JPH05209847A - Fluorescent x-ray spectroscopy method and apparatus - Google Patents

Abstract

PURPOSE:To perform an analysis in a short time accurately by an inexpensive analyzing apparatus in a fluorescent X-ray spectroscopy method and an apparatus therefor for measuring the thickness of a thin WSix film containing the same element Si as that included in a silicon substrate and concentration of W. CONSTITUTION:A primary X-ray B1 is irradiated to a measuring sample 1, and a fluorescent X-ray B2 from the measuring sample 1 is separated by a first and a second spectral elements 4A, 4B. The first spectral element 4A separates a W-Lalpha beam B3, while the second spectral element 4B separates a W-Nx beam B4. The intensity of the X-ray of the W-Lalpha beam B3 and W-Nx beam B4 are measured by a first and a second measuring instruments 5A, 5B, respectively. The film thickness (t) and the concentration of W are obtained by an operator 6 on the basis of the measured intensity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent X-ray analysis method and apparatus suitable for measuring the film thickness of a thin film provided on the surface of a large wafer and the concentration of the element to be measured.

[0002]

2. Description of the Related Art In recent years, with the high integration of LSI, silicide such as tungsten silicide (hereinafter referred to as "WSix") has a smaller resistance value than a polysilicon layer and is excellent in high speed operation. It's getting a lot of attention. It is necessary to measure the composition ratio (x) of the thin film of WSix not only in terms of film thickness, but also in terms of adhesion to the silicon substrate, and strictly control the composition ratio (tungsten concentration). An example of the fluorescent X-ray analysis method for measuring the film thickness and the composition ratio is shown in FIG.

In FIG. 8, a sample 1A to be measured is a monitor, and has a thin film 12 of WSix on the surface of a substrate 11A made of ceramic such as Al ₂ O ₃ instead of the silicon substrate. The sample 1A to be measured is irradiated with the primary X-ray B1,
W-Lα ray B3 and Si-Kα from the sample to be measured 1A
Two types of fluorescent X-rays of line B5 are measured. Here, the measured intensities of both the fluorescent X-rays B3 and B5 change depending on the film thickness t and the concentration of W (tungsten), but the intensity of the W-Lα line B3 is influenced by the film thickness t. Is large,
On the other hand, the intensity of the Si-Kα ray B5 is greatly influenced by the concentration.
Therefore, the concentrations of the film thicknesses t and W can be relatively accurately analyzed from the two measured intensities by the known fundamental parameter method.

[0004]

However, recently, as the diameter of the wafer to be manufactured becomes larger (for example, 8 inches), the substrate 11A made of Al ₂ O ₃ which is a ceramic is used.
However, it becomes very expensive in cost, so that it is necessary to measure the film thickness t and the concentration without using a monitor. If the above monitor is not used, since the same element Si is contained in both the silicon substrate and the thin film,
The analysis becomes difficult. An X-ray non-destructive inspection called Rutherford backscatter is also performed as a method of analysis without using the above-mentioned monitor, but it has a drawback that the analysis takes a long time.

Further, by irradiating a sample to be measured having a thin film of WSix on a silicon substrate with primary X-rays and measuring the intensities of W-Lα rays at a large extraction angle and an extremely small extraction angle, respectively. The film thickness and concentration can be measured. However, if the take-off angle is reduced to such an extent that the influence of the film thickness becomes extremely small, the structure of the analyzer becomes extremely special, and as a result, the analyzer becomes expensive.

The present invention has been made in view of the above conventional problems, and provides a fluorescent X-ray analysis method and apparatus for measuring the film thickness and concentration of a thin film containing the same element as that contained in a substrate, The purpose is to enable accurate analysis in a short time with an inexpensive analyzer.

