JP2706601B2 - X-ray fluorescence analysis method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention is, for example, semiconductor group
The present invention relates to an X-ray fluorescence analysis method and apparatus suitable for measuring the thickness of a thin film provided on the surface of a large wafer as a plate and the concentration of an element to be measured.

[0002]

2. Description of the Related Art In recent years, with 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 is attracting attention because it is. It is necessary to measure the composition ratio (x) of the WSix thin film from the viewpoint of not only the film thickness but also the adhesion to the silicon substrate, and strictly control the composition ratio (concentration of tungsten). FIG. 8 shows an example of a fluorescent X-ray analysis method for measuring the film thickness and the composition ratio.

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

[0004]

However, recently, as the diameter of a wafer to be manufactured has increased (for example, 8 inches), a substrate 11A made of ceramic Al ₂ O ₃ has been required.
However, it becomes very expensive in terms of cost, so that it is necessary to measure the film thickness t and the concentration without using a monitor. When 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. As a method of performing analysis without using the monitor, an X-ray nondestructive inspection called Rutherford backscatter is performed, but it has a drawback such as a long time required for analysis.

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

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

[0007]

[0008]

In order to achieve the above object, an analysis method according to the first aspect of the present invention comprises a first element identical to an element contained in a semiconductor substrate and a first element contained in the substrate. Irradiating primary X-rays to a sample to be measured provided on the surface of the substrate with a thin film containing a second element that is not included in the second element, and among the fluorescent X-rays emitted from the sample to be measured, The intensity of the hard X-ray and the intensity of the ultra-soft X-ray of the second element are measured. The measured intensity of these two fluorescent X-rays
The thickness of the thin film and the second element based on
Is determined, and from these relationships, the thickness of the thin film and the concentration of the second element are determined. Here, the combination of the hard X-ray and the super soft X-ray is any one of a combination of a K line and an M line, a K line and an N line, and an L line and an N line. In the present invention, the ultra soft X-ray refers to an M line and an N line.

According to another aspect of the present invention, there is provided an analyzer comprising a thin film containing a first element identical to an element contained in a semiconductor substrate and a second element not contained in the substrate. An X-ray source for irradiating the sample to be measured provided on the surface with primary X-rays, and hard X-rays and ultra-soft X-rays of the second element among the fluorescent X-rays from the sample to be measured which have received the primary X-rays First and second light-splitting elements for splitting light are provided. The X-ray intensity of the hard X-ray and the ultra-soft X-ray is measured by the first and second measuring instruments, respectively. Furthermore, this
The apparatus measures the intensity of hard X-rays measured by the first measuring instrument.
And the intensity of the ultra-soft X-ray measured by the second measuring instrument.
The thickness of the thin film and the second element based on each of the degrees
The relationship with the elemental concentration was determined, and from these relationships,
And an arithmetic unit for calculating the thickness of the second element and the concentration of the second element.
You. Here, the combination of the hard X-ray and the super soft X-ray is any one of a combination of a K line and an M line, a K line and an N line, and an L line and an N line.

According to these inventions, among the fluorescent X-rays of the second element contained in the thin film and not contained in the substrate, the intensity of the hard X-ray having a large influence of the film thickness is improved. Since the intensity of the ultra-soft X-ray whose influence of the film thickness is small is measured, the measured intensity of the hard X-ray and the intensity of the ultra-soft X-ray each include sensitive information regarding the film thickness and the 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.

In the analysis method according to the third aspect , among 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 X-ray in the thin film are different. The intensity of the ultra soft X-ray of the element is measured, and the film thickness and the concentration are obtained based on these two measured intensities. Here, after all,
The combination of X-ray and ultra-soft X-ray is K-line and M-line, K-line and N-line,
One of the combinations consisting of the L line and the N line.

The analyzer according to claim 4 is included in a semiconductor substrate.
A first element that is the same as the element
A thin film containing a second element that is not
An X-ray source for irradiating primary X-rays to a sample to be measured, provided in the apparatus, and a first spectral element for splitting hard X-rays of the first element among fluorescent X-rays from the sample to be subjected to primary X-rays And the above primary X
And a second spectral element that splits ultra soft X-ray of the X-ray fluorescence caries Chi second element from the measurement sample that has received the line.
The X-ray intensity of the hard X-ray and the ultra-soft X-ray is measured by the first and second measuring instruments, respectively. here
So, again, the combination of hard X-rays and ultra-soft X-rays
Any combination of M line, K line and N line, L line and N line
Is.

