JPH1114561A - Apparatus and method for measurement of x-rays - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the time for the measurement of an X-ray reflectance and for the measurement of a locking curve and to realize the measurements by an X-ray measuring apparatus whose constitution is simple. SOLUTION: An X-ray measuring apparatus is constituted so as to be provided with an X-ray source 1 which radiates divergent X-rays, with a curved monochromator 2 by which the divergent X-rays radiated from the X-ray source 1 are made monochromatic without being made parallel, with a sample base on which a sample S is arranged in the nearly converging point of the X-rays reflected by the curved monochromator 2 and with an X-ray detector 3 which detects the X-rays reflected by the sample S. Then, the divergent X-rays which are radiated from the X-ray source 1 are made incident on the curved monochromator 2 so as to be made monochromatic without being made parallel, the X-rays which are reflected from the curved monochromator 2 are made incident on the sample S at a low angle on the nearly converging point of the X-rays, and the X-rays reflected by the sample S are detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray measuring apparatus for non-destructively analyzing a sample by irradiating the sample with X-rays and detecting the X-rays reflected by the sample. The present invention relates to an X-ray measuring apparatus and a method suitable for X-ray reflectivity measurement and rocking curve measurement.

[0002]

2. Description of the Related Art X-ray reflectivity measurement As a measurement method using X-rays, there is an X-ray reflectivity measurement method for evaluating the physical properties of a sample by utilizing the specular reflection phenomenon of X-rays. This X-ray reflectivity measuring method is particularly suitable for measuring the thickness of the thin film, the roughness of the thin film surface, the roughness of the interface between the thin film and the substrate, the density of the thin film, and the like. The principle of the X-ray reflectivity measuring method is as follows (see FIGS. 7 to 10).

In FIG. 7, when X-rays are incident on a very small surface of a substance 101 having a flat surface, that is, when X-rays are incident from a low angle θ, total reflection occurs below a critical angle. This critical angle is very small, for example, for X-rays of CuKα, 0.22 ° for Si or a glass plate, and 0.42 ° for Ni.
°, and 0.57 ° for Au.

This critical angle changes depending on the electron density of the substance. As the incident angle of the X-rays becomes larger than this critical angle, the X-rays gradually penetrate deeper into the material. In a material having an ideal plane, as shown by a curve A in FIG. 8, when the critical angle is an angle equal to or more than θc, the X-ray reflectivity is proportional to θ ~ ⁴ (θ is the X-ray incident angle). And decrease sharply. In addition, if the surface of the material is rough, the degree of the reduction will be even greater, as indicated by the dashed line B. On the vertical axis of the figure, I ₀ is the incident X-ray intensity, and I is the reflected X-ray intensity.

[0005] As shown in FIG. 9, such a substance is used as a substrate 101, and another substance having a different electron density is uniformly laminated on the substrate 101 to form a thin film 102. When X-rays are incident at a low angle, the substrate 101 and the thin film 10
2 and X reflected at the surface of the thin film 102.
The lines are stronger or weaker each other. As a result, as shown in FIG. 10, a vibration pattern C due to X-ray interference appears on the reflectance curve.

From the period of the vibration pattern C, the thin film 10
2 can be determined, and surface and interface information can be obtained from the angular dependence of the amplitude of the vibration pattern C. Further, the density of the thin film 102 can be obtained by considering both the period and the amplitude of the vibration pattern. Normal X
In the line reflectance measurement, the horizontal axis 2 in FIGS.
θ is about 0 ° to 5 °, and 0 ° in a wide range.
It is measured in the range of 〜１０10 °.

FIG. 11 is a plan view showing a conventional X-ray measuring apparatus (X-ray reflectivity measuring apparatus) using the above-described principle of X-ray reflectivity measurement. In this X-ray reflectometer, the X-rays emitted from the X-ray source
Is converted into monochromatic parallel X-rays, and is incident on the sample S at a low angle. The X-rays incident on the sample S are reflected at an angle of 2θ according to the incident angle θ. Thus, X reflected by the sample S
The X-ray detector 112 detects a line and obtains the reflectance for each incident angle θ.

This type of X-ray reflectometer measures the reflectivity while changing the incident angle θ in minute units. For this reason, the apparatus is provided with a goniometer 113, and the sample S is rotated by a minute angle unit by the goniometer 113 to change the incident angle θ of the X-ray with respect to the sample S.