[0007]

In order to achieve the above object, in the analysis method of claim 1, first, a thin film containing the same first element as the element contained in the substrate is formed on the substrate. Irradiate the sample to be measured provided on the surface of
The intensity of the first fluorescent X-ray having a large influence of the thickness of the second element not contained in the substrate in the thin film, and the influence of the thickness of the second element having the influence of the film thickness on the first fluorescent X The intensity of the second fluorescent X-ray smaller than the line and having a different series from the first fluorescent X-ray is measured. These two fluorescent X
The film thickness and the concentration are obtained based on the measured intensity of the line.

In the analysis method of claim 2, the first
As the second fluorescent X-ray, the intensities of the hard X-ray and the super-soft X-ray of the second element of the fluorescent X-rays emitted from the sample to be measured are measured. In the present invention, super soft X-rays mean M-rays and X-rays having a longer wavelength (smaller energy) than M-rays, and in the case of W, the wavelength is in the range of 4.4Å to 67.6Å. X-ray.

On the other hand, the analyzer according to claim 3 separates the hard X-rays and the ultra-soft X-rays of the element to be measured from the fluorescent X-rays from the sample to be measured which have received the primary X-rays.
And a second spectroscopic element. The X-ray intensities of the hard X-ray and the super-soft X-ray are measured by the first and second measuring instruments, respectively.

According to these inventions, among fluorescent X-rays of the second element contained in the thin film and not contained in the substrate, the influence of the film thickness such as hard X-rays is large. Since the intensity of the first fluorescent X-ray and the intensity of the second fluorescent X-ray, which is less affected by the film thickness like the ultra-soft X-ray, are measured, the measured intensity of these first and second fluorescent X-rays is , Respectively, containing sensitive information about film thickness and concentration. Therefore, by calculating based on these two measured intensities,
The film thickness and the concentration of the second element can be measured relatively accurately.

Further, in the analysis method of claim 4, of the fluorescent X-rays emitted from the sample to be measured, the intensity of the hard X-ray of the first element in the substrate and the thin film and the intensity of the second hard X-ray in the thin film. The ultra-soft X-ray intensity of the element is measured, and the thin film and the concentration are obtained based on these two measured intensities.

According to a fifth aspect of the analysis apparatus, the primary X-ray is separated from a first spectroscopic element that disperses the hard X-ray of the first element among the fluorescent X-rays from the sample to be measured that has received the primary X-ray. A second spectroscopic element that disperses the super-soft X-ray of the second element to be measured among the fluorescent X-rays from the measured sample received. The X-ray intensities of the hard X-ray and the super-soft X-ray are measured by the first and second measuring instruments, respectively.

According to the invention of claim 4 or 5, the intensity of the hard X-ray of the first element in the substrate and the thin film is measured. As for the intensity of this hard X-ray, the hard X-ray is absorbed in the thin film. Therefore, when the thickness of the thin film is thin, it becomes smaller as the film thickness increases. Therefore, the measurement intensity of the hard X-ray contains sensitive information about the film thickness. Meanwhile, the second
Ultra soft X-ray measurement intensity of the element is ultra soft X with small energy
Since the lines are strongly absorbed in the thin film, they are only emitted from the very surface of the thin film, regardless of the thickness of the thin film, and thus contain sensitive information about the concentration. Therefore, this 2
By calculating based on one measurement intensity, the film thickness and the concentration of the second element can be measured relatively accurately.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the sample to be measured 1 is a substrate 11
A thin film 12 containing a first element that is the same as the element contained in the substrate 11 and a second element that is not contained in the substrate 11 is provided on the surface of the substrate 11.
1 is a wafer having a thin film 12 of WSix on its surface. The sample 1 to be measured is a sample in which the film thickness t of the thin film 12 and the composition ratio (x), that is, the concentration of W are unknown. The film thickness t of the thin film 12 is, for example, in the range of 400 Å to 2500 Å. The fluorescent X-ray analyzer 2 includes an X-ray tube (X-ray source) 3, first and second spectroscopic elements 4A and 4B, first and second measuring instruments 5A and 5B, and a calculator 6. I have it. The first and second measuring instruments 5A and 5B respectively include first and second X-ray detectors 8A and 8B and first and second counting circuit sections 9A and 9B.

