower in energy than the harmonic energy. Use an absorption plate with absorption edge energy. Specifically, an absorption plate having an absorption edge on the high energy side within a range of 5 keV or less than the used X-ray energy, or an absorption edge on a low energy side within a range of 5 keV or less than the harmonic energy of the used X-ray. It is desirable to use an absorbing plate having the same. Thereby, the harmonic component contained in the reflected X-ray is effectively removed, the noise is reduced, and the reflected X-ray intensity can be measured in a wide range (wide angle).
(3-2) The background is measured under a condition deviating from the specular reflection condition (non-specular reflection condition), and the average value is subtracted from the measured value under the specular reflection condition. As a result, a detection result from which background noise has been removed in advance is obtained, and it is possible to measure the reflected X-ray intensity at a wide angle.
[0010]
More specifically, in the first aspect of the present invention, the X-ray reflectometer includes a light source, an optical system that guides X-rays emitted from the light source to the sample surface, A sample position adjusting means for adjusting the position; a detector for detecting the intensity of the reflected X-rays reflected on the sample surface; and an absorbing plate disposed in front of the detector, wherein the absorbing plate has an energy of the X-rays. Has a first absorption edge in the vicinity of and on the high energy side.
[0011]
By inserting such an absorbing plate in front of the detector, it is possible to effectively remove harmonic components having higher energy than the fundamental wave of the irradiated X-ray and reduce background noise. As a result, it is possible to measure the reflected X-ray intensity at a wide angle.
[0012]
The absorbing plate may have a second absorption end near the harmonic energy of the X-ray used and on the lower energy side than the harmonic energy. In this case, a composite absorption plate of a material having the first absorption edge energy and a material having the second absorption edge energy can be provided. Such a composite absorbing plate can be made by laminating or bonding a material having a first absorption edge energy and a material having a second absorption edge energy, or forming an alloy in advance. As a result, harmonic components having twice or three times the energy of the irradiated X-ray can be effectively removed.
[0013]
Preferably, the optical system has a light collecting means for collecting X-rays emitted from the light source. Thereby, the intensity of the incident X-rays to the sample is increased, and the reflected X-ray intensity at a wide angle can be measured.
[0014]
The detector measures the intensity of the reflected X-ray for each divided measurement region obtained by dividing a predetermined measurement range into a plurality of measurement regions. In this case, the X-ray reflectivity measuring apparatus further includes an absorbing plate inserting means for inserting an absorbing plate having a different thickness for each of the divided measurement areas in front of the detector. By using an absorbing plate having a different thickness according to the measurement area, the intensity of the reflected X-ray is attenuated to an appropriate level that can be counted in each measurement area, and accurate measurement can be performed over a wide range.
[0015]
The detector measures the intensity of reflected X-rays under specular reflection conditions and the intensity of reflected X-rays under non-specular reflection conditions slightly deviated from the specular reflection conditions. In this case, the X-ray reflectivity measuring apparatus further includes a detection intensity calculating unit, and calculates an average value of the reflected X-ray intensity obtained under the non-specular reflection condition from the intensity of the reflected X-ray obtained under the specular reflection condition. The subtracted value is calculated as a detected value of the reflected X-ray intensity.
[0016]
As a result, the reflected X-ray intensity from which the background has been removed in advance is detected, and measurement at a wide angle becomes possible.
[0017]
According to a second aspect of the present invention, there is provided an X-ray reflectivity measuring method. This X-ray reflectivity measuring method includes: (a) a step of irradiating an X-ray while changing an incident angle with respect to a sample within a predetermined range; and (b) a reflection at the sample surface in a measurement range corresponding to the predetermined range. (C) measuring the intensity of the reflected X-ray under the specular reflection condition, measuring the intensity of the reflected X-ray under the non-specular reflection condition deviated from the specular reflection condition, and obtaining a background noise. Detecting the value obtained by subtracting the background noise obtained under the non-specular reflection condition from the reflected X-ray intensity obtained under the specular reflection condition as the intensity of the reflected X-ray.
[0018]
As one example, the reflected X-ray intensity (peak intensity) under the specular reflection condition and the reflected X-ray intensity (background) under two or more non-specular reflection conditions deviated from the specular reflection condition are individually determined for each measurement point. Then, the average value of the reflected X-ray intensity under the non-specular reflection condition is subtracted from the reflected X-ray intensity obtained under the specular reflection condition, and detected as the reflected X-ray intensity.
[0019]
In another example, a position-sensitive detector is used, and at each measurement point, the reflected X-ray intensity (peak intensity) under the specular reflection condition and the reflected X-ray intensity at the non-specular reflection condition position deviated therefrom (background) ) Is obtained at the same time, and the average value of the reflected X-ray intensity under the non-specular reflection condition is subtracted from the reflected X-ray intensity under the specular reflection condition, and detected as the reflected X-ray intensity.
