JP2003322627A - Multilayer thin film analysis method and measurement device - Google Patents

Abstract

(57) [Summary] Multi-layer thin-film analysis in which white X-rays are incident on a sample surface at an extremely low angle and a multilayer structure useful for specifying thin films and multilayer films can be determined while selecting a depth. Methods and measurement devices are provided. SOLUTION: White X-rays are incident from an X-ray tube 3 on a sample 2 to be measured in a goniometer 1 at an extremely low angle (the surface is very close). The goniometer 6 for adjusting the incident angle of the sample 2 can finely change the incident angle of white X-rays (the angle between the sample surface and the X-rays) within a range of ± 2 °. Sample 2
White X-rays are incident on the substrate at an incident angle of 0 ° to 1 ° in 0.1 ° steps, the irradiated X-rays are totally reflected, and the reflectivity of the reflected X-rays is measured by a silicon drift detector 9. To measure the energy distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray reflectance measuring method and its measuring apparatus useful for characterization of a thin film, a multilayer film or a homogeneous surface.

[0002]

2. Description of the Related Art X-ray analysis methods are widely used for analysis of components of various substances and structural analysis. A monochromatic X-ray is radiated while rotating a flat object, the reflectance of the reflected X-ray is detected, and the direction and intensity of the X-ray scattered by this are measured to measure several hundred nanometers from the surface of the object. The method of analyzing a multi-layered thin film structure with a depth of up to, that is, the principle of the X-ray reflectance measurement method is already known, and as a general method, the angular dispersion of the θ-2θ method using monochromatic X-rays is used. The scheme is commercially available.

For example, in the field of manufacturing semiconductor devices,
When a multilayer thin film is formed on the substrate, it is irradiated with monochromatic X-rays,
The interference fringes of X-rays reflected from each interface of the multilayer thin film are measured while changing the X-ray irradiation angle, and the manufacturing process of the high density memory device and integrated circuit is optimized while analyzing the structure of the thin film. There is.

An outline of this angle-dependent reflectance measuring method is shown in FIG.
Shown in. In FIG. 7A, 11 is a goniometer (2
θ rotation), 12 samples to be measured, which are arranged in a θ rotation goniometer 13. Reference numeral 14 is an X-ray detector, and 15 is a monochromator for converting white X-rays into a single color. The white X-ray is monochromaticized by the monochromator 15, and the angle of the goniometer 13 is manipulated so that the incident angle θ and the angle of the detector φ are equal, and the reflectance is measured while rotating the sample 12. Got a profile. By performing a fitting between this result and the result of the model calculation shown in FIG. 7B, the thin film or the multilayer film is characterized from the relationship between the incident angle (illumination angle, degree) and the X-ray reflectance. There is. Here, the relationship between the incident angle and the illumination angle at the incident angle is as shown in FIG.

The result of model calculation is obtained by the following calculation formula. That is, the j layer from the substrate in this order, when the (j + 1) th layer, at a refractive index of each n _j, and n j _{+ 1,} the incident angle theta _j,
When an X-ray is incident at Θ _{j + 1} , its reflectance r _j and transmittance t
_j is as follows.

## EQU1 ## r _j = (n _j cos Θ _j −n _{j + 1} cos Θ _{j + 1} ) / (n _j cos Θ _j + n _{j + 1} cos Θ _{j + 1} ) ... (1) t _j = 2 n _j cos Θ _j / (N _j cos Θ _j + n _{j + 1} cos Θ _{j + 1} ) (2) Using the above r _j and t _j , the following recurrence formula is calculated to calculate the reflectance of the entire multilayer film.

E _{j + 1} ^t : Electric field intensity of passing X-ray of j + 1 layer, E _j ^r : Electric field intensity of reflected X-ray of j-th layer, λ: Wavelength of X-ray, d _j : Thickness of j-th layer Where i is an imaginary unit and π is a circular constant (the incident angle Θ is Θ =
90 ° -θ),

[Equation 2] E _{(j + 1)} ^t = a _j E _jt ^t _j / (1 + a _{(j + 1)} ² X _{(j + 1)} r _j ) ·· (3) E _j ^r = a _j ² X in _j E _j ^t ·· (4) _{where, a j = exp (-2πid j} n j sinΘ j) / λ X j = (r j + a (j + 1) 2 X (j + 1)) / (1 + a _{(j + 1)} ² X
_{(j + 1)} r _j ) and E ₀ ^t = 0, a ₀ = 1 and X _j = 0 on the substrate, and the above recurrence formula is solved.