According to the third or fourth aspect of the invention, the intensity of the hard X-ray of the first element in the substrate and the thin film is measured. Therefore, when the thickness of the thin film is small, it becomes smaller as the thickness increases. Therefore, the measured intensity of the hard X-ray includes sensitive information on the film thickness. On the other hand, the second
The measured intensity of elemental ultra-soft X-rays is
Since the lines are largely absorbed in the thin film, they are emitted only 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 the two measurement intensities, the film thickness and the concentration of the second element can be measured relatively accurately.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a sample 1 to be measured includes a substrate 11
A thin film 12 containing the same first element as the element contained in the substrate 11 and a second element not contained in the substrate 11 is provided on the surface of the substrate 11.
1 is a wafer having a WSix thin film 12 on its surface. The sample 1 to be measured is a sample whose thickness t and composition ratio (x) of the thin film 12, that is, the concentration of W are unknown. The thickness t of the thin film 12 is, for example, in a range of about 400 ° to 2500 °. The X-ray fluorescence analyzer 2 includes an X-ray tube (X-ray source) 3, first and second spectroscopic elements 4A and 4B, first and second measuring devices 5A and 5B, and an arithmetic unit 6. Have. The first and second measuring devices 5A and 5B include first and second X-ray detectors 8A and 8B, and first and second counting circuit units 9A and 9B, respectively.

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

The two spectral elements 4A and 4B are housed in a spectral chamber 7 maintained in a vacuum atmosphere. The first spectral element 4A is made of, for example, a LiF spectral crystal, and disperses an element to be measured, that is, a W-Lα ray B3, which is a hard X-ray of W, among the fluorescent X-rays B2 from the sample 1 to be measured. . On the other hand, the second spectral element 4B is made of, for example, an artificial lattice in which a large number of carbon and nickel layers are alternately stacked on a silicon substrate. The second spectroscopic element 4 </ b> B
Among the fluorescent X-rays B2 from
The x-ray B4 is split. The W-Lα rays B3 and W-N separated by the first and second light-splitting elements 4A and 4B.
The x-rays B4 are the first and second X-ray detectors 8, respectively.
A, 8B. The extraction angle β of the W-Nx line B4
2 is set smaller than the extraction angle β1 of the W-Lα line B3.

The first and second X-ray detectors 8A and 8A
B is the incident W-Lα ray B3 and W-N, respectively.
The x-ray B4 is detected, and detection outputs e1 and e2 are output to the first and second counting circuits 9A and 9B. First and second
The counting circuits 9A and 9B respectively provide detection outputs e1 and e
2 is counted, and the W-Lα line B3 and the W-Nx line B
4 is output to the computing unit 6 as measurement signals x1 and x2. The computing unit 6 receives the measurement signals x1 and x2 and receives W
-Measured intensity of Lα line B3 and W-Nx line B4
Based on this, the relationship between the thickness t of the thin film 12 and the concentration of W
From these relationships, the film thicknesses t and W of the thin film 12 are calculated.
Find the concentration of

Next, an analysis method using the fundamental parameter method will be briefly described. First, the film thickness t
And a plurality of standard samples of known concentrations were prepared. These standard samples were analyzed using the analyzer 2 of FIG.
The intensity of the Lα line B3 and the intensity of the W-Nx line B4 were measured with both measuring instruments 5.
A, 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.

Next, the intensity of the W-Lα line B3 and the intensity of the W-Nx line B4 are measured using the analyzer 2 for the sample 1 whose thickness t and concentration are unknown. This measured intensity is converted into a theoretical intensity by the above-mentioned conversion formula. Thereafter, an appropriate film thickness t and concentration are given to a 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 film thickness t is changed, the concentration is again given, the calculation is repeated, and this calculation is repeated,
The thickness t and the concentration are obtained. Note that this calculation is based on the film thickness t.
A simultaneous equation consisting of a first equation relating to the theoretical intensity of the W-Lα line B3 whose density is unknown and a second equation relating to the theoretical intensity of the W-Nx line B4 is solved to determine the film thickness t and the concentration.