[0020]
In still another example, the reflected X-ray intensity under specular reflection conditions is measured over the entire measurement range to determine a peak intensity profile, and the reflected X-ray intensity under non-specular reflection conditions is measured over the entire measurement range to obtain a background. Is obtained, and the intensity of the reflected X-rays is detected by subtracting the profile under the non-specular condition from the profile under the specular condition.
[0021]
In any case, the value from which the background has been removed can be detected as the X-ray intensity, so that the X-ray reflectivity can be accurately measured even over a wide range of 2θ.
[0022]
The X-ray reflectance measurement method further includes (e) dividing the measurement range into a plurality of measurement regions, and (f) inserting an absorbing plate having a different thickness in each measurement region. In this case, in the measurement step under the specular reflection condition and the measurement step under the non-specular reflection condition, the intensity of the reflected X-ray is measured via an absorbing plate having a different thickness for each divided measurement region. As a result, the intensity of the reflected X-rays is attenuated to an optimal level that can be measured for each region, and X-ray measurement can be performed over a wide range.
[0023]
Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 is a diagram showing an X-ray reflectivity measuring apparatus 10 according to one embodiment of the present invention. The X-ray reflectometer 10 adjusts the angle of the sample 20 with respect to the incident X-ray while holding the sample 20 and the optical system 12 for guiding the X-ray emitted from the light source 11 to the sample 20. The apparatus includes a sample position adjusting goniometer 21, a detector 40 for detecting reflected X-rays reflected on the surface of the sample 21, and an attenuator (absorbing plate) 30 arranged in front of the detector 40.
[0025]
As the X-ray light source, for example, an X-ray tube, a rotating anode (Cu rotor light source), or radiated light can be used. When a Cu rotor light source is used, X-rays of CuKα energy (wavelength 1.543 °) are emitted from the Cu-cathode target. Note that the conversion of wavelength and energy is approximately λ (Å) = 12.4 / E (KeV).
[0026]
The optical system 12 includes a condenser mirror 13, a shutter 14, and an entrance slit 15. The condenser mirror 13 is composed of, for example, a curved crystal (bent crystal), a multilayer mirror, or a combination thereof. The monochromator including the curved crystal and the multilayer mirror condenses the light beam emitted from the X-ray light source 11 to a vertical width of about 1.0 mm and a horizontal width of about 1.0 mm and monochromatically. Thereby, the luminous flux (radiation intensity) per solid angle of the X-ray guided to the sample 20 increases. The shutter 14 blocks X-rays except during measurement. The entrance slit 15 shapes the cross-sectional shape of the X-ray incident on the sample 20 in a range of 0.05 mm × 1 mm to 0.1 mm × 1 mm.
[0027]
The X-ray reflectometer 10 also includes a vacuum path 12 inserted between the optical system 12 and the sample 20, and between the sample 20 and the attenuator 30, and a detector slit 17. By disposing the vacuum path 16 in the X-ray passage, air scattering is reduced. The window material of the vacuum path 16 uses an organic film such as Kapton. The detector slit 17 has a slit having a length of about 0.2 mm and a width of about 2 mm, thereby reducing the background from the light beam incident on the detector to some extent.
[0028]
The sample position adjusting goniometer 21 has x, y, Rx, Ry, φ, and Z drive axes, and adjusts the position of the sample 20. By driving the sample position adjusting goniometer 21, the angle of the sample surface with respect to the X-ray emitted from the light source 11, that is, the incident angle θ of the X-ray is changed by a predetermined step angle (step size) δ.
[0029]
An absorption plate insertion unit 22 is connected to the sample position adjustment goniometer 21. The X-ray reflectometer of FIG. 2 divides a predetermined measurement range corresponding to the change of the incident angle θ into two or more measurement regions in advance, and measures the intensity of the reflected X-ray in each of the divided measurement regions. I do. At this time, the absorption plate insertion unit 22 inserts an attenuator 30 having a different thickness for each measurement area in conjunction with the movement of the sample position adjustment goniometer 21.
[0030]
As the detector 40, for example, a counting X-ray detector can be used. Of course, instead of the counting type X-ray detector 40, as shown in FIG. 3, a position-sensitive X-ray detector 41 such as a charge coupled device (CCD) or a position sensitive proportional counter (PSPC) may be used. Since the ordinary counting X-ray detector 40 has no positional resolution, it is necessary to mechanically scan the space together with the slit 17 to measure the distribution of scattered X-rays. Can be dynamically detected. Note that the detector 40 or the position sensitive detector (for example, PSPC) 41 is connected to a data processing device (detection intensity calculation means) not shown.
[0031]
The attenuator 30 is a Cu absorption plate in the example of FIG. 2, and attenuates the intensity of the reflected X-rays reflected by the sample 20 to a countable intensity. Usually, the maximum count rate of a scintillation counter or a proportional counter used as an X-ray detector is about 100,000 cps (counts per second), but the intensity of the reflected X-ray is much higher. Therefore, it is necessary to attenuate the intensity of the reflected X-rays to a range that can be measured by the detector 40 used. The X-ray reflectometer 10 measures the intensity of the reflected X-ray at the corresponding measurement position (2θ) while changing the incident angle θ of the incident X-ray with respect to the sample. As described above, the measurement range of the reflected X-ray corresponding to the change in the incident angle θ is divided into a plurality of regions in advance, and attenuators having different thicknesses are inserted in each region. Thereby, the intensity of the reflected X-rays is adjusted to an optimal level at which counting can be performed so as not to exceed the maximum measurement number (count) of the detector in each measurement region.
