JP2741167B2 - X-ray diffraction method of polycrystalline thin film sample on single crystal substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray diffraction method for measuring a diffraction X-ray of a polycrystalline thin film sample on a single crystal substrate.

[0002]

2. Description of the Related Art To measure a diffraction X-ray of a polycrystalline sample,
It is common to use a powder X-ray diffractometer (called an X-ray diffractometer) using a focusing optical system. This X-ray diffractometer has the following configuration. An X-ray diverged from an X-ray source is made incident on a sample, and the X-ray diffracted by the sample is focused on a light-receiving means, for example, a light-receiving slit, passes through the slit, and is diffracted by an X-ray detector arranged behind the slit. X-ray intensity is measured. And the goniome passing through the plane of the sample
By rotating the sample about the rotation center line (sample axis) and rotating the light receiving slit and the X-ray detector at twice the angular velocity of the sample about the sample axis, the diffraction X according to the diffraction angle is obtained. The line intensity distribution can be measured.

In this type of X-ray diffractometer, it is necessary to satisfy the following geometrical arrangement conditions. In order for the X-ray diffracted at the diffraction angle 2θ to converge on the light receiving slit at an arbitrary position on the sample surface, the X-ray source, the center of the sample, and the light receiving slit need to be always located on a concentrated circle, and The surface must touch this convergence circle. Strictly speaking, the surface of the sample must be an arc surface along the concentration circle, but as the diffraction angle 2θ changes, the radius of the concentration circle also changes. Often.

In a general X-ray diffractometer, an incident X-ray distance L1 from the X-ray source to the sample is equal to a diffraction X-ray distance L2 from the sample to the light receiving slit.
In this case, the incident angle α between the sample surface and the incident X-ray
And the relative rotation of the sample, the light receiving slit and the X-ray detector so that the diffraction angle 2θ formed by the incident X-ray and the diffracted X-ray always becomes 1: 2, thereby satisfying the above concentration condition. be able to. That is, the incident angle α becomes equal to θ, which is a so-called goniometer for θ-2θ scanning.

[0005]

By the way, when a polycrystalline thin film sample formed on a single crystal substrate is measured by the above-mentioned general X-ray diffractometer, the following problems are found to occur.

In FIG. 7, when the diffraction X-ray of the Au (gold) thin film 32 formed on the Si wafer 30 is measured, in addition to the diffraction line 34 due to Au, a diffraction line 36 due to the underlying Si appears. There is a problem to come. FIG. 6B shows a sample obtained by depositing Au with a thickness of 50 nm on a single-crystal Si wafer cut so that the lattice plane (100) is parallel to the wafer surface. It is an X-ray diffraction pattern when measured with a general X-ray diffractometer (L1 = L2 = 185 mm). The horizontal axis indicates the diffraction angle 2θ, and the vertical axis indicates the intensity of the diffracted X-ray (the unit is the number of counts per second: CPS). According to this graph, Au
In addition to the diffraction line of (111), two diffraction lines of Si (400) (due to two characteristic X-rays Kα and Kβ) are very large. That is, the diffraction line of the underlying Si is detected much larger than the diffraction line of Au as the measurement object, and the original diffraction measurement of Au is hindered.

[0007] Such a problem remarkably occurs mainly due to the following two reasons. The first reason is that the sample is thin and X-rays reach the base. The second reason is that the underlayer is a single crystal. A diffraction line from a single crystal has a much higher intensity than a diffraction line from a polycrystal.

By the way, a non-reflective sample plate is known to eliminate the influence of the underlying diffraction line (for example, Journal of the Crystallographic Society of Japan 12, 162 (1970)). The non-reflection sample plate is used for applying a minute amount of sample thereon and measuring the diffraction X-ray of the minute amount sample. The non-reflective sample plate is Si
And it made of a monocrystalline material such as SiO _2, a specific crystal lattice plane that is adapted to tilt by a specific angle relative to the sample plate surface. That is, the beam is cut in a specific direction so that there is no diffracted X-ray from the base in the measurement angle range. The use of such a non-reflective sample plate can eliminate the above-mentioned influence of the diffraction line from the base in the X-ray diffraction measurement of the thin film. But,
For example, in a semiconductor manufacturing process or the like, it is generally impossible to set the underlayer of a thin film under the same conditions as the above-described non-reflection sample plate, and the crystal orientation of the Si wafer is limited to a specific orientation due to other factors. It is usually set to. That is, a normal Si wafer is (100) or (111)
Are parallel to the wafer surface. Therefore, the technique of the above-described non-reflection sample plate cannot be used for “a polycrystalline thin film sample on a single crystal substrate” in which a substrate cannot be arbitrarily selected.

