JP3348269B2 - X-ray reflectance measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring X-ray reflectivity, and more particularly, to a method for measuring the reflectivity of a thin film material based on a change in X-ray reflectivity with respect to a change in an incident angle of X-rays on a sample surface. The present invention relates to an X-ray reflectivity measuring method for evaluating physical properties.

[0002]

2. Description of the Related Art Conventionally, the X-ray reflectivity method has been used as an effective method for evaluating the surface structure of a sample having a multilayer structure in which various thin films such as semiconductor devices are deposited. It is necessary to obtain information corresponding to a wide range of X-ray incident angles in order to evaluate a very thin thin film and a detailed evaluation of a laminated film such as flatness of a laminated interface in a simple semiconductor device or the like.

The X-ray reflectivity method is a method of evaluating physical properties by matching the dependence of a reflected X-ray intensity profile on an X-ray incident angle on a sample with a simulation result. For a good sample,
The reflected X-ray intensity theoretically attenuates in inverse proportion to the fourth power of the X-ray incident angle on the sample, and more rapidly when the thin film / substrate interface is not flat.

In this case, in order to perform a highly accurate analysis, it is necessary to perform measurement in the range of the X-ray incident angle as wide as possible. Therefore, it is required to measure and detect the reflected X-ray intensity over a wide range. Will be.

In a conventional X-ray reflectivity measuring apparatus,
The limit of the measured intensity is determined by the limit of the X-ray intensity that can be detected correctly by the X-ray detector, and the measurable limit has limited the measurable X-ray incident angle.

This situation will be described with reference to FIG. Referring to FIG. 6, a conventional X-ray reflectometer measures an X-ray source 1 such as a rotating anti-cathode.
1, slit 12, channel cut crystal 13, slit 14, incident X-ray intensity monitor 15, goniometer 1
7, a slit 18, and an X-ray detector 19.
2. After monochromatizing, collimating, attenuating, and shaping through the channel cut crystal 13 and the slit 14, a predetermined X is applied to the sample 16 to be measured placed on the goniometer 17 through the incident X-ray intensity monitor 15. Light is incident at a line incident angle 22.

The incident X-ray 20 is reflected at a reflectance according to the surface structure of the sample 16 to be measured, and the reflected X-ray 21 is detected by the X-ray detector 19 through the slit 18. In this case, the measurement is performed while the angle of the sample 16 to be measured 16 with respect to the incident X-ray 20 (the rotation angle of the goniometer) is changed by the goniometer 17. In addition,
Reference numeral 23 denotes an elevation angle of the X-ray detector 19.

[0008]

However, in such an X-ray reflectivity measuring apparatus and method, the method of adjusting the X-ray intensity so that the X-ray intensity does not exceed the measurement limit is determined by an X-ray source. Either to adjust the intensity of the X-ray itself or to attenuate the X-rays by the slits 12, 14, and 18. In this method of adjusting the X-ray intensity, measurement can be performed only in a relatively narrow X-ray incident angle range. Evaluation of extremely thin thin films that cannot be performed and the X-ray reflectance profile changes slowly
When trying to evaluate the flatness or the like of the interface of a multilayer film that requires information on a region having a large line incident angle 22, it has been difficult to obtain data with sufficient accuracy to withstand the analysis.

Therefore, an object of the present invention is to provide an X-ray reflectivity measuring apparatus and a measuring method capable of measuring an X-ray reflectivity with high accuracy over a wider range of the X-ray incident angle 22. And

[0010]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. See FIG. 1. (1) The present invention relates to an X-ray path between an X-ray source and an X-ray detector.
When an X-ray reflectometer equipped with an X-ray absorber is used,
Dividing the X-ray incident angle area to be measured into two or more areas
Then, a different X-ray absorber is used for each of the divided areas.
In the X-ray reflectivity measuring method, the X-ray incident angle is small.
Scanning at an X-ray incident angle in a predetermined direction .