[0032]
For example, consider an example in which the incident angle θ is changed between 0 and 10 ° and the intensity of the reflected X-ray is measured at a position of 2θ. As described above, the intensity of the reflected X-ray is θ ⁴ Weakens in inverse proportion to Therefore, the measurement range is divided into, for example, five regions. The range where the incident angle θ exceeds 0 ° to 0.3 ° is a total reflection area, ⁷ There should be more counts. Therefore, this area is defined as a first measurement area, and the number of reflected X-rays is 10 ³ -10 ⁵ Then, a 160 μm-thick Cu absorption plate (attenuator) 30 is inserted and attenuated. Next, for example, a region from 0.3 ° to 1 ° is defined as a second measurement region. Since the reflected X-ray intensity in the second measurement area is not as strong as in the first measurement area, a count value of 10 is inserted by inserting a 120 μm thick Cu absorption plate. ³ -10 ⁵ About. Similarly, a Cu absorption plate having a thickness of 80 μm is inserted in the third measurement region, and a Cu absorption plate having a thickness of 40 μm is inserted in the fourth measurement region. In the fifth region, the position of 2θ is considerably wide-angle, and the intensity of the reflected X-rays is weakened to a level that can be sufficiently counted without being attenuated using the absorption plate. Therefore, measurement is performed without inserting a Cu absorption plate.
[0033]
The attenuator 30 to be inserted has its absorption edge at energy slightly higher than the X-ray energy used. In a preferred embodiment, the absorption edge of the absorption plate 30 is on the high energy side within a range of 5 keV or less than the X-ray energy used.
[0034]
The relationship between the absorption edge of the absorption plate 30 and the energy of the X-ray used will be described with reference to FIG. The component of the X-ray that has passed through the condenser mirror 13 includes a harmonic component having twice or three times the energy of the fundamental wave in addition to the fundamental wave. FIG. 4A is a graph showing an attenuation state when a normal absorption plate is inserted, and FIG. 4B has an absorption edge on the high energy side within a range of 5 keV or less than the energy of the irradiated X-ray. This shows an attenuation state when an absorbing plate is used.
[0035]
When a normal absorbing plate is inserted as shown in FIG. 4A, the absorptance for the X-ray wavelength (fundamental wave) is higher than the absorptance for the harmonics, and the harmonic components are not sufficiently absorbed. Therefore, the detector detects the harmonic component as well as the fundamental component of the X-ray. The detected harmonic component causes background noise.
[0036]
On the other hand, as shown in FIG. 4B, when an absorption plate having an absorption edge near the X-ray wavelength to be used (within 5 keV) and on the high energy side is inserted, the absorptivity for the harmonic component is sharp. To increase. As a result, the basic X-ray wavelength can be transmitted best, and the remaining impurity element can be effectively removed. In other words, by setting the absorptance for the fundamental wavelength of X-rays to be the lowest and setting the absorptance for other impure line components to be high, the intensity of the reflected X-rays can be detected with the background reduced.
[0037]
If the absorption edge is set higher than 5 keV, the difference between the absorptivity for the X-ray wavelength and the absorptivity for the higher harmonics becomes smaller, and the background cannot be effectively removed.
[0038]
The example of FIG. 4B shows an absorption effect (attenuation state) when a single absorption edge is set in the vicinity of the high energy side of the X-ray wavelength to be used, for example, within a range of 5 keV. On the other hand, as shown in FIG. 5, by setting the second absorption end for higher harmonics (for example, third harmonics), it becomes possible to more effectively remove impurity lines. . In this case, the second absorption edge energy is located near the higher harmonic energy and on the lower energy side than the higher harmonic energy. For example, the absorption edge is set within 5 keV on the lower energy side of the harmonic energy.
[0039]
In order to realize such absorption characteristics, it is desirable to use a synthetic absorption plate in which a material having a second absorption edge is incorporated into an absorption plate material having a first absorption edge. Examples of a method for producing such a synthetic absorption plate include laminating or bonding materials having different absorption edges, and alloying a different material in advance to form an alloy absorption plate. For example, when a Cu anti-cathode target is used as shown in FIG. 2, the reflection X is obtained by stacking or alloying platinum (Pt), gold (Au), palladium (Pb) or the like in addition to copper (Cu). Background noise can be more effectively attenuated from the lines.
[0040]
Next, an X-ray reflectivity measuring method according to the present invention will be described.