The X-ray tube 3 emits a primary X-ray B1 toward the surface of the thin film 12 of the sample 1 to be measured. The sample to be measured 1 that has received the primary X-ray B1 is excited by atoms, and the fluorescent X-ray B unique to the element contained in the sample to be measured 1 is measured.
2 is generated.

Both of the spectroscopic elements 4A and 4B are housed in a spectroscopic chamber 7 maintained in a vacuum atmosphere. The first spectroscopic element 4A is made of, for example, a LiF dispersive crystal, and disperses the element to be measured, that is, the W-Lα ray B3, which is a hard X-ray of W, from the fluorescent X-rays B2 from the measured sample 1. .. On the other hand, the second spectroscopic element 4B is made of, for example, an artificial lattice in which a large number of layers of carbon and nickel are alternately laminated on a silicon substrate. The second spectroscopic element 4B is the sample to be measured 1
Of the fluorescent X-rays B2 from
X-ray B4 is spectrally separated. The W-Lα rays B3 and W-N separated by the first and second spectroscopic elements 4A and 4B.
The x-ray B4 is the first and second x-ray detector 8 respectively.
It is incident on A and 8B. The take-off angle β of the W-Nx line B4
2 is set to be smaller than the take-out angle β1 of the W-Lα line B3.

The above-mentioned first and second X-ray detectors 8A, 8
B is the incident W-Lα ray B3 and W-N, respectively.
The x-ray B4 is detected and the detection outputs e1 and e2 are output to the first and second counting circuit units 9A and 9B. First and second
The counting circuit units 9A and 9B have detection outputs e1 and e, respectively.
2 is counted and the W-Lα line B3 and the W-Nx line B are
The intensity of 4 is output to the calculator 6 as the measurement signals x1 and x2. The calculator 6 receives the measurement signals x1 and x2, and outputs W
The concentrations of the film thickness t and W of the thin film 12 are obtained based on the measured intensities of the −Lα line B3 and the W—Nx line B4.

Next, an analysis method using the fundamental parameter method will be briefly described. First, the film thickness t
And a plurality of types of standard samples having known concentrations are prepared, and W-
The intensities of the Lα line B3 and the W-Nx line B4 are measured by both measuring devices 5.
Measure with A and 5B. A conversion formula from the measured intensity to the theoretical intensity is obtained based on the measured intensity, the film thickness t, and the concentration.

Then, the intensity of the W-Lα ray B3 and the W-Nx ray B4 of the sample 1 whose film thickness t and concentration are unknown is measured using the analyzer 2. This measured intensity is converted into theoretical intensity by the above-mentioned conversion formula. After that, an appropriate film thickness t and concentration are given to the theoretical intensity formula in which the X-ray intensity is uniquely determined by the film thickness t and the concentration, and the calculated theoretical intensity matches the theoretical intensity obtained by converting the measured intensity. Calculate whether or not. If they do not match, the thickness t is changed, the concentration is given again, and the calculation is repeated. By repeating this calculation,
The film thickness t and the concentration are obtained. This calculation is based on the film thickness t
And the film thickness t and the concentration are obtained by solving a simultaneous equation consisting of the first equation regarding the theoretical intensity of the W-Lα line B3 and the second equation regarding the theoretical intensity of the W-Nx line B4 in which the concentration is an unknown number.

Next, the reason why the W-Lα ray B3 and the W-Nx ray B4 of the fluorescent X-rays B2 are used in this analysis method will be explained. As shown in FIG. 2, the W-Lα line B3
Has a relatively short wavelength (about 1.48Å), that is, a large amount of energy, so that even those generated from the deepest part 12a of the thin film 12 are not absorbed much by the thin film 12, and therefore, the thin film 12 passes through the thin film 12 and Is emitted from all layers. Therefore, the intensity of the W-Lα ray B3 increases as the film thickness t of the thin film 12 increases, as shown by the solid line in FIG. 3, and is greatly affected by the change in the film thickness t. On the other hand, the W-Nx ray B4 in FIG. 2 has an extremely long wavelength (about 55 Å), that is, energy is very small, so that what is generated in the deep portion of the thin film 12 is absorbed by the thin film 12, and therefore the surface of the thin film 12 is absorbed. Emitted only from the layer. Therefore, as for the intensity of the W-Nx line B4, the influence of the film thickness t of the thin film 12 is extremely smaller than that of the W-Lα line B3, as shown by the broken line in FIG. 3, and as shown in FIG. Greatly affected.