Rocking Curve Measurement Another measuring method using X-rays is rocking curve measurement. This rocking curve measurement, for example,
Samples with a mixed crystal film such as an epitaxial layer grown on a substrate crystal and samples with a structure in which a set of different types of single-crystal thin films are periodically laminated on the substrate crystal (superlattice structure) are grown on the substrate crystal It is known as a method for analyzing a lattice constant of a mixed crystal film or a superlattice structure that has been made.

FIG. 12 is a diagram showing a conventional X-ray measuring device used for rocking curve measurement. In this X-ray measuring apparatus, X-rays emitted from an X-ray source 210 are converted into monochromatic parallel X-rays by a monochromator 211 called a first crystal.
The light is converted into a line and is incident on the sample S. Then, the sample S is swung by a small angle ω with respect to the incident X-ray, and the incident angle of the X-ray to the sample S is changed within the range of the small angle ω.

When the incident angle of the X-rays on the sample S is changed as described above, the X-rays are reflected (diffracted) by the substrate crystal when the incident angle matches the black angle of the substrate crystal. When the black angle of the mixed crystal film or the superlattice structure coincides with the black angle, X-rays are reflected (diffracted) by the mixed crystal film or the superlattice structure. The X-ray detector 212 detects X-rays reflected from the substrate crystal, the mixed crystal film, and the superlattice structure, and obtains a profile of the incident angle versus the intensity of the X-ray, thereby obtaining FIG.
A rocking curve as shown in FIG.

In this rocking curve, the peak profile Io of the substrate crystal and the peak profile Ip of the mixed crystal film or the superlattice structure appear separately from each other. If the X-ray incident angle (Bragg angle) at which the peak profile Io of the substrate crystal appears is known, X at which the peak profile Io of the substrate crystal appears
The difference Δθ between the X-ray incident angle and the X-ray incident angle at which the peak profile Ip relating to the mixed crystal film or the superlattice structure appears appears.
The lattice constant of a mixed crystal film or a superlattice structure can be relatively determined.

[0013]

SUMMARY OF THE INVENTION X-Ray Reflectance Measurement As described above, the conventional X-ray reflectance measurement apparatus uses the sample S
A goniometer 113 is provided to change the incident angle θ of X-rays with respect to. This goniometer 113
The sample S must be rotated in a very narrow angle range with a high degree of precision in minute angle units, and for example, an accuracy of about 10 to ⁴ ° is required. Such a goniometer 113
Extremely high-precision processing is required structurally, and the manufacturing cost is high. In addition, a complicated control program is required to perform drive control in such a small angle unit, so that the operation requires some skill.

Further, since the incident angle θ of the X-rays to the sample S is changed in small angle units and the operation of detecting the reflected X-rays is repeated at each incident angle, there is a disadvantage that the measurement time becomes long. . For example, the Applicant believes that a similarly structured X
While manufactures conventionally linear reflectance measuring apparatus, the apparatus (trade name: GXR ²⁾ when carrying out the X-ray reflectance measurement, it requires a measurement time of 20 minutes to 2 hours.

Rocking Curve Measurement As described above, the conventional X-ray measuring apparatus for performing the rocking curve measurement uses a precise rocking mechanism to rock the sample S by a small angle ω with respect to the incident X-ray. There is a drawback in that it is necessary to provide the device and the production cost is high. In addition, in order to perform measurement while oscillating the sample S, its operation time (that is, time for scanning the sample) is defined as:
A measurement time of at least several minutes was required.

The present invention has been made in view of such circumstances, and provides an X-ray measurement apparatus which has a simple structure, realizes a reduction in equipment cost, and can greatly reduce the measurement time. With the goal. It is another object of the present invention to provide an X-ray measurement method that can significantly reduce the measurement time.

[0017]

Means for Solving the Problems To achieve the above object, the present invention relates to an X-ray measuring apparatus, wherein X-rays are incident on a sample,
In an X-ray measurement device that detects X-rays reflected by a sample,
An X-ray source that emits divergent X-rays, a curved monochromator that monochromatically reflects the divergent X-rays emitted from the X-ray source without collimating, and a substantially convergent point of the X-rays reflected by the curved monochromator And a X-ray detector for detecting X-rays reflected by the sample.