[0041]
6 and 7 are diagrams for explaining the types of the measuring method of the reflected X-ray intensity according to the embodiment of the present invention. In the X-ray reflectivity measuring method of the present invention, basically, the intensity (peak intensity) of the reflected X-ray is measured under the specular reflection condition corresponding to the incident angle θ of the irradiated X-ray, and the measured value is shifted by Δ from the measured value. The background is obtained by measuring the intensity of the reflected X-ray at the non-specular reflection condition position, and the background is subtracted from the reflected X-ray intensity obtained under the specular reflection condition to obtain the detected intensity. In this case, there are measurement methods of the type shown in FIGS. 6 and 7 depending on how the background is obtained.
[0042]
FIG. 6A shows the 2θ scanning method. In the 2θ scanning method, at each measurement point corresponding to the incident angle θ, measurement is performed with the position of the detector slightly shifted. That is, the detector is shifted between a position 2θ that satisfies the specular reflection condition and a position slightly deviated therefrom (2θ ± Δ2θ), and the peak intensity and the background are measured.
[0043]
On the other hand, FIG. 6B shows the θ scan method. In the θ scan method, the detector is fixed at the position of 2θ, and the peak intensity and the background are measured at the position of 2θ while shifting the angle of the sample to θ ± Δθ at each measurement point.
[0044]
FIGS. 6A and 6B separately show the reflected X-ray intensity under the specular reflection condition and the reflected X-ray intensity under the non-specular reflection condition deviating therefrom using the counting type detector. The measurement method is shown. FIG. 7 shows a position sensitive detector method using a position sensitive detector (PSPC). When the position sensitive detection (PSPC) is used, the peak intensity under the specular reflection condition and the background under the non-specular reflection condition can be simultaneously measured at the measurement point corresponding to the incident angle θ. That is, a two-dimensional scattering intensity distribution of reflected X-rays at 2θ can be obtained while the sample position and the detector (PSPC) are fixed.
[0045]
FIG. 8 is a graph showing the scattering distribution of the reflected X-ray at the position of 2θ obtained by the method of FIG. 6 or 7. Generally, X-rays are specularly reflected on the sample surface, and a peak of the reflected X-rays appears at the specular reflection position. Specular reflection is a reflection condition under which the incident angle θ with respect to the sample is equal to the reflection angle θ ′, and 2θ (the angle formed by the detector with respect to the optical axis of the incident X-ray) satisfies the specular reflection condition, The detector count shows a peak at 2θ. The peak count, of course, includes background noise. The background exists with almost constant intensity even at other angles including 2θ.
[0046]
Therefore, the intensity at 2θ, which is the specular reflection condition, and the non-specular reflection condition (2θ ′ = 2θ ± Δ2θ) shifted by Δ2θ therefrom. _B ) Is measured, and the average value of the intensities obtained under the non-specular reflection condition is subtracted from the peak as the background to obtain the reflection intensity from which the background has been removed.
[0047]
In the examples shown in FIGS. 6 (a), 6 (b) and FIG. 8, for simplicity of description, measurement is performed one point at each side of 2θ, but the present invention is not limited to this example. By measuring the intensity at more points and performing peak fitting, the accuracy can be further improved.
[0048]
FIG. 9 is a diagram showing a processing flow of the X-ray reflectometer 10 when the 2θ scanning method shown in FIG. 6A is adopted. In this processing flow, it is assumed that the measurement range of the reflected X-ray intensity is divided in advance into a predetermined number of measurement areas.
[0049]
First, when the process starts, an attenuator for the first measurement area is set (S101). As described above, the setting of the attenuator is automatically performed by the absorption plate insertion unit (see FIG. 2) connected to the sample position adjustment goniometer. Next, the incident angle θ of the X-ray with respect to the sample surface is set (S103). Immediately after the start of processing, the first incident angle θ ₀ Set to. After setting the incident angle θ, the specular reflection condition (2θ) and the intensity of the reflected X-ray at a position shifted therefrom are measured (S105).
[0050]
As a good measurement example in step S105, first, the detector is set to 2θ−2 × Δθ. _B And set the intensity I ₁ Is measured. Next, the detector is 2 × Δθ _B Only at the plus side, the intensity I ₂ Is measured. Furthermore, the detector is 2 × Δθ _B 2θ + 2 × Δθ _B At the position I ₃ Is measured. After measuring under the specular reflection condition, instead of measuring the intensity at a position shifted to both sides, the detector position is shifted in order from the side with the smaller angle. This avoids the axial drive of the detector in the opposite direction, which contributes to a reduction in measurement speed. In the example of FIG. 9, the measurement under the non-specular condition is performed only at two points on both sides of 2θ, but it goes without saying that two or more points may be measured on each side. Also in this case, the measurement order is set so that the detector always moves in one direction (positive side).
[0051]
Next, the reflection intensity from which the background has been removed is determined (S107). That is, the non-specular reflection condition 2θ ± 2 × Δθ _B Strength I ₁ And I ₃ And calculate the average as the background BG. Further, the measured intensity I under the specular reflection condition 2θ is ₂ Subtracting the background BG from the reflection intensity I (I = I ₂ -BG). Such a calculation is automatically performed by a data processing device (not shown) or a detection intensity calculation unit connected to the detector.