Thus, in the direction in which the X-ray incident angle becomes smaller
Scanning was performed in the opposite direction by scanning at the X-ray incident angle.
In comparison with the case, the X-ray detector 6 is not damaged.
You. In other words, the X-ray incident angle increases in the direction in which the X-ray incident angle increases.
When scanning is performed, replace the X-ray absorber 2
Of X-ray absorption of the X-ray absorber 2 is too large
And the X-ray detector 6 will be damaged.
When scanning at an X-ray incident angle in a direction in which
How to replace the X-ray absorber 2 to make it thicker
Even if it is replaced, the X-ray detector 6 may be damaged immediately after replacement.
Disappears.

[0012] (2), in the above (1), the division of the X-ray incidence angle range to be measured, and performing in accordance with the reflected X-ray strength of.

In this case, the reflection X set during the measurement process
When the X-ray intensity exceeds the upper limit or falls below the set lower limit of the reflected X-ray intensity, the X-ray absorber 6 is replaced without destroying the X-ray detector 6 and a wide range of X-rays. Highly accurate measurement at the line incident angle becomes possible.

[0014] (3) Regarding the above (1), the division of the X-ray incidence angle range to be measured, and performing in accordance with the X-ray incidence angle.

In this case, the reflected X-ray intensity roughly corresponding to the X-ray incident angle is simulated in advance,
When the X-ray incidence angle set in the measurement process is exceeded, or
If the X-ray absorption ratio falls below the above range, the X-ray absorber 2 is exchanged to enable highly accurate measurement at a wide range of X-ray incident angles without destroying the X-ray detector 6. The replacement can be performed only by monitoring the rotation angle of the goniometer 4 without monitoring the line intensity.

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

FIG. 2 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of an X-ray reflectometer of the present invention. FIG. 2 shows a channel cut crystal 13 and an incident X-ray intensity monitor 15 of the conventional X-ray reflectometer shown in FIG. This corresponds to a structure in which the X-ray absorber 24 is provided between the slit 14 and the slit 14.

That is, the X-ray reflectivity measuring apparatus of the present invention comprises: an X-ray source 11 such as a rotating anti-cathode;
Slit 12 for shaping 0, channel cut crystal 13 made of a pair of parallel plate-like silicon crystals for suppressing angular divergence of incident X-rays 20 passing through slit 12, incident X
X-ray absorber 2 made of an Al plate that attenuates the intensity of wire 20
4. A slit 14 for shaping the incident X-ray 20 passing through the X-ray absorber 24, an incident X-ray intensity monitor 15 comprising an ion chamber for measuring the intensity of the incident X-ray 20 passing through the slit 14, and a sample 16 to be measured. Place the sample to be measured 1
A goniometer 17 for arbitrarily setting an X-ray incident angle 22 with respect to 6, a slit 18 for restricting the incidence of the reflected X-ray 21 from the material 16 to be measured, and a scintillation counter for detecting the reflected X-ray 21 through the slit 18 X
It comprises a line detector 19.

In this case, the slit 18 and the X-ray detector 1
Numeral 9 is attached to an arm (not shown) fixed to the goniometer 17 so as to rotate in conjunction with the rotation of the goniometer 17.
The operation is set so that the line incident angle 22 and the elevation angle 23 of the X-ray detector 19 become equal.

FIG. 3 shows the measurement results of a sample obtained by depositing a 10 nm-thick Co (cobalt) thin film on a Si substrate using this X-ray reflectivity measuring apparatus. Scan the corner 22 by X
When the intensity of the reflected X-rays 21 exceeds a preset value equal to or less than the detection limit value, the X-ray absorber 24 is set to have a larger X-ray absorption amount. Replace it with a thicker X-ray absorber 24.

In this case, after the measurement is started without using the X-ray absorber 22, the intensity of the reflected X-rays 21 exceeds a set value (about 2.5 × 10 ⁵ cps: count / second). That is, in the region where the X-ray incident angle 22 is on the low angle side, an Al plate having a thickness of 0.9 mm is inserted as the X-ray absorber 24, and the intensity of the incident X-ray 20 is increased by the 0.9 mm Al plate. Can be attenuated to approximately 1/1000 (10 ⁻³ ), and a measurement result corresponding to a value exceeding 10 ⁸ cps is obtained using the X-ray detector 19 having a detection limit of about 3 to 4 × 10 ⁵ cps. be able to.