Further, according to the present invention relating to the X-ray measuring method, the divergent X-rays are made incident on the curved monochromator to be monochromatic without being parallelized, and the X-rays reflected from the curved monochromator are converted to the X-rays of the X-ray. It is characterized in that X-rays that are incident on the sample substantially at the convergence point and are reflected by the sample are detected.

It is known that when divergent X-rays enter a curved monochromator, monochromatic X-rays are reflected without collimation. The present invention utilizes the characteristics of the curved monochromator for X-ray measurement. That is, the X-rays reflected from the curved monochromator are
X-rays in a certain angle range can be simultaneously incident on the sample when the X-rays are incident on the sample substantially at the convergence point of the line. Therefore, the X-rays are reflected from the sample in a certain angle range according to the incident angle range of the X-rays. By detecting X-rays within a certain angle range reflected from the sample in this way, X-ray reflectivity measurement and rocking curve measurement can be performed in a short time.

When measuring the X-ray reflectivity using the X-ray measuring apparatus of the present invention, the incident angle of the X-rays to be incident on the sample from the curved monochromator is adjusted to the low angle required for the X-ray reflectivity measurement. What is necessary is just to set to an angle range. When a rocking curve measurement is performed on a sample having a mixed crystal film or a superlattice structure grown on a substrate crystal having a known Bragg angle, the average of X-rays incident on the sample from a curved monochromator is measured. It is preferable to set the incident angle near the known Bragg angle. With this setting, the peak profile of the X-ray reflected (diffracted) from the mixed crystal film or the superlattice structure can be determined based on the peak profile of the X-ray reflected (diffracted) from a crystal having a known Bragg angle. Can be obtained at the same time. The Bragg angle is an angle (X at which the X-ray diffraction phenomenon occurs on the crystal lattice plane).
(Angle of incidence of line).

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a plan configuration diagram of an X-ray measurement apparatus according to an embodiment of the present invention. As shown in the figure, the X-ray measuring apparatus of the present embodiment includes an X-ray source 1, a curved monochromator 2, a sample stage (not shown) as a sample placement unit, and an X-ray detector 3. . Reference numeral 4 denotes a slit for adjusting the divergence angle of the divergent X-ray radiated from the X-ray source 1.

The curved monochromator 2 has a function of making incident X-rays monochromatic and reflecting them. That is, when X-rays are incident on the curved monochromator 2, characteristic X-rays (for example,
Kα ₁ ) is obtained by reflection. The curved monochromator 2 can be manufactured by thinly slicing a substantially perfect crystal material such as α-quartz, Si, Ge or the like, polishing the surface to a mirror surface, and forming a curved surface at a predetermined curvature. In general, two types of curved monochromator 2 are known: a Johansson type and a Johans type.

FIG. 2 is a plan view showing a Johansson type curved monochromator. The Johansson-type curved monochromator 2 'has a structure in which the surface is curved along a Rowland circle (concentrated circle) 10 having a radius R and the lattice plane inside the crystal is curved with a radius 2R as shown in FIG. ing. The Johansson-type curved monochromator 2 ′ arranges a focal point P of divergent X-rays at an arbitrary point set on the Roland circle 10 and irradiates the divergent X-rays on the surface, and converts monochromatic divergent X-rays into a predetermined color. Reflect at an angle. Then, the reflected X-ray is a predetermined point (convergence point Q) on the Roland circle 10
Converges to

FIG. 3 is a plan view showing a Johann type curved monochromator. The Johann type curved monochromator 2 ″ has a configuration in which the surface is curved at a radius of 2R with respect to a Rowland circle 10 having a radius R as shown in the figure. The lattice plane inside the crystal is parallel to the surface. The Johann-type curved monochromator 2 ″ has a focal point P for divergent X-rays at an arbitrary point set on the Roland circle 10. When the surface is irradiated with the divergent X-rays, the monochromatic divergent X-rays are reflected at a predetermined angle. The reflected X-ray converges at a predetermined point (convergence point Q), but does not converge at one point but has a spread. However, this spread is small in a small range of the X-ray divergence angle, and does not hinder practically any problem.