[0052]
Next, the incident angle θ is changed by δ (S109). The change (step size) δ of the incident angle θ is the shift angle Δθ for obtaining the background. _B (Δ> Δθ) _B ). By setting in this way, at the time of transition to the next measurement point, the detector is driven only in one direction, and shaft driving in the opposite direction is avoided.
[0053]
Next, it is determined whether or not the current divided measurement area has ended (S111). If the measurement in the current divided measurement area is not completed (NO in S111), the newly set incident angle in step S109 is set as the current incident angle θ (S103), and steps S105 to S107 are repeated. . As described above, the peak intensity under the specular reflection condition and the background under the non-specular reflection condition are obtained for each measurement point while sequentially changing the incident angle θ in the divided measurement region. Then, the detected intensity of the reflected X-ray is calculated by subtracting the average value of the background from the peak intensity.
[0054]
If the measurement in the current divided area has been completed in step S111 (YES in S111), it is determined whether or not the entire measurement range has been completed (S113). If the entire measurement range has not been completed (NO in S113), the process returns to step S101 to shift to the next divided measurement region (for example, the second measurement region), and an attenuator having a thickness suitable for the next divided measurement region. Insert Then, the last set θ in the previous divided measurement area is set as the first incident angle θ in the next divided measurement area (S103).
[0055]
Hereinafter, similarly, steps 105 to 109 are repeated to detect the reflection intensity from which the background has been removed at each measurement point. If the measurement has been completed over the entire measurement range in step S113 (YES in S113), the process ends.
[0056]
FIG. 10 is a processing flow of the X-ray reflectometer 10 when the θ scanning method shown in FIG. 6B is employed. First, when the process starts, an attenuator for the first measurement area is set (S201). The setting of the attenuator is automatically performed by an absorption plate insertion unit (see FIG. 2) interlocked with the sample position adjustment goniometer. Next, the detector position is set to the measurement position 2θ (S203). At the start of the process, 2θ is set to the first measurement point. Next, the sample position adjusting goniometer (FIG. 2) is adjusted so that the incident angle θ of the X-ray with respect to the sample surface is set to Δθ so as to create a specular reflection condition and a non-specular reflection condition at a position shifted therefrom. _B While shifting only, the intensity of the reflected X-rays is measured by the detector set at the position of 2θ (S205).
[0057]
As a good measurement example in step S205, first, the incident angle θ of the X-ray with respect to the sample surface is 2θ / 2−Δθ _B And the intensity I at the position of 2θ on the reflection side. ₁ Is measured. Next, the sample position is set to Δθ _B And the position is set so that the incident angle θ is 2θ / 2 (that is, 2θ satisfies the specular reflection condition), and the intensity I at the position of 2θ on the reflection side is shifted. ₂ Is measured. Further, the sample position is set to Δθ _B And the incident angle θ with respect to the sample surface is 2θ / 2 + Δθ _B And the intensity I at the position of 2θ on the reflection side. ₃ Is measured. As described above, since the sample position is moved in order from the side having the smaller angle, the axial movement of the sample position adjusting goniometer in the opposite direction is avoided, and the measurement speed is reduced. In the example of FIG. 10, the measurement under the non-specular condition is performed only at two points on both sides of 2θ, but it goes without saying that two or more points may be measured on each side. Also in this case, the sample position adjusting goniometer is driven so that the sample position always moves in one direction (+ side).
[0058]
Next, the reflection intensity from which the background has been removed is determined (S207). That is, the position of the sample is ± Δθ _B X of reflected X-ray intensity ₁ And I ₃ , And this is used as the background BG. Then, the measurement intensity I under the specular reflection condition ₂ Subtracting the background BG from the reflection intensity I (I = I ₂ -BG).
[0059]
Next, the position 2θ of the detector with respect to the optical axis of the incident X-ray is changed by δ (S209). The change amount (step size) δ is the shift angle Δθ for obtaining the background. _B (Δ> Δθ) _B ). With this setting, the driving of the sample position with respect to the incident X-ray can be performed in one direction, and the axial driving in the opposite direction is avoided.
[0060]
Next, it is determined whether or not the current divided measurement area has ended (S211). Such a determination is made, for example, by a microcomputer (not shown) connected to the detector 40 and the sample position adjusting goniometer 21 shown in FIG. If the measurement in the current divided measurement area has not been completed (NO in S211), the position of the detector newly set in step S209 is set as the current 2θ (S203), and steps S205 to S207 are repeated. . As described above, the peak intensity under the specular reflection condition and the background under the non-specular reflection condition are obtained at a new measurement point while sequentially changing the 2θ angle in the divided measurement region. Then, the detected intensity of the reflected X-ray is calculated by subtracting the average value of the background from the peak intensity.