As described above, the measured intensity of the W-Lα ray B3 in FIG. 3 includes the reliable information about the film thickness t because the influence of the film thickness t is large, while the measurement intensity of the W-Nx ray B4 is measured. Since the strength is less affected by the film thickness t, it contains reliable information on the concentration. That is, the change in the film thickness t appears as a large change in the measured intensity of the W-Lα line B3, while the change in the concentration appears as a change in the measured intensity of the W-Nx line B4. Therefore, the W-Lα line B3 and the W-Nx line B
By measuring the intensity of No. 4, the film thickness t and the concentration can be accurately measured.

By the way, the present invention is not limited to W-L.
It is not necessary to measure the intensities of the α ray B3 and the W-Nx ray B4, and the first fluorescent X-ray (having a large influence of the film thickness of the second element (W) not included in the substrate 11 of FIG. 1 ( The intensity of B3) and the film thickness are small, and the second fluorescent X-ray (B3) is different in series from the first fluorescent X-ray (B3).
The intensity of 4) may be measured, and the film thickness t and the concentration may be determined based on these two measured intensities. For example, thin film 1
Hard X-rays (K-rays or L-rays) and ultra-soft X-rays (M-rays or N-rays) depending on the type (composition) of the elements that make up 2
May be measured and analyzed based on these two measured intensities. As an example, the thin film 12 is MoSix.
In such a case, the intensities of Mo-Lα ray and Mo-Mα ray may be measured, and analysis may be performed based on these two measured intensities.

However, the WSix thin film 12 of this embodiment is used.
With regard to, with soft X-rays such as W-Mα rays, the energy is too large and the intensity thereof is greatly affected by the film thickness t, so a slight measurement error appears as a large concentration error. Therefore, for the thin film 12 of WSix, W-
It is not preferable to use Mα rays, and it is generally preferable to use N rays and ultra-soft X rays having a longer wavelength than N rays.

By the way, in the above embodiment, the W-Nx line B
The extraction angle β2 of No. 4 is set to be slightly smaller than the extraction angle β1 of the W-Lα line B3. Therefore, the W-Nx line B4 is
It is more likely to be absorbed in the thin film 12 of WSix. Therefore, the intensity of the W-Nx ray B4 is much less affected by the film thickness t, and a more accurate analysis result can be obtained.

Further, in the above embodiment, the intensity of the hard X-ray (for example, W-Lα ray) B3 of the second element (W) of the fluorescent X-rays B2 was measured as the intensity of the first fluorescent X-ray. .. However, in the present invention, the fluorescent X-ray B is used as the first fluorescent X-ray.
Of the two, the intensity of the hard X-ray of the first element (Si) may be measured. This principle will be described with reference to FIGS.

In FIG. 5, the Si-Kα ray B5 which is a hard X-ray of the first element Si is the Si in the thin film 12.
From the Si-Kα ray B5s and S in the substrate 11
There is a Si-Kα ray B5b emitted from i. As shown in FIG. 6A, in the range where the thin film t is thin, the X-ray intensity of the Si-Kα ray B5s from the thin film 12 increases as the film thickness t increases, and the thin film t has a predetermined thickness. When the thickness is larger than the value, the X-ray intensity becomes saturated and becomes constant.
On the other hand, as shown in FIG. 6B, Si-Kα from the substrate 11
Since the line B5b is absorbed by the thin film 12, in the range where the film thickness t is thin, the X-ray intensity becomes significantly smaller as the film thickness t becomes thicker, and when the film thickness t becomes thicker than a predetermined value, The X-ray intensity becomes zero. Therefore, the Si-Kα ray B5 emitted from the entire measured sample 1 is as shown in FIG.
As shown in FIG. 6C, which is a combination of FIG. 6B and FIG. 6B, in the range where the film thickness t is extremely thin (for example, 10Å to 5,000Å), the X-ray intensity becomes smaller as the thin film t becomes thicker. Become. Therefore, when the film thickness t is thin, the measured intensity of the Si-Kα line B5 includes certain information regarding the film thickness t, so that instead of the W-Lα line B3 (FIG. 1), S
The X-ray intensity of i-Kα ray B5 may be measured.