However, in the angle-dependent reflectance measurement method, the intensity of the incident light is attenuated to make the incident light monochromatic, and the rotation of the sample is complicated due to the mechanical structure, and a complicated spectral analysis is required to obtain a monochromatic X-ray. Since the apparatus is required, the apparatus becomes large in size, there are many adjustment points such as the optical axis adjustment, and there is a drawback that a high angular resolution is required to perform an angle operation in seconds. In order to improve this defect, a white X-ray that uses a semiconductor detector has been proposed.

In recent years, so-called thin films and multilayer thin films have been actively used for electronic parts and the like, and since the thickness of one layer tends to become thinner, it is indispensable to evaluate thin films on the nanometer scale. It was In order to meet this demand, the energy distribution of the reflected X-rays is utilized by utilizing the total reflection phenomenon that occurs when white X-rays are incident on a substrate having an optically flat surface at a very shallow angle with respect to the sample surface. An energy dispersive X-ray spectroscope has been developed which can measure a thin film by a semiconductor detector and substantially analyze the thin film by using the refractive indexes of the thin film and the substrate.

Next, FIG. 8 shows an outline of the energy dispersive X-ray reflectance measuring method. In FIG. 8 (A), 21 is a goniometer (2θ rotation), 22 is a sample to be measured, which is arranged in a θ rotation goniometer 23. 24 is a semiconductor detector. Here, white X-rays are incident on the sample 22, the incident angle and the angle of the detector are fixed at a certain position, and the energy (wavelength) and intensity of the X-rays are detected. Thus, the energy dispersive reflectance is measured using white X-rays, and the model calculation shown in FIG. 8B and the fitting of the measurement results are performed to characterize the thin film or the multilayer film. .

Therefore, the same X-ray tube can be used to obtain incident X-rays of higher intensity, which is advantageous for in-situ observation such as thin film growth, and simplification of the apparatus and adjustment of the optical axis. It has the advantage that it is simple and does not require angle operation, but since a semiconductor detector becomes unreliable as a detector when it exceeds 10,000 counts per second, a filter is required in terms of S / N and the X-ray optical axis It was not practical unless a thin film filter intended to selectively absorb the energy of a specific X-ray was inserted thereinto. The reflectance of X-rays needs to be measured by a dynamic range of 10,000 or more, and the intensity of X-rays is reduced by inserting a filter.
A high-intensity X-ray tube such as a rotating anode X-ray tube is required, and the fine structure of the thin film filter interferes with the measurement, which complicates the measurement and prevents accurate thin film structure analysis.

[0011]

As described above, in the conventional angle dispersion method, the intensity of the incident light is attenuated in order to make the incident light monochromatic, and the rotation of the sample is complicated due to the mechanical structure, and the monochromatic X-ray is used. In order to obtain a complicated spectroscope, the device becomes large in size, there are many adjustment points such as optical axis adjustment, and high angular resolution is required to perform angle operation in seconds. there were. In addition, the energy dispersive X-ray reflectivity measurement method has a drawback that the average of the entire multilayer film structure from the surface to the deep position is measured, and a filter is always required in terms of S / N, which makes the measurement complicated. Was there.

Therefore, according to the present invention, white X-rays are incident on the surface of the sample in a gradual manner, and the angle is changed to change the energy dispersion of X-rays.
A multi-layer structure that can measure line reflectance and determine a multi-layer structure that is useful for characterizing a thin film or a multi-layer film such as abdominal thickness, density, flatness, and diffusion of atoms while selecting depth. An object of the present invention is to provide a thin film analysis method and a measuring device.