[0061]
If the measurement in the current divided area has been completed in step S211 (YES in S211), it is determined whether or not the entire measurement range has been completed (S213). If the entire measurement range has not been completed (NO in S213), the process returns to step S201 to shift to the next divided measurement region (for example, the second measurement region), and the attenuator having a thickness suitable for the new divided measurement region Insert Then, 2θ set last in the previous divided measurement area is set as the first detection angle 2θ in the new divided measurement area (S203).
[0062]
Hereinafter, similarly, steps S205 to S209 are repeated to detect the reflection intensity from which the background has been removed at each measurement point. If the measurement has been completed over the entire measurement range in step S213 (YES in S213), the process ends.
[0063]
FIG. 11 is a diagram showing a processing flow of the position sensitive detector method when the position sensitive detector (PSPC) is used. As described above, when the position sensitive detector (PSPC) is used, the intensity distribution of the reflected X-rays with respect to a certain incident angle θ can be obtained at a time without separately measuring the background at a position shifted from the specular reflection condition. be able to. In the example shown in FIG. 11, the position sensitive detector is combined with the 2θ scanning method, and the peak intensity at 2θ and the background intensity distributed on both sides can be obtained by one measurement. When a position sensitive detector (PSPC) is used, the entire measurement range is divided into a plurality of measurement regions, and an optimal attenuator (absorption plate) is used for each measurement region.
[0064]
First, after the processing is started, an attenuator for the first divided measurement area is set (S301). Next, the incident angle θ of the X-ray with respect to the sample surface is set (S303). Immediately after the start of processing, the first incident angle θ in the measurement range ₀ Set to. Next, on the reflection side, the position sensitive detector is set at the position of 2θ = 2 × θ, and the intensity distribution of the reflected X-ray with respect to the incident angle θ is measured. In this case, a two-dimensional distribution as shown in FIG. 8 can be obtained. From the obtained intensity distribution, the peak intensity I ₀ And background BG, and the value obtained by subtracting the background from the peak intensity (I ₀ −BG) as the detection intensity I (S305).
[0065]
Next, the incident angle θ is changed by the step size δ (S307). It is determined whether the first measurement area has ended at the new angle after the change (S309), and if not (NO in S309), steps S303 to S307 are repeated to reflect at the new measurement position. An X-ray intensity distribution is obtained, and a detected intensity I is obtained therefrom.
[0066]
If the first measurement area has ended (YES in S309), it is determined whether or not the entire measurement range has ended (S311). If the entire measurement range has not been completed (NO in S311), the process returns to step S301 to set an attenuator for the next (second) divided measurement region (S301). Hereinafter, steps S303 to S307 are similarly repeated. Then, when the entire measurement range ends (YES in S311), the process ends.
[0067]
The position-sensitive detector method can reduce the number of movements and the number of measurements of the detector, so that the entire measurement time can be reduced.
[0068]
FIG. 12 shows a processing flow of another measurement method. In another measurement method, first, the reflected X-ray intensity under the specular reflection condition is continuously measured over the entire measurement range. Next, the reflected X-ray intensity under the non-specular reflection condition deviating from the specular reflection condition is continuously measured over the entire measurement range. As the non-specular reflection condition, two or more different conditions can be set, and the measurement is performed individually and continuously under each condition.
[0069]
First, after the processing is started, a first attenuator for the first divided measurement area is set (S401). Then, θ / 2θ measurement is performed in the first divided measurement area (S403). In the θ / 2θ measurement, the detector position is moved while the incident angle θ is changed in increments of δ, for example, and the reflected X-ray intensity is sequentially measured at the position of 2θ. When the first divided measurement area is completed, a second attenuator for the second divided measurement area is set (S401), and θ / 2θ measurement is performed in the second divided measurement area. In this manner, the intensity I under the specular reflection condition (2θ) is used over the entire measurement range by using the attenuator sequentially adjusted to the divided measurement area. ₀ Get.
[0070]
Next, returning to the first divided measurement area, the first attenuator is set again (S405), and the reflected X-ray intensity is measured under the first non-specular reflection condition. That is, while the incident angle θ is changed, the measurement of the reflected X-ray intensity is continuously performed at the position of 2θ−Δ for each θ (S407). When the θ / 2θ-Δ measurement is completed in the first divided measurement area, the process moves to the second divided measurement area, and a second attenuator for the second divided measurement area is set (S405). Then, θ / 2θ−Δ measurement is performed in this divided measurement area (S407). This is performed over the entire range to obtain the intensity (BG1) under the first non-specular reflection condition. BG1 may be represented as a function of θ by fitting to reduce the statistical error.
[0071]
Next, the intensity of the reflected X-ray is measured under the second non-specular reflection condition. That is, an attenuator for the first divided measurement area is set (S409), and θ / 2θ + Δ measurement is performed in the first divided measurement area (S411). Next, an attenuator for the second divided measurement area is set (S409), and θ / 2θ + Δ measurement is performed in the second divided measurement area (S411). This is repeated over the entire measurement range to obtain the intensity (BG2) under the second non-specular reflection condition. BG2 may also be represented as a function of θ by fitting.