In the above-described curved monochromator 2,
When the arrangement is such that the optical path lengths of the incident X-rays and the reflected X-rays are equal, symmetrical reflection occurs. However, there is a case where it is desired to bring the curved monochromator 2 closer to the focal point P of the incident X-rays and increase the optical path length of the reflected X-rays. In order to obtain such asymmetric reflection, the crystal lattice plane 2a may be inclined by δ (δ <θ) with respect to the surface, as shown in FIG. Θ is the angle of incidence of X-rays on the crystal lattice plane. With this configuration, the distance PO from the focal point P to the incident point O of the curved monochromator 2 and the distance OQ from the incident point O to the convergence point Q are expressed by the following equations, respectively. PO = 2R sin (θ−δ) OQ = 2R sin (θ + δ)

As the X-ray source 1, an X-ray tube that emits divergent X-rays is used. The X-ray source 1 preferably has a fine focus of, for example, about 0.1 mm or less. The focal point P of the divergent X-ray radiated from the X-ray source 1 is arranged on the Rowland circle 10 of the curved monochromator 2 as described above. X-ray source 1
When the focal point P of the divergent X-ray radiated from
A micro focus may be formed by disposing a slit in front of the source 1. In this case, the slit is curved monochromator 2
Are arranged on the Roland circle 10.

The sample S is mounted on a sample table (not shown), and the sample surface is arranged at a convergence point Q of the X-ray reflected by the curved monochromator 2. As shown in FIG. 5A, when the sample surface Sa is arranged parallel to one side edge of the X-ray optical path reflected from the curved monochromator 2, the convergence angle of the incident X-ray from the sample surface Sa In the low angle range up to Ω (0 ° to Ω),
X-ray reflectivity measurement can be performed simultaneously. In addition, as shown in FIG. 5B, the sample surface Sa is shifted by ε with respect to one side edge of the X-ray optical path reflected from the curved monochromator 2.
When the sample surface is tilted only by X, the X-ray reflectivity can be measured simultaneously in a low angle region of ε to Ω with the sample surface Sa as the origin (0 °).

As described above, the critical angle at which total reflection occurs when X-rays are incident on a substance is very small.
For uKα X-ray, 0.22 ° for Si or glass plate,
It is 0.42 ° for Ni and 0.57 ° for Au. Therefore, the convergence angle Ω of the X-ray irradiating the sample S is
When the angle is about 1 °, the X-ray reflectivity can be sufficiently measured. The convergence angle Ω of the X-rays reflected by the curved monochromator 2 depends on the size of the monochromator 2, the radius of curvature, the incident angle of the X-rays, etc., but an X-ray having a convergence angle Ω of about 1 ° is obtained. It's easy.

In order to measure the rocking curve of a sample having a mixed crystal film or a superlattice structure grown on a substrate crystal having a known Bragg angle by the above-mentioned X-ray measuring apparatus, As shown in FIG. 5 (c),
The average incident angle λ of the X-rays reflected from the curved monochromator 2 with respect to the sample surface Sa may be set near the known Bragg angle θ. With this setting, X reflected and diffracted from the substrate crystal whose Bragg angle θ is known
The X-ray peak profile reflected from the mixed crystal film or the superlattice structure can be simultaneously obtained based on the X-ray peak profile.

As the X-ray detector 3, various detectors capable of detecting the X-ray intensity in one or two dimensions can be used. For example, an imaging plate (IP), a CCD for X-ray detection, a one-dimensional PSD, or the like can be applied as the X-ray detector 3. Now, in the X-ray reflectivity measurement, X
The X-ray intensity I detected by the line detector 3 is Imin = 1c
There is an intensity difference from ps / s to Imax = 10 ⁶ cps / s. Therefore, the X-ray detector 3 having a narrow dynamic range may not be able to measure.

In this case, it is preferable to insert an X-ray absorber 5 made of an X-ray absorbing material into the optical path of the X-ray reflected by the sample S as shown in FIG. The intensity of the X-ray reflected from the sample S decreases as the reflection angle increases. Therefore, the X-ray absorber 5 is formed such that the width of the portion through which the X-ray reflected at a low angle is transmitted is wide and the width of the portion through which the X-ray having a large reflection angle is transmitted is small. This makes it possible to increase the attenuation rate of the X-rays having a high intensity and to decrease the attenuation rate of the X-rays having a low intensity, thereby reducing the difference in the intensity of the X-rays. As a specific shape of the X-ray absorber 5, for example, a wedge shape or a stepped shape can be considered. When the X-ray absorber 5 is inserted as described above, the true X-ray intensity may be calculated by correcting the measurement result according to the X-ray attenuation rate of the absorber 5.