On the other hand, as a conventional example of the X-ray diffraction method of a thin film sample, measurement by low-angle incidence by a parallel beam method is known (Japanese Patent Application Laid-Open No. 60-263841). In this method, incident X-rays are converted into parallel beams, X-rays are incident on the thin film sample at a very low angle, and the intensity of the diffracted X-rays therefrom is measured by changing the diffraction angle 2θ. It is. According to this method, the distance of the X-ray traveling in the sample can be increased, and the intensity of the diffracted X-ray can be relatively increased. However, since this method uses the parallel beam method, the detection intensity of diffracted X-rays is weaker and the resolution is inferior to that of the focusing method.

Accordingly, an object of the present invention is to eliminate the influence of diffraction lines from an underlayer even when a concentrated method is used in X-ray diffraction measurement of a polycrystalline thin film on an arbitrary single crystal substrate. is there.

[0011]

SUMMARY OF THE INVENTION The present invention uses an asymmetric focusing optical system to avoid diffraction X-rays from a single crystal substrate and to detect only diffraction X-rays from a thin film sample. It is. That is, according to the X-ray diffraction method of the present invention, the X-ray source, the sample, and the light-receiving means are arranged on the concentrated circle, and the X-ray radiated from the X-ray source is changed while changing the relative positional relationship of these three elements. In the X-ray diffraction method in which the X-ray diffracted by this sample is focused on the light receiving means and the distribution of the diffracted X-ray intensity corresponding to the diffraction angle is measured, the sample is placed on a single crystal substrate as a sample. Using the polycrystalline thin film formed in the above, an incident X-ray distance L1 from the X-ray source to the sample and a diffracted X-ray distance L2 from the sample to the light receiving means are used.
Are different from each other and the ratio of the diffracted X-ray distance L2 to the incident X-ray distance L1 is kept constant, the incident angle α between the sample surface and the incident X-ray, the incident X-ray and the diffracted X-ray And the relative positional relationship between the sample, the X-ray source, and the light receiving means is controlled so that the diffraction angle 2θ formed by the following equation (1) is satisfied.

[0012]

(Equation 2)

In the present invention, the "polycrystal" of the polycrystalline thin film is used.
The term refers to a substance in which each crystal grain is oriented in a random direction to the extent that powder X-ray diffraction is possible, such as a substance formed on a single-crystal substrate and a substance coated with a powder sample on a single-crystal substrate. Including. The term "thin film" to which the present invention is effectively applied refers to a film having a thickness such that X-rays can substantially reach the base, and the thickness varies depending on the material of the film. That is, a sample that easily transmits X-rays, even a very thick sample, corresponds to the “thin film” in the present invention. In general, a thickness up to about several hundred μm may be considered. However, in the case of a material such as a polymer material through which X-rays are very easily transmitted, the present invention is effective to a thicker material.

[0014]

FIG. 1 is a diagram showing the principle of the optical system of the concentrated method in a state where the incident X-ray distance L1 and the diffracted X-ray distance L2 are different (hereinafter, referred to as asymmetric arrangement). The present invention is to measure a polycrystalline thin film on a single crystal substrate by using the asymmetric X-ray diffraction method. Therefore, first, the general principle of the optical system of the concentrated method of the asymmetric arrangement will be described in detail below.

In FIG. 1, the X-ray focal point F, the center of the sample 4, that is, the sample axis ω, and the center R of the light receiving slit are located on the concentration circle 12. The surface of the sample 4 is in contact with the concentration circle 12 at the point ω. The angle of the incident X-ray with respect to the surface of the sample 4, that is, the incident angle is α, and the angle of the diffracted X-ray with respect to the surface of the sample 4 is β. Since the angle of the diffracted X-ray with respect to the incident X-ray, that is, the diffraction angle is 2θ, the sum of α and β is equal to 2θ. Θ is the angle between the crystal lattice plane that causes the diffraction phenomenon and the incident X-ray.