[0072]
Finally, background detection is performed to determine the detection intensity (S413). That is, the intensity I obtained under the specular reflection condition ₀ , The average of the background ((B1 + B2) / 2 in the example of FIG. 12) is subtracted to obtain the detected intensity.
[0073]
As described above, no matter which of the methods shown in FIGS. 9 to 12 is employed, the intensity of the reflected X-ray from which the background has been removed in advance is detected from the measured peak value of the reflected X-ray. Therefore, even at a wide angle where the value of 2θ is large, a detection result with little noise can be obtained, and the evaluation of the ultrathin film can be performed accurately.
[0074]
In the method shown in FIGS. 9 and 12, the 2θ increment (step size) δ becomes 2θ the background evaluation deviation Δ2θ during the 2θ scan. _B It is set larger. Thereby, the angle of the detector is set to 2θ−Δ2θ for a certain incident angle θ. _B , 2θ, 2θ + Δ2θ _B , The measuring angle 2θ with respect to the next incident angle θ (= θ + δ) can be set by moving only in the increasing direction without returning the detector. As a result, a faster measurement is realized.
[0075]
Similarly, in the method shown in FIG. _B Shift by Δθ _B Is set to be smaller than the step angle (step size) δ of θ. As a result, the sample position is set to θ−Δθ. _B , Θ, θ + Δθ _B After the measurement, the sample can be moved to the next measurement position θ (= θ + δ) without driving in the opposite direction.
(Supplementary Note 1) A light source that emits X-rays, an optical system that guides X-rays emitted from the light source to the surface of the sample, a sample position adjusting unit that adjusts the position of the sample with respect to the X-rays emitted from the light source, and a sample. A detector for detecting the intensity of the reflected X-rays reflected by the surface of the first and second detectors; and an absorbing plate disposed in front of the detector. An X-ray reflectivity measuring device having an absorption edge of
(Supplementary note 2) The X-ray reflectometer according to Supplementary note 1, wherein the first absorption edge is located on the high energy side within a range of 5 keV from the X-ray energy.
(Supplementary note 3) The X-ray reflectometer according to Supplementary note 1, wherein the absorbing plate has a second absorption end near the harmonic energy of the X-ray and at a lower energy side than the harmonic energy.
(Supplementary note 4) The X-ray reflectometer according to Supplementary note 3, wherein the second absorption edge is on the lower energy side than the harmonic energy within a range of 5 keV from the harmonic energy of the X-ray. .
(Supplementary Note 5) The detector measures the intensity of the reflected X-ray for each of the divided measurement regions obtained by dividing the predetermined measurement range into a plurality of measurement regions, and the X-ray reflectometer differs for each of the divided measurement regions. 2. The X-ray reflectometer according to claim 1, further comprising an absorbing plate inserting means for inserting an absorbing plate having a thickness into a stage preceding the detector.
(Supplementary Note 6) In the measurement range, the detector measures the intensity of the reflected X-ray under the specular reflection condition and the intensity of the reflected X-ray under the non-specular reflection condition deviating from the specular reflection condition. The line reflectivity measuring device calculates a value obtained by subtracting the reflected X-ray intensity obtained under the non-specular reflection condition from the reflected X-ray intensity obtained under the specular reflection condition as a reflected X-ray intensity. The X-ray reflectometer according to claim 1, further comprising:
(Supplementary Note 7) The X-ray reflectometer according to Supplementary Note 1, wherein the optical system includes a light collecting unit that collects X-rays emitted from a light source.
(Supplementary Note 8) A step of irradiating X-rays while changing an incident angle with respect to the sample in a predetermined range, and a step of measuring the intensity of the reflected X-rays reflected on the surface of the sample in a measurement range corresponding to the predetermined range. Measuring the intensity of the reflected X-rays under non-specular reflection conditions deviated from the specular reflection conditions to obtain background noise; and measuring the non-specular surface from the reflected X-ray intensity obtained under the specular reflection conditions. Detecting a value obtained by subtracting background noise obtained under reflection conditions as the intensity of the reflected X-rays.
(Supplementary Note 9) The method further includes a step of dividing the measurement range into a plurality of measurement areas, and a step of inserting an absorbing plate having a different thickness for each of the measurement areas. The X-ray reflectivity measurement method according to claim 8, wherein the measurement step under the condition is performed via an absorption plate having a different thickness for each measurement region.
(Supplementary note 10) The X-ray reflection according to Supplementary note 8 or 9, wherein the measurement under the specular reflection condition and the measurement under the non-specular reflection condition are individually performed for each measurement point corresponding to an incident angle. Rate measurement method.
(Supplementary note 11) The X-ray reflection according to Supplementary note 8 or 9, wherein the measurement under the specular reflection condition and the measurement under the non-specular reflection condition are performed simultaneously for each measurement point corresponding to the incident angle. Rate measurement method.