[0013]

In order to solve the above-mentioned problems, the method for analyzing a multilayer thin film according to claim 1 of the present invention irradiates the surface of a sample to be measured having a layered structure with X-rays, In the method of measuring the reflectance and measuring the energy distribution, a white X-ray is irradiated at a very low angle of incidence on the sample to be measured and the angle of incidence is changed to totally reflect the X-ray, The X-ray intensity is detected to measure the energy dispersion X-ray reflectance.

The method for analyzing a multilayer thin film according to claim 2 of the present invention is a method for irradiating a surface of a sample to be measured having a layered structure with X-rays, measuring a reflectance of the X-rays and measuring an energy distribution. X-ray reflection of energy dispersal by detecting the intensity of the reflected X-rays by irradiating white X-rays at a very low angle of incidence on the measurement sample and changing the angle of incidence to irradiate white X-rays. By measuring the ratio and controlling the X-ray incidence angle, the depth in the sample to be measured is selected, and the type and density of the element at the desired depth position are analyzed.

In the method for analyzing a multilayer thin film according to claim 3 of the present invention, the surface of a sample to be measured having a layered structure is irradiated with X-rays, the reflectance of the X-rays is measured, and the energy distribution is measured. X-ray reflection of energy dispersal by detecting the intensity of the reflected X-rays by irradiating white X-rays at a very low angle of incidence on the measurement sample and changing the angle of incidence to irradiate white X-rays. The rate was measured and the energy distribution was measured to analyze the flatness of the interface and the diffusion of atoms in the case of a layered structure.

With this, it is possible to determine a multi-layered film structure which is useful for film thickness, density, flatness, atomic diffusion, etc. of thin film or multi-layered film while selecting depth. The film thickness, density of the multilayer film, interdiffusion at the interface, and process evaluation / control of the multilayer film production are possible, energy dispersive reflectance measurement is realized by a simple method, and depth information is selectively obtained. It can be used for analysis in the domain.

According to a fourth aspect of the present invention, there is provided a multi-layer thin film analysis and measurement apparatus which comprises a white X-ray source, a slit for narrowing the X-ray beam, a goniometer for tilting the sample to change the X-ray incident angle, and an incident X-ray. The detector is configured to detect reflected X-rays in the same plane with a high dynamic range.

According to a fifth aspect of the present invention, there is provided a multi-layer thin film analysis and measurement apparatus, a white X-ray source, a slit for narrowing an X-ray beam, a goniometer for tilting a sample to change an X-ray incident angle, and an incident X-ray. A silicon drift detector for detecting reflected X-rays in the same plane with a high dynamic range is adopted.

This makes it possible to measure X-rays exceeding 1 million counts per second by using a silicon drift detector as a detector, which is a complicated mechanism for liquid nitrogen cooling and rotational movement like a semiconductor detector. Since it is not necessary, it is small and lightweight and can be easily rotated and moved due to the electronic cooling system. Also, because we do not use a precise monochromatic X-ray mechanism or filter,
It is possible to analyze the elemental composition, the density, the flatness of the interface, and the interdiffusion for each depth of the sample quickly, lightweight, and easily.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The multilayer thin film analysis method and measuring apparatus of the present invention will be described below with reference to FIGS. The present invention is an X-ray reflectivity measurement method using the X-ray surface traveling wave method, and therefore the X-ray surface traveling wave will be described first with reference to FIG.

As shown in FIG. 1, when white X-rays are incident on the surface of the thin film sample at a grazing angle, X-rays having a smaller energy than a certain amount are reflected, and X-rays having an energy value higher than that are refracted. Penetrate into the sample. The invading X-rays further cause reflection refraction at the interface with the substrate, and the reflected X-rays interfere with the reflected light on the sample surface. Such reflected light and refracted light exist substantially parallel to the surface and interface. Therefore, these are referred to as an X-ray surface traveling wave, and a novel analysis method using this traveling wave can be referred to as an X-ray surface traveling wave method.