In the case of the geometrical arrangement as shown in FIG. 1, X-rays diffracted at a diffraction angle 2θ at an arbitrary position on the sample surface are approximately converged at point R. Distance L from point F to point ω
1 is L1 = Dsinα, and the distance L2 from the ω point to the R point is L2 = Dsinβ. Also, β = (2θ−
α). Therefore, the following equation (1) holds.

[0017]

(Equation 3)

That is, if the diffraction X-ray intensity distribution corresponding to the diffraction angle 2θ is obtained while rotating the X-ray source, the sample, and the light receiving slit so as to satisfy the expression (1), the powder of the sample in an asymmetric arrangement is obtained. The X-ray diffraction pattern can be measured. By the way, Expression (1) is a ratio of the diffraction distance L2 to the incident X-ray distance L1 (hereinafter, referred to as a distance ratio K).
And the relationship between the three variables of the incident angle α and the diffraction angle 2θ can be understood.

In equation (1), K = (L2 / L
Assuming that 1) = 1, α = θ, which is the conventional symmetrical X-ray diffractometer itself.

To obtain a powder X-ray diffraction pattern, 2θ
It is necessary to measure the diffraction X-ray intensity distribution according to
Equation (1) can be seen as showing how the incident angle α and the distance ratio K should be changed when 2θ is changed. In general, the following three diffraction methods are possible in a concentrated optical system having an asymmetric arrangement while satisfying the condition of Expression (1).

(A) A method in which the angle of incidence α is changed while changing the diffraction angle 2θ while keeping the distance ratio K at a constant value.

(B) A method in which the diffraction ratio 2θ is changed while the incident angle α is kept at a constant value, and the distance ratio K is changed accordingly.

(C) A method in which both the distance ratio K and the incident angle α are changed while changing the diffraction angle 2θ.

According to the present invention, a polycrystalline thin film on a single crystal substrate is measured by using the above-mentioned diffraction method (a).
The diffraction method (a) itself is known,
It is described in detail in JP-A-357445.

There is also a known technique for the above-mentioned diffraction method (b). "J. Appl. Cryst. (1970) Vol.
No. 3,372 "discloses an X-ray diffractometer based on the Seeman-Bohlin method for X-ray diffraction measurement of a thin film sample. In this document, while the incident angle α is kept constant (that is, the X-ray source and the sample are stationary), the light receiving slit and the X-ray detector are rotated around the sample, and the distance between the sample and the light receiving slit is increased. The distance is changed according to the diffraction angle, so that the light receiving slit is located on the concentrated circle. In this method, the concentration circle remains stationary even when 2θ is changed.

Further, there is a known technique for the above-mentioned diffraction method (c). Japanese Patent Publication No. 60-22292 discloses a diffraction angle 2θ under the condition that an angle between a crystal lattice plane contributing to diffraction and a sample surface always keeps a constant value.
And the distance ratio K and the incident angle α satisfy the concentration condition of Expression (1). That is, the technique disclosed in Japanese Patent Publication No. 60-22292 discloses one specific example of the above-mentioned diffraction method (c). In the diffraction method (c), in general, countless combinations of the distance ratio K and the incident angle α can be considered for one value of 2θ. A known technique disclosed in Japanese Patent Publication No. 60-22292 is
By adding the condition that the angle between the crystal lattice plane contributing to diffraction and the sample surface always keeps a constant value, one is selected from the myriad combinations of distance ratio K and incident angle α. Will be.

After all, the present invention provides the above (a) and (b)
Among the asymmetric X-ray diffraction methods (c), the diffraction method (a) is used to measure a polycrystalline thin film on a single crystal substrate.

The diffraction method (a) performs asymmetric X-ray diffraction while keeping the distance ratio constant. Compared with other asymmetric X-ray diffraction methods, the distance between the incident X-rays during the diffraction measurement is different from that of the other methods. And the diffraction X-ray distance can be kept constant. At this time, the case where the diffraction X-ray distance L2 is longer than the incident X-ray distance L1 and the case where the diffraction X-ray distance L2 is longer than the incident X-ray distance L1
It may be shorter. In the former case, while maintaining the X-ray intensity as much as the incident X-ray distance is reduced, the diffraction X
The resolution in the X-ray diffraction measurement can be improved by the length of the line distance. In the latter case, a significantly larger X-ray source can be used. Also, in this case,
Since the diffracted X-ray distance is kept short, a decrease in X-ray intensity can be suppressed as much as possible.