Next, the reason why the W-Lα ray B3 and the W-Nx ray B4 among the fluorescent X-rays B2 are used in this analysis method will be described. As shown in FIG. 2, the W-Lα line B3
Has a relatively short wavelength (approximately 1.48 °), that is, has a large energy, so that the one generated from the deepest portion 12a of the thin film 12 is not so much absorbed by the thin film 12, so that it passes through the thin film 12, Are emitted from all the layers. Therefore, as shown by the solid line in FIG. 3, the intensity of the W-Lα line B3 increases as the thickness t of the thin film 12 increases, and is greatly affected by the change in the thickness t. On the other hand, the wavelength of the W-Nx line B4 in FIG. 2 is extremely long (about 55 °), that is, the energy is extremely small, so that the one generated at a deep part of the thin film 12 is absorbed by the thin film 12, so that the surface of the thin film 12 Emitted only from the layer. Therefore, as shown by the broken line in FIG. 3, the intensity of the W-Nx line B4 is much less affected by the thickness t of the thin film 12 than that of the W-Lα line B3, and as shown in FIG. Affected significantly.

As described above, since the measured intensity of the W-Lα line B3 in FIG. 3 is greatly influenced by the film thickness t, it contains reliable information on the film thickness t. Since the intensity has little influence on the film thickness t, the intensity includes reliable information on the concentration. That is, a change in the film thickness t appears as a large change in the measured intensity of the W-Lα line B3, while a 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.

Incidentally, the present invention is not necessarily limited to WL
It is not necessary to measure the intensity of the α ray B3 and the W-Nx ray B4, and it depends on the type (composition) of the element constituting the thin film 12.
Te, a second element that is not contained in the substrate 11 of FIG. 1 (W)
X-ray (B3), which is greatly affected by film thickness, and film thickness
As a combination of ultra-soft X-rays (B4) with little effect of
And M line, K line and N line, L line and N line
The respective intensities may be measured, and the film thickness t and the concentration may be obtained based on these two measured intensities .

However, the WSix thin film 12 of this embodiment
For W-Mα ray, the energy is too large,
Since the intensity is greatly affected by the film thickness t, a slight measurement error appears as a large concentration error. Therefore, for the WSix thin film 12, it is not preferable to use the W-Mα line, but generally it is preferable to use the N line .

In the above embodiment, the W-Nx line B
4 is set slightly smaller than the extraction angle β1 of the W-Lα line B3. Therefore, the W-Nx line B4 is
It is more easily absorbed in the WSix thin film 12. Therefore, the intensity of the W-Nx line B4 is less affected by the film thickness t, so that a more accurate analysis result can be obtained.

In the above embodiment, as the intensity of the first fluorescent X-ray, the intensity of the hard X-ray (for example, W-Lα ray) B3 of the second element (W) among the fluorescent X-rays B2 was measured. . However, in the present invention, the fluorescent X-ray B
The intensity of the hard X-ray of the first element (Si) among the two 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 for the first element Si,
Si—Kα ray B5s emitted from the substrate 11 and S
i-rays B5b emitted from i. As shown in FIG. 6A, the X-ray intensity of the Si-Kα ray B5s from the thin film 12 increases as the thickness t increases in a range where the thin film t is thin. When the thickness is larger than the value, the X-ray intensity is saturated and becomes constant.
On the other hand, as shown in FIG.
Since the line B5b is absorbed by the thin film 12, in a range where the film thickness t is small, as the film thickness t increases, the X-ray intensity becomes extremely small, and when the film thickness t becomes larger than a predetermined value, The X-ray intensity becomes zero. Therefore, the Si-Kα ray B5 emitted from the entire sample 1 to be measured is as shown in FIG.
As shown in FIG. 6C, which is a combination of FIG. 6B and FIG. 6B, when the film thickness t is extremely small (for example, 10 ° to 5,000 °), as the thin film t becomes thicker, the X-ray intensity becomes smaller. Become. Therefore, when the film thickness t is small, the measured intensity of the Si-Kα line B5 contains reliable information on the film thickness t, and therefore, instead of the W-Lα line B3 (FIG. 1), S
The X-ray intensity of the i-Kα ray B5 may be measured.

In the case of the embodiment shown in FIG. 5, the first spectral element 4A in FIG. 1 splits the Si-Kα ray B5 (FIG. 5), and the first X-ray detector 8A splits the Si-Kα ray B5. (FIG. 5) is detected. Other configurations are the same as those of the embodiment of FIG. 1, and detailed description and illustration thereof are omitted.

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

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

On the other hand, as the first fluorescent X-ray, FIG.
In the case (b) of measuring the X-ray intensity of the W-Lα ray B3 (in the case of the embodiment of FIG. 1), the W-Lα ray B3 is generated on the surface more 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 under the WSix thin film 12, the thickness t and the concentration of the WSix thin film 12 can be accurately determined. Can be measured.