(Supplementary Note 12) The measurement under the specular reflection condition is continuously performed over the entire measurement range, and the measurement under the non-specular reflection condition is continuously performed over the entire measurement range. 10. The method for measuring an X-ray reflectivity according to 8 or 9.
[0076]
【The invention's effect】
As described above, according to the X-ray reflectivity measuring apparatus and method of the present invention, background noise can be effectively removed, and the reflected X-ray intensity can be measured even at a wide angle 2θ position.
[0077]
As a result, it becomes possible to accurately evaluate the characteristics of the ultra-thin film.
[Brief description of the drawings]
FIG. 1A is a diagram for explaining interference of reflected X-rays, and FIG. 1B is a diagram for explaining reflected X-rays appearing at a position of 2θ.
FIG. 2 is a diagram illustrating a configuration example of an X-ray reflectance measuring apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram showing a configuration example using a position-sensitive X-ray detector (PSPC) instead of the counting X-ray detector shown in FIG. 2;
4A and 4B are diagrams for explaining an effect of the absorbing plate used in one embodiment of the present invention. FIG. 4A shows an attenuation state when a normal absorbing plate is inserted, and FIG. FIG. 3 is a graph showing an attenuation state when an absorption plate having an absorption edge on the higher side in the range of 5 keV than the X-ray wavelength used according to the present invention is inserted.
FIG. 5 is a graph showing an attenuation state in a case where a synthetic absorption plate having absorption edges corresponding to a plurality of higher-order harmonics is used as a modification of the attenuator used in the X-ray reflectometer of FIG. is there.
FIGS. 6A and 6B are diagrams for explaining types of the X-ray reflectivity measuring method according to the present invention. FIG. 6A is a diagram illustrating a 2θ scan method, and FIG. 6B is a diagram illustrating a θ scan method. .
FIG. 7 is a diagram for explaining types of the X-ray reflectivity measuring method according to the present invention, and is a diagram illustrating a position-sensitive detector method using a position-sensitive X-ray detector (PSPC).
FIG. 8 is a graph showing the distribution of the peak intensity of reflected X-rays and the background noise.
FIG. 9 is a view showing a processing flow when the 2θ scanning method is employed in the X-ray reflectivity measuring method according to the present invention.
FIG. 10 is a diagram showing a processing flow when the θ scanning method is employed in the X-ray reflectivity measuring method according to the present invention.
FIG. 11 is a diagram showing a processing flow when a position sensitive detector method is employed in the X-ray reflectivity measuring method according to the present invention.
FIG. 12: In the X-ray reflectivity measurement method according to the present invention, after measuring the peak of the reflected X-ray over the entire measurement range, separately measure the background at a position shifted by ± Δ over the entire measurement range. FIG. 7 is a diagram showing a processing flow of another measurement method.
[Explanation of symbols]
10 X-ray reflectance measuring device
11 Light source
12 Optical system
13 Focusing mirror
14 Shutter
15 entrance slit
16 Vacuum path
17 Detector slit
20 samples
21 Sample Position Adjustment Goniometer
22 Absorption plate insertion unit
30 Attenuator (absorption plate)
40 detector
41 Position sensitive X-ray detector (PSPC)

Claims (5)

A light source that emits X-rays,
An optical system for guiding X-rays emitted from the light source to the surface of the sample,
Sample position adjusting means for adjusting the position of the sample with respect to X-rays emitted from the light source,
A detector for detecting the intensity of the reflected X-rays reflected on the surface of the sample;
X-ray reflectivity measurement, comprising: an absorption plate arranged in front of the detector, wherein the absorption plate has a first absorption edge near the energy of the X-rays and on the high energy side. apparatus. 2. The X-ray reflectometer according to claim 1, wherein the absorption plate has a second absorption end near a harmonic energy of the X-ray and on a lower energy side than the harmonic energy. 3. The detector measures the intensity of the reflected X-ray for each divided measurement region obtained by dividing a predetermined measurement range into a plurality of measurement regions,
2. The X-ray reflectivity measuring apparatus according to claim 1, further comprising an absorbing plate inserting means for inserting absorbing plates having different thicknesses in front of the detector for each of the divided measurement areas. Irradiating X-rays while changing the incident angle with respect to the sample within a predetermined range;
In the measurement range corresponding to the predetermined range, a step of measuring the intensity of the reflected X-rays reflected on the surface of the sample under specular reflection conditions,
Determining the background noise by measuring the intensity of the reflected X-rays under non-specular reflection conditions deviated from the specular reflection conditions;
Detecting a value obtained by subtracting background noise obtained under non-specular reflection conditions from reflected X-ray intensity obtained under specular reflection conditions as intensity of reflected X-rays. Method. Dividing the measurement range into a plurality of measurement regions,
Further comprising a step of inserting an absorbing plate having a different thickness for each of the measurement areas, the measurement step under the specular reflection condition, and the measurement step under the non-specular reflection condition, wherein the thickness of the measurement area is different for each measurement area. The method according to claim 4, wherein the measurement is performed via an absorption plate.

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