Next, FIG. 2 shows an outline of the measuring apparatus of the present invention. In FIG. 2, 1 is a goniometer (2θ rotation), 2
Is a sample to be measured, 3 is an X-ray tube, 4 is a slit for narrowing the X-ray beam, 5 is a divergence slit, 6 is a goniometer (θ rotation), 7 is a manual stage, 8 is a hole slit, and 9 is a silicon drift detector. is there.

Mo is used as the target of the X-ray tube 3 to generate white X-rays. A 0.15 mm solar slit 4 and a 0.1 ° divergence slit 5 are arranged between the sample 2. Sample 2 is a goniometer 6 for adjusting the incident angle.
And is fixed to a manual stage 7 whose vertical height can be adjusted. The detector is a silicon drift detector (SDD: Si
licon Drift Detector) was used and fixed to the goniometer so that the angle of the detector could be changed. A 1 mmφ hole slit 8 is arranged in front of the detector. Here, by using the silicon drift detector, it has become possible to measure X-rays exceeding 1 million counts per second.

The θ axis and φ axis for adjusting the incident angle and the detector angle are controlled by a personal computer so that they can be changed independently. The optical axis is adjusted from the position of the detector 9 with respect to the incident light. First, the detector 9 is fixed, and the θ axis of the sample 2 is shaken to determine the parallelism between the sample 2 and the incident light. Then, the height of the sample is adjusted by directly operating the manual stage 7 so that the intensity becomes half of that when the light enters the detector 9. This operation is repeated several times, and the relative 0
Determine °. Here, both the θ axis and the φ axis are positive in the counterclockwise direction.

The measurement sample is used in the embodiment of the present invention, as shown in FIG. 3, B ₄ C for 38Å silicon substrate
And 31Å Mo is a multilayer film having 30 layers each (Mo / B
₄ C) ₃₀ / Si was used.

The sample to be measured 2 in the measuring container 1 from the X-ray tube 3
A white X-ray is made incident on a very low angle (smooth surface).
For the sample 2, the incident angle of white X-rays (angle between the sample surface and the X-rays) was adjusted by the goniometer 6 for adjusting the incident angle.
It can be finely changed within the range of 2 °. White X on sample 2
An X-ray is incident at a step of 0.1 ° from an incident angle of 0 to 1 °, the irradiated X-ray is totally reflected, and the intensity of the reflected X-ray is measured by measuring the reflectance with a silicon drift detector 9 to obtain an energy distribution. Was measured.

FIG. 4 shows (Mo / B ₄ C) ₃₀ / Si,
Measurement is performed while changing the incident angle every 0.1 °,
The result of comparing the measured value and the model calculated value is shown. The horizontal axis shows energy, the vertical axis shows reflectance, and the left side is the measured value.
The right side is the result of model calculation. As is clear from the figure, the peak values exist at almost the same energy positions,
It shifts to the lower energy side as the incident angle increases. The peak value tended to become broader as the incident angle became smaller. Although the second and third peaks appeared in the model calculation, they could be observed by actual measurement.

FIG. 5 shows the fitting of (Mo / B ₄ C) ₃₀ / Si. 20 layers of Mo ・ B ₄ C periodic structure
When the model calculation was performed while changing the layers,
As shown on the left, the peak value tended to become broader as the periodic structure decreased. This is considered to be because the shallower the incident angle, the shallower the penetration depth of X-rays and the reflection occurs only on the sample surface. Therefore, the depth of penetration of the X-ray into the sample to be measured depends on the incident angle. Therefore, by changing the incident angle, the measurement depth (film thickness) according to the incident angle can be changed.
It can be seen that can be selected to characterize the sample.

Further, when the calculation was performed while changing the film thickness of the sample, as shown in FIG. 5, the energy of the peak value tended to shift to the left as the film became thicker. From this, it can be understood that the actual film thickness can be measured.

Similarly, in FIG. 6, (Mo / B ₄ C) ₃₀ / S
The result of performing the fitting of i is shown. According to this, it became clear that it is possible to measure the energy dispersive reflectance, which has the same tendency as the model calculation.
And if energy and angle information are obtained at the same time,
For example, at an incident angle of 0.2 °, information of two layers, that is, a surface layer of only 140Å was obtained. At an incident angle of 0.6 °, information of 5 layers, that is, a film thickness of 350 Å was obtained.