When the X-ray absorber 24 is inserted, the intensity of the reflected X-rays 21 before and after the insertion is measured at the same X-ray incidence angle 22 when the X-ray absorber 24 is inserted. Then, the intensity of the reflected X-ray 21 after insertion is corrected so that the measurement results are continuous, and the layer structure of the sample 16 to be measured is evaluated.

For example, when the results shown in FIG. 3 are obtained, the sample 1 to be measured is analyzed by the analysis based on the Fresnel equation.
The layer structure of No. 6 is not a 10 nm Co film, but actually consists of three layers having different densities.
At 10 nm and 2 nm, the unevenness of each interface is evaluated to be several Å.

As described above, according to the intensity of the reflected X-ray 21, X
By exchanging the line absorber 24 and measuring the intensity of the reflected X-rays 21, it is possible to perform measurement in a region where the X-ray incident angle 22 is large by using the incident X-rays 20 having a large intensity. Even with the shortening, highly accurate measurement can be performed.

Further, as in the first embodiment, by scanning the X-ray incident angle 22 so that the X-ray incident angle 22 decreases, the profile of the intensity of the reflected X-ray 21 can be checked. Since the X-ray absorber 24 having an appropriate thickness can be replaced, the accuracy of the profile is not impaired.

In such a measurement of the X-ray reflectivity, the intensity is wavy as is apparent from the figure, so that the X-ray incident angle is set so as not to impair the accuracy of the profile in such a case. When the intensity of the reflected X-rays 21 decreases on the way and falls below a preset value in spite of scanning so as to reduce the number 22, the X-ray absorber 24 having a smaller absorption amount is replaced with a thin X-ray absorber 24. The measurement may be performed.

In the first embodiment, the X-ray absorber 24 is inserted only once, that is, when the thickness is zero.
It is equivalent to replacing the X-ray absorber 24 having a thickness of 0.9 mm with the X-ray absorber 24 having a thickness of 0.9 mm, but in order to measure the X-ray incident angle 22 more precisely and over a wide range, a plurality of times are required. May be exchanged.

In the first embodiment, the X-ray absorber 24 is replaced by the intensity of the reflected X-rays 21. However, the intensity of the reflected X-rays 21 and the intensity of the incident X-rays 20 are different. If a rough state of the correlation is known, a set value may be provided for the X-ray incident angle 22, and if the set value falls below this set value, the X-ray absorber 24 may be replaced with a thicker X-ray absorber 24.

Further, the scanning direction of the X-ray incident angle 22 may be reversed. In this case, the thickest X-ray absorber 24 is inserted first, and when the X-ray absorber 24 falls below a predetermined set value, the scanning direction becomes larger. What is necessary is just to replace it with a thin X-ray absorber 24.

However, in this case, if the amount of X-ray absorption of the replaced X-ray absorber 24 is excessively reduced during replacement, the X-ray detector 19 will be damaged, and the replacement will be performed. If the degree of decrease in the amount of X-ray absorption of the X-ray absorber 24 is too small, frequent replacement is required, so that caution is required.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 conceptually illustrates the measurement method according to the second embodiment, in which the X-ray incident angle region is divided into two regions, that is, a low-angle region A and a high-angle region B. 4 (a) shows the reflected X-ray intensity, and FIG. 4 (b) shows the incident X-ray intensity. in this case,
In order to smoothly connect the measurement data, a connection area C where the low-angle area A and the high-angle area B overlap is provided.

Referring to FIG. 4A, the intensity of the reflected X-rays 21 in the high-angle area B is measured without using the X-ray absorber 24 while scanning so that the X-ray incident angle 22 is reduced. In the region C, the measurement is performed for the case where the X-ray absorber 24 is inserted and the case where the X-ray absorber 24 is removed, and in the subsequent low-angle region A, the measurement is performed with the X-ray absorber 24 inserted.

When the measurement data is connected, the connection is performed such that the average value of the data in the low-angle area A and the average value of the data in the high-angle area B in the connection area C are equal to each other. Is apparently
The measurement exceeds the upper limit of the measurement of the X-ray detector 19, and the measurement is performed over a wider range of the X-ray intensity than the conventional X-ray reflectivity profile, that is, the measurement is performed within the range of the X-ray incident angle 22. Therefore, it is possible to evaluate the surface structure of the substrate with higher accuracy than before.