If the length of either the incident X-ray distance or the diffracted X-ray distance is set as short as possible, the size of the entire X-ray diffraction apparatus can be reduced accordingly.

The diffraction method (a) performs asymmetric X-ray diffraction while keeping the distance ratio constant. The distance ratio may be a value unique to the apparatus or may be variable.

FIG. 2 shows a comparison between the general symmetrically arranged X-ray diffractometer and the optical system having the above-mentioned asymmetrical arrangement (a). The alternate long and short dash line indicates a symmetric arrangement, and the solid line indicates an asymmetric arrangement. In both cases, the diffraction angle 2θ is shown as being the same, and the position of the incident X-ray is made exactly the same. In the case of the symmetric arrangement, the incident X-ray distance and the diffracted X-ray distance are equal, and the X-ray incident angle with respect to the sample S1 is equal to θ.
The X-ray source F and the light receiving slit R1 are at line-symmetric positions with respect to the surface normal N1 of the sample S1. On the other hand, in the case of the asymmetric arrangement, the incident X-ray distance and the diffracted X-ray distance are different, and the X-ray incident angle α with respect to the sample S2 is not equal to θ. Sample S2
The X-ray source F and the light receiving slit R2 are not axisymmetric with respect to the surface normal N2.

Here, a polycrystalline thin film on a single crystal substrate is considered as a sample, and it is assumed that the lattice plane of the single crystal substrate is parallel to the substrate surface. In the case of the symmetrical arrangement, if the Bragg diffraction condition is satisfied, both the diffraction line from the polycrystalline thin film and the diffraction line from the underlying single crystal substrate pass through the light receiving slit R1 and are detected by the X-ray detector. Is detected. On the other hand, in the case of the asymmetric arrangement, only the diffraction lines from the polycrystalline thin film can pass through the light receiving slit R2, and the diffraction lines from the single crystal substrate do not go in the direction of the light receiving slit R2. This is for the following reasons. A polycrystalline thin film is a collection of a large number of crystal grains, each of which is oriented in a random direction. Therefore, even if the incident angle of the X-rays is α with respect to the thin film surface, there are some crystal grains whose lattice planes are inclined by θ with respect to the incident X-rays. I have. If the lattice plane satisfies the Bragg condition, the diffracted X-rays from the crystal grains travel in the direction of the diffraction angle 2θ, which reaches the light receiving slit R2. On the other hand, since the lattice plane of the single crystal substrate is parallel to the substrate surface, even if the Bragg condition is satisfied, diffracted X-rays 20 from this lattice plane enter the substrate surface. Will exit at the same angle α as the angle. Thereby, the diffraction line of the polycrystalline thin film on the single crystal substrate can be measured with high accuracy without being affected by the diffraction line from the single crystal substrate.

[0033]

FIG. 3 is a plan view of an embodiment of an X-ray diffraction apparatus for carrying out the X-ray diffraction method according to the present invention. In FIG. 1, an X-ray diverging from an X-ray focal point F of a target 2 provided in an X-ray tube 1 is incident on a sample 4 mounted on a sample stage 3 and diffracted. Are focused on the light receiving slit 5 and pass through this slit, and the intensity thereof is measured by the X-ray detector 6 arranged behind the slit 5. In this case, the three elements of the X-ray focal point F, the sample surface of the sample 4, and the light receiving slit 5 placed at the focal point of the diffracted X-ray are located on the concentration circle 12. The light receiving slit 5 in this embodiment corresponds to a light receiving means in the present invention.

Here, the angle formed between the incident X-ray and the diffracted X-ray passing from the X-ray focal point F and passing through the center (sample axis) ω of the sample 4 is 2θ, and the angle formed between the sample surface and the incident X-ray is α. And the angle between the sample surface and the diffracted X-ray is β.