In the case of the embodiment of FIG. 5, the first spectroscopic element 4A of FIG. 1 disperses the Si-Kα ray B5 (FIG. 5), and the first X-ray detector 8A disperses the Si-Kα ray B5. (FIG. 5) is detected. The other structure is similar to that of the embodiment shown in FIG. 1, and detailed description and illustration thereof will be omitted.

Next, as shown in FIG. 7, the Si substrate 11
The case of the sample to be measured 1 in which the thin film 12A of SiO _{2 and} the thin film 12 of WSix are laminated on the above will be described.

In this case, as shown in FIG.
When the X-ray intensity of the Si-Kα ray B5 as the first fluorescent X-ray is measured, the Si-Kα ray B5b from the Si substrate 11 is
It is also absorbed in the intermediate SiO ₂ thin film 12A. Therefore, if the thickness of the SiO ₂ thin film 12A changes, WSi
x Even if the thickness of the thin film 12 is constant, the entire Si-Kα ray B5
X-ray intensity changes. Therefore, in the method of FIG. 7A, when the thickness of the SiO ₂ thin film 12A is known, W
The thickness t and the concentration of W of the Six thin film 12 can be obtained.
If the thickness of the O ₂ thin film 12A is unknown, WSix
The film thickness t of the thin film 12 and the concentration of W cannot be accurately obtained.

On the other hand, the first fluorescent X-ray shown in FIG.
In the case of measuring the X-ray intensity of the W-Lα line B3 in (b) (in the case of the embodiment of FIG. 1), the W-Lα line B3 is generated on the surface rather than the SiO ₂ thin film 12A. The strength of B3 is not affected by the thickness of the SiO ₂ thin film 12A. Therefore, in this case, even if the thickness or the like of the SiO ₂ thin film 12A is unknown, that is, even if there is another thin film or the like under the WSix thin film 12, the thickness t and the concentration of the WSix thin film 12 can be accurately measured. Can be measured.

[0031]

As described above, according to the present invention, among the fluorescent X-rays of the second element contained in the thin film and not contained in the substrate, hard X-rays are preferable. Of the intensity of the first fluorescent X-ray, which is greatly affected by the film thickness, and the intensity of the second fluorescent X-ray, which is less affected by the film thickness, such as M-ray or ultra-soft X-ray having a longer wavelength than the M-line. Therefore, the film thickness and the concentration can be accurately measured based on the two measured intensities. Similarly, the intensity of the hard X-ray of the first element and the second
Even when the film thickness and the concentration are obtained based on the ultra-soft X-ray intensity of the element, these can be accurately measured.

Further, since the calculation can be easily performed using the well-known fundamental parameter method by the arithmetic unit, unlike the conventional measurement by the Rutherford backscatter, the analysis can be performed in a short time. Further, since it is not necessary to make the take-out angle extremely small, the shape of the analyzer does not become a special shape, and the cost of the analyzer does not increase significantly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fluorescent X-ray analyzer showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a sample to be measured showing the principle of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the intensity of fluorescent X-rays and the film thickness and W concentration.

FIG. 4 is a characteristic diagram showing a relationship between W-Nx line intensity, film thickness and W concentration.

FIG. 5 is an enlarged cross-sectional view of a sample to be measured showing the principle of another embodiment.

FIG. 6 is a characteristic diagram showing the relationship between the X-ray intensity of Si-Kα rays and the film thickness.