According to the X-ray measuring apparatus described above, the X-ray source 1
Emitted divergent X-rays from is monochromatic incident on the curved monochromator 2, for example only K [alpha ₁ is reflected from the surface. The X-rays reflected from the curved monochromator 2 have an angle range of the convergence angle Ω, and the X-rays with the convergence angle Ω enter the sample S. X-rays are reflected from the sample S according to the incident angle of the X-rays.

Then, the X-ray detector 3 detects the reflection angle and the X-ray intensity of the X-ray reflected from the sample S, thereby measuring the X-ray reflectivity and the rocking curve for all necessary angles. Measurements can be taken simultaneously. Thus, for all required angles, X
Since the X-ray reflectivity measurement and the rocking curve measurement can be performed simultaneously, for example, the X-ray measurement apparatus of the present embodiment is provided during the thin film manufacturing process, and the X-ray reflectivity measurement and the rocking curve measurement are performed in parallel with the thin film manufacture. Measurement can also be performed. Note that the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications or applications are possible.

[0034]

As described above, according to the X-ray measuring apparatus of the present invention, the structure is simple, the equipment cost can be reduced, and the measuring time can be greatly reduced. Further, according to the X-ray measurement method of the present invention, X-ray measurement can be performed simultaneously for all measurement angles required for the sample, so that the measurement time can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing an X-ray measurement apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view showing a Johansson type curved monochromator applied to the apparatus.

FIG. 3 is a plan view showing a Johann type curved monochromator applied to the apparatus.

FIG. 4 is a plan view showing a configuration for realizing asymmetrical reflection by a curved monochromator.

FIG. 5 is a schematic diagram illustrating a relationship between an incident angle and a reflection angle of an X-ray with respect to a sample.

FIG. 6 is a plan view showing a configuration of an X-ray measuring apparatus in which an X-ray absorber is inserted.

FIG. 7 is a schematic diagram for explaining the principle of X-ray reflectivity measurement.

FIG. 8 is a graph showing an example of an X-ray reflectance curve.

FIG. 9 is another schematic diagram for explaining the principle of X-ray reflectivity measurement.

FIG. 10 is a graph showing another example of the X-ray reflectance curve.

FIG. 11 is a plan view showing a conventional X-ray measuring device used for measuring X-ray reflectivity.

FIG. 12 shows a conventional X used for rocking curve measurement.
It is a top view showing the outline of a line measuring device.

FIG. 13 is a diagram illustrating an example of a rocking curve.

[Explanation of symbols]

 1: X-ray source 2: curved monochromator 3: X-ray detector 4: slit 5: X-ray absorber S: sample

Claims (6)

[Claims] 1. X-rays incident on a sample and reflected by the sample
An X-ray measuring device for detecting X-rays, comprising: an X-ray source that emits divergent X-rays; a curved monochromator that monochromatically reflects the divergent X-rays emitted from the X-ray source without collimating the reflected X-rays; An X-ray measuring apparatus comprising: a sample arranging means for arranging a sample at a substantially converging point of X-rays reflected by a monochromator; and an X-ray detecting means for detecting X-rays reflected by the sample. 2. The X-ray measuring apparatus according to claim 1, wherein an incident angle of the X-ray to be incident on the sample from the curved monochromator is set to a low angle range necessary for measuring the X-ray reflectivity. X-ray measurement device. 3. A rocking curve measurement for a sample having a mixed crystal film or a superlattice structure grown on a substrate crystal having a known Bragg angle, as a measurement target.
The X-ray measuring apparatus according to claim 1, wherein an average incident angle of X-rays to be incident on the sample from the curved monochromator is set near the known Bragg angle. 4. An X-ray incident on a sample and reflected by the sample.
In the X-ray measurement method for detecting X-rays, the divergent X-rays are made incident on a curved monochromator to be monochromatic without being parallelized, and the X-rays reflected from the curved monochromator are substantially converged on the X-ray. Detecting an X-ray incident on the sample and reflected by the sample. 5. The X-ray measuring method according to claim 4, wherein an incident angle of the X-ray to be incident on the sample from the curved monochromator is set to a low angle range necessary for measuring the X-ray reflectivity. X-ray measurement method. 6. The X-ray measurement method according to claim 4, wherein a sample having a mixed crystal film or a superlattice structure grown on a substrate crystal having a known Bragg angle is set as a measurement target, and the sample is transferred from the curved monochromator to the sample. An X-ray measuring method, wherein an average incident angle of X-rays to be incident is set near the known Bragg angle.