The sample table 3 on which the sample 4 is mounted is provided on a goniometer base 7, and a counter arm 9 is fixed to a rotating disk 8 provided around the sample table 3. . The light receiving slit 5 and the X-ray detector 6 are located near the tip of the counter arm 9. A goniometer drive mechanism 10 is disposed inside the goniometer base 7, and the drive mechanism 10 allows the sample table 3 and the counter arm rotating disk 8 to be independent of each other and centered on the sample axis ω. It is driven to rotate. The rotation of the counter arm rotating disk 8 changes the arm rotation angle 2θ, while the rotation of the sample stage 3 causes the sample 4 to rotate.
X-ray incident angle α with respect to

In this embodiment, the distance from the sample 4 to the light receiving slit 5, that is, the diffraction X-ray distance L2
Is set longer than the distance from the X-ray focal point F, which is the X-ray source, to the sample 4, that is, the incident X-ray distance L1. That is, the incident X-ray distance L1 is set to 185 mm, and the diffracted X-ray distance L2 is set to 270 mm.

The light receiving slit 5 and the X-ray detector 6 are fixed on a slide member 11,
The position 1 can be changed in the direction of arrow A, that is, in the direction of approaching or moving away from the sample 4. Thereby, the diffraction X-ray distance L2 can be freely changed.

Further, the whole of the goniometer base 7 having the built-in drive mechanism 10 for the goniometer is connected to an X-ray direct beam.
If it is configured to be movable in the direction of the system (the direction of arrow B in FIG. 2), the incident X-ray distance L1 can be freely changed.

Since the incident X-ray distance L1 and the diffracted X-ray distance L2 are different, the sample table 3 and the counter arm 9 are
With the angular velocity ratio of 2: 2, it is not possible to obtain a target X-ray concentration condition. Therefore, in the case of such an asymmetric arrangement, control is performed so as to satisfy the following expression (1) as described above.

[0040]

(Equation 4)

In this case, L2 with respect to L1 during the diffraction measurement
Is constant. It is convenient to rotate at a constant angular velocity of 2θ in order to obtain a diffraction pattern. Therefore, it is practical to rotate the sample stage 3 by obtaining the incident angle α according to the change of 2θ while continuously or stepwise rotating the counter arm 9 at a constant angular velocity. The incident angle α is obtained by transforming equation (1) to obtain the following equation (2).
Can be obtained by

[0042]

(Equation 5)

FIG. 4 is a graph of equation (2), and shows the relationship between 2θ and α using the value of L2 / L1 as a parameter.

FIG. 5 is an enlarged sectional view of the sample. In this sample, a polycrystalline Au thin film 32 is formed with a thickness of 50 nm on a Si single crystal wafer 30, and the sample itself is the same as that shown in FIG. When the measurement is performed using the apparatus shown in FIG. 3, the incident angle of the X-ray to the surface of the thin film 32 is α. There is a light receiving slit in the direction of the diffraction angle 2θ. Among the many crystal grains of the polycrystalline thin film 32, there is one in which the lattice plane 33 is inclined by an angle θ with respect to the incident X-ray 31. When the Bragg condition is satisfied, the diffraction line 35 from this lattice plane 33 becomes The light reaches the light receiving slit. On the other hand, for the Si wafer 30, if the Bragg condition is satisfied,
A diffraction line 37 from the (400) plane exits at an angle α with respect to the (100) plane of Si. The diffraction line 37 is in a direction different from the direction of the light receiving slit. In this way,
The diffraction line 37 of the Si substrate can be excluded from the measurement result. The reflection from the Si (100) surface is a non-reflection condition, and is a reflection from the Si (400) surface as described above.

The angle of the diffraction line 35 of the thin film 32 with respect to the incident X-ray 31 is 2θ.
The angle of the diffraction line 37 of the wafer 30 is 2α. Therefore, the direction of the diffraction line 35 of the thin film 32 and the Si wafer 3
The direction of the diffraction line 37 of 0 is an angle, and (2θ−2α)
Are separated by the absolute value of This separation angle is at least
It is necessary to make the divergence angle of the incident X-ray larger. Thereby, the influence of the diffraction line of the Si wafer can be eliminated. This separation angle can be easily calculated from the above equation (2), and its value depends on 2θ. As can be easily understood from the graph of FIG. 4, the ratio of the incident X-ray distance to the diffracted X-ray distance is 1
The separation angle increases as the distance from the distance increases. In reality,
It is sufficient if the separation angle is several degrees or more over the measurement angle range.