[0031]

As described above, according to the present invention, the influence of the film thickness of the fluorescent X-rays of the second element contained in the thin film and not contained in the substrate is obtained.
Since the intensity of the large hard X-ray and the intensity of the ultra-soft X-ray whose influence of the film thickness is small are measured, the film thickness and the concentration can be accurately measured based on the two measured intensities. Similarly, when the film thickness and the concentration are obtained based on the intensity of the hard X-ray of the first element and the intensity of the ultra-soft X-ray of the second element, these can be accurately measured. .

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

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an X-ray fluorescence analyzer showing one 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 a relationship between the intensity of fluorescent X-rays, the film thickness, and the concentration of W.

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

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

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

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

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

[Explanation of symbols]

Reference numeral 1 denotes a sample to be measured, 3 denotes an X-ray source, 4A denotes a first spectral element,
4B: second spectral 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 (4)

(57) [Claims] 1. A test sample in which a thin film containing a first element identical to an element contained in a semiconductor substrate and a second element not contained in the substrate is provided on the surface of the substrate. Irradiating a primary X-ray, the second of the fluorescent X-rays emitted from the sample to be measured
The intensity of the hard X-ray of the element and the intensity of the ultra-soft X-ray of the second element are measured, and the thickness of the thin film and the second intensity are determined based on the measured intensity of the two fluorescent X-rays . Former
A fluorescent X-ray analysis method for determining the relationship between the concentration of the second element and the film thickness of the thin film and the concentration of the second element based on the relationship between the hard X-ray and the ultra-soft X-ray. An X-ray fluorescence analysis method, which is one of a combination of K-line and M-line, K-line and N-line, and L-line and N-line. 2. A test sample in which a thin film containing a first element identical to an element contained in a semiconductor substrate and a second element not contained in the substrate is provided on the surface of the substrate. An X-ray source for irradiating primary X-rays, a first spectral element for dispersing hard X-rays of the second element among fluorescent X-rays from the sample to be measured that has received the primary X-rays, A second spectroscopic element for splitting ultra-soft X-rays of the second element among the fluorescent X-rays from the sample to be measured that has received the X-rays, a first measuring device for measuring the intensity of the hard X-rays, the second measuring device for measuring the intensity of the ultrasonic soft X-rays, and measuring the intensity of the hard X-rays measured by the first measuring device, upper
The intensity of the ultra-soft X-ray measured by the second measuring instrument
The thickness of the thin film and the concentration of the second element based on each
From these relationships, and from these relationships, the thickness of the thin film and
An X-ray fluorescence analyzer comprising a calculator for determining the concentration of a second element, wherein the combination of the hard X-ray and the ultra-soft X-ray is K-line and M-line, K-line and N-line, and L-line X-ray fluorescence analyzer which is one of the combination consisting of 3. A sample to be measured in which a thin film containing a first element identical to an element contained in a semiconductor substrate and a second element not contained in the substrate is provided on the surface of the substrate.
Irradiating primary X-rays, the first of fluorescent X-rays emitted from the sample to be measured
The intensity of the hard X-ray of the element and the intensity of the ultra- soft X-ray of the second element are measured, and the thickness of the thin film and the intensity of the second element are determined based on the measured intensity of the two fluorescent X-rays . A fluorescent X-ray analysis method for obtaining a concentration, wherein the combination of the hard X-ray and the ultra-soft X-ray is such that K-ray and M-ray and K-ray
Fluorescence that is one of N-line, a combination of L-line and N-line
X-ray analysis method . 4. The same element as the element contained in the semiconductor substrate.
A first element and a second element not contained in the substrate
A thin film containing
An X-ray source for irradiating primary X-rays, and a fluorescent X-ray from a sample to be measured that has received the primary X-ray
A first spectroscopic element for dispersing hard X-rays of the first element; and a fluorescent X-ray from a sample to be measured that has received the primary X-rays.
A second spectroscopic element for splitting ultra- soft X-rays of the second element, a first measuring device for measuring the intensity of the hard X-rays, and a second measurement for measuring the intensity of the ultra-soft X-rays A fluorescent X-ray analyzer comprising a device , wherein the combination of the hard X-ray and the ultra-soft X-ray is
Fluorescence that is one of N-line, a combination of L-line and N-line
X-ray analyzer .