FIG. 7 is an enlarged cross-sectional view showing the measurement principle when a SiO ₂ thin film is below the WSix thin film.

FIG. 8 is an enlarged cross-sectional view of a sample to be measured showing a conventional analysis method.

[Explanation of symbols]

1 ... Sample to be measured, 3 ... X-ray source, 4A ... First spectroscopic element,
4B ... Second spectroscopic element, 5A ... First measuring instrument, 5B ... Second measuring instrument, 11 ... Substrate, 12 ... Thin film, B1 ... Primary X
Line, B2 ... fluorescent X-ray, B3 ... hard X-ray (first fluorescent X-ray
Line), B4 ... Super soft X-ray (second fluorescent X-ray).

Claims (5)

[Claims] 1. A measurement sample comprising a thin film containing a first element which is the same as the element contained in the substrate and a second element which is not contained in the substrate on the surface of the substrate. A fluorescent X-ray analysis method for measuring the thickness of a thin film and the concentration of a second element, the method comprising irradiating the sample to be measured with a primary X-ray and being greatly affected by the thickness of the second element. Of the intensity of the fluorescent X-rays and the film thickness of the second element are smaller than those of the first fluorescent X-rays, and the intensity of the second fluorescent X-rays different in series from the first fluorescent X-rays And a fluorescent X-ray analysis method for determining the film thickness and the concentration based on the measured intensities of these two fluorescent X-rays. 2. A thin film containing a first element which is the same as the element contained in the substrate and a second element which is not contained in the substrate is provided on the surface of the substrate, A fluorescent X-ray analysis method for measuring the film thickness of a thin film and the concentration of a second element, the method comprising irradiating the sample to be measured with primary X-rays, and measuring the first of the fluorescent X-rays emitted from the sample to be measured. The intensity of the hard X-ray of the second element and the intensity of the M-ray of the second element or the super-soft X-ray having a longer wavelength than the M-ray are respectively measured, and based on the measured intensities of these two fluorescent X-rays. A fluorescent X-ray analysis method for obtaining the above-mentioned film thickness and concentration. 3. An X-ray source for irradiating a sample to be measured with primary X-rays, and a method for separating hard X-rays of an element to be measured out of fluorescent X-rays from the sample to be measured which have received the primary X-rays. A second spectroscopic element for spectroscopically analyzing the super-soft X-rays having a wavelength longer than the M-rays of the element to be measured among the fluorescent X-rays from the sample to be measured which has received the primary X-rays. An X-ray fluorescence analyzer provided with a spectroscopic element, a first measuring instrument for measuring the intensity of the hard X-rays, and a second measuring instrument for measuring the intensity of the super-soft X-rays. 4. A thin film containing a first element which is the same as the element contained in the substrate and a second element which is not contained in the substrate is provided on the surface of the substrate, A fluorescent X-ray analysis method for measuring the film thickness of a thin film and the concentration of a second element, the method comprising irradiating the sample to be measured with primary X-rays, and measuring the first of the fluorescent X-rays emitted from the sample to be measured. The intensity of the hard X-ray of the element 1 and the intensity of the M-ray of the second element or the super-soft X-ray having a longer wavelength than the M-ray are respectively measured, and based on the measured intensities of these two fluorescent X-rays. A fluorescent X-ray analysis method for obtaining the above-mentioned film thickness and concentration. 5. An X-ray source for irradiating a sample to be measured with a primary X-ray, and a first X-ray for spectrally analyzing a hard X-ray of a first element of fluorescent X-rays from the sample to be measured which has received the primary X-ray. And the spectroscopic element of
A second spectroscopic element that disperses M-rays of the second element to be measured or ultra-soft X-rays having a longer wavelength than the M-rays, out of the fluorescent X-rays from the measurement sample that has received the primary X-rays; An X-ray fluorescence analyzer provided with a first measuring instrument for measuring the intensity of the hard X-ray and a second measuring instrument for measuring the intensity of the super-soft X-ray.