FIG. 6A is an X-ray diffraction pattern obtained by measuring the sample of FIG. 5 with the apparatus of FIG. L1 = 1
85 mm and L2 = 270 mm. The horizontal axis is the diffraction angle 2
0, the vertical axis indicates the intensity of the diffracted X-ray (the unit is the number of counts per second: CPS). According to this graph, Si (40) as seen in the diffraction pattern of FIG.
0) the two high intensity diffraction lines are gone and instead
Weak diffraction lines of Au are detected. That is, Au
In addition to the strong diffraction line of (111), Au (200), A
u (220), Au (311), Au (222) weak
Diffraction lines appear. In FIG. 6B, these weak diffraction lines were hidden by the underlying Si diffraction lines and could not be detected at all, and could be detected for the first time by the present embodiment. Further, the background of the diffraction pattern of FIG. 6A is different from that of FIG.
It is smaller overall and the S / N ratio is improved. It is considered that a considerable part of the background in FIG. 6B is a result of continuous X-rays included in the incident X-rays diffracted by the Si wafer.

In the above embodiment, Au on the Si wafer is used.
Although the measurement example of the thin film has been described, the single crystal substrate and the polycrystalline thin film in the present invention can be made of various materials other than the above. For example, instead of Au thin film,
A polysilicon thin film or a polycrystalline thin film of SiO ₂ may be used.

[0048]

According to the present invention, since the diffraction line of a polycrystalline thin film on a single crystal substrate is measured using an asymmetric focusing optical system, the diffraction line from the underlying single crystal substrate is measured. The influence can be eliminated, and the diffraction line of the polycrystalline thin film on the single crystal substrate can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a plan view showing a principle diagram of an asymmetric X-ray diffraction method.

FIG. 2 is a plan view showing a comparison between optical systems of a symmetric arrangement and an asymmetric arrangement in a concentrated manner.

FIG. 3 is a plan view showing an embodiment of an X-ray diffraction apparatus for performing the method of the present invention.

FIG. 4 is a graph showing a relationship between 2θ and α.

FIG. 5 is an enlarged sectional view of a sample in an example.

FIG. 6 is a graph showing a comparison between X-ray diffraction patterns of Example (A) and Conventional Example (B).

FIG. 7 is an enlarged sectional view of a sample in a conventional example.

[Explanation of symbols]

 Reference Signs List 1 X-ray tube 4 Sample 5 Reception slit 10 Goniometer 12 Concentrated circle 30 Si wafer 32 Au thin film L1 Incident X-ray distance L2 Diffracted X-ray distance α Incident angle 2θ Diffraction angle F X-ray focal point ω Sample center axis R Receiving slit Center of

Continuation of the front page (56) References JP-A-4-357445 (JP, A) JP-A-5-113322 (JP, A) JP-A-2-140648 (JP, A) G. FIG. TISSOT & R. P. GOEHNER, "DIFFRACTION ON PEAKS IN X-RAY SPECTROCOPY: FRIE NDOR FOE?", ADVANCE ES IN X-RAY ANALYS IS (1993) Vol. 36, PP. 89−96

Claims (1)

(57) [Claims] 1. An X-ray source, a sample, and light receiving means are arranged on a concentrated circle, and X-rays radiated from the X-ray source are made incident on the sample while changing the relative positional relationship of these three elements. In the X-ray diffraction method of converging X-rays diffracted by this sample on a light receiving means and measuring the distribution of diffracted X-ray intensity corresponding to the diffraction angle, the method comprises the steps of: Using a thin film, the incident X-ray distance L1 from the X-ray source to the sample and the diffracted X-ray distance L2 from the sample to the light receiving means are different from each other, and the ratio of the diffracted X-ray distance L2 to the incident X-ray distance L1 Is kept constant, the incident angle α between the sample surface and the incident X-ray and the diffraction angle 2θ between the incident X-ray and the diffracted X-ray satisfy the following expression (1): Controlling the relative positional relationship between the sample, the X-ray source, and the light receiving means Sign
X-ray diffraction method of a polycrystalline thin film sample on a single crystal substrate. (Equation 1)