Referring to FIG. 4B, the connection between the data in the low-angle area A and the data in the high-angle area B in the connection area C in this case is represented by a reflection X
The measurement may be performed by using the measured value of the intensity of the incident X-ray 20 on the incident X-ray intensity monitor 15 shown in FIG.

In any case, the connection of the data in the low-angle area A and the data in the high-angle area B in the connection area C may be performed by any method as long as the deviation between them is minimized. Yes, usually using the least squares method.

FIG. 5A shows a sample in which a 10 nm thick Co (cobalt) thin film is deposited on a Si substrate using the X-ray reflectometer shown in FIG. 3 shows the measurement results of the same sample. First, without using the X-ray absorber 24,
While scanning so that the line incident angle 22 decreases, the intensity of the reflected X-ray 21 in the high-angle region B is measured. In the connection region C, at the 200 measurement points of the X-ray incident angle 22,
The measurement was performed for the case where the X-ray absorber 24 was inserted and for the case where the X-ray absorber 24 was removed.
Insert and measure.

In this case, after measuring from the high angle area B to the boundary of the low angle area A of the connection area C with the X-ray absorber 24 removed, the rotation angle of the goniometer 17 is measured to the boundary of the high angle area B of the connection area C. The X-ray absorber 24 can be inserted back, and the subsequent measurement can be performed. However, in that case, the reproducibility of the value of the X-ray incident angle 22 deteriorates.

However, in the case of the embodiment of the present invention,
Since the measurement can be performed while the direction of the rotation angle of the goniometer 17 is kept constant, the X-ray incidence angle 22 equivalent to the accuracy (2/1000 degrees) of the rotation angle of the goniometer 17 is used.
Is obtained.

Referring to FIG. 5B, when connecting the measurement data, the connection area C
Are connected so that the average value of the data in the low-angle area A and the average value of the data in the high-angle area B are the same,
As is apparent from the figure, the X-ray reflectivity profile apparently exceeds the upper limit of the measurement of the X-ray detector 19, and measurement over a wider range of the X-ray intensity than the conventional X-ray reflectivity profile, that is, The measurement results are obtained in a wide range of the X-ray incident angle 22. Therefore, it is possible to evaluate the layer structure of the substrate with higher accuracy than before.

When the result as shown in FIG. 5B is obtained, the layer structure of the sample 16 to be measured has different densities by analysis based on the Fresnel equation, as in the case of FIG. Each layer has a thickness of 2 nm, 10 nm, 2 nm from the surface.
In nm, the unevenness of each interface is evaluated to be several Å.

In the second embodiment, the measurement is performed at 200 measurement points in the connection area C.
The measurement may be performed at least at one measurement point, and it is desirable to perform the measurement at two or more measurement points.

In such measurement of the X-ray reflectivity, the intensity is wavy as is apparent from the figure, as in the first embodiment, so that the accuracy of the profile in such a case is reduced. In order to increase the intensity of the reflected X-rays 21 in the middle of the scan so as to decrease the X-ray incident angle 22 and decrease below the preset value,
The measurement may be performed by replacing the X-ray absorber 24 with a smaller absorption amount.

In the second embodiment, the X-ray absorber 24 is only inserted once, that is, the X-ray absorber 24 having a thickness of 0 mm is shifted from the X-ray absorber 24 having a thickness of 0.9 mm. This is equivalent to replacing with the absorber 24, but may be replaced a plurality of times in order to measure the X-ray incident angle 22 more precisely and over a wide range.

In the second embodiment, the X-ray absorber 24 is exchanged according to the intensity of the reflected X-rays 21. However, the intensity of the reflected X-rays 21 and the intensity of the incident X-rays 20 are different. If a rough state of the correlation is known, a set value may be provided for the X-ray incident angle 22, and if the set value falls below this set value, the X-ray absorber 24 may be replaced with a thicker X-ray absorber 24.

Further, the scanning direction of the X-ray incidence angle 22 may be reversed. In this case, when the X-ray absorber 24 is first inserted into the thickest, and the X-ray absorber 24 falls below a predetermined set value, What is necessary is just to replace it with a thinner X-ray absorber 24.