According to the multilayer thin film analysis method and the measuring apparatus of the present invention, the thickness measurement of the multilayer film (the analysis of the position of the fringe,
Fourier transform, etc.), layer thickness measurement from the surface of the multilayer to a specific depth (angle change), multilayer density (reflection intensity analysis), measurement of the degree of mutual diffusion at the multilayer interface (fringe) Sharpness), oxidation state of interface (from density), process control of multilayer film manufacturing process, control of multilayer film manufacturing process, process parameter determination, and non-destructive / rapid measurement in nanometer range.

[0032]

As described above, according to the present invention, white X-rays are incident on the surface of the sample at a grazing low angle, the X-ray reflectance of energy dispersion is measured by changing the angle, and a thin film, a multilayer film or the like is measured. It is possible to determine a multi-layered film structure that is useful for characterizing such as film thickness, density, flatness, and diffusion of atoms while selecting depth. This makes it possible to evaluate and control the film thickness, density of the multilayer film, mutual diffusion at the interface, and the process of manufacturing the multilayer film.The energy dispersive reflectance measurement can be realized by a simple method, and depth information can be selectively obtained. It is expected to be utilized for analysis in the nano area.

Further, by using a silicon drift detector as a detector, it is possible to measure X-rays exceeding 1 million counts per second, which is complicated for liquid nitrogen cooling and rotational movement like a semiconductor detector. It does not require a mechanism, and because it is an electronic cooling system, it is small and lightweight and can be easily rotated. Further, since a precise monochromatic X-ray mechanism and a filter are not used, it is possible to quickly and easily analyze the elemental composition, density, interface flatness and mutual diffusion for each depth of the sample.

[Brief description of drawings]

FIG. 1 is an explanatory view of an X-ray surface traveling wave of the present invention.

FIG. 2 is a schematic diagram of a multilayer thin film analysis and measurement apparatus of the present invention.

FIG. 3 is a measured sample structure used in an embodiment of the present invention.

FIG. 4 is a comparison diagram of measured values and model calculated values of a measured sample.

FIG. 5 is a fitting diagram of a sample to be measured.

FIG. 6 is a fitting diagram of another measured sample.

FIG. 7 is a schematic diagram of a conventional angle-dependent reflectance measuring method.

FIG. 8 is a schematic diagram of a conventional energy dispersive X-ray reflectance measurement method.

[Explanation of symbols]

1,11,21 Goniometer (2θ rotation) 2,12,22 Sample to be measured 3 X-ray tube 4 solar slit 5 Divergence slit 6,13,23 Goniometer (θ rotation) 7 Manual stage 8 hole slit 9 Silicon drift detector 14,24 X-ray detector 15 Monochromator

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G001 AA01 AA09 BA15 CA01 DA01                       GA01 GA08 GA13 JA01 JA06                       JA07 JA11 KA01 KA20 MA05                       PA14 SA01 SA07

Claims (5)

[Claims] 1. A method of irradiating an X-ray on a surface of a sample to be measured having a layered structure and measuring an X-ray reflectance to measure an energy distribution. The X-ray reflectance of energy dispersion is measured by detecting the intensity of the reflected X-rays by irradiating the white X-rays with different incident angles to totally reflect the X-rays. The multilayer thin film analysis method described. 2. By controlling the incident angle of X-rays,
2. The method for analyzing a multilayer thin film according to claim 1, wherein the depth in the sample to be measured is selected and the type and density of the element at a desired depth position are analyzed. 3. The method for analyzing a multilayer thin film according to claim 1, wherein in the case of a layered structure, the flatness of the interface and the diffusion of atoms are analyzed by measuring the energy distribution. 4. A white X-ray source, a slit that narrows the X-ray beam, a goniometer that changes the incident angle of the X-ray by tilting the sample, and a reflected X-ray with a high dynamic range in the same plane as the incident X-ray. A multi-layered thin film analysis and measurement apparatus comprising: 5. The multi-layer thin film analysis and measurement apparatus according to claim 4, wherein the detector is a silicon drift detector.