In each of the above embodiments, X
Although the exchange means of the wire absorber 24 is not mentioned,
It is also possible to use means for automatically exchanging according to the measured intensity of the reflected X-ray 21, the measured intensity of the incident X-ray 20, or the X-ray incident angle 22, that is, the rotation angle of the goniometer 17.

For example, the reflection X detected by the X-ray detector 19
The intensity of the line 21 is input to a comparison amplifier and compared with a measurement limit, generally a set value lower than the measurement upper limit, and a step motor or the like is driven by the output to cause the X-ray absorber 24 to reduce the amount of absorption. What is necessary is just to replace it with a different X-ray absorber 24.

The intensity of the reflected X-rays 21 depends on the intensity of the incident X-rays.
Since the measurement is performed by the X-ray intensity monitor 15, the reflected X-ray intensity standardized by the incident X-ray intensity measured by the incident X-ray intensity monitor 15 is obtained, so that the reflected X-ray intensity is standardized. The X-ray reflectivity in the range of the X-ray incident angle 22 can be directly observed, and the measured sample 1
Rough evaluation of the surface structure of No. 6 can be performed in real time.

In this case, for example, by changing the amplification factor of an amplifier (not shown) provided after the X-ray detector 19 in accordance with the incident X-ray intensity measured by the incident X-ray intensity monitor 15, the apparent value is changed. In addition, connected data can be obtained smoothly.

It is to be noted that normalization by the incident X-ray intensity is equivalent to normalization by the X-ray absorption rate of the X-ray absorber 24, that is, normalization by the thickness of the X-ray absorber 24.
The amplification factor of an amplifier (not shown) provided after the X-ray detector 19 may be changed according to the thickness of the inserted X-ray absorber 24.

In each of the above embodiments, X
The ray absorber 24 is inserted at a position where the incident X-ray 20 is attenuated, but is attached to the arm fixed to the goniometer 17 and provided between the goniometer 17 and the slit 18 to attenuate the reflected X-ray 21. In such a case, the intensity of the incident X-rays 20 can be arbitrarily increased, so that the measurement intensity is improved and the measurement time is shortened.

[0063]

According to the present invention, the X-ray detector is damaged.
The X-ray detector can detect X-rays correctly and can measure in the range of apparently exceeding the detection limit, so the accuracy and reliability of material evaluation by the X-ray reflectivity method are greatly improved. Can be done.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a schematic configuration of an X-ray reflectance measuring device of the present invention.

FIG. 3 is an explanatory diagram of a measurement result according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a measuring method according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of a measurement result according to the second embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional X-ray reflectivity measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 X-ray source 2 X-ray absorber 3 Incident X-ray intensity monitor 4 Goniometer 5 Sample to be measured 6 X-ray detector 7 X-ray path 8 X-ray path 11 X-ray source 12 Slit 13 Channel cut crystal 14 Slit 15 Incident X Line intensity monitor 16 Sample to be measured 17 Goniometer 18 Slit 19 X-ray detector 20 Incident X-ray 21 Reflected X-ray 22 X-ray incident angle 23 Elevation angle 24 X-ray absorber

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-311165 (JP, A) JP-A-5-142166 (JP, A) JP-A-5-196583 (JP, A) JP-A-2- 186250 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 23/20

Claims (3)

(57) [Claims] 1. An X-ray path between an X-ray source and an X-ray detector.
With the use of an X-ray reflectometer equipped with an X-ray absorber
Divided the X-ray incident angle area to be measured into two or more areas
Then, a different X-ray absorber is used for each of the divided areas.
In the X-ray reflectivity measuring method, the X-ray incident angle is small.
X-ray scanning at an incident angle of X-ray in a predetermined direction
Reflectance measurement method. 2. The division of the X-ray incident angle region to be measured is
2. The method according to claim 1, wherein the measurement is performed in accordance with the intensity of the reflected X-ray. 3. The division of the X-ray incident angle area to be measured is as follows :
2. The method according to claim 1, wherein the measurement is performed in accordance with the X-ray incident angle.